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x86: macrofying inline asm for better compilation

PATCH Superseded Nadav Amit 4 participants 16 messages Aug 9, 2018 – Sep 10, 2018

Subsystems (9)

v7 of 9 Superseded Latest is v9 →

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Nadav Amit

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#0 lore raw

v7 cover x86: macrofying inline asm for better compilation

This patch-set deals with an interesting yet stupid problem: kernel code that does not get inlined despite its simplicity. There are several causes for this behavior: "cold" attribute on __init, different function optimization levels; conditional constant computations based on __builtin_constant_p(); and finally large inline assembly blocks.

This patch-set deals with the inline assembly problem. I separated these patches from the others (that were sent in the RFC) for easier inclusion. I also separated the removal of unnecessary new-lines which would be sent separately.

The problem with inline assembly is that inline assembly is often used by the kernel for things that are other than code - for example, assembly directives and data. GCC however is oblivious to the content of the blocks and assumes their cost in space and time is proportional to the number of the perceived assembly "instruction", according to the number of newlines and semicolons. Alternatives, paravirt and other mechanisms are affected, causing code not to be inlined, and degrading compilation quality in general.

The solution that this patch-set carries for this problem is to create an assembly macro, and then call it from the inline assembly block. As a result, the compiler sees a single "instruction" and assigns the more appropriate cost to the code.

To avoid uglification of the code, as many noted, the macros are first precompiled into an assembly file, which is later assembled together with the C files. This also enables to avoid duplicate implementation that was set before for the asm and C code. This can be seen in the exception table changes.

Overall this patch-set slightly increases the kernel size (my build was done using my Ubuntu 18.04 config + localyesconfig for the record):

text data bss dec hex filename
18140829 10224724 2957312 31322865 1ddf2f1 ./vmlinux before 18163608 10227348 2957312 31348268 1de562c ./vmlinux after (+0.1%)

The number of static functions in the image is reduced by 379, but actually inlining is even better, which does not always shows in these
numbers: a function may be inlined causing the calling function not to be inlined.

I ran some limited number of benchmarks, and in general the performance impact is not very notable. You can still see >10 cycles shaved off some syscalls that manipulate page-tables (e.g., mprotect()), in which paravirt caused many functions not to be inlined. In addition this patch-set can prevent issues such as [1], and improves code readability and maintainability.

[1] https://patchwork.kernel.org/patch/10450037/

v6->v7: * Fix context switch tracking (Ingo)
* Fix xtensa build error (Ingo)
* Rebase on 4.18-rc8

v5->v6: * Removing more code from jump-labels (PeterZ)
* Fix build issue on i386 (0-day, PeterZ)

v4->v5: * Makefile fixes (Masahiro, Sam)

v3->v4: * Changed naming of macros in 2 patches (PeterZ)
* Minor cleanup of the paravirt patch

v2->v3: * Several build issues resolved (0-day)
* Wrong comments fix (Josh)
* Change asm vs C order in refcount (Kees)

v1->v2: * Compiling the macros into a separate .s file, improving
readability (Linus)
* Improving assembly formatting, applying most of the comments according to my judgment (Jan)
* Adding exception-table, cpufeature and jump-labels
* Removing new-line cleanup; to be submitted separately

Cc Masahiro Yamada <[email protected]>
Cc Sam Ravnborg <[email protected]>
Cc Alok Kataria <[email protected]>
Cc Christopher Li <[email protected]>
Cc Greg Kroah-Hartman <[email protected]>
Cc "H. Peter Anvin" <[email protected]>
Cc Ingo Molnar <[email protected]>
Cc Jan Beulich <[email protected]>
Cc Josh Poimboeuf <[email protected]>
Cc Juergen Gross <[email protected]>
Cc Kate Stewart <[email protected]>
Cc Kees Cook <[email protected]>
Cc Peter Zijlstra <[email protected]>
Cc Philippe Ombredanne <[email protected]>
Cc Thomas Gleixner <[email protected]>
Cc Linus Torvalds <[email protected]>
Cc Chris Zankel <[email protected]>
Cc Max Filippov <[email protected]>

Nadav Amit (10):
xtensa: defining LINKER_SCRIPT for the linker script
Makefile: Prepare for using macros for inline asm
x86: objtool: use asm macro for better compiler decisions
x86: refcount: prevent gcc distortions
x86: alternatives: macrofy locks for better inlining
x86: bug: prevent gcc distortions
x86: prevent inline distortion by paravirt ops
x86: extable: use macros instead of inline assembly
x86: cpufeature: use macros instead of inline assembly
x86: jump-labels: use macros instead of inline assembly

 Makefile                               |  9 ++-
 arch/x86/Makefile                      | 11 ++-
 arch/x86/entry/calling.h               |  2 +-
 arch/x86/include/asm/alternative-asm.h | 20 ++++--
 arch/x86/include/asm/alternative.h     | 11 +--
 arch/x86/include/asm/asm.h             | 61 +++++++---------
 arch/x86/include/asm/bug.h             | 98 +++++++++++++++-----------
 arch/x86/include/asm/cpufeature.h      | 82 ++++++++++++---------
 arch/x86/include/asm/jump_label.h      | 77 ++++++++------------
 arch/x86/include/asm/paravirt_types.h  | 56 +++++++--------
 arch/x86/include/asm/refcount.h        | 74 +++++++++++--------
 arch/x86/kernel/macros.S               | 16 +++++
 arch/xtensa/kernel/Makefile            |  4 +-
 include/asm-generic/bug.h              |  8 +--
 include/linux/compiler.h               | 56 +++++++++++----
 scripts/Kbuild.include                 |  4 +-
 scripts/mod/Makefile                   |  2 +
 17 files changed, 333 insertions(+), 258 deletions(-)
 create mode 100644 arch/x86/kernel/macros.S
Signature · 1 line
2.17.1
author
#1 lore raw

PATCH v7 1/10 xtensa: defining LINKER_SCRIPT for the linker script

Defining the LINKER_SCRIPT when building the linker script as being done in other architectures. This is required for the next Makefile changes would otherwise break things.

---
 arch/xtensa/kernel/Makefile | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
arch/xtensa/kernel/Makefile +2 -2
index 91907590d183..8dff506caf07 100644
@@ -35,8 +35,8 @@ sed-y = -e ':a; s/\*(\([^)]*\)\.text\.unlikely/*(\1.literal.unlikely .{text}.unl
 	-e 's/\.{text}/.text/g'
 
 quiet_cmd__cpp_lds_S = LDS     $@
-cmd__cpp_lds_S = $(CPP) $(cpp_flags) -P -C -Uxtensa -D__ASSEMBLY__ $<    \
-                 | sed $(sed-y) >$@
+cmd__cpp_lds_S = $(CPP) $(cpp_flags) -P -C -Uxtensa -D__ASSEMBLY__ \
+		 -DLINKER_SCRIPT $< | sed $(sed-y) >$@
 
 $(obj)/vmlinux.lds: $(src)/vmlinux.lds.S FORCE
 	$(call if_changed_dep,_cpp_lds_S)
Signature · 1 line
2.17.1
maintainer Acked-by on v7 1/10
#2 lore raw

Re: [PATCH v7 01/10] xtensa: defining LINKER_SCRIPT for the linker script

Quoted 11 lines · Nadav Amit

Defining the LINKER_SCRIPT when building the linker script as being done in other architectures. This is required for the next Makefile changes would otherwise break things.

---
 arch/xtensa/kernel/Makefile | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
Signature · 2 lines
Thanks.
-- Max
author
#3 lore raw

PATCH v7 2/10 Makefile: Prepare for using macros for inline asm

In reply to Nadav Amit

Using macros for inline assembly improves both readability and compilation decisions that are distorted by big assembly blocks that use alternative sections. Compile macros.S and use it to assemble all C files. Currently, only x86 will use it.

