linux: generalize sections, ranges and linker tables

From: "Luis R. Rodriguez" <[email protected]>

This v4 addresses feedback from the previous v3 series [0], and also addresses a huge array of additional tests against many architectures outside of what 0-day provides. As I mentioned in my last v3 series, 0-day had only found one issue with the series, a blackfin architecture linker issue with the last series. Guenter Rock was kind enough to give my series a test spin on his test bed and he found quite a bit of other oddball issues with obscure architectures, and even on x86 with an old toolchain. After a lot of work and coordinating with a few maintainers I'm happy to report all issues found so far through all possible testing I could do are now fixed, this series also addresses all feedback from the last series, as such this goes submitted as PATCH form.

In addressing fixing this work on a few architectures some of the previous patches are further simplified. The kprobes port to linker tables is made much easier now that I've addressed moving out core kprobe declarations into asm-generic/kprobes.h. Refer to the patch "kprobes: move kprobe declarations to asm-generic/kprobes.h". This makes for a much cleaner solution across architectures.

Boris feedback on making the code bit rot feature optional is addressed by using a new Kconfig symbol for this, CONFIG_BUILD_AVOID_BITROT, but given Greg's concerns over lack of clarity over what this was all about I've ripped that functionality out into its own patch with a bit more extensive documentation and re-wording. See the patch "kbuild: enable option to force compile force-obj-y and force-lib-y". I hope makes it clear how linker tables can help with avoiding code bit rot. I've gone with a new Kconfig symbol CONFIG_BUILD_AVOID_BITROT given CONFIG_COMPILE_TEST is not available on UML, this feature is desirable on all architectures.

The documentation is revamped, now that the DocBook format is deprecated I ported the documention into the trendy hipster Sphinx documentation format.

AT Boris' request I've adapated the userspace linker table application forintegration into the kernel under tools/ to make it easier to keep things in sync, however since this requires a bit of changes to some headers in tools/ I'll submit that separately.

[0] https://lkml.kernel.org/r/[email protected]

If you'd like this in git-form, you can get it on the 20160819-linker-table-v4 branch of my linux-next tree on kernel.org, this also includes the series of the linker table userspace sandbox:

https://git.kernel.org/cgit/linux/kernel/git/mcgrof/linux-next.git/log/?h=20160819-linker-table-v4

Please let me know if there are any concerns or questions.

Luis R. Rodriguez (16):
x86: remove LTO_REFERENCE_INITCALL()
dell-smo8800: include uaccess.h scripts/module-common.lds: enable generation
generic-sections: add section core helpers
xtensa: skip adding literal when SORT() is used ranges.h: add helpers to build and identify Linux section ranges tables.h: add linker table support
kbuild: enable option to force compile force-obj-y and force-lib-y firmware/Makefile: force recompilation if makefile changes
firmware: port built-in section to linker table
jump_label: move guard #endif down where it belongs
jump_label: port __jump_table to linker tables
dynamic_debug: port to use linker tables
kprobes: move kprobe declarations to asm-generic/kprobes.h
kprobes: port .kprobes.text to section range
kprobes: port blacklist kprobes to linker table

 .gitignore                                         |   2 +
 Documentation/index.rst                            |   1 +
 Documentation/kbuild/makefiles.txt                 |  36 ++
 Documentation/sections/conf.py                     |   4 +
 Documentation/sections/index.rst                   |  13 +
 Documentation/sections/linker-tables.rst           | 202 +++++++
 Documentation/sections/ranges.rst                  |  49 ++
 Documentation/sections/section-core.rst            | 153 +++++
 MAINTAINERS                                        |  37 ++
 Makefile                                           |   6 +-
 arch/alpha/include/asm/Kbuild                      |   4 +
 arch/arc/include/asm/Kbuild                        |   3 +
 arch/arc/include/asm/kprobes.h                     |   6 +-
 arch/arc/kernel/vmlinux.lds.S                      |   1 -
 arch/arm/include/asm/Kbuild                        |   3 +
 arch/arm/include/asm/jump_label.h                  |   6 +-
 arch/arm/include/asm/kprobes.h                     |   4 +
 arch/arm/kernel/entry-armv.S                       |   3 +-
 arch/arm/kernel/vmlinux-xip.lds.S                  |   1 -
 arch/arm/kernel/vmlinux.lds.S                      |   1 -
 arch/arm/probes/decode.h                           |   1 +
 arch/arm64/include/asm/Kbuild                      |   3 +
 arch/arm64/include/asm/jump_label.h                |   6 +-
 arch/arm64/include/asm/kprobes.h                   |   4 +
 arch/arm64/kernel/armv8_deprecated.c               |   1 +
 arch/arm64/kernel/insn.c                           |   1 +
 arch/arm64/kernel/probes/kprobes.c                 |   4 +-
 arch/arm64/kernel/vmlinux.lds.S                    |   1 -
 arch/avr32/include/asm/Kbuild                      |   3 +
 arch/avr32/include/asm/kprobes.h                   |   4 +
 arch/avr32/kernel/entry-avr32b.S                   |  13 +-
 arch/avr32/kernel/vmlinux.lds.S                    |   1 -
 arch/blackfin/include/asm/Kbuild                   |   4 +
 arch/blackfin/kernel/vmlinux.lds.S                 |   1 -
 arch/c6x/include/asm/Kbuild                        |   3 +
 arch/c6x/include/asm/tables.h                      |  26 +
 arch/c6x/kernel/vmlinux.lds.S                      |   1 -
 arch/cris/include/asm/Kbuild                       |   4 +
 arch/frv/include/asm/Kbuild                        |   4 +
 arch/h8300/include/asm/Kbuild                      |   4 +
 arch/hexagon/include/asm/Kbuild                    |   4 +
 arch/hexagon/kernel/vmlinux.lds.S                  |   1 -
 arch/ia64/include/asm/Kbuild                       |   3 +
 arch/ia64/include/asm/kprobes.h                    |   7 +-
 arch/ia64/kernel/jprobes.S                         |   3 +-
 arch/ia64/kernel/vmlinux.lds.S                     |   1 -
 arch/ia64/lib/flush.S                              |   6 +-
 arch/m32r/include/asm/Kbuild                       |   4 +
 arch/m68k/include/asm/Kbuild                       |   4 +
 arch/metag/include/asm/Kbuild                      |   4 +
 arch/metag/kernel/vmlinux.lds.S                    |   1 -
 arch/microblaze/include/asm/Kbuild                 |   4 +
 arch/microblaze/kernel/vmlinux.lds.S               |   1 -
 arch/mips/include/asm/Kbuild                       |   3 +
 arch/mips/include/asm/jump_label.h                 |   6 +-
 arch/mips/include/asm/kprobes.h                    |   6 +-
 arch/mips/kernel/vmlinux.lds.S                     |   1 -
 arch/mn10300/include/asm/Kbuild                    |   3 +
 arch/mn10300/include/asm/kprobes.h                 |   4 +
 arch/mn10300/kernel/vmlinux.lds.S                  |   1 -
 arch/nios2/include/asm/Kbuild                      |   4 +
 arch/nios2/kernel/vmlinux.lds.S                    |   1 -
 arch/openrisc/include/asm/Kbuild                   |   4 +
 arch/openrisc/kernel/vmlinux.lds.S                 |   1 -
 arch/parisc/include/asm/Kbuild                     |   4 +
 arch/parisc/kernel/vmlinux.lds.S                   |   1 -
 arch/powerpc/include/asm/Kbuild                    |   3 +
 arch/powerpc/include/asm/jump_label.h              |   8 +-
 arch/powerpc/include/asm/kprobes.h                 |   6 +
 arch/powerpc/include/asm/ppc_asm.h                 |   7 +-
 arch/powerpc/kernel/vmlinux.lds.S                  |   1 -
 arch/s390/include/asm/Kbuild                       |   3 +
 arch/s390/include/asm/jump_label.h                 |   6 +-
 arch/s390/include/asm/kprobes.h                    |   4 +
 arch/s390/kernel/entry.S                           |   5 +-
 arch/s390/kernel/kprobes.c                         |   6 +-
 arch/s390/kernel/mcount.S                          |   3 +-
 arch/s390/kernel/vmlinux.lds.S                     |   1 -
 arch/score/include/asm/Kbuild                      |   4 +
 arch/score/kernel/vmlinux.lds.S                    |   1 -
 arch/sh/include/asm/Kbuild                         |   3 +
 arch/sh/include/asm/kprobes.h                      |   2 +
 arch/sh/kernel/vmlinux.lds.S                       |   1 -
 arch/sparc/include/asm/Kbuild                      |   3 +
 arch/sparc/include/asm/jump_label.h                |   6 +-
 arch/sparc/include/asm/kprobes.h                   |   5 +
 arch/sparc/kernel/vmlinux.lds.S                    |   1 -
 arch/sparc/mm/ultra.S                              |   3 +-
 arch/tile/include/asm/Kbuild                       |   3 +
 arch/tile/include/asm/kprobes.h                    |   6 +-
 arch/tile/kernel/vmlinux.lds.S                     |   1 -
 arch/um/include/asm/Kbuild                         |   4 +
 arch/unicore32/include/asm/Kbuild                  |   3 +
 arch/unicore32/include/asm/section-core.h          |  19 +
 arch/x86/include/asm/Kbuild                        |   3 +
 arch/x86/include/asm/jump_label.h                  |  10 +-
 arch/x86/include/asm/kprobes.h                     |   6 +
 arch/x86/kernel/cpu/microcode/core.c               |   8 +-
 arch/x86/kernel/kprobes/core.c                     |  11 +-
 arch/x86/kernel/vmlinux.lds.S                      |   1 -
 arch/x86/tools/relocs.c                            |   4 +
 arch/xtensa/include/asm/Kbuild                     |   4 +
 arch/xtensa/kernel/Makefile                        |   8 +-
 drivers/base/firmware_class.c                      |  12 +-
 drivers/platform/x86/dell-smo8800.c                |   1 +
 firmware/Makefile                                  |   6 +-
 include/asm-generic/kprobes.h                      |  26 +
 include/asm-generic/ranges.h                       | 103 ++++
 include/asm-generic/section-core.h                 | 341 +++++++++++
 include/asm-generic/sections.h                     |   4 +-
 include/asm-generic/tables.h                       |  50 ++
 include/asm-generic/vmlinux.lds.h                  |  73 +--
 include/linux/compiler.h                           |   8 -
 include/linux/dynamic_debug.h                      |   5 +-
 include/linux/init.h                               |  20 +-
 include/linux/jump_label.h                         |   8 +-
 include/linux/kprobes.h                            |  24 +-
 include/linux/ranges.h                             | 128 +++++
 include/linux/sections.h                           | 111 ++++
 include/linux/tables.h                             | 638 +++++++++++++++++++++
 init/Kconfig                                       |  22 +
 kernel/jump_label.c                                |  17 +-
 kernel/kprobes.c                                   |  17 +-
 lib/dynamic_debug.c                                |  13 +-
 scripts/Makefile.build                             |   7 +-
 scripts/Makefile.clean                             |   2 +
 scripts/Makefile.lib                               |  11 +
 scripts/Makefile.modpost                           |   2 +-
 scripts/mod/modpost.c                              |   2 +-
 scripts/{module-common.lds => module-common.lds.S} |   6 +
 scripts/recordmcount.c                             |   2 +-
 scripts/recordmcount.pl                            |   2 +-
 tools/objtool/special.c                            |   2 +-
 133 files changed, 2328 insertions(+), 214 deletions(-)
 create mode 100644 Documentation/sections/conf.py
 create mode 100644 Documentation/sections/index.rst
 create mode 100644 Documentation/sections/linker-tables.rst
 create mode 100644 Documentation/sections/ranges.rst
 create mode 100644 Documentation/sections/section-core.rst
 create mode 100644 arch/c6x/include/asm/tables.h
 create mode 100644 arch/unicore32/include/asm/section-core.h
 create mode 100644 include/asm-generic/kprobes.h
 create mode 100644 include/asm-generic/ranges.h
 create mode 100644 include/asm-generic/section-core.h
 create mode 100644 include/asm-generic/tables.h
 create mode 100644 include/linux/ranges.h
 create mode 100644 include/linux/sections.h
 create mode 100644 include/linux/tables.h
 rename scripts/{module-common.lds => module-common.lds.S} (80%)

2.9.2

From: "Luis R. Rodriguez" <[email protected]>

The setup for LTO never made it upstream, and although this has some users, this is now really old stuff for a gcc 4.7 LTO problem. We know that at least LTO_REFERENCE_INITCALL() work around can be removed if LTO is not supported on v4.7 anymore.

As per Andi the DISABLE_LTO and LTO_CFLAGS are still neeeded though.

v3: added to this series, removing LTO_REFERENCE_INITCALL()
justifies that other future similar macros do not need a respective LTO_REFERENCE_INITCALL() on them therefore simplifying new code.

---
 include/linux/init.h | 20 +-------------------
 1 file changed, 1 insertion(+), 19 deletions(-)

index 1e5c131d5c9a..aa662ad80d9c 100644
@@ -151,23 +151,6 @@ extern bool initcall_debug;
 
 #ifndef __ASSEMBLY__
 
-#ifdef CONFIG_LTO
-/* Work around a LTO gcc problem: when there is no reference to a variable
- * in a module it will be moved to the end of the program. This causes
- * reordering of initcalls which the kernel does not like.
- * Add a dummy reference function to avoid this. The function is
- * deleted by the linker.
- */
-#define LTO_REFERENCE_INITCALL(x) \
-	; /* yes this is needed */			\
-	static __used __exit void *reference_##x(void)	\
-	{						\
-		return &x;				\
-	}
-#else
-#define LTO_REFERENCE_INITCALL(x)
-#endif
-
 /* initcalls are now grouped by functionality into separate 
  * subsections. Ordering inside the subsections is determined
  * by link order. 

@@ -180,8 +163,7 @@ extern bool initcall_debug;
 
 #define __define_initcall(fn, id) \
 	static initcall_t __initcall_##fn##id __used \
-	__attribute__((__section__(".initcall" #id ".init"))) = fn; \
-	LTO_REFERENCE_INITCALL(__initcall_##fn##id)
+	__attribute__((__section__(".initcall" #id ".init"))) = fn;
 
 /*
  * Early initcalls run before initializing SMP.

2.9.2

From: "Luis R. Rodriguez" <[email protected]>

sections.h is currently included and it provides dell-smo8800 with what it needs, an upcoming change will decouple uaccess.h from sections.h. This driver needs to explicitly require uaccess.h before this change.

v3: new to this series -- needed due to collateral of the split of
old linker tables from tables.h into 3 files: sections.h, ranges.h and tables.h

---
 drivers/platform/x86/dell-smo8800.c | 1 +
 1 file changed, 1 insertion(+)

index 0aec4fd4c48e..37e646034ef8 100644
@@ -24,6 +24,7 @@
 #include <linux/acpi.h>
 #include <linux/interrupt.h>
 #include <linux/miscdevice.h>
+#include <linux/uaccess.h>
 
 struct smo8800_device {
 	u32 irq;                     /* acpi device irq */

2.9.2


_______________________________________________
Xen-devel mailing list
[email protected]
https://lists.xen.org/xen-devel

From: "Luis R. Rodriguez" <[email protected]>

scripts/module-common.lds is currently pretty static, in the future this may change and we will want access to kernel macros to help expands certain areas. To get access to use macros we need to generate module-common.lds from module-common.lds.S, for now though only enable the generation. We'll later expand on this as needed.

Since this file is now generated add it to .gitignore.

v4: add file to MAINTAINERS
v3: new to this series

---
 .gitignore                                         | 2 ++
 MAINTAINERS                                        | 1 +
 Makefile                                           | 6 +++++-
 scripts/Makefile.modpost                           | 2 +-
 scripts/{module-common.lds => module-common.lds.S} | 0
 5 files changed, 9 insertions(+), 2 deletions(-)
 rename scripts/{module-common.lds => module-common.lds.S} (100%)

index c2ed4ecb0acd..0f0702054fdb 100644
@@ -114,3 +114,5 @@ all.config
 
 # Kdevelop4
 *.kdev4
+
+scripts/module-common.lds

index d635ab047f3a..5aec01883020 100644
@@ -7887,6 +7887,7 @@ M:	Rusty Russell <[email protected]>
 S:	Maintained
 F:	include/linux/module.h
 F:	kernel/module.c
+F:	scripts/module-common.lds.S
 
 MOTION EYE VAIO PICTUREBOOK CAMERA DRIVER
 W:	http://popies.net/meye/

index 5c18baad7218..b3e5ea78d582 100644
@@ -408,6 +408,10 @@ KBUILD_AFLAGS_MODULE  := -DMODULE
 KBUILD_CFLAGS_MODULE  := -DMODULE
 KBUILD_LDFLAGS_MODULE := -T $(srctree)/scripts/module-common.lds
 
+$(srctree)/scripts/module-common.lds: $(srctree)/scripts/module-common.lds.S
+	$(Q)$(CC) $(CFLAGS) $(INCLUDES) $(LINUXINCLUDE) -E -P \
+		-D__ASSEMBLY__ -DLINKER_SCRIPT -o $@ $<
+
 # Read KERNELRELEASE from include/config/kernel.release (if it exists)
 KERNELRELEASE = $(shell cat include/config/kernel.release 2> /dev/null)
 KERNELVERSION = $(VERSION)$(if $(PATCHLEVEL),.$(PATCHLEVEL)$(if $(SUBLEVEL),.$(SUBLEVEL)))$(EXTRAVERSION)

@@ -1174,7 +1178,7 @@ all: modules
 # using awk while concatenating to the final file.
 
