Kbuild: generate debug info in building

This patch will generate kernel debuginfo in Kbuild when invoking "make debug_info". The separate debug files are in .debug under building tree. They can help the cases of requiring debug info for tracing/debug tools, especially cross-compilation. Moreover, it can simplify or standardize the packaging process for the distributions those will provide kernel-debuginfo.

---
 Makefile                 |   14 ++++++++++++++
 scripts/Makefile.modpost |   14 ++++++++++++++
 2 files changed, 28 insertions(+), 0 deletions(-)

index 7f9ff9b..eed7510 100644
@@ -814,6 +814,20 @@ define rule_vmlinux-modpost
 	$(Q)echo 'cmd_$@ := $(cmd_vmlinux-modpost)' > $(dot-target).cmd
 endef
 
+ifdef CONFIG_DEBUG_INFO
+quiet_cmd_vmlinux_debug = GEN     $<.debug
+      cmd_vmlinux_debug = mkdir -p .debug;                          \
+                          $(OBJCOPY) --only-keep-debug              \
+                                     $< .debug/$<.debug
+targets += vmlinux.debug
+endif
+
+debug_info: vmlinux FORCE
+ifdef CONFIG_DEBUG_INFO
+	$(call if_changed,vmlinux_debug)
+	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost $@
+endif
+
 # vmlinux image - including updated kernel symbols
 vmlinux: $(vmlinux-lds) $(vmlinux-init) $(vmlinux-main) vmlinux.o

$(kallsyms.o) FORCE
ifdef CONFIG_HEADERS_CHECK

index f4053dc..0df73b2 100644
@@ -137,6 +137,20 @@ $(modules): %.ko :%.o %.mod.o FORCE
 
 targets += $(modules)
 
+modules-debug := $(modules:.ko=.ko.debug)
+ifdef CONFIG_DEBUG_INFO
+quiet_cmd_debug_ko = GEN     $@
+      cmd_debug_ko = mkdir -p .debug/`dirname $@`;			\
+		     $(OBJCOPY) --only-keep-debug $< .debug/$@
+targets += $(modules-debug)
+endif
+
+debug_info: $(modules-debug) FORCE
+
+$(modules-debug): $(modules) FORCE
+ifdef CONFIG_DEBUG_INFO
+	$(call if_changed,debug_ko)
+endif
 
 # Add FORCE to the prequisites of a target to force it to be always

rebuilt.
#
---------------------------------------------------------------------------

1.5.6

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Hi Wenji.

Can you tell a bit more why we need this?
I do not see anyone really asking for this.

Apart form the rationale why this is needed I have a few comments to your patch.

Why do we need to hide this in a hidden directory?

Sam

Thanks for your comments. The debug info files are important to some kernel tracing/debug tools, for example systemtap, crashdumps, etc. We have several considerations:
* The debuginfo extracting machinery could be integrated into the
kbuild system. This way it's not just done via RPM macros. So
generating debuginfo RPMS or something alike can be simplified and
standardized, also distribution independent.
* Reduce the size of current file which mixes executable and
debug sections. Maybe cut the time of analysis for
elfutils/binutils which is used by some other tools.

Please see updated one.

Regards,
Wenji

index 7b1f238..4151f53 100644
@@ -814,6 +814,19 @@ define rule_vmlinux-modpost
        $(Q)echo 'cmd_$@ := $(cmd_vmlinux-modpost)' > $(dot-target).cmd
 endef
 
+quiet_cmd_vmlinux_debug = GEN     $<.debug
+      cmd_vmlinux_debug = mkdir -p debug; 
        \
+                          $(OBJCOPY) --only-keep-debug 
        \
+                                     $< debug/$<.debug
+targets += vmlinux.debug
+
+PHONY += debug_info
+debug_info: vmlinux FORCE
+ifdef CONFIG_DEBUG_INFO
+       $(call if_changed,vmlinux_debug)
+       $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost $@
+endif
+
 # vmlinux image - including updated kernel symbols

vmlinux: $(vmlinux-lds) $(vmlinux-init) $(vmlinux-main) vmlinux.o
$(kallsyms.o) FORCE
ifdef CONFIG_HEADERS_CHECK
@@ -1250,6 +1263,7 @@ help:

        @echo  '  all             - Build all targets marked with [*]'
        @echo  '* vmlinux         - Build the bare kernel'
        @echo  '* modules         - Build all modules'
+       @echo  '  debug_info      - Generate debug info files in debug'
        @echo  '  modules_install - Install all modules to 

INSTALL_MOD_PATH (default: /)'
@echo ' firmware_install- Install all firmware to
INSTALL_FW_PATH'
@echo ' (default:
$$(INSTALL_MOD_PATH)/lib/firmware)'

index f4053dc..6e630e6 100644
@@ -137,6 +137,18 @@ $(modules): %.ko :%.o %.mod.o FORCE
 
 targets += $(modules)
 
+modules-debug := $(modules:.ko=.ko.debug)
+quiet_cmd_debug_ko = GEN     $@
+      cmd_debug_ko = mkdir -p debug/$(dir $@);                         \
+                    $(OBJCOPY) --only-keep-debug $< debug/$@
+targets += $(modules-debug)
+
+debug_info: $(modules-debug) FORCE
+
+ifdef CONFIG_DEBUG_INFO
+$(modules-debug): $(modules) FORCE
+       $(call if_changed,debug_ko)
+endif
 
 # Add FORCE to the prequisites of a target to force it to be always 

rebuilt.
#
---------------------------------------------------------------------------

Hi,
I got the following building error for 2.6.29-rc1.