Cc Sam Ravnborg <[email protected]>
Cc Masahiro Yamada <[email protected]>
Cc Michal Marek <[email protected]>
Cc Thomas Gleixner <[email protected]>
Cc Ingo Molnar <[email protected]>
Cc "H. Peter Anvin" <[email protected]>
---
 Makefile                 |  9 +++++++--
 arch/x86/Makefile        | 11 +++++++++--
 arch/x86/kernel/macros.S |  7 +++++++
 scripts/Kbuild.include   |  4 +++-
 scripts/mod/Makefile     |  2 ++
 5 files changed, 28 insertions(+), 5 deletions(-)
 create mode 100644 arch/x86/kernel/macros.S
Makefile +7 -2
index 7a3c4548162b..39d790e74e0d 100644
@@ -1051,7 +1051,7 @@ scripts: scripts_basic include/config/auto.conf include/config/tristate.conf \
 # version.h and scripts_basic is processed / created.
 
 # Listed in dependency order
-PHONY += prepare archprepare prepare0 prepare1 prepare2 prepare3
+PHONY += prepare archprepare macroprepare prepare0 prepare1 prepare2 prepare3
 
 # prepare3 is used to check if we are building in a separate output directory,
 # and if so do:
@@ -1075,7 +1075,9 @@ prepare1: prepare2 $(version_h) $(autoksyms_h) include/generated/utsrelease.h \
                    include/config/auto.conf
 	$(cmd_crmodverdir)
 
-archprepare: archheaders archscripts prepare1 scripts_basic
+macroprepare: prepare1 archmacros
+
+archprepare: archheaders archscripts macroprepare scripts_basic
 
 prepare0: archprepare gcc-plugins
 	$(Q)$(MAKE) $(build)=.
@@ -1143,6 +1145,9 @@ archheaders:
 PHONY += archscripts
 archscripts:
 
+PHONY += archmacros
+archmacros:
+
 PHONY += __headers
 __headers: $(version_h) scripts_basic uapi-asm-generic archheaders archscripts
 	$(Q)$(MAKE) $(build)=scripts build_unifdef
arch/x86/Makefile +9 -2
index a08e82856563..a4b90ac1629b 100644
@@ -235,8 +235,8 @@ ifdef CONFIG_X86_64
 LDFLAGS += $(call ld-option, -z max-page-size=0x200000)
 endif
 
-# Speed up the build
-KBUILD_CFLAGS += -pipe
+# We cannot use -pipe flag since we give an additional .s file to the compiler
+#KBUILD_CFLAGS += -pipe
 # Workaround for a gcc prelease that unfortunately was shipped in a suse release
 KBUILD_CFLAGS += -Wno-sign-compare
 #
@@ -258,6 +258,13 @@ archscripts: scripts_basic
 archheaders:
 	$(Q)$(MAKE) $(build)=arch/x86/entry/syscalls all
 
+archmacros:
+	$(Q)$(MAKE) $(build)=arch/x86/kernel arch/x86/kernel/macros.s
+
+ASM_MACRO_FLAGS = -Wa,arch/x86/kernel/macros.s
+export ASM_MACRO_FLAGS
+KBUILD_CFLAGS += $(ASM_MACRO_FLAGS)
+
 ###
 # Kernel objects
 
arch/x86/kernel/macros.S new file +7 -0
new file mode 100644
index 000000000000..cfc1c7d1a6eb
@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * This file includes headers whose assembly part includes macros which are
+ * commonly used. The macros are precompiled into assmebly file which is later
+ * assembled together with each compiled file.
+ */
scripts/Kbuild.include +3 -1
index 86321f06461e..d7b7aadb6cd8 100644
@@ -115,7 +115,9 @@ __cc-option = $(call try-run,\
 
 # Do not attempt to build with gcc plugins during cc-option tests.
 # (And this uses delayed resolution so the flags will be up to date.)
-CC_OPTION_CFLAGS = $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS))
+# In addition, do not include the asm macros which are built later.
+CC_OPTION_FILTERED = $(GCC_PLUGINS_CFLAGS) $(ASM_MACRO_FLAGS)
+CC_OPTION_CFLAGS = $(filter-out $(CC_OPTION_FILTERED),$(KBUILD_CFLAGS))
 
 # cc-option
 # Usage: cflags-y += $(call cc-option,-march=winchip-c6,-march=i586)
scripts/mod/Makefile +2 -0
index 42c5d50f2bcc..a5b4af47987a 100644
@@ -4,6 +4,8 @@ OBJECT_FILES_NON_STANDARD := y
 hostprogs-y	:= modpost mk_elfconfig
 always		:= $(hostprogs-y) empty.o
 
+CFLAGS_REMOVE_empty.o := $(ASM_MACRO_FLAGS)
+
 modpost-objs	:= modpost.o file2alias.o sumversion.o
 
 devicetable-offsets-file := devicetable-offsets.h
Signature · 1 line
2.17.1
Acked-by on v7 2/10
#4 lore raw

Re: [PATCH v7 02/10] Makefile: Prepare for using macros for inline asm

Hi Nadav,

2018-08-10 5:15 GMT+09:00 Nadav Amit <[email protected]>:

Quoted 7 lines

Using macros for inline assembly improves both readability and compilation decisions that are distorted by big assembly blocks that use alternative sections. Compile macros.S and use it to assemble all C files. Currently, only x86 will use it.

Cc Sam Ravnborg <[email protected]>
Cc Masahiro Yamada <[email protected]>

I added this in the previous version.

When you send a new version,
please make sure to add Acked-by/Reviewed-by reviewers have given.

Thanks.

Quoted 128 lines
---
 Makefile                 |  9 +++++++--
 arch/x86/Makefile        | 11 +++++++++--
 arch/x86/kernel/macros.S |  7 +++++++
 scripts/Kbuild.include   |  4 +++-
 scripts/mod/Makefile     |  2 ++
 5 files changed, 28 insertions(+), 5 deletions(-)
 create mode 100644 arch/x86/kernel/macros.S
Makefile +7 -2
index 7a3c4548162b..39d790e74e0d 100644
@@ -1051,7 +1051,7 @@ scripts: scripts_basic include/config/auto.conf include/config/tristate.conf \
 # version.h and scripts_basic is processed / created.
 
 # Listed in dependency order
-PHONY += prepare archprepare prepare0 prepare1 prepare2 prepare3
+PHONY += prepare archprepare macroprepare prepare0 prepare1 prepare2 prepare3
 
 # prepare3 is used to check if we are building in a separate output directory,
 # and if so do:
@@ -1075,7 +1075,9 @@ prepare1: prepare2 $(version_h) $(autoksyms_h) include/generated/utsrelease.h \
                    include/config/auto.conf
        $(cmd_crmodverdir)
 
-archprepare: archheaders archscripts prepare1 scripts_basic
+macroprepare: prepare1 archmacros
+
+archprepare: archheaders archscripts macroprepare scripts_basic
 
 prepare0: archprepare gcc-plugins
        $(Q)$(MAKE) $(build)=.
@@ -1143,6 +1145,9 @@ archheaders:
 PHONY += archscripts
 archscripts:
 
+PHONY += archmacros
+archmacros:
+
 PHONY += __headers
 __headers: $(version_h) scripts_basic uapi-asm-generic archheaders archscripts
        $(Q)$(MAKE) $(build)=scripts build_unifdef
arch/x86/Makefile +9 -2
index a08e82856563..a4b90ac1629b 100644
@@ -235,8 +235,8 @@ ifdef CONFIG_X86_64
 LDFLAGS += $(call ld-option, -z max-page-size=0x200000)
 endif
 