 PHONY += modules
-modules: $(vmlinux-dirs) $(if $(KBUILD_BUILTIN),vmlinux) modules.builtin
+modules: $(srctree)/scripts/module-common.lds $(vmlinux-dirs) $(if $(KBUILD_BUILTIN),vmlinux) modules.builtin
 	$(Q)$(AWK) '!x[$$0]++' $(vmlinux-dirs:%=$(objtree)/%/modules.order) > $(objtree)/modules.order
 	@$(kecho) '  Building modules, stage 2.';
 	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost

index 1366a94b6c39..2d8aff7735d6 100644
@@ -121,7 +121,7 @@ quiet_cmd_ld_ko_o = LD [M]  $@
                              $(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE) \
                              -o $@ $(filter-out FORCE,$^)
 
-$(modules): %.ko :%.o %.mod.o FORCE
+$(modules): %.ko : $(srctree)/scripts/module-common.lds %.o %.mod.o FORCE
 	$(call if_changed,ld_ko_o)
 
 targets += $(modules)

similarity index 100%
rename from scripts/module-common.lds
rename to scripts/module-common.lds.S

2.9.2


_______________________________________________
Xen-devel mailing list
[email protected]
https://lists.xen.org/xen-devel

From: "Luis R. Rodriguez" <[email protected]>

Linux makes extensive use of custom ELF header sections, documentation for these are well scatterred. Unify this documentation in a central place and provide helpers to build custom Linux sections.

This also generalizes sections code to enable avoiding modifying the linker scripts when we want to add new custom Linux sections. In order to make this generally useful we need to ensure all architectures can make use of core section helpers but that they can also override should this be needed. Instead of relying on section.h this adds a sections-core.h since this will be targetted to be safe to be used on asm code, linker scripts and C code.

v4:

o Port to shiny new sphinx documentation format

o fix a unicore32 build, turns out this actually fixes unicore32 defconfig builds which were failing for a long while. unicore32 does not seem to grok well the type passed on a section declaration, this ignores it.

o Use VMLINUX_SYMBOL() in more user symbols (extern C code), not doing this was causing final linker issues with blackfin -- this is a CONFIG_HAVE_UNDERSCORE_SYMBOL_PREFIX=y architecture. The other one being metatag. metatag is not supported on 0-day so I cannot confirm compilation there.

o Added SECTION_CORE() for C code, used later by __LINUX_RANGE()

o Since SECTION_CORE() is defined for linker script and C code, share the same helper and just use a __stringify() for the C code as is done for the other C helpers.

o move generic sections to asm-generic/section-core.h instead. PowerPC compilation blows up if asm/jump_labels.h gets section.h included, fixing this is not in any way easy. The list of issues are endless. Moving new data to a new simple file resolves this.

o since things are now in asm-generic/section-core.h the guard changes on asm-generic/sections.h and each architecture sections.h are no longer needed

o Give generic sections some maintainer love, that change is Acked-by Arnd Bergmann, Josh and hpa.

o A few checkpatch.pl style fixes

o As suggested by James Hogan use generic-y to copy generic header files on architectures that do not have a sections.h instead of writing a simple file only to include the generic one.

v3:

o add missing sections.h for architectures that did not have it

o move generic sections to asm-generic/sections.h

o add generic asm helpers section_type(), section_type_asmtype(), push_section_type() -- these helpers enable easy use for for later declaring and using of custom linux sections using more standard APIs in both C code, asm code (C asm calls, or asm files), enabling future standardized section types to be more immediately accessible to asm code, not just C code. Note for ASM_CMD_SEP we use by default "\n", architectures needed to override can do so on their own sections.h prior to inclusion of asm-generic/sections.h

---
 Documentation/index.rst                   |   1 +
 Documentation/sections/conf.py            |   4 +
 Documentation/sections/index.rst          |  11 +
 Documentation/sections/section-core.rst   | 153 ++++++++++++++
 MAINTAINERS                               |  14 ++
 arch/alpha/include/asm/Kbuild             |   1 +
 arch/arc/include/asm/Kbuild               |   1 +
 arch/arm/include/asm/Kbuild               |   1 +
 arch/arm64/include/asm/Kbuild             |   1 +
 arch/avr32/include/asm/Kbuild             |   1 +
 arch/blackfin/include/asm/Kbuild          |   1 +
 arch/c6x/include/asm/Kbuild               |   1 +
 arch/cris/include/asm/Kbuild              |   1 +
 arch/frv/include/asm/Kbuild               |   1 +
 arch/h8300/include/asm/Kbuild             |   1 +
 arch/hexagon/include/asm/Kbuild           |   1 +
 arch/ia64/include/asm/Kbuild              |   1 +
 arch/m32r/include/asm/Kbuild              |   1 +
 arch/m68k/include/asm/Kbuild              |   1 +
 arch/metag/include/asm/Kbuild             |   1 +
 arch/microblaze/include/asm/Kbuild        |   1 +
 arch/mips/include/asm/Kbuild              |   1 +
 arch/mn10300/include/asm/Kbuild           |   1 +
 arch/nios2/include/asm/Kbuild             |   1 +
 arch/openrisc/include/asm/Kbuild          |   1 +
 arch/parisc/include/asm/Kbuild            |   1 +
 arch/powerpc/include/asm/Kbuild           |   1 +
 arch/s390/include/asm/Kbuild              |   1 +
 arch/score/include/asm/Kbuild             |   1 +
 arch/sh/include/asm/Kbuild                |   1 +
 arch/sparc/include/asm/Kbuild             |   1 +
 arch/tile/include/asm/Kbuild              |   1 +
 arch/um/include/asm/Kbuild                |   1 +
 arch/unicore32/include/asm/section-core.h |  19 ++
 arch/x86/include/asm/Kbuild               |   1 +
 arch/xtensa/include/asm/Kbuild            |   1 +
 include/asm-generic/section-core.h        | 341 ++++++++++++++++++++++++++++++
 include/asm-generic/sections.h            |   2 +
 include/asm-generic/vmlinux.lds.h         |  27 +--
 include/linux/sections.h                  | 111 ++++++++++
 40 files changed, 700 insertions(+), 13 deletions(-)
 create mode 100644 Documentation/sections/conf.py
 create mode 100644 Documentation/sections/index.rst
 create mode 100644 Documentation/sections/section-core.rst
 create mode 100644 arch/unicore32/include/asm/section-core.h
 create mode 100644 include/asm-generic/section-core.h
 create mode 100644 include/linux/sections.h

index a15f81855b39..10c9b867e326 100644
@@ -14,6 +14,7 @@ Contents:
    kernel-documentation
    media/index
    gpu/index
+   sections/index
 
 Indices and tables
 ==================

new file mode 100644
index 000000000000..faa1c57595e1
@@ -0,0 +1,4 @@
+# -*- coding: utf-8; mode: python -*-
+
+project = 'Linux Kernel ELF sections'
+html_search_language = 'en'

new file mode 100644
index 000000000000..d411e9b22eb3
@@ -0,0 +1,11 @@
+=========================
+Linux Kernel ELF sections
+=========================
+
+This book documents the Linux kernel's use of ELF sections, as well as helpers
+used throughout the kernel to help declare and define them.
+
+.. toctree::
+   :maxdepth: 4
+
+   section-core

index 5aec01883020..689c12075842 100644
@@ -5217,6 +5217,20 @@ S:	Supported
 F:	drivers/base/power/domain*.c
 F:	include/linux/pm_domain.h
 
+GENERIC SECTIONS
+M:	"Luis R. Rodriguez" <[email protected]>
+M:	Josh Poimboeuf <[email protected]>
+M:	"H. Peter Anvin" <[email protected]>
+L:	[email protected]
+L:	[email protected]
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux.git for-arnd
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux-next.git for-arnd
+S:	Supported
+F:	include/asm-generic/section-core.h
+F:	include/asm-generic/sections.h
+F:	include/asm-generic/vmlinux.lds.h
+F:	Documentation/sections/section-core.rst
+
 GENERIC UIO DRIVER FOR PCI DEVICES
 M:	"Michael S. Tsirkin" <[email protected]>
 L:	[email protected]

index bf8475ce85ee..5422827f1585 100644
@@ -10,3 +10,4 @@ generic-y += mm-arch-hooks.h
 generic-y += preempt.h
 generic-y += sections.h
 generic-y += trace_clock.h
+generic-y += section-core.h

index 0b10ef2a4372..9a0929576de1 100644
@@ -50,3 +50,4 @@ generic-y += user.h
 generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
+generic-y += section-core.h

index 0745538b26d3..47923635be16 100644
@@ -39,3 +39,4 @@ generic-y += termios.h
 generic-y += timex.h
 generic-y += trace_clock.h
 generic-y += unaligned.h
+generic-y += section-core.h

index f43d2c44c765..42d00806e4fb 100644
@@ -52,3 +52,4 @@ generic-y += unaligned.h
 generic-y += user.h
 generic-y += vga.h
 generic-y += xor.h
+generic-y += section-core.h

index 241b9b9729d8..f2c3b656a0e7 100644
@@ -22,3 +22,4 @@ generic-y += trace_clock.h
 generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
+generic-y += section-core.h

index 91d49c0a3118..7de674411bed 100644
@@ -48,3 +48,4 @@ generic-y += unaligned.h
 generic-y += user.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
+generic-y += section-core.h

index 64465e7e2245..38127ce747be 100644
@@ -62,3 +62,4 @@ generic-y += user.h
 generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
+generic-y += section-core.h

index 1778805f6380..385cd88a9d9e 100644
@@ -45,3 +45,4 @@ generic-y += types.h
 generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
+generic-y += section-core.h

index 1fa084cf1a43..46d7c599d9b8 100644
@@ -8,3 +8,4 @@ generic-y += mm-arch-hooks.h
 generic-y += preempt.h
 generic-y += trace_clock.h
 generic-y += word-at-a-time.h
+generic-y += section-core.h

index 373cb23301e3..1ec04ec1c82b 100644
@@ -75,3 +75,4 @@ generic-y += unaligned.h
 generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
+generic-y += section-core.h

index db8ddabc6bd2..37d7bfae7619 100644
@@ -60,3 +60,4 @@ generic-y += unaligned.h
 generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
+generic-y += section-core.h

index 502a91d8dbbd..672c6d5da18c 100644
@@ -9,3 +9,4 @@ generic-y += preempt.h
 generic-y += trace_clock.h
 generic-y += vtime.h
 generic-y += word-at-a-time.h
+generic-y += section-core.h

index 860e440611c9..6111e1523750 100644
@@ -11,3 +11,4 @@ generic-y += preempt.h
 generic-y += sections.h
 generic-y += trace_clock.h
 generic-y += word-at-a-time.h
+generic-y += section-core.h

index eb85bd9c6180..eef72c464c9b 100644
@@ -35,3 +35,4 @@ generic-y += trace_clock.h
 generic-y += types.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
+generic-y += section-core.h

index 29acb89daaaa..50ebd5a30d16 100644
@@ -56,3 +56,4 @@ generic-y += user.h
 generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
+generic-y += section-core.h

index b0ae88c9fed9..c6c2cf6edc98 100644
@@ -11,3 +11,4 @@ generic-y += preempt.h
 generic-y += syscalls.h
 generic-y += trace_clock.h
 generic-y += word-at-a-time.h
+generic-y += section-core.h

index 9740066cc631..12f7c5984c03 100644
@@ -20,3 +20,4 @@ generic-y += trace_clock.h
 generic-y += user.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
+generic-y += section-core.h

index 1c8dd0f5cd5d..f8145bc85835 100644
@@ -10,3 +10,4 @@ generic-y += preempt.h
 generic-y += sections.h
 generic-y += trace_clock.h
 generic-y += word-at-a-time.h
+generic-y += section-core.h

index d63330e88379..c9c7cb82b00f 100644
@@ -63,3 +63,4 @@ generic-y += user.h
 generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
+generic-y += section-core.h

index 2832f031fb11..86175e701869 100644
@@ -71,3 +71,4 @@ generic-y += user.h
 generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
+generic-y += section-core.h

index f9b3a81aefcd..6f43f33f0e0f 100644
@@ -29,3 +29,4 @@ generic-y += user.h
 generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
+generic-y += section-core.h

index ab9f4e0ed4cf..b49fab7bab2f 100644
@@ -7,3 +7,4 @@ generic-y += mcs_spinlock.h
 generic-y += preempt.h
 generic-y += rwsem.h
 generic-y += vtime.h
+generic-y += section-core.h

index 20f196b82a6e..89e74b59f32d 100644
@@ -8,3 +8,4 @@ generic-y += mm-arch-hooks.h
 generic-y += preempt.h
 generic-y += trace_clock.h
 generic-y += word-at-a-time.h
+generic-y += section-core.h

index a05218ff3fe4..f089a264cd38 100644
@@ -14,3 +14,4 @@ generic-y += trace_clock.h
 generic-y += xor.h
 generic-y += serial.h
 generic-y += word-at-a-time.h
+generic-y += section-core.h

index 751c3373a92c..7b0356dca562 100644
@@ -39,3 +39,4 @@ generic-y += termios.h
 generic-y += trace_clock.h
 generic-y += ucontext.h
 generic-y += xor.h
+generic-y += section-core.h

index cfc918067f80..d51b84d6b4b7 100644
@@ -22,3 +22,4 @@ generic-y += serial.h
 generic-y += trace_clock.h
 generic-y += types.h
 generic-y += word-at-a-time.h
+generic-y += section-core.h

index ba35c41c71ff..7b8a652e43ae 100644
@@ -41,3 +41,4 @@ generic-y += termios.h
 generic-y += trace_clock.h
 generic-y += types.h
 generic-y += xor.h
+generic-y += section-core.h

index 904f3ebf4220..e9849834d55e 100644
@@ -27,3 +27,4 @@ generic-y += topology.h
 generic-y += trace_clock.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
+generic-y += section-core.h

new file mode 100644
index 000000000000..ebffeed8835d
@@ -0,0 +1,19 @@
+#ifndef __UNICORE_SECTION_CORE_ASM_H__
+#define __UNICORE_SECTION_CORE_ASM_H__
+/*
+ * Copyright (C) 2016 Luis R. Rodriguez <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of copyleft-next (version 0.3.1 or later) as published
+ * at http://copyleft-next.org/.
+ */
+
+/* Unicore32 has known to not work properly with the type set, so ignore it */
+
+#define __set_section_core_type(___section, ___core, ___name,		\
+				___level, ___flags, ___type)		\
+	.section ___section.___core.___name.___level, ___flags
+
+#include <asm-generic/section-core.h>
+
+#endif /* __UNICORE_SECTION_CORE_ASM_H__ */

index 2cfed174e3c9..f6914a57bc16 100644
@@ -16,3 +16,4 @@ generic-y += dma-contiguous.h
 generic-y += early_ioremap.h
 generic-y += mcs_spinlock.h
 generic-y += mm-arch-hooks.h
+generic-y += section-core.h

index 28cf4c5d65ef..81ca6816bd72 100644
@@ -31,3 +31,4 @@ generic-y += topology.h
 generic-y += trace_clock.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
+generic-y += section-core.h

index af0254c09424..298252df3c81 100644
@@ -1,6 +1,8 @@
 #ifndef _ASM_GENERIC_SECTIONS_H_
 #define _ASM_GENERIC_SECTIONS_H_
 
+#include <asm/section-core.h>
+
 /* References to section boundaries */
 
 #include <linux/compiler.h>

index 24563970ff7b..731087276a32 100644
@@ -55,6 +55,7 @@
 #endif
 
 #include <linux/export.h>
+#include <asm/section-core.h>
 
 /* Align . to a 8 byte boundary equals to maximum function alignment. */
 #define ALIGN_FUNCTION()  . = ALIGN(8)

@@ -198,8 +199,8 @@
 
 /* .data section */
 #define DATA_DATA							\
-	*(.data)							\
-	*(.ref.data)							\
+	*(SECTION_DATA)							\
+	*(SECTION_REF_DATA)						\
 	*(.data..shared_aligned) /* percpu related */			\
 	MEM_KEEP(init.data)						\
 	MEM_KEEP(exit.data)						\

@@ -262,9 +263,9 @@
  */
 #define RO_DATA_SECTION(align)						\
 	. = ALIGN((align));						\
-	.rodata           : AT(ADDR(.rodata) - LOAD_OFFSET) {		\
+	SECTION_RODATA    : AT(ADDR(SECTION_RODATA) - LOAD_OFFSET) {	\
 		VMLINUX_SYMBOL(__start_rodata) = .;			\
-		*(.rodata) *(.rodata.*)					\
+		*(SECTION_RODATA) *(SECTION_ALL(SECTION_RODATA))	\
 		RO_AFTER_INIT_DATA	/* Read only after init */	\
 		*(__vermagic)		/* Kernel version magic */	\
 		. = ALIGN(8);						\

@@ -394,7 +395,7 @@
 									\
 	/* __*init sections */						\
 	__init_rodata : AT(ADDR(__init_rodata) - LOAD_OFFSET) {		\
-		*(.ref.rodata)						\
+		*(SECTION_REF_RODATA)					\
 		MEM_KEEP(init.rodata)					\
 		MEM_KEEP(exit.rodata)					\
 	}								\

@@ -432,8 +433,8 @@
  * during second ld run in second ld pass when generating System.map */
 #define TEXT_TEXT							\
 		ALIGN_FUNCTION();					\
-		*(.text.hot .text .text.fixup .text.unlikely)		\
-		*(.ref.text)						\
+		*(.text.hot SECTION_TEXT .text.fixup .text.unlikely)	\
+		*(SECTION_REF)						\
 	MEM_KEEP(init.text)						\
 	MEM_KEEP(exit.text)						\
 

@@ -527,11 +528,11 @@
 
 /* init and exit section handling */
 #define INIT_DATA							\
-	*(.init.data)							\
+	*(SECTION_INIT_DATA)						\
 	MEM_DISCARD(init.data)						\
 	KERNEL_CTORS()							\
 	MCOUNT_REC()							\
-	*(.init.rodata)							\
+	*(SECTION_INIT_RODATA)						\
 	FTRACE_EVENTS()							\
 	TRACE_SYSCALLS()						\
 	KPROBE_BLACKLIST()						\

@@ -549,24 +550,24 @@
 	EARLYCON_TABLE()
 
 #define INIT_TEXT							\
-	*(.init.text)							\
+	*(SECTION_INIT)							\
 	*(.text.startup)						\
 	MEM_DISCARD(init.text)
 
 #define EXIT_DATA							\
-	*(.exit.data)							\
+	*(SECTION_EXIT_DATA)						\
 	*(.fini_array)							\
 	*(.dtors)							\
 	MEM_DISCARD(exit.data)						\
 	MEM_DISCARD(exit.rodata)
 
 #define EXIT_TEXT							\
-	*(.exit.text)							\
+	*(SECTION_EXIT)							\
 	*(.text.exit)							\
 	MEM_DISCARD(exit.text)
 
 #define EXIT_CALL							\
-	*(.exitcall.exit)
+	*(SECTION_EXIT_CALL)
 
 /*
  * bss (Block Started by Symbol) - uninitialized data

2.9.2


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Hi Luis,

The linker stuff in the kernel definitely needs someone to take care of it, so it's good to see some effort to clean up and generalize some of it.

Not all your patches seem to depend on each other, so it might be good to push some of the cleanups through first. And some of these core patches could go in bit by bit if necessary.

On this specific patch: while the as and ld sections syntax and semantics are pretty ugly and esoteric, I question how much of this is actually an improvement. Some of it seems to just be wrapping one name with another, or hiding some behaviour in a maybe not intuitive way.

There's two goals by using a macro for these core names. One is to allow us to easily aggregate documentation in central place for each, the second is to then provide more easily grep'able helpers so we can use them when devising extensions or using them in extensions which further customize the sections in the kernel.

On x86 and powerpc .rodata follows .text. On power currently the comment above in .rodata is:

/* Text, read only data and other permanent read-only sections */

When this was introduced however read commit 14cf11af6cf60 ("powerpc: Merge enough to start building in arch/powerpc.")

/* Read-only sections, merged into text segment: */

The format and style of putting rodata after text is kept from the older commits.

This begs the question. What the hell is this thing talking about?

On Linux this is done via mark_rodata_ro() on init/main.c when CONFIG_DEBUG_RODATA on architectures that support it. Architectures that implement this typically use issues set_memory_ro() -- on x86 a start address used is PFN_ALIGN(_text) with an end address of &__end_rodata_hpage_align.

When architectures do not have CONFIG_DEBUG_RODATA() you end up with:

static inline void mark_readonly(void)

{                                                                               
        pr_warn("This architecture does not have kernel memory protection.\n"); 
}

So -- I should I clarify then in Linux we strive to have helpers adjust text and rodata set to ro with memory protection implemented via mark_readonly(). Architectures that do not support memory protection will lack a mark_readonly() implementation.

For now I figured a less controversial introduction to the documentation as bland as it was above in my original patch would suffice, we can then expand on it with something like the above. Thoughts?

Its not intended to grab .text but rather its for helpers that provide customizations based on a core section as base, in this case given your example it would be used by section ranges and linker tables for .text. Both section ranges and linker tables use postfix .something for their customizations. The SECTION_ALL() macro then is a helper for customizations on a core section.

If the name is misleading would SECTION_CORE_ALL() be better with some documentation explaining this and the above goal ?

Help me bikeshed, any name suggestions?

Indeed, it actually seems we don't have much in this area, so this is small baby step in that direction.

I thought about this -- I'd be adding a new asm-generic/asm.h -- are folks OK with that right now? Or should we do that as a secondary step ? I preferred to do this as a secondary step as this series is long enough already and there is quite a bit that can be dumped in a common asm-generic/asm.h, a few thoughts on this already:

o x86's asm/asm.h's use of __ASM_FORM() and include/linux/stringify.h share some traits which deserve possible consideration / rebranding.
o Since C asm() just wrap things in strings defining a core set of helpers for a task seems justifiable, so for example we have __set_section_core_type(). Raw asm code then would use __set_section_core_type() directly and C asm() would just __stringify() it.

I figured a bit of bikeshedding would be possible here, so I decided to leave this for a later set of patches. But indeed, I agree with you. If we want this meshed out now.. let me know and lets bikeshed away...

We have ELF standard sections, and we have then sections which Linux has introduced over the years which are now just known to be expected part of Linux, such as init stuff which we free after boot. The combination of the ELF standard sections and series of expected sections in Linux across all architectures is what this refers to as Linux de-facto/standard/common sections. The header file is intended to document these, step by step, and also provide helpers which allow further customizations based on these sections.

I'm not so sure about this for section stuff -- are we certain we won't ever clash with some built in compiler things? I'm fine to drop the prefix -- bikeshedding -- will drop it for the next series unless I hear otherwise...

Luis

Documentation is good, but not necessary to have the extra name indirection. Sections tend (not always, but it would be nice if they did) to follow the .name convention, which makes them reasonably easy to grep for. They are also the names you'll be grepping for when you look at disassembly.

But follows is not the same as combined. And together with the comment that RODATA is for code (which is wrong, it's data), it make it seem like it is actually combined.

Right, I wasn't talking about arch implementation of how the ro protection is done, so much as just the comments being a bit misleading.

I think comments are one of the key features of this patch series (or at least this patch, I've not looked through the others so much yet). I'm no expert on linker stuff, but I think a lot of arch maintainers aren't necessarily either so you tend to get a lot of copy and paste without always people knowing what exactly is happening. It would be really good to have some longer explanations and justifications/examples IMO. So I don't think that would be controversial if you wanted to expand on it.

Right, it's just that .text.* is *immediately* obvious. SECTION_ALL() is not.

I don't know... not to be glib, but .section.* would be better and not require documentation.

CORE does not really add anything as far as I can see. Other types of .text including ones which are automatically generated by the compiler, for better or worse, are .text.x sections too.

I would like to see more standardisation of naming convention -- some sections start with .., some start with no dots, some use . to separate logical "subsections", others use underscores or something else. I just don't see it would be a problem to simply use the raw names and linker wildcards for it.

BTW, I'm not trying to bikeshed :) This doesn't affect the value of your patch at all, it was just an offhand thing I saw.

It's fine, I don't mind too much. I think asm-generic/asm.h should be fine for generic asm'isms though. Or assembler.h to match compiler.h.

Well but your macros are not linker sections. They are "Linux sections", which appear to give you a start and end symbol name, but does not direct the linker to create a specific output section. I just can't work out what exactly is a "custom Linux section", and what DECLARE_LINUX_SECTION(), for example, actaully gives you.

Thanks,
Nick

Just thought of more more justification I had forgotten. I cover it below.

Fair point.

git grep .text doesn't work but that is typically expected... git grep \.text doesn't work as expected

Ah finally:

git grep "\.text" seems to work. But WTF.

But:

git grep SECTION_TEXT works as expected immediately.

I guess its a matter of perspective.

Sure but if you're grepping asm, you very likely know what to look for.

True and as I confirmed below, on PowerPC this is certainly not true.

Where did I have that? If you refer to the above SECTION_TEXT documentation, it refers to SECTION_TEXT being for code, but the goal was to highlight that SECTION_TEXT is for execution, while SECTION_RODATA was for data. This certainly can use some love though, thanks, will just drop the SECTION_RODATA reference *or* properly explain the whole thing below.

Will fix to ensure this is understood in proper context.

Sure, got it, thanks, will fix.

Definitely -- the goal was to give us central place to document some of this obscure dark magic only a few witches and warlocks tend to be aware of.

:) Yes indeed, the little crusade over the PowerPC linker script comments on .text and ro data is an example of how easily things can be misleading.

Sure, but what I was trying to say above is I'd rather have the basic layout of the documentation finalized before we start getting into very specific detailed elaborate details on some of these things. For instance we still haven't decided if we wanted SECTION_TEXT or just require everyone to hard code in .text in every place a user wants to use .text sections. I'd rather settle that before trying to document mark_readonly().

Which is why I was suggesting perhaps an alternative name.

Well consider the issues below for a second... and keep in mind with linker tables we are about to open the prospect to add more things into the kernel's sections more easily than before.

Actually, sorry, in this case SECTION_ALL() *was* intended for things that are not linker tables or section ranges, instead this was for globs that want to use the new section macro names, so we only use this for:
*(SECTION_ALL(SECTION_RODATA)) at this time. It would seem we just did not have .text.* and friends (other section names documented here). So this is more of a reaction to provide a way to use a glob for section names if they have a macro name.

The idea was to add helpers to do the globbing more easily.

The glob for sections now documented is SECTION_ALL()
The glob that is range specific is SECTION_RNG_ALL()
The glob that is linker table specific is SECTION_TBL_ALL()

The only one needing SECTION_ALL() it turns out was .rodata:

-               *(.rodata) *(.rodata.*)                                 \
+               *(SECTION_RODATA) *(SECTION_ALL(SECTION_RODATA))        \

Agreed... Actually while at it -- anyone happen to know why the two dot thing started creeping up?

A concern here is more abuse over this if we now expose APIs to users to more easily customize sections. So let's review what the chances are.

$ git grep DEFINE_SECTION_RANGE| egrep -v "tools|include|Document"
kernel/kprobes.c:DEFINE_SECTION_RANGE(kprobes, SECTION_TEXT);

These require the actual desired section specified. Do we want to just hide that ? Or are we OK in assuming users willing to use proper names here?

For linker tables we actually provide full helpers for each section type. So we have:

$ git grep DEFINE_LINKTABLE| egrep -v "tools|include|Document"
drivers/base/firmware_class.c:DEFINE_LINKTABLE_RO(struct builtin_fw, builtin_fw);
kernel/jump_label.c:DEFINE_LINKTABLE(struct jump_entry, __jump_table);
kernel/kprobes.c:DEFINE_LINKTABLE_INIT_DATA(unsigned long, _kprobe_blacklist);
lib/dynamic_debug.c:DEFINE_LINKTABLE(struct _ddebug, __verbose);

So for linker tables we're safe from abuse as we provide all direct use of the section up to the implementation behind the scenes.

If we're happy then with people using a proper section name for section ranges then I think we can require the full section name being spelled out.

Just saying, if you say its ugly please help me with a different name then.

I'd like address this in asm.h but I would hope we can do this as a secondary step, given the length of this patch set already. Thoughts ?

You're right the above can use some love to help explain this better.

How about:

At the top just use "Linux sections helpers"

Then:

/**
* DOC: Introduction
*
* We document below a dedicated set of helpers used in Linux to make sections
* defined in the Linux linker script accessible in C code in a generic form and
* and provide certain attributes about them.
*/

Its a way to replace the:

extern char foo[], foo__end[];

So this provides a generalized form to use declarations used in C code to make the linker script start and end symbols from esctions accessible in C code. Since DEFINE_SECTION_RANGE() and DEFINE_LINKTABLE() macros use this, then the DECLARE_LINUX_SECTION() is only needed if you need access to these symbols in C code outside of the one that is defining and mainly in charge of managing the section. We provide DECLARE_*() helpers for section ranges and linker tables though so those can be used instead to help annotate the type of a custom section they are.

So for instance, since the following tables are used in C code outside of the code that implemented and manages them:

mcgrof@ergon ~/linux-next (git::20160822-linker-table-v5)$ git grep DECLARE_LINKTA| egrep -v "Documentation|tools|tables" arch/x86/kernel/cpu/microcode/core.c:DECLARE_LINKTABLE_RO(struct builtin_fw, builtin_fw); include/linux/dynamic_debug.h:DECLARE_LINKTABLE(struct _ddebug, __verbose); include/linux/jump_label.h:DECLARE_LINKTABLE(struct jump_entry, __jump_table); include/linux/kprobes.h:DECLARE_LINKTABLE(unsigned long, _kprobe_blacklist);

Note that the big trick here was to enable users to associate a new custom section in C to a well defined already existing Linux section without modifying the Linux linker script. Then, since as we observe and study uses of how Linux sections are used, we've noticed a pattern -- most declarations of these sections of really of two types, a section ranges or linker table. The patch set then provides generic building blocks for these and ports a few existing custom Linux sections to them as an example.

Luis

This is simply how grep works though.

After you have gone through the extra layer of naming indirection to work out what it is. I'm still not sold on the name indirection and hiding wildcards. Not just for asm grepping, but I don't think it's a negative thing for devs working on the linker to know what actual section names and commands are being used, as much as possible.

OK.

+/**
+ * DOC: SECTION_RODATA
+ *
+ * Macro name for code which must be protected from write access, read only
+ * data.
+ */
+#define SECTION_RODATA .rodata

This together with the "combined with .text" part confused me.

Thanks.

I still don't see this is better than

.text*
.text.*
.text.range.*
.text.table.*
etc.

I'm not sure, but I suspect it may have been due to . not being a valid C symbol name. I'm not saying it's always the wrong thing to do, but I think copy&paste and lack of documentation has left the naming conventions in need of some love.

The section names themselves of course can and should have some greppable distinguishing conventions -- we don't need macro name for that.

For me, DEFINE_SECTION_RANGE(kprobes, .text) would be fine.

Sure, but point taken it's more productive to discuss fundamentals first. Let's consider exact details afterward.

It's not a big deal, so whatever suits you. Some of the bugfixes and cleanups could be pushed through various arch and other maintainers first too, which would make the core series look more managable and touch fewer parts.

Oh, that makes more sense. The SECTION stuff and custom sections was confusing me. I would prefer just to drop all the LINUX_SECTION naming and make it match the functionality you're using. For example:

+DEFINE_LINKTABLE(struct jump_entry, __jump_table);
+
/* mutex to protect coming/going of the the jump_label table */ static DEFINE_MUTEX(jump_label_mutex);

@@ -274,8 +277,6 @@ static void __jump_label_update(struct static_key *key,

void __init jump_label_init(void)
{
- struct jump_entry *iter_start = __start___jump_table;
- struct jump_entry *iter_stop = __stop___jump_table;
struct static_key *key = NULL;
struct jump_entry *iter;

@@ -292,9 +293,10 @@ void __init jump_label_init(void)
return;

jump_label_lock();
- jump_label_sort_entries(iter_start, iter_stop);
+ jump_label_sort_entries(LINUX_SECTION_START(__jump_table),
+ LINUX_SECTION_END(__jump_table));

Now I think this is a fine abstraction to have. I think it would look even cleaner if you had:

LINKTABLE_START(__jump_table)
LINKTABLE_END(__jump_table)

Then do we need to even have the LINUX_SECTION middle man at all?

Thanks,
Nick

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OK lets see what it looks like after dropping them. Will try that.

OK will drop it.

OK will keep this one.

Ah, thing is we use this for both linktables and section ranges. Or do we want macros for both that do the same thing ?