-# Speed up the build
-KBUILD_CFLAGS += -pipe
+# We cannot use -pipe flag since we give an additional .s file to the compiler
+#KBUILD_CFLAGS += -pipe
 # Workaround for a gcc prelease that unfortunately was shipped in a suse release
 KBUILD_CFLAGS += -Wno-sign-compare
 #
@@ -258,6 +258,13 @@ archscripts: scripts_basic
 archheaders:
        $(Q)$(MAKE) $(build)=arch/x86/entry/syscalls all
 
+archmacros:
+       $(Q)$(MAKE) $(build)=arch/x86/kernel arch/x86/kernel/macros.s
+
+ASM_MACRO_FLAGS = -Wa,arch/x86/kernel/macros.s
+export ASM_MACRO_FLAGS
+KBUILD_CFLAGS += $(ASM_MACRO_FLAGS)
+
 ###
 # Kernel objects
 
arch/x86/kernel/macros.S new file +7 -0
new file mode 100644
index 000000000000..cfc1c7d1a6eb
@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * This file includes headers whose assembly part includes macros which are
+ * commonly used. The macros are precompiled into assmebly file which is later
+ * assembled together with each compiled file.
+ */
scripts/Kbuild.include +3 -1
index 86321f06461e..d7b7aadb6cd8 100644
@@ -115,7 +115,9 @@ __cc-option = $(call try-run,\
 
 # Do not attempt to build with gcc plugins during cc-option tests.
 # (And this uses delayed resolution so the flags will be up to date.)
-CC_OPTION_CFLAGS = $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS))
+# In addition, do not include the asm macros which are built later.
+CC_OPTION_FILTERED = $(GCC_PLUGINS_CFLAGS) $(ASM_MACRO_FLAGS)
+CC_OPTION_CFLAGS = $(filter-out $(CC_OPTION_FILTERED),$(KBUILD_CFLAGS))
 
 # cc-option
 # Usage: cflags-y += $(call cc-option,-march=winchip-c6,-march=i586)
scripts/mod/Makefile +2 -1
index 42c5d50f2bcc..a5b4af47987a 100644
@@ -4,6 +4,8 @@ OBJECT_FILES_NON_STANDARD := y
 hostprogs-y    := modpost mk_elfconfig
 always         := $(hostprogs-y) empty.o
 
+CFLAGS_REMOVE_empty.o := $(ASM_MACRO_FLAGS)
+
 modpost-objs   := modpost.o file2alias.o sumversion.o
 
 devicetable-offsets-file := devicetable-offsets.h
--

2.17.1

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Signature · 2 lines
Best Regards
Masahiro Yamada
author
#5 lore raw

PATCH v7 3/10 x86: objtool: use asm macro for better compiler decisions

In reply to Nadav Amit

GCC considers the number of statements in inlined assembly blocks, according to new-lines and semicolons, as an indication to the cost of the block in time and space. This data is distorted by the kernel code, which puts information in alternative sections. As a result, the compiler may perform incorrect inlining and branch optimizations.

In the case of objtool, this distortion is extreme, since anyhow the annotations of objtool are discarded during linkage.

The solution is to set an assembly macro and call it from the inline assembly block. As a result GCC considers the inline assembly block as a single instruction.

This patch slightly increases the kernel size.

text data bss dec hex filename
18140829 10224724 2957312 31322865 1ddf2f1 ./vmlinux before 18140970 10225412 2957312 31323694 1ddf62e ./vmlinux after (+829)

Static text symbols:
Before: 40321
After: 40302 (-19)

---
 arch/x86/kernel/macros.S |  2 ++
 include/linux/compiler.h | 56 ++++++++++++++++++++++++++++++----------
 2 files changed, 45 insertions(+), 13 deletions(-)
arch/x86/kernel/macros.S +2 -0
index cfc1c7d1a6eb..cee28c3246dc 100644
@@ -5,3 +5,5 @@
  * commonly used. The macros are precompiled into assmebly file which is later
  * assembled together with each compiled file.
  */
+
+#include <linux/compiler.h>
include/linux/compiler.h +43 -13

71 lines not on this page · raw message

Signature · 1 line
2.17.1
author
#6 lore raw

PATCH v7 4/10 x86: refcount: prevent gcc distortions

In reply to Nadav Amit

GCC considers the number of statements in inlined assembly blocks, according to new-lines and semicolons, as an indication to the cost of the block in time and space. This data is distorted by the kernel code, which puts information in alternative sections. As a result, the compiler may perform incorrect inlining and branch optimizations.

The solution is to set an assembly macro and call it from the inlined assembly block. As a result GCC considers the inline assembly block as a single instruction.

This patch allows to inline functions such as __get_seccomp_filter(). Interestingly, this allows more aggressive inlining while reducing the kernel size.

text data bss dec hex filename
18140970 10225412 2957312 31323694 1ddf62e ./vmlinux before 18140140 10225284 2957312 31322736 1ddf270 ./vmlinux after (-958)

Static text symbols:
Before: 40302
After: 40286 (-16)

Functions such as kref_get(), free_user(), fuse_file_get() now get inlined.

Cc Thomas Gleixner <[email protected]>
Cc Ingo Molnar <[email protected]>
Cc "H. Peter Anvin" <[email protected]>
Cc Kees Cook <[email protected]>
Cc Jan Beulich <[email protected]>
Cc Josh Poimboeuf <[email protected]>
---
 arch/x86/include/asm/refcount.h | 74 ++++++++++++++++++++-------------
 arch/x86/kernel/macros.S        |  1 +
 2 files changed, 46 insertions(+), 29 deletions(-)
arch/x86/include/asm/refcount.h +45 -29
index 4cf11d88d3b3..6b2809a4d8e9 100644
@@ -4,6 +4,41 @@
  * x86-specific implementation of refcount_t. Based on PAX_REFCOUNT from
  * PaX/grsecurity.
  */
+
+#ifdef __ASSEMBLY__
+
+#include <asm/asm.h>
+#include <asm/bug.h>
+
+.macro REFCOUNT_EXCEPTION counter:req
+	.pushsection .text..refcount
+111:	lea \counter, %_ASM_CX
+112:	ud2
+	ASM_UNREACHABLE
+	.popsection
+113:	_ASM_EXTABLE_REFCOUNT(112b, 113b)
+.endm
+
+/* Trigger refcount exception if refcount result is negative. */
+.macro REFCOUNT_CHECK_LT_ZERO counter:req
+	js 111f
+	REFCOUNT_EXCEPTION counter="\counter"
+.endm
+
+/* Trigger refcount exception if refcount result is zero or negative. */
+.macro REFCOUNT_CHECK_LE_ZERO counter:req
+	jz 111f
+	REFCOUNT_CHECK_LT_ZERO counter="\counter"
+.endm
+
+/* Trigger refcount exception unconditionally. */
+.macro REFCOUNT_ERROR counter:req
+	jmp 111f
+	REFCOUNT_EXCEPTION counter="\counter"
+.endm
+
+#else /* __ASSEMBLY__ */
+
 #include <linux/refcount.h>
 