Luis

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Thank you for considering it, I appreciate that.

I think it would make the code using it more readable.

Thanks,
Nick

Alrighty... so:

LINKTABLE_START()
LINKTABLE_END()

SECTION_RANGE_START()
SECTION_RANGE_END()

And these macros do the exact same thing. Ie, nothing shared. Right?

Luis

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Yeah I think so. Internally they would probably be aliased to the same common definition (unless you had some type check or something), but user would know about such details.

Thanks,
Nick

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was

naming

static_key *key,

What name should we use for such common macro definition ?

Luis

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Ah, not really sure. I guess the "link table" is some kind of section range? I haven't actually looked closely at both of them in the subsequent patches. It matters less if it's not expected to be used as an API though.

OK well, going with LINUX_SECTION_START() so we'll have:

#define LINKTABLE_START LINUX_SECTION_START
#define LINKTABLE_END LINUX_SECTION_END

#define SECTION_RANGE_START LINUX_SECTION_START
#define SECTION_RANGE_END LINUX_SECTION_END

Is that OK?

Luis

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I guess so, without having seen the updated, although I don't see why you'd not just

#define LINKTABLE_START SECTION_RANGE_START

From: "Luis R. Rodriguez" <[email protected]>

When SORT(foo.*) is used the current sed replacements add SORT(foo.literal foo.*), this breaks linking. Avoid adding literals for SORT globs, if needed, these need to be added manually.

---
 arch/xtensa/kernel/Makefile | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

index c31f5d5afc7d..8180850ed147 100644
@@ -29,10 +29,10 @@ AFLAGS_mxhead.o += -mtext-section-literals
 #
 # Replicate rules in scripts/Makefile.build
 
-sed-y = -e ':a; s/\*(\([^)]*\)\.text\.unlikely/*(\1.literal.unlikely .{text}.unlikely/; ta; ' \
-	-e ':b; s/\*(\([^)]*\)\.text\(\.[a-z]*\)/*(\1.{text}\2.literal .{text}\2/; tb; ' \
-	-e ':c; s/\*(\([^)]*\)\(\.[a-z]*it\|\.ref\)\.text/*(\1\2.literal \2.{text}/; tc; ' \
-	-e ':d; s/\*(\([^)]\+ \|\)\.text/*(\1.literal .{text}/; td; ' \
+sed-y = -e ':a; s/\*(\([^)SORT]*\)\.text\.unlikely/*(\1.literal.unlikely .{text}.unlikely/; ta; ' \
+	-e ':b; s/\*(\([^)SORT]*\)\.text\(\.[a-z]*\)/*(\1.{text}\2.literal .{text}\2/; tb; ' \
+	-e ':c; s/\*(\([^SORT)]*\)\(\.[a-z]*it\|\.ref\)\.text/*(\1\2.literal \2.{text}/; tc; ' \
+	-e ':d; s/\*(\([^SORT)]\+ \|\)\.text/*(\1.literal .{text}/; td; ' \
 	-e 's/\.{text}/.text/g'
 
 quiet_cmd__cpp_lds_S = LDS     $@

2.9.2


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From: "Luis R. Rodriguez" <[email protected]>

Section ranges are on one of the types of custom sections types used in Linux. This provides a series of helpers for defining them and using them. Most importantly this also enables us to avoid modifying the linker script when we add a new section range.

It turns out a lot of custom sections are actually section ranges, and these are typically spelled out in their architecture specific asm/sections.h file -- we anable architectures to override what asm is used for section ranges but start by default trusting the asm-generic version all around.

v4:

o tons of documentation love
o fix arch/x86/tools/relocs.c typo - which caused compilation issues on old toolchains
o port to new shiny sphinx documentation
o sprinkle a few more needed VMLINUX_SYMBOL() - fixes compilation on blackfin
o name changes as suggested by Boris:
- %s/SECTION_TYPE_RANGES/rng/g
- %s/SECTION_TYPE/SECTION_CORE/g
- %s/section_type_asmtype/section_core_type/g
- %s/section_type/section_core/g
- %s/section_rng/set_section_rng/g
- rebrand DECLARE_SECTION_RNG() as DEFINE_SECTION_RANGE() - this is the asm version of the respective C version, this will have a userspace C demo added later.
o move __LINUX_RANGE() and __LINUX_RANGE_ORDER() - fixes builds on sparc
o adds section ranges to linker script
o rename SECTION_RANGE_ALL()
o use default alignment, fixes builds on powerpc and arm for both __LINUX_RANGE() and __LINUX_RANGE_ORDER()
o expand documentation to document modules support
o add maintainers
o use generic-y

v3: new in this series, uses copyleft-next

---
 Documentation/sections/index.rst   |   1 +
 Documentation/sections/ranges.rst  |  49 ++++++++++++++
 MAINTAINERS                        |  10 +++
 arch/alpha/include/asm/Kbuild      |   1 +
 arch/arc/include/asm/Kbuild        |   1 +
 arch/arm/include/asm/Kbuild        |   1 +
 arch/arm64/include/asm/Kbuild      |   1 +
 arch/avr32/include/asm/Kbuild      |   1 +
 arch/blackfin/include/asm/Kbuild   |   1 +
 arch/c6x/include/asm/Kbuild        |   1 +
 arch/cris/include/asm/Kbuild       |   1 +
 arch/frv/include/asm/Kbuild        |   1 +
 arch/h8300/include/asm/Kbuild      |   1 +
 arch/hexagon/include/asm/Kbuild    |   1 +
 arch/ia64/include/asm/Kbuild       |   1 +
 arch/m32r/include/asm/Kbuild       |   1 +
 arch/m68k/include/asm/Kbuild       |   1 +
 arch/metag/include/asm/Kbuild      |   1 +
 arch/microblaze/include/asm/Kbuild |   1 +
 arch/mips/include/asm/Kbuild       |   1 +
 arch/mn10300/include/asm/Kbuild    |   1 +
 arch/nios2/include/asm/Kbuild      |   1 +
 arch/openrisc/include/asm/Kbuild   |   1 +
 arch/parisc/include/asm/Kbuild     |   1 +
 arch/powerpc/include/asm/Kbuild    |   1 +
 arch/s390/include/asm/Kbuild       |   1 +
 arch/score/include/asm/Kbuild      |   1 +
 arch/sh/include/asm/Kbuild         |   1 +
 arch/sparc/include/asm/Kbuild      |   1 +
 arch/tile/include/asm/Kbuild       |   1 +
 arch/um/include/asm/Kbuild         |   1 +
 arch/unicore32/include/asm/Kbuild  |   1 +
 arch/x86/include/asm/Kbuild        |   1 +
 arch/x86/tools/relocs.c            |   2 +
 arch/xtensa/include/asm/Kbuild     |   1 +
 include/asm-generic/ranges.h       |  89 ++++++++++++++++++++++++++
 include/asm-generic/vmlinux.lds.h  |  12 +++-
 include/linux/ranges.h             | 128 +++++++++++++++++++++++++++++++++++++
 38 files changed, 320 insertions(+), 2 deletions(-)
 create mode 100644 Documentation/sections/ranges.rst
 create mode 100644 include/asm-generic/ranges.h
 create mode 100644 include/linux/ranges.h

index d411e9b22eb3..6dd93ddd5dbe 100644
@@ -9,3 +9,4 @@ used throughout the kernel to help declare and define them.
    :maxdepth: 4
 
    section-core
+   ranges

index 689c12075842..1a217751aa8a 100644
@@ -5217,6 +5217,16 @@ S:	Supported
 F:	drivers/base/power/domain*.c
 F:	include/linux/pm_domain.h
 
+GENERIC SECTION RANGES
+M:	"Luis R. Rodriguez" <[email protected]>
+M:	"H. Peter Anvin" <[email protected]>
+L:	[email protected]
+L:	[email protected]
+S:	Supported
+F:	include/asm-generic/ranges.h
+F:	include/linux/ranges.h
+F:	Documentation/sections/ranges.rst
+
 GENERIC SECTIONS
 M:	"Luis R. Rodriguez" <[email protected]>
 M:	Josh Poimboeuf <[email protected]>

index 5422827f1585..e44c896b91c4 100644
@@ -11,3 +11,4 @@ generic-y += preempt.h
 generic-y += sections.h
 generic-y += trace_clock.h
 generic-y += section-core.h
+generic-y += ranges.h

index 9a0929576de1..e5295413fdf8 100644
@@ -51,3 +51,4 @@ generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
+generic-y += ranges.h

index 47923635be16..8e52300e1eed 100644
@@ -40,3 +40,4 @@ generic-y += timex.h
 generic-y += trace_clock.h
 generic-y += unaligned.h
 generic-y += section-core.h
+generic-y += ranges.h

index 42d00806e4fb..5ff184574976 100644
@@ -53,3 +53,4 @@ generic-y += user.h
 generic-y += vga.h
 generic-y += xor.h
 generic-y += section-core.h
+generic-y += ranges.h

index f2c3b656a0e7..edc176348d7c 100644
@@ -23,3 +23,4 @@ generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
+generic-y += ranges.h

index 7de674411bed..35b7752e65c0 100644
@@ -49,3 +49,4 @@ generic-y += user.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
+generic-y += ranges.h

index 38127ce747be..cede2a950fbf 100644
@@ -63,3 +63,4 @@ generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
+generic-y += ranges.h

index 385cd88a9d9e..fb8bb4112773 100644
@@ -46,3 +46,4 @@ generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
+generic-y += ranges.h

index 46d7c599d9b8..5191fec655d7 100644
@@ -9,3 +9,4 @@ generic-y += preempt.h
 generic-y += trace_clock.h
 generic-y += word-at-a-time.h
 generic-y += section-core.h
+generic-y += ranges.h

index 1ec04ec1c82b..7929a992566c 100644
@@ -76,3 +76,4 @@ generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
+generic-y += ranges.h

index 37d7bfae7619..af17ee334788 100644
@@ -61,3 +61,4 @@ generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
+generic-y += ranges.h

index 672c6d5da18c..d8f226b35a0a 100644
@@ -10,3 +10,4 @@ generic-y += trace_clock.h
 generic-y += vtime.h
 generic-y += word-at-a-time.h
 generic-y += section-core.h
+generic-y += ranges.h

index 6111e1523750..1c6504d29312 100644
@@ -12,3 +12,4 @@ generic-y += sections.h
 generic-y += trace_clock.h
 generic-y += word-at-a-time.h
 generic-y += section-core.h
+generic-y += ranges.h

index eef72c464c9b..d465f51c2088 100644
@@ -36,3 +36,4 @@ generic-y += types.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
+generic-y += ranges.h

index 50ebd5a30d16..c869b1ebd583 100644
@@ -57,3 +57,4 @@ generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
+generic-y += ranges.h

index c6c2cf6edc98..63c083a1f8da 100644
@@ -12,3 +12,4 @@ generic-y += syscalls.h
 generic-y += trace_clock.h
 generic-y += word-at-a-time.h
 generic-y += section-core.h
+generic-y += ranges.h

index 12f7c5984c03..ed225600c8a4 100644
@@ -21,3 +21,4 @@ generic-y += user.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
+generic-y += ranges.h

index f8145bc85835..656af7b69940 100644
@@ -11,3 +11,4 @@ generic-y += sections.h
 generic-y += trace_clock.h
 generic-y += word-at-a-time.h
 generic-y += section-core.h
+generic-y += ranges.h

index c9c7cb82b00f..c55880659d67 100644
@@ -64,3 +64,4 @@ generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
+generic-y += ranges.h

index 86175e701869..7d6a704b808c 100644
@@ -72,3 +72,4 @@ generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
+generic-y += ranges.h

index 6f43f33f0e0f..1a263a7158e2 100644
@@ -30,3 +30,4 @@ generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
+generic-y += ranges.h

index b49fab7bab2f..065c6e84fb67 100644
@@ -8,3 +8,4 @@ generic-y += preempt.h
 generic-y += rwsem.h
 generic-y += vtime.h
 generic-y += section-core.h
+generic-y += ranges.h

index 89e74b59f32d..3e8b95927cb5 100644
@@ -9,3 +9,4 @@ generic-y += preempt.h
 generic-y += trace_clock.h
 generic-y += word-at-a-time.h
 generic-y += section-core.h
+generic-y += ranges.h

index f089a264cd38..f0cdb2cbca4d 100644
@@ -15,3 +15,4 @@ generic-y += xor.h
 generic-y += serial.h
 generic-y += word-at-a-time.h
 generic-y += section-core.h
+generic-y += ranges.h

index 7b0356dca562..c9bb7932a3d1 100644
@@ -40,3 +40,4 @@ generic-y += trace_clock.h
 generic-y += ucontext.h
 generic-y += xor.h
 generic-y += section-core.h
+generic-y += ranges.h

index d51b84d6b4b7..79664d10e63b 100644
@@ -23,3 +23,4 @@ generic-y += trace_clock.h
 generic-y += types.h
 generic-y += word-at-a-time.h
 generic-y += section-core.h
+generic-y += ranges.h

index 7b8a652e43ae..951fa4be571d 100644
@@ -42,3 +42,4 @@ generic-y += trace_clock.h
 generic-y += types.h
 generic-y += xor.h
 generic-y += section-core.h
+generic-y += ranges.h

index e9849834d55e..99be54949b99 100644
@@ -28,3 +28,4 @@ generic-y += trace_clock.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
+generic-y += ranges.h

index 256c45b3ae34..6c35905fe371 100644
@@ -64,3 +64,4 @@ generic-y += user.h
 generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
+generic-y += ranges.h

index f6914a57bc16..f790756fdb48 100644
@@ -17,3 +17,4 @@ generic-y += early_ioremap.h
 generic-y += mcs_spinlock.h
 generic-y += mm-arch-hooks.h
 generic-y += section-core.h
+generic-y += ranges.h

index 0c2fae8d929d..c215db049920 100644
@@ -68,6 +68,8 @@ static const char * const sym_regex_kernel[S_NSYMTYPES] = {
 	"__end_rodata|"
 	"__initramfs_start|"
 	"(jiffies|jiffies_64)|"
+	".rodata.rng.*|"
+	".init.text.rng.*|"
 #if ELF_BITS == 64
 	"__per_cpu_load|"
 	"init_per_cpu__.*|"

index 81ca6816bd72..221b6b652500 100644
@@ -32,3 +32,4 @@ generic-y += trace_clock.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
+generic-y += ranges.h

index 731087276a32..ad843555e6a4 100644
@@ -56,6 +56,7 @@
 
 #include <linux/export.h>
 #include <asm/section-core.h>
+#include <asm/ranges.h>
 
 /* Align . to a 8 byte boundary equals to maximum function alignment. */
 #define ALIGN_FUNCTION()  . = ALIGN(8)

@@ -200,6 +201,7 @@
 /* .data section */
 #define DATA_DATA							\
 	*(SECTION_DATA)							\
+	*(SORT(SECTION_RNG_ALL(SECTION_DATA)))				\
 	*(SECTION_REF_DATA)						\
 	*(.data..shared_aligned) /* percpu related */			\
 	MEM_KEEP(init.data)						\

@@ -265,7 +267,9 @@
 	. = ALIGN((align));						\
 	SECTION_RODATA    : AT(ADDR(SECTION_RODATA) - LOAD_OFFSET) {	\
 		VMLINUX_SYMBOL(__start_rodata) = .;			\
-		*(SECTION_RODATA) *(SECTION_ALL(SECTION_RODATA))	\
+		*(SECTION_RODATA)					\
+		*(SORT(SECTION_RNG_ALL(SECTION_RODATA)))		\
+		*(SECTION_ALL(SECTION_RODATA))				\
 		RO_AFTER_INIT_DATA	/* Read only after init */	\
 		*(__vermagic)		/* Kernel version magic */	\
 		. = ALIGN(8);						\

@@ -433,7 +437,9 @@
  * during second ld run in second ld pass when generating System.map */
 #define TEXT_TEXT							\
 		ALIGN_FUNCTION();					\
-		*(.text.hot SECTION_TEXT .text.fixup .text.unlikely)	\
+		*(.text.hot SECTION_TEXT)				\
+		*(SORT(SECTION_RNG_ALL(SECTION_TEXT)))			\
+		*(.text.fixup .text.unlikely)				\
 		*(SECTION_REF)						\
 	MEM_KEEP(init.text)						\
 	MEM_KEEP(exit.text)						\

@@ -529,6 +535,7 @@
 /* init and exit section handling */
 #define INIT_DATA							\
 	*(SECTION_INIT_DATA)						\
+	*(SORT(SECTION_RNG_ALL(SECTION_INIT_DATA)))			\
 	MEM_DISCARD(init.data)						\
 	KERNEL_CTORS()							\
 	MCOUNT_REC()							\

@@ -551,6 +558,7 @@
 
 #define INIT_TEXT							\
 	*(SECTION_INIT)							\
+	*(SORT(SECTION_RNG_ALL(SECTION_INIT)))				\
 	*(.text.startup)						\
 	MEM_DISCARD(init.text)
 

2.9.2


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From: "Luis R. Rodriguez" <[email protected]>

A linker table is a data structure that is stitched together from items in multiple object files. Linux has historically implicitly used linker tables for ages, however they were all built in an adhoc manner which requires linker script modifications, per architecture. This adds a general linker table solution so that a new linker table can be implemented by changing C code only. The Linux linker table was inspired by Michael Brown's iPXE's linker table solution, it has been been completely re-written and adapted for integration and use on Linux.