 /*
@@ -14,34 +49,11 @@
  * central refcount exception. The fixup address for the exception points
  * back to the regular execution flow in .text.
  */
-#define _REFCOUNT_EXCEPTION				\
-	".pushsection .text..refcount\n"		\
-	"111:\tlea %[counter], %%" _ASM_CX "\n"		\
-	"112:\t" ASM_UD2 "\n"				\
-	ASM_UNREACHABLE					\
-	".popsection\n"					\
-	"113:\n"					\
-	_ASM_EXTABLE_REFCOUNT(112b, 113b)
-
-/* Trigger refcount exception if refcount result is negative. */
-#define REFCOUNT_CHECK_LT_ZERO				\
-	"js 111f\n\t"					\
-	_REFCOUNT_EXCEPTION
-
-/* Trigger refcount exception if refcount result is zero or negative. */
-#define REFCOUNT_CHECK_LE_ZERO				\
-	"jz 111f\n\t"					\
-	REFCOUNT_CHECK_LT_ZERO
-
-/* Trigger refcount exception unconditionally. */
-#define REFCOUNT_ERROR					\
-	"jmp 111f\n\t"					\
-	_REFCOUNT_EXCEPTION
 
 static __always_inline void refcount_add(unsigned int i, refcount_t *r)
 {
 	asm volatile(LOCK_PREFIX "addl %1,%0\n\t"
-		REFCOUNT_CHECK_LT_ZERO
+		"REFCOUNT_CHECK_LT_ZERO counter=\"%[counter]\""
 		: [counter] "+m" (r->refs.counter)
 		: "ir" (i)
 		: "cc", "cx");
@@ -50,7 +62,7 @@ static __always_inline void refcount_add(unsigned int i, refcount_t *r)
 static __always_inline void refcount_inc(refcount_t *r)
 {
 	asm volatile(LOCK_PREFIX "incl %0\n\t"
-		REFCOUNT_CHECK_LT_ZERO
+		"REFCOUNT_CHECK_LT_ZERO counter=\"%[counter]\""
 		: [counter] "+m" (r->refs.counter)
 		: : "cc", "cx");
 }
@@ -58,7 +70,7 @@ static __always_inline void refcount_inc(refcount_t *r)
 static __always_inline void refcount_dec(refcount_t *r)
 {
 	asm volatile(LOCK_PREFIX "decl %0\n\t"
-		REFCOUNT_CHECK_LE_ZERO
+		"REFCOUNT_CHECK_LE_ZERO counter=\"%[counter]\""
 		: [counter] "+m" (r->refs.counter)
 		: : "cc", "cx");
 }
@@ -66,13 +78,15 @@ static __always_inline void refcount_dec(refcount_t *r)
 static __always_inline __must_check
 bool refcount_sub_and_test(unsigned int i, refcount_t *r)
 {
-	GEN_BINARY_SUFFIXED_RMWcc(LOCK_PREFIX "subl", REFCOUNT_CHECK_LT_ZERO,
+	GEN_BINARY_SUFFIXED_RMWcc(LOCK_PREFIX "subl",
+				  "REFCOUNT_CHECK_LT_ZERO counter=\"%0\"",
 				  r->refs.counter, "er", i, "%0", e, "cx");
 }
 
 static __always_inline __must_check bool refcount_dec_and_test(refcount_t *r)
 {
-	GEN_UNARY_SUFFIXED_RMWcc(LOCK_PREFIX "decl", REFCOUNT_CHECK_LT_ZERO,
+	GEN_UNARY_SUFFIXED_RMWcc(LOCK_PREFIX "decl",
+				 "REFCOUNT_CHECK_LT_ZERO counter=\"%0\"",
 				 r->refs.counter, "%0", e, "cx");
 }
 
@@ -90,7 +104,7 @@ bool refcount_add_not_zero(unsigned int i, refcount_t *r)
 
 		/* Did we try to increment from/to an undesirable state? */
 		if (unlikely(c < 0 || c == INT_MAX || result < c)) {
-			asm volatile(REFCOUNT_ERROR
+			asm volatile("REFCOUNT_ERROR counter=\"%[counter]\""
 				     : : [counter] "m" (r->refs.counter)
 				     : "cc", "cx");
 			break;
@@ -106,4 +120,6 @@ static __always_inline __must_check bool refcount_inc_not_zero(refcount_t *r)
 	return refcount_add_not_zero(1, r);
 }
 
+#endif /* __ASSEMBLY__ */
+
 #endif
arch/x86/kernel/macros.S +1 -0
index cee28c3246dc..f1fe1d570365 100644
@@ -7,3 +7,4 @@
  */
 
 #include <linux/compiler.h>
+#include <asm/refcount.h>
Signature · 1 line
2.17.1
author
#7 lore raw

PATCH v7 5/10 x86: alternatives: macrofy locks for better inlining

In reply to Nadav Amit

GCC considers the number of statements in inlined assembly blocks, according to new-lines and semicolons, as an indication to the cost of the block in time and space. This data is distorted by the kernel code, which puts information in alternative sections. As a result, the compiler may perform incorrect inlining and branch optimizations.

The solution is to set an assembly macro and call it from the inlined assembly block. As a result GCC considers the inline assembly block as a single instruction.

This patch handles the LOCK prefix, allowing more aggresive inlining.

text data bss dec hex filename
18140140 10225284 2957312 31322736 1ddf270 ./vmlinux before 18146889 10225380 2957312 31329581 1de0d2d ./vmlinux after (+6845)

Static text symbols:
Before: 40286
After: 40218 (-68)

---
 arch/x86/include/asm/alternative-asm.h | 20 ++++++++++++++------
 arch/x86/include/asm/alternative.h     | 11 ++---------
 arch/x86/kernel/macros.S               |  1 +
 3 files changed, 17 insertions(+), 15 deletions(-)
arch/x86/include/asm/alternative-asm.h +14 -6
index 31b627b43a8e..8e4ea39e55d0 100644
@@ -7,16 +7,24 @@
 #include <asm/asm.h>
 
 #ifdef CONFIG_SMP
-	.macro LOCK_PREFIX
-672:	lock
+.macro LOCK_PREFIX_HERE
 	.pushsection .smp_locks,"a"
 	.balign 4
-	.long 672b - .
+	.long 671f - .		# offset
 	.popsection
-	.endm
+671:
+.endm
+
+.macro LOCK_PREFIX insn:vararg
+	LOCK_PREFIX_HERE
+	lock \insn
+.endm
 #else
-	.macro LOCK_PREFIX
-	.endm
+.macro LOCK_PREFIX_HERE
+.endm
+
+.macro LOCK_PREFIX insn:vararg
+.endm
 #endif
 
 /*
arch/x86/include/asm/alternative.h +2 -9
index 4cd6a3b71824..d7faa16622d8 100644
@@ -31,15 +31,8 @@
  */
 
 #ifdef CONFIG_SMP
-#define LOCK_PREFIX_HERE \
-		".pushsection .smp_locks,\"a\"\n"	\
-		".balign 4\n"				\
-		".long 671f - .\n" /* offset */		\
-		".popsection\n"				\
-		"671:"
-
-#define LOCK_PREFIX LOCK_PREFIX_HERE "\n\tlock; "
-
+#define LOCK_PREFIX_HERE "LOCK_PREFIX_HERE\n\t"
+#define LOCK_PREFIX "LOCK_PREFIX "
 #else /* ! CONFIG_SMP */
 #define LOCK_PREFIX_HERE ""
 #define LOCK_PREFIX ""
arch/x86/kernel/macros.S +1 -0
index f1fe1d570365..852487a9fc56 100644
@@ -8,3 +8,4 @@
 
 #include <linux/compiler.h>
 #include <asm/refcount.h>
+#include <asm/alternative-asm.h>
Signature · 1 line
2.17.1
author
#8 lore raw

PATCH v7 6/10 x86: bug: prevent gcc distortions

In reply to Nadav Amit

GCC considers the number of statements in inlined assembly blocks, according to new-lines and semicolons, as an indication to the cost of the block in time and space. This data is distorted by the kernel code, which puts information in alternative sections. As a result, the compiler may perform incorrect inlining and branch optimizations.

The solution is to set an assembly macro and call it from the inlinedv assembly block. As a result GCC considers the inline assembly block as a single instruction.