The same philosophy is borrowed, extended and further simplified:

Linker tables enable an extremely light weight linker build time solution for feature ordering and selection, this can help to both simplify init sequences in a generic fashion and helps avoiding code bit-rotting when desirable. Further changes will be added later which will make more evident how code bit rot can be avoided using linker tables.

v4:

o Split out kbuild additions to help with code bit rot into its own patch
o tons of documentation love
o fix arch/x86/tools/relocs.c typo - which caused compilation issues on old toolchains
o add c6x toolchain work around as discussed with Mark Salter
o sprinkle a few more needed VMLINUX_SYMBOL() - fixes compilation on blackfin
o suggested name changes by boris:
- %s/SECTION_TYPE_RANGES/rng/g
- %s/SECTION_TYPE/SECTION_CORE/g
- %s/section_type_asmtype/section_core_type/g
- %s/section_type/section_core/g
- %s/section_rng/set_section_rng/g
- Drop DECLARE_SECTION_TBL() -- this is an asm equivalent DEFINE_LINKTABLE() -- this however is not used yet, and it requires a bit more work to match the C code definitions.
o drop tools/include/linux/sections.h in favor of the more popular open coding the names for tools
o expand documentation to include module support
o add maintaners
o Use generic-y
o move .text.tbl before unlikely to match the other sections

v3:

o addressed initial modular support test cases
o added generic asm macros so linker tables can be used in asm code / C asm calls
o section ranges are now split up into their own set of files
o use asm/sections.h instead of linux/sections.h for the linker script
o add a sections.h file for each architecture that was missing one, this is needed now as we'll be relying on sections.h for custom section types in code rather than custom architecture specific linker script hacks.
o full rewrite at this point, decided to pick copyleft-next license for this work

v2:

o modified completely to match feedback by community, made equivalent modifications to userspace solution. This is pretty much a complete rewrite of how we present and use linker tables. By using standard sections we no longer have to make custom linker script extensions for each new linker table solution, you just pick a linker table type by section type.
o extend documention considerably, including use of kdoc
o drop ICC hacks per popular request to ignore such issues for now
o use sections.h - this lets us streamline a clean use case of well documented sections. To help further with this make use of SECTION_TBL() to allow use of these in code and SECTION_TBL_ALL() on linker scripts, as well as SECTION_TBL_ALL_STR() on relocs.c when needed.

---
 Documentation/sections/index.rst         |   1 +
 Documentation/sections/linker-tables.rst | 187 ++++++++++
 MAINTAINERS                              |  12 +
 arch/alpha/include/asm/Kbuild            |   1 +
 arch/arc/include/asm/Kbuild              |   1 +
 arch/arm/include/asm/Kbuild              |   1 +
 arch/arm64/include/asm/Kbuild            |   1 +
 arch/avr32/include/asm/Kbuild            |   1 +
 arch/blackfin/include/asm/Kbuild         |   1 +
 arch/c6x/include/asm/tables.h            |  26 ++
 arch/cris/include/asm/Kbuild             |   1 +
 arch/frv/include/asm/Kbuild              |   1 +
 arch/h8300/include/asm/Kbuild            |   1 +
 arch/hexagon/include/asm/Kbuild          |   1 +
 arch/ia64/include/asm/Kbuild             |   1 +
 arch/m32r/include/asm/Kbuild             |   1 +
 arch/m68k/include/asm/Kbuild             |   1 +
 arch/metag/include/asm/Kbuild            |   1 +
 arch/microblaze/include/asm/Kbuild       |   1 +
 arch/mips/include/asm/Kbuild             |   1 +
 arch/mn10300/include/asm/Kbuild          |   1 +
 arch/nios2/include/asm/Kbuild            |   1 +
 arch/openrisc/include/asm/Kbuild         |   1 +
 arch/parisc/include/asm/Kbuild           |   1 +
 arch/powerpc/include/asm/Kbuild          |   1 +
 arch/s390/include/asm/Kbuild             |   1 +
 arch/score/include/asm/Kbuild            |   1 +
 arch/sh/include/asm/Kbuild               |   1 +
 arch/sparc/include/asm/Kbuild            |   1 +
 arch/tile/include/asm/Kbuild             |   1 +
 arch/um/include/asm/Kbuild               |   1 +
 arch/unicore32/include/asm/Kbuild        |   1 +
 arch/x86/include/asm/Kbuild              |   1 +
 arch/x86/tools/relocs.c                  |   2 +
 arch/xtensa/include/asm/Kbuild           |   1 +
 include/asm-generic/ranges.h             |  14 +
 include/asm-generic/tables.h             |  50 +++
 include/asm-generic/vmlinux.lds.h        |   6 +
 include/linux/tables.h                   | 567 +++++++++++++++++++++++++++++++
 scripts/Makefile.clean                   |   2 +
 40 files changed, 897 insertions(+)
 create mode 100644 Documentation/sections/linker-tables.rst
 create mode 100644 arch/c6x/include/asm/tables.h
 create mode 100644 include/asm-generic/tables.h
 create mode 100644 include/linux/tables.h

index 6dd93ddd5dbe..4514c5738b33 100644
@@ -10,3 +10,4 @@ used throughout the kernel to help declare and define them.
 
    section-core
    ranges
+   linker-tables

index 1a217751aa8a..e3569ed12c86 100644
@@ -5200,6 +5200,18 @@ S:	Maintained
 F:	include/asm-generic/
 F:	include/uapi/asm-generic/
 
+GENERIC LINKER TABLES
+M:	"Luis R. Rodriguez" <[email protected]>
+M:	"H. Peter Anvin" <[email protected]>
+L:	[email protected]
+L:	[email protected]
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux.git sections
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux-next.git sections
+S:	Supported
+F:	include/asm-generic/tables.h
+F:	include/linux/tables.h
+F:	Documentation/sections/linker-tables.rst
+
 GENERIC PHY FRAMEWORK
 M:	Kishon Vijay Abraham I <[email protected]>
 L:	[email protected]

index e44c896b91c4..f3bdc31d3c97 100644
@@ -12,3 +12,4 @@ generic-y += sections.h
 generic-y += trace_clock.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index e5295413fdf8..70f252472cb9 100644
@@ -52,3 +52,4 @@ generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index 8e52300e1eed..d13700f573d0 100644
@@ -41,3 +41,4 @@ generic-y += trace_clock.h
 generic-y += unaligned.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index 5ff184574976..a1991517aad6 100644
@@ -54,3 +54,4 @@ generic-y += vga.h
 generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index edc176348d7c..a6cd145515ae 100644
@@ -24,3 +24,4 @@ generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index 35b7752e65c0..b71893b1cd53 100644
@@ -50,3 +50,4 @@ generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

new file mode 100644
index 000000000000..09a9e31c573a
@@ -0,0 +1,26 @@
+#ifndef _ASM_C6X_ASM_TABLES_H
+#define _ASM_C6X_ASM_TABLES_H
+/*
+ * Copyright (C) 2016 Luis R. Rodriguez <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of copyleft-next (version 0.3.1 or later) as published
+ * at http://copyleft-next.org/.
+ */
+
+/*
+ * The c6x toolchain has a bug present even on gcc-6 when non-weak attributes
+ * are used and sends them to .rodata even though const data with weak
+ * attributes are put in .const, this forces the linker to believe the address
+ * is relative relative to the a base + offset and you end up with SB-relative
+ * reloc error upon linking. Work around this by by forcing both start and
+ * ending const RO waek linker table entry to be .const to fix this for now.
+ *
+ * [0] https://lkml.kernel.org/r/[email protected]
+ */
+
+#define SECTION_TBL_RO		.const
+
+#include <asm-generic/tables.h>
+
+#endif /* _ASM_C6X_ASM_TABLES_H */

index fb8bb4112773..7062c1be7913 100644
@@ -47,3 +47,4 @@ generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index 5191fec655d7..4a59cbda5091 100644
@@ -10,3 +10,4 @@ generic-y += trace_clock.h
 generic-y += word-at-a-time.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index 7929a992566c..d79968d93c12 100644
@@ -77,3 +77,4 @@ generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index af17ee334788..d59ac1c1858b 100644
@@ -62,3 +62,4 @@ generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index d8f226b35a0a..76540f143473 100644
@@ -11,3 +11,4 @@ generic-y += vtime.h
 generic-y += word-at-a-time.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index 1c6504d29312..24088f3c733c 100644
@@ -13,3 +13,4 @@ generic-y += trace_clock.h
 generic-y += word-at-a-time.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index d465f51c2088..65c0df17f70e 100644
@@ -37,3 +37,4 @@ generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index c869b1ebd583..2538224899fd 100644
@@ -58,3 +58,4 @@ generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index 63c083a1f8da..01afb1b420f5 100644
@@ -13,3 +13,4 @@ generic-y += trace_clock.h
 generic-y += word-at-a-time.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index ed225600c8a4..07009c0863f6 100644
@@ -22,3 +22,4 @@ generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index 656af7b69940..6c8d12f3fe44 100644
@@ -12,3 +12,4 @@ generic-y += trace_clock.h
 generic-y += word-at-a-time.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index c55880659d67..ee6220dac1e8 100644
@@ -65,3 +65,4 @@ generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index 7d6a704b808c..ceafe458e295 100644
@@ -73,3 +73,4 @@ generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index 1a263a7158e2..99211477bfb2 100644
@@ -31,3 +31,4 @@ generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index 065c6e84fb67..bbd54aa1571e 100644
@@ -9,3 +9,4 @@ generic-y += rwsem.h
 generic-y += vtime.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index 3e8b95927cb5..92c2250a1521 100644
@@ -10,3 +10,4 @@ generic-y += trace_clock.h
 generic-y += word-at-a-time.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index f0cdb2cbca4d..16ea15a3e432 100644
@@ -16,3 +16,4 @@ generic-y += serial.h
 generic-y += word-at-a-time.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index c9bb7932a3d1..d0ea768d15ae 100644
@@ -41,3 +41,4 @@ generic-y += ucontext.h
 generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index 79664d10e63b..0e7663749c97 100644
@@ -24,3 +24,4 @@ generic-y += types.h
 generic-y += word-at-a-time.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index 951fa4be571d..8f3e38c981cd 100644
@@ -43,3 +43,4 @@ generic-y += types.h
 generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index 99be54949b99..eea5dd842992 100644
@@ -29,3 +29,4 @@ generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index 6c35905fe371..5c31eafbf1fd 100644
@@ -65,3 +65,4 @@ generic-y += vga.h
 generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += ranges.h
+generic-y += tables.h

index f790756fdb48..cd0fa76b32a3 100644
@@ -18,3 +18,4 @@ generic-y += mcs_spinlock.h
 generic-y += mm-arch-hooks.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index c215db049920..45733a182ac2 100644
@@ -69,7 +69,9 @@ static const char * const sym_regex_kernel[S_NSYMTYPES] = {
 	"__initramfs_start|"
 	"(jiffies|jiffies_64)|"
 	".rodata.rng.*|"
+	".rodata.tbl.*|"
 	".init.text.rng.*|"
+	".init.text.tbl.*|"
 #if ELF_BITS == 64
 	"__per_cpu_load|"
 	"init_per_cpu__.*|"

index 221b6b652500..ae48f8fd9212 100644
@@ -33,3 +33,4 @@ generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += tables.h

index 74cd941aa2f8..8cf21a1497c6 100644
@@ -86,4 +86,18 @@
 
 #endif /* __ASSEMBLY__ */
 
+#ifdef __ASSEMBLER__
+
+#ifndef DEFINE_SECTION_RANGE
+#define DEFINE_SECTION_RANGE(section, name)				\
+  push_section_rng_level(section, name,,) ;					\
+  .globl name ;								\
+name: ;									\
+  .popsection								\
+									\
+  push_section_rng_level(section, name, ~,) ;					\
+  .popsection
+#endif
+#endif /* __ASSEMBLER__ */
+
 #endif /* _ASM_GENERIC_RANGES_H_ */

index ad843555e6a4..4b6a3d820883 100644
@@ -57,6 +57,7 @@
 #include <linux/export.h>
 #include <asm/section-core.h>
 #include <asm/ranges.h>
+#include <asm/tables.h>
 
 /* Align . to a 8 byte boundary equals to maximum function alignment. */
 #define ALIGN_FUNCTION()  . = ALIGN(8)

@@ -202,6 +203,7 @@
 #define DATA_DATA							\
 	*(SECTION_DATA)							\
 	*(SORT(SECTION_RNG_ALL(SECTION_DATA)))				\
+	*(SORT(SECTION_TBL_ALL(SECTION_DATA)))				\
 	*(SECTION_REF_DATA)						\
 	*(.data..shared_aligned) /* percpu related */			\
 	MEM_KEEP(init.data)						\

@@ -269,6 +271,7 @@
 		VMLINUX_SYMBOL(__start_rodata) = .;			\
 		*(SECTION_RODATA)					\
 		*(SORT(SECTION_RNG_ALL(SECTION_RODATA)))		\
+		*(SORT(SECTION_TBL_ALL(SECTION_RODATA)))		\
 		*(SECTION_ALL(SECTION_RODATA))				\
 		RO_AFTER_INIT_DATA	/* Read only after init */	\
 		*(__vermagic)		/* Kernel version magic */	\

@@ -439,6 +442,7 @@
 		ALIGN_FUNCTION();					\
 		*(.text.hot SECTION_TEXT)				\
 		*(SORT(SECTION_RNG_ALL(SECTION_TEXT)))			\
+		*(SORT(SECTION_TBL_ALL(SECTION_TEXT)))			\
 		*(.text.fixup .text.unlikely)				\
 		*(SECTION_REF)						\
 	MEM_KEEP(init.text)						\

@@ -536,6 +540,7 @@
 #define INIT_DATA							\
 	*(SECTION_INIT_DATA)						\
 	*(SORT(SECTION_RNG_ALL(SECTION_INIT_DATA)))			\
+	*(SORT(SECTION_TBL_ALL(SECTION_INIT_DATA)))			\
 	MEM_DISCARD(init.data)						\
 	KERNEL_CTORS()							\
 	MCOUNT_REC()							\

@@ -559,6 +564,7 @@
 #define INIT_TEXT							\
 	*(SECTION_INIT)							\
 	*(SORT(SECTION_RNG_ALL(SECTION_INIT)))				\
+	*(SORT(SECTION_TBL_ALL(SECTION_INIT)))				\
 	*(.text.startup)						\
 	MEM_DISCARD(init.text)
 

index 50616ea25131..2b54546237d6 100644
@@ -36,6 +36,8 @@ subdir-ymn	:= $(addprefix $(obj)/,$(subdir-ymn))
 # directory
 
 __clean-files	:= $(extra-y) $(extra-m) $(extra-)       \
+		   $(force-obj-y) $(force-obj-m) $(force-obj-)       \
+		   $(force-lib-y) $(force-lib-m) $(force-lib-)       \
 		   $(always) $(targets) $(clean-files)   \
 		   $(host-progs)                         \
 		   $(hostprogs-y) $(hostprogs-m) $(hostprogs-) \

2.9.2

From: "Luis R. Rodriguez" <[email protected]>

Linux provides a rich array of features, enabling each feature however increases the size of the kernel and there are many features which users often want disabled. The traditional solution to this problem is for each feature to have its own Kconfig symbol, followed by a series of #ifdef statements in C code and header files, allowing the feature to be compiled only when desirable. As the variability of Linux increases build tests can and are often done with random kernel configurations, allyesconfig, and allmodconfig to help find code issues. This however doesn't catch all errors and as a consequence code that is typically not enabled often can suffer from bit-rot over time.

An alternative approach for subsystems, which refer to as the 'build-all link-selectively philosophy' is to keep the Kconfig symbols, replace the #ifdef approach by having each feature implemented it its own C file, and force compilation for all features to avoid the code bit-rot problem. With this strategy only features that are enabled via Kconfig get linked into the kernel, so the forced compilation has no size impact on the kernel. The practice of having each feature implemented in its own C file is already prevalent in many subsystems, however #ifdefs are still typically required during feature initialization. For instance in:

  #ifdef CONFIG_FOO
  foo_init();
  #endif

We cannot remove the #ifdef and leave foo_init() as we'd either need to always enable the feature or add a respective #ifdef in a foo.h which makes foo_init() do nothing when CONFIG_FOO is disabled.