This patch increases the kernel size:

text data bss dec hex filename
18146889 10225380 2957312 31329581 1de0d2d ./vmlinux before 18147336 10226688 2957312 31331336 1de1408 ./vmlinux after (+1755)

But enables more aggressive inlining (and probably branch decisions). The number of static text symbols in vmlinux is lower.

Static text symbols:
Before: 40218
After: 40053 (-165)

---
 arch/x86/include/asm/bug.h | 98 ++++++++++++++++++++++----------------
 arch/x86/kernel/macros.S   |  1 +
 include/asm-generic/bug.h  |  8 ++--
 3 files changed, 61 insertions(+), 46 deletions(-)
arch/x86/include/asm/bug.h +56 -42
index 6804d6642767..5090035e6d16 100644
@@ -4,6 +4,8 @@
 
 #include <linux/stringify.h>
 
+#ifndef __ASSEMBLY__
+
 /*
  * Despite that some emulators terminate on UD2, we use it for WARN().
  *
@@ -20,53 +22,15 @@
 
 #define LEN_UD2		2
 
-#ifdef CONFIG_GENERIC_BUG
-
-#ifdef CONFIG_X86_32
-# define __BUG_REL(val)	".long " __stringify(val)
-#else
-# define __BUG_REL(val)	".long " __stringify(val) " - 2b"
-#endif
-
-#ifdef CONFIG_DEBUG_BUGVERBOSE
-
-#define _BUG_FLAGS(ins, flags)						\
-do {									\
-	asm volatile("1:\t" ins "\n"					\
-		     ".pushsection __bug_table,\"aw\"\n"		\
-		     "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n"	\
-		     "\t"  __BUG_REL(%c0) "\t# bug_entry::file\n"	\
-		     "\t.word %c1"        "\t# bug_entry::line\n"	\
-		     "\t.word %c2"        "\t# bug_entry::flags\n"	\
-		     "\t.org 2b+%c3\n"					\
-		     ".popsection"					\
-		     : : "i" (__FILE__), "i" (__LINE__),		\
-			 "i" (flags),					\
-			 "i" (sizeof(struct bug_entry)));		\
-} while (0)
-
-#else /* !CONFIG_DEBUG_BUGVERBOSE */
-
 #define _BUG_FLAGS(ins, flags)						\
 do {									\
-	asm volatile("1:\t" ins "\n"					\
-		     ".pushsection __bug_table,\"aw\"\n"		\
-		     "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n"	\
-		     "\t.word %c0"        "\t# bug_entry::flags\n"	\
-		     "\t.org 2b+%c1\n"					\
-		     ".popsection"					\
-		     : : "i" (flags),					\
+	asm volatile("ASM_BUG ins=\"" ins "\" file=%c0 line=%c1 "	\
+		     "flags=%c2 size=%c3"				\
+		     : : "i" (__FILE__), "i" (__LINE__),                \
+			 "i" (flags),                                   \
 			 "i" (sizeof(struct bug_entry)));		\
 } while (0)
 
-#endif /* CONFIG_DEBUG_BUGVERBOSE */
-
-#else
-
-#define _BUG_FLAGS(ins, flags)  asm volatile(ins)
-
-#endif /* CONFIG_GENERIC_BUG */
-
 #define HAVE_ARCH_BUG
 #define BUG()							\
 do {								\
@@ -82,4 +46,54 @@ do {								\
 
 #include <asm-generic/bug.h>
 
+#else /* __ASSEMBLY__ */
+
+#ifdef CONFIG_GENERIC_BUG
+
+#ifdef CONFIG_X86_32
+.macro __BUG_REL val:req
+	.long \val
+.endm
+#else
+.macro __BUG_REL val:req
+	.long \val - 2b
+.endm
+#endif
+
+#ifdef CONFIG_DEBUG_BUGVERBOSE
+
+.macro ASM_BUG ins:req file:req line:req flags:req size:req
+1:	\ins
+	.pushsection __bug_table,"aw"
+2:	__BUG_REL val=1b	# bug_entry::bug_addr
+	__BUG_REL val=\file	# bug_entry::file
+	.word \line		# bug_entry::line
+	.word \flags		# bug_entry::flags
+	.org 2b+\size
+	.popsection
+.endm
+
+#else /* !CONFIG_DEBUG_BUGVERBOSE */
+
+.macro ASM_BUG ins:req file:req line:req flags:req size:req
+1:	\ins
+	.pushsection __bug_table,"aw"
+2:	__BUG_REL val=1b	# bug_entry::bug_addr
+	.word \flags		# bug_entry::flags
+	.org 2b+\size
+	.popsection
+.endm
+
+#endif /* CONFIG_DEBUG_BUGVERBOSE */
+
+#else /* CONFIG_GENERIC_BUG */
+
+.macro ASM_BUG ins:req file:req line:req flags:req size:req
+	\ins
+.endm
+
+#endif /* CONFIG_GENERIC_BUG */
+
+#endif /* __ASSEMBLY__ */
+
 #endif /* _ASM_X86_BUG_H */
arch/x86/kernel/macros.S +1 -0
index 852487a9fc56..66ccb8e823b1 100644
@@ -9,3 +9,4 @@
 #include <linux/compiler.h>
 #include <asm/refcount.h>
 #include <asm/alternative-asm.h>
+#include <asm/bug.h>
include/asm-generic/bug.h +4 -4
index a7613e1b0c87..cf7f4ef4749e 100644
@@ -17,10 +17,8 @@
 #ifndef __ASSEMBLY__
 #include <linux/kernel.h>
 
-#ifdef CONFIG_BUG
-
-#ifdef CONFIG_GENERIC_BUG
 struct bug_entry {
+#ifdef CONFIG_GENERIC_BUG
 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
 	unsigned long	bug_addr;
 #else
@@ -35,8 +33,10 @@ struct bug_entry {
 	unsigned short	line;
 #endif
 	unsigned short	flags;
-};
 #endif	/* CONFIG_GENERIC_BUG */
+};
+
+#ifdef CONFIG_BUG
 
 /*
  * Don't use BUG() or BUG_ON() unless there's really no way out; one
Signature · 1 line
2.17.1
author
#9 lore raw

PATCH v7 7/10 x86: prevent inline distortion by paravirt ops

In reply to Nadav Amit

GCC considers the number of statements in inlined assembly blocks, according to new-lines and semicolons, as an indication to the cost of the block in time and space. This data is distorted by the kernel code, which puts information in alternative sections. As a result, the compiler may perform incorrect inlining and branch optimizations.

The solution is to set an assembly macro and call it from the inlined assembly block. As a result GCC considers the inline assembly block as a single instruction.