Linker tables enable lifting the requirement to use of #ifdefs during initialization. With linker tables initialization sequences can instead be aggregated into a custom ELF section at link time, during run time the table can be iterated over and each init sequence enabled can be called. A feature's init routine is only added to a table when its respective Kconfig symbols has been enabled and therefore linked in. Linker tables enable subsystems to completely do away with #ifdefs if one is comfortable in accepting all subsystem's feature's structural size implications.

Subsystems which want to follow the 'build-all link-selectively philosophy' still need a way to easily express and annotate that they wish for all code to always be compiled to help avoid code bit rot, as such two new targets force-obj-y and force-lib-y are provided to help with this. Its not fair to require everyone to force compilation of all features of a subsystem though, so as a compromise, the new targets only force compilation when CONFIG_BUILD_AVOID_BITROT is enabled.

Only built-in features are supported at the moment. Module support is expected to be added after a generic solution to add linker tables to modules more easily is developed.

v4: this patch was added to this series, it was split off from the
linker tables addition due to the confusion over the code bit rot alternatives that are possible with linker tables.

---
 Documentation/kbuild/makefiles.txt       | 36 ++++++++++++++++
 Documentation/sections/linker-tables.rst | 15 +++++++
 include/linux/tables.h                   | 71 ++++++++++++++++++++++++++++++++
 init/Kconfig                             | 22 ++++++++++
 scripts/Makefile.build                   |  7 ++--
 scripts/Makefile.lib                     | 11 +++++
 6 files changed, 159 insertions(+), 3 deletions(-)

index 385a5ef41c17..01c260913f5c 100644
@@ -1089,6 +1089,42 @@ When kbuild executes, the following steps are followed (roughly):
 	In this example, extra-y is used to list object files that
 	shall be built, but shall not be linked as part of built-in.o.
 
+    force-obj-y force-lib-y
+
+	When CONFIG_BUILD_AVOID_BITROT is enabled using these targets for your
+	kconfig symbols forces compilation of the associated objects if the
+	kconfig's symbol's dependencies are met, the objects however are only
+	linked into to the kernel if and only if the kconfig symbol was
+	enabled. If CONFIG_BUILD_AVOID_BITROT is disabled the force-obj-y and
+	force-lib-y targets are functionally equilvalent to obj-y and lib-y
+	respectively.
+
+	Using force-obj-y and force-lib-y are part of a code architecture and
+	build philosophy further enabled by linker tables, for more details
+	refer to the documention in include/linux/tables.h, refer to the
+	sections:
+
+		o The code bit-rot problem
+		o The build-all selective-link philosophy
+		o Avoiding the code bit-rot problem with linker tables
+		o Linker table module support
+
+	Modules support is expected to be enhanced in the future, so for now
+	only built-in features are supported.
+
+	Example use:
+
+		force-obj-$(CONFIG_FEATURE_FOO) += foo.o
+
+	An alternative to using force-obj-y, is to use extra-y followed by the
+	respective obj-y:
+
+		extra-y += foo.o
+		obj-$(CONFIG_FEATURE_FOO) += foo.o
+
+	Using force-obj-y and force-lib-y can be used to help annotate the
+	targets follow the 'build-all selective-link philosophy' further
+	enabled by linker tables.
 
 --- 6.7 Commands useful for building a boot image
 

index df11c632dca7..e425c5cd36d6 100644
@@ -30,6 +30,21 @@ How linker tables simplify initialization code
 .. kernel-doc:: include/linux/tables.h
    :doc: How linker tables simplify initialization code
 
+The code bit-rot problem
+------------------------
+.. kernel-doc:: include/linux/tables.h
+   :doc: The code bit-rot problem
+
+The build-all selective-link philosophy
+---------------------------------------
+.. kernel-doc:: include/linux/tables.h
+   :doc: The build-all selective-link philosophy
+
+Avoiding the code bit-rot problem with linker tables
+----------------------------------------------------
+.. kernel-doc:: include/linux/tables.h
+   :doc: Avoiding the code bit-rot problem with linker tables
+
 Using linker tables in Linux
 ============================
 

index cac3f096050d..ef09e83b9196 100644
@@ -53,6 +53,28 @@ config CROSS_COMPILE
 	  need to set this unless you want the configured kernel build
 	  directory to select the cross-compiler automatically.
 
+config BUILD_AVOID_BITROT
+	bool "Enable force building of force-obj-y and force-lib-y"
+	default n
+	help
+	  When enabled objects under the force-obj-y and force-lib-y targets
+	  using a Kconfig symbol will be forced to compile if the Kconfig
+	  symbol's dependencies are met but only linked into the kernel if
+	  the Kconfig symbol is enabled. If a Kconfig symbol on a force-obj-y
+	  or force-lib-y target is disabled, it will be compiled but not linked
+	  into the kernel.
+
+	  The force-obj-y and force-lib-y targets can be used by subsystems
+	  which wish to want to follow the 'build-all selective-link philosophy'
+	  documented under include/linux/tables.h.
+
+	  Say Y if you have a decent build machine and would like to help test
+	  building code for more subsystems. Say N if you do you not have a
+	  good build machine or only want to compile what you've enabled for
+	  your kernel.
+
+	  Enabling this option never increases the size of your kernel.
+
 config COMPILE_TEST
 	bool "Compile also drivers which will not load"
 	depends on !UML

index cd9bf22bb027..cc2c7241d193 100644
@@ -92,7 +92,8 @@ modorder-target := $(obj)/modules.order
 
 # We keep a list of all modules in $(MODVERDIR)
 
-__build: $(if $(KBUILD_BUILTIN),$(builtin-target) $(lib-target) $(extra-y)) \
+__build: $(if $(KBUILD_BUILTIN),$(builtin-target) $(lib-target) $(extra-y) \
+				$(force-obj-y)) \
 	 $(if $(KBUILD_MODULES),$(obj-m) $(modorder-target)) \
 	 $(subdir-ym) $(always)
 	@:

@@ -326,8 +327,8 @@ cmd_as_o_S       = $(CC) $(a_flags) -c -o $@ $<
 $(obj)/%.o: $(src)/%.S $(objtool_obj) FORCE
 	$(call if_changed_rule,as_o_S)
 
-targets += $(real-objs-y) $(real-objs-m) $(lib-y)
-targets += $(extra-y) $(MAKECMDGOALS) $(always)
+targets += $(real-objs-y) $(real-objs-m) $(lib-y) $(force-lib-y)
+targets += $(extra-y) $(force-obj-y) $(MAKECMDGOALS) $(always)
 
 # Linker scripts preprocessor (.lds.S -> .lds)
 # ---------------------------------------------------------------------------

index 0a07f9014944..d1cb0cfdf1bf 100644
@@ -12,6 +12,15 @@ export KBUILD_SUBDIR_CCFLAGS := $(KBUILD_SUBDIR_CCFLAGS) $(subdir-ccflags-y)
 # Figure out what we need to build from the various variables
 # ===========================================================================
 
+ifeq ($(CONFIG_BUILD_AVOID_BITROT),y)
+extra-y += $(force-obj-) $(force-lib-)
+endif
+
+obj-m += $(force-obj-m)
+obj-y += $(force-obj-y)
+lib-m += $(force-lib-m)
+lib-y += $(force-lib-y)
+
 # When an object is listed to be built compiled-in and modular,
 # only build the compiled-in version
 

@@ -72,6 +81,8 @@ real-objs-m := $(foreach m, $(obj-m), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y)
 # Add subdir path
 
 extra-y		:= $(addprefix $(obj)/,$(extra-y))
+force-obj-y		:= $(addprefix $(obj)/,$(force-obj-y))
+force-obj-m		:= $(addprefix $(obj)/,$(force-obj-m))
 always		:= $(addprefix $(obj)/,$(always))
 targets		:= $(addprefix $(obj)/,$(targets))
 modorder	:= $(addprefix $(obj)/,$(modorder))

2.9.2

From: "Luis R. Rodriguez" <[email protected]>

If you modify the target asm we currently do not force the recompilation of the firmware files. The target asm is in the firmware/Makefile, peg this file as a dependency to require re-compilation of firmware targets when the asm changes.

v3: introduced in this series

---
 firmware/Makefile | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

index e297e1b52636..fa3e81c2a97b 100644
@@ -176,7 +176,8 @@ quiet_cmd_fwbin = MK_FW   $@
 wordsize_deps := $(wildcard include/config/64bit.h include/config/32bit.h \
 		include/config/ppc32.h include/config/ppc64.h \
 		include/config/superh32.h include/config/superh64.h \
-		include/config/x86_32.h include/config/x86_64.h)
+		include/config/x86_32.h include/config/x86_64.h \
+		firmware/Makefile)
 
 $(patsubst %,$(obj)/%.gen.S, $(fw-shipped-y)): %: $(wordsize_deps)
 	$(call cmd,fwbin,$(patsubst %.gen.S,%,$@))

2.9.2

From: "Luis R. Rodriguez" <[email protected]>

This ports built-in firmware to use linker tables, this replaces the custom section solution with a generic solution.

This also demos the use of the .rodata (SECTION_RO) linker tables.

Tested with 0 built-in firmware, 1 and 2 built-in firmwares successfully.

v4:

o work around c6x toolchain bug by using SECTION_TBL_RO

o fix compilation on blackfin

v3:
o explicitly include tables.h as we no longer include tables.h from sections.h

o use new section_tbl_asmtype() helper on firmware/Makefile to enable having to unfold things on our own.

v2: introduced this file in this version of the series

---
 arch/x86/kernel/cpu/microcode/core.c |  8 ++++----
 drivers/base/firmware_class.c        | 12 ++++++------
 firmware/Makefile                    |  3 ++-
 include/asm-generic/vmlinux.lds.h    |  7 -------
 4 files changed, 12 insertions(+), 18 deletions(-)

index df04b2d033f6..3e7c08d99601 100644
@@ -31,6 +31,7 @@
 #include <linux/cpu.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
+#include <linux/tables.h>
 
 #include <asm/microcode_intel.h>
 #include <asm/cpu_device_id.h>

@@ -91,15 +92,14 @@ static bool __init check_loader_disabled_bsp(void)
 	return *res;
 }
 
-extern struct builtin_fw __start_builtin_fw[];
-extern struct builtin_fw __end_builtin_fw[];
+DECLARE_LINKTABLE_RO(struct builtin_fw, builtin_fw);
 
 bool get_builtin_firmware(struct cpio_data *cd, const char *name)
 {
 #ifdef CONFIG_FW_LOADER
-	struct builtin_fw *b_fw;
+	const struct builtin_fw *b_fw;
 
-	for (b_fw = __start_builtin_fw; b_fw != __end_builtin_fw; b_fw++) {
+	LINKTABLE_FOR_EACH(b_fw, builtin_fw) {
 		if (!strcmp(name, b_fw->name)) {
 			cd->size = b_fw->size;
 			cd->data = b_fw->data;

index 22d1760a4278..8fbf03c3e4c2 100644
@@ -30,6 +30,7 @@
 #include <linux/syscore_ops.h>
 #include <linux/reboot.h>
 #include <linux/security.h>
+#include <linux/tables.h>
 
 #include <generated/utsrelease.h>
 

@@ -43,15 +44,14 @@ MODULE_LICENSE("GPL");
 
 #ifdef CONFIG_FW_LOADER
 
-extern struct builtin_fw __start_builtin_fw[];
-extern struct builtin_fw __end_builtin_fw[];
+DEFINE_LINKTABLE_RO(struct builtin_fw, builtin_fw);
 
 static bool fw_get_builtin_firmware(struct firmware *fw, const char *name,
 				    void *buf, size_t size)
 {
-	struct builtin_fw *b_fw;
+	const struct builtin_fw *b_fw;
 
-	for (b_fw = __start_builtin_fw; b_fw != __end_builtin_fw; b_fw++) {
+	LINKTABLE_FOR_EACH(b_fw, builtin_fw) {
 		if (strcmp(name, b_fw->name) == 0) {
 			fw->size = b_fw->size;
 			fw->data = b_fw->data;

@@ -67,9 +67,9 @@ static bool fw_get_builtin_firmware(struct firmware *fw, const char *name,
 
 static bool fw_is_builtin_firmware(const struct firmware *fw)
 {
-	struct builtin_fw *b_fw;
+	const struct builtin_fw *b_fw;
 
-	for (b_fw = __start_builtin_fw; b_fw != __end_builtin_fw; b_fw++)
+	LINKTABLE_FOR_EACH(b_fw, builtin_fw)
 		if (fw->data == b_fw->data)
 			return true;
 

index fa3e81c2a97b..9e701bf4ced2 100644
@@ -155,6 +155,7 @@ quiet_cmd_fwbin = MK_FW   $@
 		  ASM_ALIGN=$(if $(CONFIG_64BIT),3,2);			     \
 		  PROGBITS=$(if $(CONFIG_ARM),%,@)progbits;		     \
 		  echo "/* Generated by firmware/Makefile */"		> $@;\
+		  echo "\#include <asm/tables.h>"			>>$@;\
 		  echo "    .section .rodata"				>>$@;\
 		  echo "    .p2align $${ASM_ALIGN}"			>>$@;\
 		  echo "_fw_$${FWSTR}_bin:"				>>$@;\

@@ -164,7 +165,7 @@ quiet_cmd_fwbin = MK_FW   $@
 		  echo "    .p2align $${ASM_ALIGN}"			>>$@;\
 		  echo "_fw_$${FWSTR}_name:"				>>$@;\
 		  echo "    .string \"$$FWNAME\""			>>$@;\
-		  echo "    .section .builtin_fw,\"a\",$${PROGBITS}"	>>$@;\
+		  echo "    set_section_tbl_type(SECTION_TBL_RO, builtin_fw, SECTION_ORDER_ANY, a,$${PROGBITS})" >>$@;\
 		  echo "    .p2align $${ASM_ALIGN}"			>>$@;\
 		  echo "    $${ASM_WORD} _fw_$${FWSTR}_name"		>>$@;\
 		  echo "    $${ASM_WORD} _fw_$${FWSTR}_bin"		>>$@;\

index 4b6a3d820883..2413444c048d 100644
@@ -316,13 +316,6 @@
 		VMLINUX_SYMBOL(__end_pci_fixups_suspend_late) = .;	\
 	}								\
 									\
-	/* Built-in firmware blobs */					\
-	.builtin_fw        : AT(ADDR(.builtin_fw) - LOAD_OFFSET) {	\
-		VMLINUX_SYMBOL(__start_builtin_fw) = .;			\
-		*(.builtin_fw)						\
-		VMLINUX_SYMBOL(__end_builtin_fw) = .;			\
-	}								\
-									\
 	TRACEDATA							\
 									\
 	/* Kernel symbol table: Normal symbols */			\

2.9.2

From: "Luis R. Rodriguez" <[email protected]>

The ending header guard is misplaced. This has no
functional change, this is just an eye-sore.

---
 include/linux/jump_label.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index 661af564fae8..1256f543b002 100644
@@ -384,6 +384,6 @@ extern bool ____wrong_branch_error(void);
 #define static_branch_enable(x)		static_key_enable(&(x)->key)
 #define static_branch_disable(x)	static_key_disable(&(x)->key)
 
-#endif	/* _LINUX_JUMP_LABEL_H */
-
 #endif /* __ASSEMBLY__ */
+
+#endif	/* _LINUX_JUMP_LABEL_H */

2.9.2

From: "Luis R. Rodriguez" <[email protected]>

Move the __jump_table from the a custom section solution to a generic solution, this avoiding extra vmlinux.lds.h customizations.

This also demos the use of the .data (SECTION_DATA) linker table and of the shared asm call push_section_tbl().

Built-in kernel functionality was tested with CONFIG_STATIC_KEYS_SELFTEST. Moduler kernel functionality was tested with CONFIG_TEST_STATIC_KEYS. Both work as expected.

Since __jump_table sections are also supported per module this also required expanding module-common.lds.S to capture and fold all .data.tlb.__jump_table.* onto the the section __jump_table -- in this case for modules need to keep a reference in place, given the alternative is to use DEFINE_LINKTABLE(struct jump_entry, __jump_table) per module -- and later through macro hacks instantiate the jump entries per module upon init. This is doable but we'd loose out on the sorting of the table using the linker, to sort we'd always still need to expand the module common linker script. An alternative mechanism is possible which would make these custom module sections extensions dynamic without requiring manual changes, this however is best done later through a separate evolution once linker tables are in place.