The effect of the patch is a more aggressive inlining, which also causes a size increase of kernel.

text data bss dec hex filename
18147336 10226688 2957312 31331336 1de1408 ./vmlinux before 18162555 10226288 2957312 31346155 1de4deb ./vmlinux after (+14819)

Static text symbols:
Before: 40053
After: 39942 (-111)

---
 arch/x86/include/asm/paravirt_types.h | 56 +++++++++++++--------------
 arch/x86/kernel/macros.S              |  1 +
 2 files changed, 28 insertions(+), 29 deletions(-)
arch/x86/include/asm/paravirt_types.h +27 -29
index 180bc0bff0fb..dd55d3d1c32a 100644
@@ -343,23 +343,11 @@ extern struct pv_lock_ops pv_lock_ops;
 #define paravirt_clobber(clobber)		\
 	[paravirt_clobber] "i" (clobber)
 
-/*
- * Generate some code, and mark it as patchable by the
- * apply_paravirt() alternate instruction patcher.
- */
-#define _paravirt_alt(insn_string, type, clobber)	\
-	"771:\n\t" insn_string "\n" "772:\n"		\
-	".pushsection .parainstructions,\"a\"\n"	\
-	_ASM_ALIGN "\n"					\
-	_ASM_PTR " 771b\n"				\
-	"  .byte " type "\n"				\
-	"  .byte 772b-771b\n"				\
-	"  .short " clobber "\n"			\
-	".popsection\n"
-
 /* Generate patchable code, with the default asm parameters. */
-#define paravirt_alt(insn_string)					\
-	_paravirt_alt(insn_string, "%c[paravirt_typenum]", "%c[paravirt_clobber]")
+#define paravirt_call							\
+	"PARAVIRT_CALL type=\"%c[paravirt_typenum]\""			\
+	" clobber=\"%c[paravirt_clobber]\""				\
+	" pv_opptr=\"%c[paravirt_opptr]\";"
 
 /* Simple instruction patching code. */
 #define NATIVE_LABEL(a,x,b) "\n\t.globl " a #x "_" #b "\n" a #x "_" #b ":\n\t"
@@ -387,16 +375,6 @@ unsigned native_patch(u8 type, u16 clobbers, void *ibuf,
 
 int paravirt_disable_iospace(void);
 
-/*
- * This generates an indirect call based on the operation type number.
- * The type number, computed in PARAVIRT_PATCH, is derived from the
- * offset into the paravirt_patch_template structure, and can therefore be
- * freely converted back into a structure offset.
- */
-#define PARAVIRT_CALL					\
-	ANNOTATE_RETPOLINE_SAFE				\
-	"call *%c[paravirt_opptr];"
-
 /*
  * These macros are intended to wrap calls through one of the paravirt
  * ops structs, so that they can be later identified and patched at
@@ -534,7 +512,7 @@ int paravirt_disable_iospace(void);
 		/* since this condition will never hold */		\
 		if (sizeof(rettype) > sizeof(unsigned long)) {		\
 			asm volatile(pre				\
-				     paravirt_alt(PARAVIRT_CALL)	\
+				     paravirt_call			\
 				     post				\
 				     : call_clbr, ASM_CALL_CONSTRAINT	\
 				     : paravirt_type(op),		\
@@ -544,7 +522,7 @@ int paravirt_disable_iospace(void);
 			__ret = (rettype)((((u64)__edx) << 32) | __eax); \
 		} else {						\
 			asm volatile(pre				\
-				     paravirt_alt(PARAVIRT_CALL)	\
+				     paravirt_call			\
 				     post				\
 				     : call_clbr, ASM_CALL_CONSTRAINT	\
 				     : paravirt_type(op),		\
@@ -571,7 +549,7 @@ int paravirt_disable_iospace(void);
 		PVOP_VCALL_ARGS;					\
 		PVOP_TEST_NULL(op);					\
 		asm volatile(pre					\
-			     paravirt_alt(PARAVIRT_CALL)		\
+			     paravirt_call				\
 			     post					\
 			     : call_clbr, ASM_CALL_CONSTRAINT		\
 			     : paravirt_type(op),			\
@@ -691,6 +669,26 @@ struct paravirt_patch_site {
 extern struct paravirt_patch_site __parainstructions[],
 	__parainstructions_end[];
 
+#else	/* __ASSEMBLY__ */
+
+/*
+ * This generates an indirect call based on the operation type number.
+ * The type number, computed in PARAVIRT_PATCH, is derived from the
+ * offset into the paravirt_patch_template structure, and can therefore be
+ * freely converted back into a structure offset.
+ */
+.macro PARAVIRT_CALL type:req clobber:req pv_opptr:req
+771:	ANNOTATE_RETPOLINE_SAFE
+	call *\pv_opptr
+772:	.pushsection .parainstructions,"a"
+	_ASM_ALIGN
+	_ASM_PTR 771b
+	.byte \type
+	.byte 772b-771b
+	.short \clobber
+	.popsection
+.endm
+
 #endif	/* __ASSEMBLY__ */
 
 #endif	/* _ASM_X86_PARAVIRT_TYPES_H */
arch/x86/kernel/macros.S +1 -0
index 66ccb8e823b1..71d8b716b111 100644
@@ -10,3 +10,4 @@
 #include <asm/refcount.h>
 #include <asm/alternative-asm.h>
 #include <asm/bug.h>
+#include <asm/paravirt.h>
Signature · 1 line
2.17.1
author
#10 lore raw

PATCH v7 8/10 x86: extable: use macros instead of inline assembly

In reply to Nadav Amit

Use assembly macros for exception-tables and call them from inline assembly. This not only makes the code more readable and allows to avoid the duplicate implementation, but also improves compilation decision, specifically inline decisions which GCC base on the number of new lines in inline assembly.

text data bss dec hex filename
18162555 10226288 2957312 31346155 1de4deb ./vmlinux before 18162879 10226256 2957312 31346447 1de4f0f ./vmlinux after (+292)

This allows to inline functions such as nested_vmx_exit_reflected(), set_segment_reg(), __copy_xstate_to_user().

---
 arch/x86/include/asm/asm.h | 61 +++++++++++++++++---------------------
 arch/x86/kernel/macros.S   |  1 +
 2 files changed, 28 insertions(+), 34 deletions(-)
arch/x86/include/asm/asm.h +27 -34
index 990770f9e76b..e47a2256c64e 100644
@@ -117,28 +117,44 @@
 # define CC_OUT(c) [_cc_ ## c] "=qm"
 #endif
 
-/* Exception table entry */
 #ifdef __ASSEMBLY__
 # define _ASM_EXTABLE_HANDLE(from, to, handler)			\
-	.pushsection "__ex_table","a" ;				\
-	.balign 4 ;						\
-	.long (from) - . ;					\
-	.long (to) - . ;					\
-	.long (handler) - . ;					\
-	.popsection
+	ASM_EXTABLE_HANDLE from to handler
+
+#else /* __ASSEMBLY__ */
+
+# define _ASM_EXTABLE_HANDLE(from, to, handler)			\
+	"ASM_EXTABLE_HANDLE from=" #from " to=" #to		\
+	" handler=\"" #handler "\"\n\t"
+
+/* For C file, we already have NOKPROBE_SYMBOL macro */
+
+#endif /* __ASSEMBLY__ */
 
-# define _ASM_EXTABLE(from, to)					\
+#define _ASM_EXTABLE(from, to)					\
 	_ASM_EXTABLE_HANDLE(from, to, ex_handler_default)
 
-# define _ASM_EXTABLE_FAULT(from, to)				\
+#define _ASM_EXTABLE_FAULT(from, to)				\
 	_ASM_EXTABLE_HANDLE(from, to, ex_handler_fault)
 
-# define _ASM_EXTABLE_EX(from, to)				\
+#define _ASM_EXTABLE_EX(from, to)				\
 	_ASM_EXTABLE_HANDLE(from, to, ex_handler_ext)
 
-# define _ASM_EXTABLE_REFCOUNT(from, to)			\
+#define _ASM_EXTABLE_REFCOUNT(from, to)				\
 	_ASM_EXTABLE_HANDLE(from, to, ex_handler_refcount)
 
+/* Exception table entry */
+#ifdef __ASSEMBLY__
+
+.macro ASM_EXTABLE_HANDLE from:req to:req handler:req
+	.pushsection "__ex_table","a"
+	.balign 4
+	.long (\from) - .
+	.long (\to) - .
+	.long (\handler) - .
+	.popsection
+.endm
+
 # define _ASM_NOKPROBE(entry)					\
 	.pushsection "_kprobe_blacklist","aw" ;			\
 	_ASM_ALIGN ;						\
@@ -169,29 +185,6 @@
 	_ASM_EXTABLE(101b,103b)
 	.endm
 