A careful reviewer may note that some architectures use "\n\t" to separate asm code, while others just use a new line. Upon review last time it was deemed reasonable to for all architectures to just use "\n", this is defined as ASM_CMD_SEP, and if an architecture needs to override they can do so on their architecture sections.h prior to including asm-generic/sections.h

v4:

o Some architectures allow linker scripts to follow including header files, some others do not, so if you need a helper on a linker script you need to explicitly include it. So for instance although scripts/module-common.lds.S includes <asm/tables.h> and this file includes <asm/section-core.h>, you still need to explicitly include it on the linker script. This issue is present on ARM.

o as per Josh Poimboeuf open code the section table name instead of including the kernel section headers, the simplicity and independence from the kernel is preferred.

v3:

o More elaborate tests performed
o first modular support use case, module tested was CONFIG_TEST_STATIC_KEYS (lib/test_static_keys.ko), this required us to extend module-common.lds.S
o use generic push_section_tbl_any() for all architectures
o Makes use of ASM_CMD_SEP to enable architectures to override later if needed
o guard tables.h inclusion and table definition with __KERNEL__

v2: introduced in this series

---
 arch/arm/include/asm/jump_label.h     |  6 ++++--
 arch/arm64/include/asm/jump_label.h   |  6 ++++--
 arch/mips/include/asm/jump_label.h    |  6 ++++--
 arch/powerpc/include/asm/jump_label.h |  8 +++++---
 arch/s390/include/asm/jump_label.h    |  6 ++++--
 arch/sparc/include/asm/jump_label.h   |  6 ++++--
 arch/x86/include/asm/jump_label.h     | 10 ++++++----
 include/asm-generic/vmlinux.lds.h     |  4 ----
 include/linux/jump_label.h            |  4 ++--
 kernel/jump_label.c                   | 17 ++++++++++-------
 scripts/module-common.lds.S           |  5 +++++
 tools/objtool/special.c               |  2 +-
 12 files changed, 49 insertions(+), 31 deletions(-)

index 34f7b6980d21..960135a7b88e 100644
@@ -1,6 +1,8 @@
 #ifndef _ASM_ARM_JUMP_LABEL_H
 #define _ASM_ARM_JUMP_LABEL_H
 
+#include <asm/tables.h>
+
 #ifndef __ASSEMBLY__
 
 #include <linux/types.h>

@@ -12,7 +14,7 @@ static __always_inline bool arch_static_branch(struct static_key *key, bool bran
 {
 	asm_volatile_goto("1:\n\t"
 		 WASM(nop) "\n\t"
-		 ".pushsection __jump_table,  \"aw\"\n\t"
+		 push_section_tbl_any(SECTION_DATA, __jump_table, aw)
 		 ".word 1b, %l[l_yes], %c0\n\t"
 		 ".popsection\n\t"
 		 : :  "i" (&((char *)key)[branch]) :  : l_yes);

@@ -26,7 +28,7 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key, bool
 {
 	asm_volatile_goto("1:\n\t"
 		 WASM(b) " %l[l_yes]\n\t"
-		 ".pushsection __jump_table,  \"aw\"\n\t"
+		 push_section_tbl_any(SECTION_DATA, __jump_table, aw)
 		 ".word 1b, %l[l_yes], %c0\n\t"
 		 ".popsection\n\t"
 		 : :  "i" (&((char *)key)[branch]) :  : l_yes);

index 1b5e0e843c3a..aa52cd2607e3 100644
@@ -19,6 +19,8 @@
 #ifndef __ASM_JUMP_LABEL_H
 #define __ASM_JUMP_LABEL_H
 
+#include <asm/tables.h>
+
 #ifndef __ASSEMBLY__
 
 #include <linux/types.h>

@@ -29,7 +31,7 @@
 static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
 {
 	asm goto("1: nop\n\t"
-		 ".pushsection __jump_table,  \"aw\"\n\t"
+		 push_section_tbl_any(SECTION_DATA, __jump_table, aw)
 		 ".align 3\n\t"
 		 ".quad 1b, %l[l_yes], %c0\n\t"
 		 ".popsection\n\t"

@@ -43,7 +45,7 @@ l_yes:
 static __always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)
 {
 	asm goto("1: b %l[l_yes]\n\t"
-		 ".pushsection __jump_table,  \"aw\"\n\t"
+		 push_section_tbl_any(SECTION_DATA, __jump_table, aw)
 		 ".align 3\n\t"
 		 ".quad 1b, %l[l_yes], %c0\n\t"
 		 ".popsection\n\t"

index e77672539e8e..78e70cb98592 100644
@@ -8,6 +8,8 @@
 #ifndef _ASM_MIPS_JUMP_LABEL_H
 #define _ASM_MIPS_JUMP_LABEL_H
 
+#include <asm/tables.h>
+
 #ifndef __ASSEMBLY__
 
 #include <linux/types.h>

@@ -30,7 +32,7 @@ static __always_inline bool arch_static_branch(struct static_key *key, bool bran
 {
 	asm_volatile_goto("1:\t" NOP_INSN "\n\t"
 		"nop\n\t"
-		".pushsection __jump_table,  \"aw\"\n\t"
+		push_section_tbl_any(SECTION_DATA, __jump_table, aw)
 		WORD_INSN " 1b, %l[l_yes], %0\n\t"
 		".popsection\n\t"
 		: :  "i" (&((char *)key)[branch]) : : l_yes);

@@ -44,7 +46,7 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key, bool
 {
 	asm_volatile_goto("1:\tj %l[l_yes]\n\t"
 		"nop\n\t"
-		".pushsection __jump_table,  \"aw\"\n\t"
+		push_section_tbl_any(SECTION_DATA, __jump_table, aw)
 		WORD_INSN " 1b, %l[l_yes], %0\n\t"
 		".popsection\n\t"
 		: :  "i" (&((char *)key)[branch]) : : l_yes);

index 9a287e0ac8b1..a1225f66887e 100644
@@ -10,6 +10,8 @@
  * 2 of the License, or (at your option) any later version.
  */
 
+#include <asm/tables.h>
+
 #ifndef __ASSEMBLY__
 #include <linux/types.h>
 

@@ -23,7 +25,7 @@ static __always_inline bool arch_static_branch(struct static_key *key, bool bran
 {
 	asm_volatile_goto("1:\n\t"
 		 "nop # arch_static_branch\n\t"
-		 ".pushsection __jump_table,  \"aw\"\n\t"
+		 push_section_tbl_any(SECTION_DATA, __jump_table, aw)
 		 JUMP_ENTRY_TYPE "1b, %l[l_yes], %c0\n\t"
 		 ".popsection \n\t"
 		 : :  "i" (&((char *)key)[branch]) : : l_yes);

@@ -37,7 +39,7 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key, bool
 {
 	asm_volatile_goto("1:\n\t"
 		 "b %l[l_yes] # arch_static_branch_jump\n\t"
-		 ".pushsection __jump_table,  \"aw\"\n\t"
+		 push_section_tbl_any(SECTION_DATA, __jump_table, aw)
 		 JUMP_ENTRY_TYPE "1b, %l[l_yes], %c0\n\t"
 		 ".popsection \n\t"
 		 : :  "i" (&((char *)key)[branch]) : : l_yes);

@@ -62,7 +64,7 @@ struct jump_entry {
 #else
 #define ARCH_STATIC_BRANCH(LABEL, KEY)		\
 1098:	nop;					\
-	.pushsection __jump_table, "aw";	\
+	push_section_tbl_any(SECTION_DATA, __jump_table, aw); \
 	FTR_ENTRY_LONG 1098b, LABEL, KEY;	\
 	.popsection
 #endif

index 9be198f5ee79..17f02aec4644 100644
@@ -1,6 +1,8 @@
 #ifndef _ASM_S390_JUMP_LABEL_H
 #define _ASM_S390_JUMP_LABEL_H
 
+#include <asm/tables.h>
+
 #ifndef __ASSEMBLY__
 
 #include <linux/types.h>

@@ -16,7 +18,7 @@
 static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
 {
 	asm_volatile_goto("0:	brcl 0,"__stringify(JUMP_LABEL_NOP_OFFSET)"\n"
-		".pushsection __jump_table, \"aw\"\n"
+		push_section_tbl_any(SECTION_DATA, __jump_table, aw)
 		".balign 8\n"
 		".quad 0b, %l[label], %0\n"
 		".popsection\n"

@@ -30,7 +32,7 @@ label:
 static __always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)
 {
 	asm_volatile_goto("0:	brcl 15, %l[label]\n"
-		".pushsection __jump_table, \"aw\"\n"
+		push_section_tbl_any(SECTION_DATA, __jump_table, aw)
 		".balign 8\n"
 		".quad 0b, %l[label], %0\n"
 		".popsection\n"

index 62d0354d1727..dde1275233f7 100644
@@ -1,6 +1,8 @@
 #ifndef _ASM_SPARC_JUMP_LABEL_H
 #define _ASM_SPARC_JUMP_LABEL_H
 
+#include <asm/tables.h>
+
 #ifndef __ASSEMBLY__
 
 #include <linux/types.h>

@@ -12,7 +14,7 @@ static __always_inline bool arch_static_branch(struct static_key *key, bool bran
 	asm_volatile_goto("1:\n\t"
 		 "nop\n\t"
 		 "nop\n\t"
-		 ".pushsection __jump_table,  \"aw\"\n\t"
+		 push_section_tbl_any(SECTION_DATA, __jump_table, aw)
 		 ".align 4\n\t"
 		 ".word 1b, %l[l_yes], %c0\n\t"
 		 ".popsection \n\t"

@@ -28,7 +30,7 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key, bool
 	asm_volatile_goto("1:\n\t"
 		 "b %l[l_yes]\n\t"
 		 "nop\n\t"
-		 ".pushsection __jump_table,  \"aw\"\n\t"
+		 push_section_tbl_any(SECTION_DATA, __jump_table, aw)
 		 ".align 4\n\t"
 		 ".word 1b, %l[l_yes], %c0\n\t"
 		 ".popsection \n\t"

index adc54c12cbd1..d25fafa3df4b 100644
@@ -1,6 +1,8 @@
 #ifndef _ASM_X86_JUMP_LABEL_H
 #define _ASM_X86_JUMP_LABEL_H
 
+#include <asm/tables.h>
+
 #ifndef HAVE_JUMP_LABEL
 /*
  * For better or for worse, if jump labels (the gcc extension) are missing,

@@ -34,7 +36,7 @@ static __always_inline bool arch_static_branch(struct static_key *key, bool bran
 {
 	asm_volatile_goto("1:"
 		".byte " __stringify(STATIC_KEY_INIT_NOP) "\n\t"
-		".pushsection __jump_table,  \"aw\" \n\t"
+		push_section_tbl_any(SECTION_DATA, __jump_table, aw)
 		_ASM_ALIGN "\n\t"
 		_ASM_PTR "1b, %l[l_yes], %c0 + %c1 \n\t"
 		".popsection \n\t"

@@ -50,7 +52,7 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key, bool
 	asm_volatile_goto("1:"
 		".byte 0xe9\n\t .long %l[l_yes] - 2f\n\t"
 		"2:\n\t"
-		".pushsection __jump_table,  \"aw\" \n\t"
+		push_section_tbl_any(SECTION_DATA, __jump_table, aw)
 		_ASM_ALIGN "\n\t"
 		_ASM_PTR "1b, %l[l_yes], %c0 + %c1 \n\t"
 		".popsection \n\t"

@@ -85,7 +87,7 @@ struct jump_entry {
 	.else
 	.byte		STATIC_KEY_INIT_NOP
 	.endif
-	.pushsection __jump_table, "aw"
+	push_section_tbl_any(SECTION_DATA, __jump_table, aw)
 	_ASM_ALIGN
 	_ASM_PTR	.Lstatic_jump_\@, \target, \key
 	.popsection

@@ -101,7 +103,7 @@ struct jump_entry {
 	.long		\target - .Lstatic_jump_after_\@
 .Lstatic_jump_after_\@:
 	.endif
-	.pushsection __jump_table, "aw"
+	push_section_tbl_any(SECTION_DATA, __jump_table, aw)
 	_ASM_ALIGN
 	_ASM_PTR	.Lstatic_jump_\@, \target, \key + 1
 	.popsection

index 2413444c048d..140fbed4a817 100644
@@ -212,10 +212,6 @@
 	STRUCT_ALIGN();							\
 	*(__tracepoints)						\
 	/* implement dynamic printk debug */				\
-	. = ALIGN(8);                                                   \
-	VMLINUX_SYMBOL(__start___jump_table) = .;                       \
-	*(__jump_table)                                                 \
-	VMLINUX_SYMBOL(__stop___jump_table) = .;                        \
 	. = ALIGN(8);							\
 	VMLINUX_SYMBOL(__start___verbose) = .;                          \
 	*(__verbose)                                                    \

index 1256f543b002..842a24892a91 100644
@@ -115,6 +115,7 @@ enum jump_label_type {
 struct module;
 
 #ifdef HAVE_JUMP_LABEL
+#include <linux/tables.h>
 
 #define JUMP_TYPE_FALSE	0UL
 #define JUMP_TYPE_TRUE	1UL

@@ -130,8 +131,7 @@ static __always_inline bool static_key_true(struct static_key *key)
 	return !arch_static_branch(key, true);
 }
 
-extern struct jump_entry __start___jump_table[];
-extern struct jump_entry __stop___jump_table[];
+DECLARE_LINKTABLE(struct jump_entry, __jump_table);
 
 extern void jump_label_init(void);
 extern void jump_label_lock(void);

index 93ad6c1fb9b6..7582ca28e3b8 100644
@@ -15,9 +15,12 @@
 #include <linux/static_key.h>
 #include <linux/jump_label_ratelimit.h>
 #include <linux/bug.h>
+#include <linux/tables.h>
 
 #ifdef HAVE_JUMP_LABEL
 
+DEFINE_LINKTABLE(struct jump_entry, __jump_table);
+
 /* mutex to protect coming/going of the the jump_label table */
 static DEFINE_MUTEX(jump_label_mutex);
 

@@ -274,8 +277,6 @@ static void __jump_label_update(struct static_key *key,
 
 void __init jump_label_init(void)
 {
-	struct jump_entry *iter_start = __start___jump_table;
-	struct jump_entry *iter_stop = __stop___jump_table;
 	struct static_key *key = NULL;
 	struct jump_entry *iter;
 

@@ -292,9 +293,10 @@ void __init jump_label_init(void)
 		return;
 
 	jump_label_lock();
-	jump_label_sort_entries(iter_start, iter_stop);
+	jump_label_sort_entries(LINUX_SECTION_START(__jump_table),
+				LINUX_SECTION_END(__jump_table));
 
-	for (iter = iter_start; iter < iter_stop; iter++) {
+	LINKTABLE_FOR_EACH(iter, __jump_table) {
 		struct static_key *iterk;
 
 		/* rewrite NOPs */

@@ -539,8 +541,9 @@ early_initcall(jump_label_init_module);
  */
 int jump_label_text_reserved(void *start, void *end)
 {
-	int ret = __jump_label_text_reserved(__start___jump_table,
-			__stop___jump_table, start, end);
+	int ret = __jump_label_text_reserved(LINUX_SECTION_START(__jump_table),
+					     LINUX_SECTION_END(__jump_table),
+					     start, end);
 
 	if (ret)
 		return ret;

@@ -553,7 +556,7 @@ int jump_label_text_reserved(void *start, void *end)
 
 static void jump_label_update(struct static_key *key)
 {
-	struct jump_entry *stop = __stop___jump_table;
+	struct jump_entry *stop = LINUX_SECTION_END(__jump_table);
 	struct jump_entry *entry = static_key_entries(key);
 #ifdef CONFIG_MODULES
 	struct module *mod;

index 73a2c7da0e55..be3bde1ea0ce 100644
@@ -3,6 +3,10 @@
  * Archs are free to supply their own linker scripts.  ld will
  * combine them automatically.
  */
+
+#include <asm/section-core.h>
+#include <asm/tables.h>
+
 SECTIONS {
 	/DISCARD/ : { *(.discard) }
 

@@ -16,6 +20,7 @@ SECTIONS {
 	__kcrctab_unused	0 : { *(SORT(___kcrctab_unused+*)) }
 	__kcrctab_unused_gpl	0 : { *(SORT(___kcrctab_unused_gpl+*)) }
 	__kcrctab_gpl_future	0 : { *(SORT(___kcrctab_gpl_future+*)) }
+	__jump_table		0 : { *(SORT(SECTION_TBL(SECTION_DATA, __jump_table, *))) }
 
 	. = ALIGN(8);
 	.init_array		0 : { *(SORT(.init_array.*)) *(.init_array) }

index bff8abb3a4aa..6f7f519abacc 100644
@@ -63,7 +63,7 @@ struct special_entry entries[] = {
 		.feature = ALT_FEATURE_OFFSET,
 	},
 	{
-		.sec = "__jump_table",
+		.sec = ".data.tbl.__jump_table.any",
 		.jump_or_nop = true,
 		.size = JUMP_ENTRY_SIZE,
 		.orig = JUMP_ORIG_OFFSET,

2.9.2

From: "Luis R. Rodriguez" <[email protected]>

This removes the custom vmlinux.lds.h hacks and uses the generalized solution for .data (SECTION_DATA) entries.