-#else
-# define _EXPAND_EXTABLE_HANDLE(x) #x
-# define _ASM_EXTABLE_HANDLE(from, to, handler)			\
-	" .pushsection \"__ex_table\",\"a\"\n"			\
-	" .balign 4\n"						\
-	" .long (" #from ") - .\n"				\
-	" .long (" #to ") - .\n"				\
-	" .long (" _EXPAND_EXTABLE_HANDLE(handler) ") - .\n"	\
-	" .popsection\n"
-
-# define _ASM_EXTABLE(from, to)					\
-	_ASM_EXTABLE_HANDLE(from, to, ex_handler_default)
-
-# define _ASM_EXTABLE_FAULT(from, to)				\
-	_ASM_EXTABLE_HANDLE(from, to, ex_handler_fault)
-
-# define _ASM_EXTABLE_EX(from, to)				\
-	_ASM_EXTABLE_HANDLE(from, to, ex_handler_ext)
-
-# define _ASM_EXTABLE_REFCOUNT(from, to)			\
-	_ASM_EXTABLE_HANDLE(from, to, ex_handler_refcount)
-
-/* For C file, we already have NOKPROBE_SYMBOL macro */
 #endif
 
 #ifndef __ASSEMBLY__
arch/x86/kernel/macros.S +1 -0
index 71d8b716b111..7baa40d5bf16 100644
@@ -11,3 +11,4 @@
 #include <asm/alternative-asm.h>
 #include <asm/bug.h>
 #include <asm/paravirt.h>
+#include <asm/asm.h>
Signature · 1 line
2.17.1
author
#11 lore raw

PATCH v7 9/10 x86: cpufeature: use macros instead of inline assembly

In reply to Nadav Amit

Use assembly macros for static_cpu_has() and call them from inline assembly. This not only makes the code more readable, but also improves compilation decision, specifically inline decisions which GCC base on the number of new lines in inline assembly.

The patch slightly increases the kernel size:

text data bss dec hex filename
18162879 10226256 2957312 31346447 1de4f0f ./vmlinux before 18163528 10226300 2957312 31347140 1de51c4 ./vmlinux after (+693)

And enables the inlining of function such as free_ldt_pgtables().

---
 arch/x86/include/asm/cpufeature.h | 82 ++++++++++++++++++-------------
 arch/x86/kernel/macros.S          |  1 +
 2 files changed, 48 insertions(+), 35 deletions(-)
arch/x86/include/asm/cpufeature.h +47 -35
index aced6c9290d6..7d442722ef24 100644
@@ -2,10 +2,10 @@
 #ifndef _ASM_X86_CPUFEATURE_H
 #define _ASM_X86_CPUFEATURE_H
 
-#include <asm/processor.h>
-
-#if defined(__KERNEL__) && !defined(__ASSEMBLY__)
+#ifdef __KERNEL__
+#ifndef __ASSEMBLY__
 
+#include <asm/processor.h>
 #include <asm/asm.h>
 #include <linux/bitops.h>
 
@@ -161,37 +161,10 @@ extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit);
  */
 static __always_inline __pure bool _static_cpu_has(u16 bit)
 {
-	asm_volatile_goto("1: jmp 6f\n"
-		 "2:\n"
-		 ".skip -(((5f-4f) - (2b-1b)) > 0) * "
-			 "((5f-4f) - (2b-1b)),0x90\n"
-		 "3:\n"
-		 ".section .altinstructions,\"a\"\n"
-		 " .long 1b - .\n"		/* src offset */
-		 " .long 4f - .\n"		/* repl offset */
-		 " .word %P[always]\n"		/* always replace */
-		 " .byte 3b - 1b\n"		/* src len */
-		 " .byte 5f - 4f\n"		/* repl len */
-		 " .byte 3b - 2b\n"		/* pad len */
-		 ".previous\n"
-		 ".section .altinstr_replacement,\"ax\"\n"
-		 "4: jmp %l[t_no]\n"
-		 "5:\n"
-		 ".previous\n"
-		 ".section .altinstructions,\"a\"\n"
-		 " .long 1b - .\n"		/* src offset */
-		 " .long 0\n"			/* no replacement */
-		 " .word %P[feature]\n"		/* feature bit */
-		 " .byte 3b - 1b\n"		/* src len */
-		 " .byte 0\n"			/* repl len */
-		 " .byte 0\n"			/* pad len */
-		 ".previous\n"
-		 ".section .altinstr_aux,\"ax\"\n"
-		 "6:\n"
-		 " testb %[bitnum],%[cap_byte]\n"
-		 " jnz %l[t_yes]\n"
-		 " jmp %l[t_no]\n"
-		 ".previous\n"
+	asm_volatile_goto("STATIC_CPU_HAS bitnum=%[bitnum] "
+			  "cap_byte=\"%[cap_byte]\" "
+			  "feature=%P[feature] t_yes=%l[t_yes] "
+			  "t_no=%l[t_no] always=%P[always]"
 		 : : [feature]  "i" (bit),
 		     [always]   "i" (X86_FEATURE_ALWAYS),
 		     [bitnum]   "i" (1 << (bit & 7)),
@@ -226,5 +199,44 @@ static __always_inline __pure bool _static_cpu_has(u16 bit)
 #define CPU_FEATURE_TYPEVAL		boot_cpu_data.x86_vendor, boot_cpu_data.x86, \
 					boot_cpu_data.x86_model
 
-#endif /* defined(__KERNEL__) && !defined(__ASSEMBLY__) */
+#else /* __ASSEMBLY__ */
+
+.macro STATIC_CPU_HAS bitnum:req cap_byte:req feature:req t_yes:req t_no:req always:req
+1:
+	jmp 6f
+2:
+	.skip -(((5f-4f) - (2b-1b)) > 0) * ((5f-4f) - (2b-1b)),0x90
+3:
+	.section .altinstructions,"a"
+	.long 1b - .		/* src offset */
+	.long 4f - .		/* repl offset */
+	.word \always		/* always replace */
+	.byte 3b - 1b		/* src len */
+	.byte 5f - 4f		/* repl len */
+	.byte 3b - 2b		/* pad len */
+	.previous
+	.section .altinstr_replacement,"ax"
+4:
+	jmp \t_no
+5:
+	.previous
+	.section .altinstructions,"a"
+	.long 1b - .		/* src offset */
+	.long 0			/* no replacement */
+	.word \feature		/* feature bit */
+	.byte 3b - 1b		/* src len */
+	.byte 0			/* repl len */
+	.byte 0			/* pad len */
+	.previous
+	.section .altinstr_aux,"ax"
+6:
+	testb \bitnum,\cap_byte
+	jnz \t_yes
+	jmp \t_no
+	.previous
+.endm
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* __KERNEL__ */
 #endif /* _ASM_X86_CPUFEATURE_H */
arch/x86/kernel/macros.S +1 -0
index 7baa40d5bf16..bf8b9c93e255 100644
@@ -12,3 +12,4 @@
 #include <asm/bug.h>
 #include <asm/paravirt.h>
 #include <asm/asm.h>
+#include <asm/cpufeature.h>
Signature · 1 line
2.17.1
author
#12 lore raw

PATCH v7 10/10 x86: jump-labels: use macros instead of inline assembly

In reply to Nadav Amit

Use assembly macros for jump-labels and call them from inline assembly. This not only makes the code more readable, but also improves compilation decision, specifically inline decisions which GCC base on the number of new lines in inline assembly.

As a result the code size is slightly increased.

text data bss dec hex filename
18163528 10226300 2957312 31347140 1de51c4 ./vmlinux before 18163608 10227348 2957312 31348268 1de562c ./vmlinux after (+1128)

And functions such as intel_pstate_adjust_policy_max(), kvm_cpu_accept_dm_intr(), kvm_register_readl() are inlined.