This is much more potential for further fine tuning here though in the future. For instance, linker tables enable an extra postfix for order level annotations, this could easily be used as the KBUILD_MODNAME and with a bit of linker table changes we may be able to get a direct O(1) count of the entries for that KBUILD_MODNAME: it would just be a count on the number of entries for the given order level. This should help make dynamic_debug_init() cleaner and also reduce the amount of time it takes at boot time. Instead of iterating over each print until we have all for a KBUILD_MODNAME, we'd instead directly operate on each KBUILD_MODNAME directly.

Tested dynamic debug with dyndbg query ana debugfs control and it works as expected, for both built-in code and modules.

v4: fix compilation on blackfin
v3: added modular support
v2: introduced this patch into the series

---
 include/asm-generic/vmlinux.lds.h |  5 -----
 include/linux/dynamic_debug.h     |  5 +++--
 lib/dynamic_debug.c               | 13 ++++++-------
 scripts/module-common.lds.S       |  1 +
 4 files changed, 10 insertions(+), 14 deletions(-)

index 140fbed4a817..ba49b7ad7af2 100644
@@ -211,11 +211,6 @@
 	*(.data.unlikely)						\
 	STRUCT_ALIGN();							\
 	*(__tracepoints)						\
-	/* implement dynamic printk debug */				\
-	. = ALIGN(8);							\
-	VMLINUX_SYMBOL(__start___verbose) = .;                          \
-	*(__verbose)                                                    \
-	VMLINUX_SYMBOL(__stop___verbose) = .;				\
 	LIKELY_PROFILE()		       				\
 	BRANCH_PROFILE()						\
 	TRACE_PRINTKS()							\

index 546d68057e3b..a52618a77b09 100644
@@ -4,6 +4,7 @@
 #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
 #include <linux/jump_label.h>
 #endif
+#include <linux/tables.h>
 
 /*
  * An instance of this structure is created in a special

@@ -50,6 +51,7 @@ int ddebug_add_module(struct _ddebug *tab, unsigned int n,
 				const char *modname);
 
 #if defined(CONFIG_DYNAMIC_DEBUG)
+DECLARE_LINKTABLE(struct _ddebug, __verbose);
 extern int ddebug_remove_module(const char *mod_name);
 extern __printf(2, 3)
 void __dynamic_pr_debug(struct _ddebug *descriptor, const char *fmt, ...);

@@ -71,8 +73,7 @@ void __dynamic_netdev_dbg(struct _ddebug *descriptor,
 			  const char *fmt, ...);
 
 #define DEFINE_DYNAMIC_DEBUG_METADATA_KEY(name, fmt, key, init)	\
-	static struct _ddebug  __aligned(8)			\
-	__attribute__((section("__verbose"))) name = {		\
+	static LINKTABLE(__verbose, SECTION_ORDER_ANY) name = {	\
 		.modname = KBUILD_MODNAME,			\
 		.function = __func__,				\
 		.filename = __FILE__,				\

index da796e2dc4f5..f0060c84c654 100644
@@ -37,8 +37,7 @@
 #include <linux/device.h>
 #include <linux/netdevice.h>
 
-extern struct _ddebug __start___verbose[];
-extern struct _ddebug __stop___verbose[];
+DEFINE_LINKTABLE(struct _ddebug, __verbose);
 
 struct ddebug_table {
 	struct list_head link;

@@ -978,14 +977,14 @@ static int __init dynamic_debug_init(void)
 	int n = 0, entries = 0, modct = 0;
 	int verbose_bytes = 0;
 
-	if (__start___verbose == __stop___verbose) {
-		pr_warn("_ddebug table is empty in a CONFIG_DYNAMIC_DEBUG build\n");
+	if (LINUX_SECTION_EMPTY(__verbose)) {
+		pr_warn("dynamic debug linker table empty on CONFIG_DYNAMIC_DEBUG build\n");
 		return 1;
 	}
-	iter = __start___verbose;
+	iter = LINUX_SECTION_START(__verbose);
 	modname = iter->modname;
 	iter_start = iter;
-	for (; iter < __stop___verbose; iter++) {
+	LINKTABLE_FOR_EACH(iter, __verbose) {
 		entries++;
 		verbose_bytes += strlen(iter->modname) + strlen(iter->function)
 			+ strlen(iter->filename) + strlen(iter->format);

@@ -1008,7 +1007,7 @@ static int __init dynamic_debug_init(void)
 	ddebug_init_success = 1;
 	vpr_info("%d modules, %d entries and %d bytes in ddebug tables, %d bytes in (readonly) verbose section\n",
 		 modct, entries, (int)(modct * sizeof(struct ddebug_table)),
-		 verbose_bytes + (int)(__stop___verbose - __start___verbose));
+		 verbose_bytes + (int)(LINUX_SECTION_SIZE(__verbose)));
 
 	/* apply ddebug_query boot param, dont unload tables on err */
 	if (ddebug_setup_string[0] != '\0') {

index be3bde1ea0ce..be57ca0994dc 100644
@@ -21,6 +21,7 @@ SECTIONS {
 	__kcrctab_unused_gpl	0 : { *(SORT(___kcrctab_unused_gpl+*)) }
 	__kcrctab_gpl_future	0 : { *(SORT(___kcrctab_gpl_future+*)) }
 	__jump_table		0 : { *(SORT(SECTION_TBL(SECTION_DATA, __jump_table, *))) }
+	__verbose		0 : { *(SORT(SECTION_TBL(SECTION_DATA, __verbose, *))) }
 
 	. = ALIGN(8);
 	.init_array		0 : { *(SORT(.init_array.*)) *(.init_array) }

2.9.2

From: "Luis R. Rodriguez" <[email protected]>

Often all is needed is these small helpers, instead of compiler.h or a full kprobes.h. This is important for asm helpers, in fact even some asm/kprobes.h make use of these helpers... instead just keep a generic asm file with helpers useful for asm code with the least amount of clutter as possible.

Likewise we need now to also address what to do about this file for both when architectures have CONFIG_HAVE_KPROBES, and when they do not. Then for when architectures have CONFIG_HAVE_KPROBES but have disabled CONFIG_KPROBES.

Right now most asm/kprobes.h do not have guards against CONFIG_KPROBES, this means most architecture code cannot include asm/kprobes.h safely. Correct this and add guards for architectures missing them. Additionally provide architectures that not have kprobes support with the default asm-generic solution. This lets us force asm/kprobes.h on the header include/linux/kprobes.h always, but most importantly we can now safely include just asm/kprobes.h on architecture code without bringing the full kitchen sink of header files.

Two architectures already provided a guard against CONFIG_KPROBES on its kprobes.h: sh, arch. The rest of the architectures needed gaurds added. We avoid including any not-needed headers on asm/kprobes.h unless kprobes have been enabled.

In a subsequent atomic change we can try now to remove compiler.h from include/linux/kprobes.h.

---
 arch/alpha/include/asm/Kbuild      |  1 +
 arch/arc/include/asm/kprobes.h     |  6 ++++--
 arch/arm/include/asm/kprobes.h     |  4 ++++
 arch/arm/probes/decode.h           |  1 +
 arch/arm64/include/asm/kprobes.h   |  4 ++++
 arch/arm64/kernel/insn.c           |  1 +
 arch/avr32/include/asm/kprobes.h   |  4 ++++
 arch/blackfin/include/asm/Kbuild   |  1 +
 arch/c6x/include/asm/Kbuild        |  1 +
 arch/cris/include/asm/Kbuild       |  1 +
 arch/frv/include/asm/Kbuild        |  1 +
 arch/h8300/include/asm/Kbuild      |  1 +
 arch/hexagon/include/asm/Kbuild    |  1 +
 arch/ia64/include/asm/kprobes.h    |  7 ++++++-
 arch/m32r/include/asm/Kbuild       |  1 +
 arch/m68k/include/asm/Kbuild       |  1 +
 arch/metag/include/asm/Kbuild      |  1 +
 arch/microblaze/include/asm/Kbuild |  1 +
 arch/mips/include/asm/kprobes.h    |  6 +++++-
 arch/mn10300/include/asm/kprobes.h |  4 ++++
 arch/nios2/include/asm/Kbuild      |  1 +
 arch/openrisc/include/asm/Kbuild   |  1 +
 arch/parisc/include/asm/Kbuild     |  1 +
 arch/powerpc/include/asm/kprobes.h |  6 ++++++
 arch/s390/include/asm/kprobes.h    |  4 ++++
 arch/score/include/asm/Kbuild      |  1 +
 arch/sh/include/asm/kprobes.h      |  2 ++
 arch/sparc/include/asm/kprobes.h   |  5 +++++
 arch/tile/include/asm/kprobes.h    |  6 +++++-
 arch/um/include/asm/Kbuild         |  1 +
 arch/unicore32/include/asm/Kbuild  |  1 +
 arch/x86/include/asm/kprobes.h     |  6 ++++++
 arch/xtensa/include/asm/Kbuild     |  1 +
 include/asm-generic/kprobes.h      | 25 +++++++++++++++++++++++++
 include/linux/compiler.h           |  8 --------
 include/linux/kprobes.h            | 19 +++----------------
 36 files changed, 107 insertions(+), 29 deletions(-)
 create mode 100644 include/asm-generic/kprobes.h

index f3bdc31d3c97..54d388fd026f 100644
@@ -13,3 +13,4 @@ generic-y += trace_clock.h
 generic-y += section-core.h
 generic-y += ranges.h
 generic-y += tables.h
+generic-y += kprobes.h

index 944dbedb38b5..00bdbe167615 100644
@@ -9,6 +9,8 @@
 #ifndef _ARC_KPROBES_H
 #define _ARC_KPROBES_H
 
+#include <asm-generic/kprobes.h>
+
 #ifdef CONFIG_KPROBES
 
 typedef u16 kprobe_opcode_t;

@@ -55,6 +57,6 @@ void trap_is_kprobe(unsigned long address, struct pt_regs *regs);
 static void trap_is_kprobe(unsigned long address, struct pt_regs *regs)
 {
 }
-#endif
+#endif /* CONFIG_KPROBES */
 
-#endif
+#endif /* _ARC_KPROBES_H */

index 3ea9be559726..59655459da59 100644
@@ -16,6 +16,9 @@
 #ifndef _ARM_KPROBES_H
 #define _ARM_KPROBES_H
 
+#include <asm-generic/kprobes.h>
+
+#ifdef CONFIG_KPROBES
 #include <linux/types.h>
 #include <linux/ptrace.h>
 #include <linux/notifier.h>

@@ -83,4 +86,5 @@ struct arch_optimized_insn {
 	 */
 };
 
+#endif /* CONFIG_KPROBES */
 #endif /* _ARM_KPROBES_H */

index f9b08ba7fe73..548d622a3159 100644
@@ -22,6 +22,7 @@
 #include <linux/types.h>
 #include <linux/stddef.h>
 #include <asm/probes.h>
+#include <asm/kprobes.h>
 
 void __init arm_probes_decode_init(void);
 

index 1737aecfcc5e..6deb8d726041 100644
@@ -16,6 +16,9 @@
 #ifndef _ARM_KPROBES_H
 #define _ARM_KPROBES_H
 
+#include <asm-generic/kprobes.h>
+
+#ifdef CONFIG_KPROBES
 #include <linux/types.h>
 #include <linux/ptrace.h>
 #include <linux/percpu.h>

@@ -57,4 +60,5 @@ int kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr);
 void kretprobe_trampoline(void);
 void __kprobes *trampoline_probe_handler(struct pt_regs *regs);
 
+#endif /* CONFIG_KPROBES */
 #endif /* _ARM_KPROBES_H */

index 63f9432d05e8..cc38f3241927 100644
@@ -32,6 +32,7 @@
 #include <asm/fixmap.h>
 #include <asm/opcodes.h>
 #include <asm/insn.h>
+#include <asm/kprobes.h>
 
 #define AARCH64_INSN_SF_BIT	BIT(31)
 #define AARCH64_INSN_N_BIT	BIT(22)

index 45f563ed73fd..09f39d8749ea 100644
@@ -11,6 +11,9 @@
 #ifndef __ASM_AVR32_KPROBES_H
 #define __ASM_AVR32_KPROBES_H
 
+#include <asm-generic/kprobes.h>
+
+#ifdef CONFIG_KPROBES
 #include <linux/types.h>
 
 typedef u16	kprobe_opcode_t;

@@ -46,4 +49,5 @@ extern int kprobe_exceptions_notify(struct notifier_block *self,
 
 #define flush_insn_slot(p)	do { } while (0)
 
+#endif /* CONFIG_KPROBES */
 #endif /* __ASM_AVR32_KPROBES_H */

index b71893b1cd53..f56a68697353 100644
@@ -51,3 +51,4 @@ generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
 generic-y += tables.h
+generic-y += kprobes.h

index cede2a950fbf..c54f7cc1f63e 100644
@@ -64,3 +64,4 @@ generic-y += word-at-a-time.h
 generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
+generic-y += kprobes.h

index 7062c1be7913..051d355feae3 100644
@@ -48,3 +48,4 @@ generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
 generic-y += tables.h
+generic-y += kprobes.h

index 4a59cbda5091..b58b9fc49383 100644
@@ -11,3 +11,4 @@ generic-y += word-at-a-time.h
 generic-y += section-core.h
 generic-y += ranges.h
 generic-y += tables.h
+generic-y += kprobes.h

index d79968d93c12..cfca7de52b37 100644
@@ -78,3 +78,4 @@ generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
 generic-y += tables.h
+generic-y += kprobes.h

index d59ac1c1858b..d7cc35451f30 100644
@@ -63,3 +63,4 @@ generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
 generic-y += tables.h
+generic-y += kprobes.h

index d5505d6f2382..36999c55f3f2 100644
@@ -23,6 +23,10 @@
  * 2005-Apr     Rusty Lynch <[email protected]> and Anil S Keshavamurthy
  *              <[email protected]> adapted from i386
  */
+#include <asm-generic/kprobes.h>
+
+#ifdef CONFIG_KPROBES
+
 #include <linux/types.h>
 #include <linux/ptrace.h>
 #include <linux/percpu.h>

@@ -124,4 +128,5 @@ extern void invalidate_stacked_regs(void);
 extern void flush_register_stack(void);
 extern void arch_remove_kprobe(struct kprobe *p);
 
-#endif				/* _ASM_KPROBES_H */
+#endif /* CONFIG_KPROBES */
+#endif /* _ASM_KPROBES_H */

index 24088f3c733c..198ad591ab41 100644
@@ -14,3 +14,4 @@ generic-y += word-at-a-time.h
 generic-y += section-core.h
 generic-y += ranges.h
 generic-y += tables.h
+generic-y += kprobes.h

index 65c0df17f70e..ae86bb91e13b 100644
@@ -38,3 +38,4 @@ generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
 generic-y += tables.h
+generic-y += kprobes.h

index 2538224899fd..10f36ed301e1 100644
@@ -59,3 +59,4 @@ generic-y += xor.h
 generic-y += section-core.h
 generic-y += ranges.h
 generic-y += tables.h
+generic-y += kprobes.h

index 01afb1b420f5..865ce3d96443 100644
@@ -14,3 +14,4 @@ generic-y += word-at-a-time.h
 generic-y += section-core.h
 generic-y += ranges.h
 generic-y += tables.h
+generic-y += kprobes.h

index daba1f9a4f79..291846d9ba83 100644
@@ -22,6 +22,9 @@
 #ifndef _ASM_KPROBES_H
 #define _ASM_KPROBES_H
 
+#include <asm-generic/kprobes.h>
+
+#ifdef CONFIG_KPROBES
 #include <linux/ptrace.h>
 #include <linux/types.h>
 

@@ -94,4 +97,5 @@ struct kprobe_ctlblk {
 extern int kprobe_exceptions_notify(struct notifier_block *self,
 				    unsigned long val, void *data);
 
-#endif				/* _ASM_KPROBES_H */
+#endif /* CONFIG_KPROBES */
+#endif /* _ASM_KPROBES_H */

index c800b590183a..5729bb5b972a 100644
@@ -21,6 +21,9 @@
 #ifndef _ASM_KPROBES_H
 #define _ASM_KPROBES_H
 
+#include <asm-generic/kprobes.h>
+
+#ifdef CONFIG_KPROBES
 #include <linux/types.h>
 #include <linux/ptrace.h>
 

@@ -47,4 +50,5 @@ extern int kprobe_exceptions_notify(struct notifier_block *self,
 
 extern void arch_remove_kprobe(struct kprobe *p);
 
+#endif /* CONFIG_KPROBES */
 #endif /* _ASM_KPROBES_H */