Cc Thomas Gleixner <[email protected]>
Cc Ingo Molnar <[email protected]>
Cc "H. Peter Anvin" <[email protected]>
Cc Greg Kroah-Hartman <[email protected]>
Cc Kate Stewart <[email protected]>
Cc Philippe Ombredanne <[email protected]>
---
 arch/x86/entry/calling.h          |  2 +-
 arch/x86/include/asm/jump_label.h | 77 +++++++++++--------------------
 arch/x86/kernel/macros.S          |  1 +
 3 files changed, 30 insertions(+), 50 deletions(-)
arch/x86/entry/calling.h +1 -1
index 352e70cd33e8..708b46a54578 100644
@@ -338,7 +338,7 @@ For 32-bit we have the following conventions - kernel is built with
 .macro CALL_enter_from_user_mode
 #ifdef CONFIG_CONTEXT_TRACKING
 #ifdef HAVE_JUMP_LABEL
-	STATIC_JUMP_IF_FALSE .Lafter_call_\@, context_tracking_enabled, def=0
+	STATIC_BRANCH_JMP l_yes=.Lafter_call_\@, key=context_tracking_enabled, branch=1
 #endif
 	call enter_from_user_mode
 .Lafter_call_\@:
arch/x86/include/asm/jump_label.h +28 -49

113 lines not on this page · raw message

arch/x86/kernel/macros.S +1 -0
index bf8b9c93e255..161c95059044 100644
@@ -13,3 +13,4 @@
 #include <asm/paravirt.h>
 #include <asm/asm.h>
 #include <asm/cpufeature.h>
+#include <asm/jump_label.h>
Signature · 1 line
2.17.1
author
#13 lore raw
In reply to Nadav Amit

Ping.

Quoted 132 lines · Nadav Amit

This patch-set deals with an interesting yet stupid problem: kernel code that does not get inlined despite its simplicity. There are several causes for this behavior: "cold" attribute on __init, different function optimization levels; conditional constant computations based on __builtin_constant_p(); and finally large inline assembly blocks.

This patch-set deals with the inline assembly problem. I separated these patches from the others (that were sent in the RFC) for easier inclusion. I also separated the removal of unnecessary new-lines which would be sent separately.

The problem with inline assembly is that inline assembly is often used by the kernel for things that are other than code - for example, assembly directives and data. GCC however is oblivious to the content of the blocks and assumes their cost in space and time is proportional to the number of the perceived assembly "instruction", according to the number of newlines and semicolons. Alternatives, paravirt and other mechanisms are affected, causing code not to be inlined, and degrading compilation quality in general.

The solution that this patch-set carries for this problem is to create an assembly macro, and then call it from the inline assembly block. As a result, the compiler sees a single "instruction" and assigns the more appropriate cost to the code.

To avoid uglification of the code, as many noted, the macros are first precompiled into an assembly file, which is later assembled together with the C files. This also enables to avoid duplicate implementation that was set before for the asm and C code. This can be seen in the exception table changes.

Overall this patch-set slightly increases the kernel size (my build was done using my Ubuntu 18.04 config + localyesconfig for the record):

text data bss dec hex filename
18140829 10224724 2957312 31322865 1ddf2f1 ./vmlinux before 18163608 10227348 2957312 31348268 1de562c ./vmlinux after (+0.1%)

The number of static functions in the image is reduced by 379, but actually inlining is even better, which does not always shows in these
numbers: a function may be inlined causing the calling function not to be inlined.

I ran some limited number of benchmarks, and in general the performance impact is not very notable. You can still see >10 cycles shaved off some syscalls that manipulate page-tables (e.g., mprotect()), in which paravirt caused many functions not to be inlined. In addition this patch-set can prevent issues such as [1], and improves code readability and maintainability.

[1] https://patchwork.kernel.org/patch/10450037/

v6->v7: * Fix context switch tracking (Ingo)
* Fix xtensa build error (Ingo)
* Rebase on 4.18-rc8

v5->v6: * Removing more code from jump-labels (PeterZ)
* Fix build issue on i386 (0-day, PeterZ)

v4->v5: * Makefile fixes (Masahiro, Sam)

v3->v4: * Changed naming of macros in 2 patches (PeterZ)
* Minor cleanup of the paravirt patch

v2->v3: * Several build issues resolved (0-day)
* Wrong comments fix (Josh)
* Change asm vs C order in refcount (Kees)

v1->v2: * Compiling the macros into a separate .s file, improving
readability (Linus)
* Improving assembly formatting, applying most of the comments according to my judgment (Jan)
* Adding exception-table, cpufeature and jump-labels
* Removing new-line cleanup; to be submitted separately

Cc Masahiro Yamada <[email protected]>
Cc Sam Ravnborg <[email protected]>
Cc Alok Kataria <[email protected]>
Cc Christopher Li <[email protected]>
Cc Greg Kroah-Hartman <[email protected]>
Cc "H. Peter Anvin" <[email protected]>
Cc Ingo Molnar <[email protected]>
Cc Jan Beulich <[email protected]>
Cc Josh Poimboeuf <[email protected]>
Cc Juergen Gross <[email protected]>
Cc Kate Stewart <[email protected]>
Cc Kees Cook <[email protected]>
Cc Peter Zijlstra <[email protected]>
Cc Philippe Ombredanne <[email protected]>
Cc Thomas Gleixner <[email protected]>
Cc Linus Torvalds <[email protected]>
Cc Chris Zankel <[email protected]>
Cc Max Filippov <[email protected]>

Nadav Amit (10):
xtensa: defining LINKER_SCRIPT for the linker script
Makefile: Prepare for using macros for inline asm
x86: objtool: use asm macro for better compiler decisions
x86: refcount: prevent gcc distortions
x86: alternatives: macrofy locks for better inlining
x86: bug: prevent gcc distortions
x86: prevent inline distortion by paravirt ops
x86: extable: use macros instead of inline assembly
x86: cpufeature: use macros instead of inline assembly
x86: jump-labels: use macros instead of inline assembly

Makefile                               |  9 ++-
arch/x86/Makefile                      | 11 ++-
arch/x86/entry/calling.h               |  2 +-
arch/x86/include/asm/alternative-asm.h | 20 ++++--
arch/x86/include/asm/alternative.h     | 11 +--
arch/x86/include/asm/asm.h             | 61 +++++++---------
arch/x86/include/asm/bug.h             | 98 +++++++++++++++-----------
arch/x86/include/asm/cpufeature.h      | 82 ++++++++++++---------
arch/x86/include/asm/jump_label.h      | 77 ++++++++------------
arch/x86/include/asm/paravirt_types.h  | 56 +++++++--------
arch/x86/include/asm/refcount.h        | 74 +++++++++++--------
arch/x86/kernel/macros.S               | 16 +++++
arch/xtensa/kernel/Makefile            |  4 +-
include/asm-generic/bug.h              |  8 +--
include/linux/compiler.h               | 56 +++++++++++----
scripts/Kbuild.include                 |  4 +-
scripts/mod/Makefile                   |  2 +
17 files changed, 333 insertions(+), 258 deletions(-)

create mode 100644 arch/x86/kernel/macros.S

Signature · 1 line
2.17.1
#14 lore raw
Quoted 1 line · Nadav Amit

Ping.

Masahiro Yamada noted that some Reviewed-by tags were not added - could you please double check past mails and add them and re-send against the latest kernel?

Thanks,

Ingo

author
#15 lore raw
Quoted 7 lines · Ingo Molnar
Quoted 1 line · Nadav Amit

Ping.

Masahiro Yamada noted that some Reviewed-by tags were not added - could you please double check past mails and add them and re-send against the latest kernel?

One (his) was missing. I’ll add it, rebase and send.