# make
  CHK     include/linux/version.h
  CHK     include/linux/utsrelease.h
  SYMLINK include/asm -> include/asm-x86
  CALL    scripts/checksyscalls.sh
  CHK     include/linux/compile.h
  IHEX    firmware/e100/d101m_ucode.bin
  AS      firmware/e100/d101m_ucode.bin.gen.o
  IHEX    firmware/e100/d101s_ucode.bin
  AS      firmware/e100/d101s_ucode.bin.gen.o
  IHEX    firmware/e100/d102e_ucode.bin
  AS      firmware/e100/d102e_ucode.bin.gen.o
  LD      firmware/built-in.o
  LD      vmlinux.o
  MODPOST vmlinux.o
  GEN     .version
  CHK     include/linux/compile.h
  UPD     include/linux/compile.h
  CC      init/version.o
  LD      init/built-in.o
  LD      .tmp_vmlinux1
  STRIP   .tmp_vmlinux1.stripped
objcopy: unrecognized option `--strip-unneeded-symbols'

# objcopy --version
GNU objcopy 2.15.92.0.2 20040927
Copyright 2004 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of the GNU General Public License.  This program has absolutely no warranty.

The option --strip-unneeded-symbols is only available on higher version, but not exists on binutils-2.15.

Seems to keep Makefile compatible on all kinds of circumstances. Like,

quiet_cmd_kstrip = STRIP $@

      cmd_kstrip = $(OBJCOPY) --wildcard $(addprefix --strip-symbols 

,$(filter %/scripts/strip-symbols,$^)) $< $@

Regards,
Wenji

Hi,

Sorry, resend it in terms of correct subject.

I got the following building error for 2.6.29-rc1.

# make
  CHK     include/linux/version.h
  CHK     include/linux/utsrelease.h
  SYMLINK include/asm -> include/asm-x86
  CALL    scripts/checksyscalls.sh
  CHK     include/linux/compile.h
  IHEX    firmware/e100/d101m_ucode.bin
  AS      firmware/e100/d101m_ucode.bin.gen.o
  IHEX    firmware/e100/d101s_ucode.bin
  AS      firmware/e100/d101s_ucode.bin.gen.o
  IHEX    firmware/e100/d102e_ucode.bin
  AS      firmware/e100/d102e_ucode.bin.gen.o
  LD      firmware/built-in.o
  LD      vmlinux.o
  MODPOST vmlinux.o
  GEN     .version
  CHK     include/linux/compile.h
  UPD     include/linux/compile.h
  CC      init/version.o
  LD      init/built-in.o
  LD      .tmp_vmlinux1
  STRIP   .tmp_vmlinux1.stripped
objcopy: unrecognized option `--strip-unneeded-symbols'

# objcopy --version
GNU objcopy 2.15.92.0.2 20040927
Copyright 2004 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of the GNU General Public License.  This program has absolutely no warranty.

The option --strip-unneeded-symbols is only available on higher version, but not exists on binutils-2.15.

Seems to keep Makefile compatible on all kinds of circumstances. Like,

quiet_cmd_kstrip = STRIP $@

      cmd_kstrip = $(OBJCOPY) --wildcard $(addprefix --strip-symbols 

,$(filter %/scripts/strip-symbols,$^)) $< $@

Regards,
Wenji

When I upgraded binutils to 2.18 and enabled CONFIG_RELOCATABLE, there are still mismatched symbols between kernel and debuginfo.

For example, to verify buildid (bytes from __start_notes to __stop_notes) will get failed. The __stop_notes of running kernel doesn't match the one in debuginfo.

$ uname -r
2.6.29-rc1
$ cat /proc/kallsyms |grep __stop_notes
c0543610 T __stop_notes
$ readelf -s /lib/modules/2.6.29-rc1/build/vmlinux |grep __stop_notes
 48985: c1343610     0 NOTYPE  GLOBAL DEFAULT    5 __stop_notes
$ cat /lib/modules/2.6.29-rc1/build/.config|grep CONFIG_RELOCATABLE
CONFIG_RELOCATABLE=y
$ gcc -v
Reading specs from /usr/lib/gcc/i386-redhat-linux/3.4.6/specs
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --enable-shared --enable-threads=posix --disable-checking --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-java-awt=gtk --host=i386-redhat-linux
Thread model: posix
gcc version 3.4.6 20060404 (Red Hat 3.4.6-9.0.1)
$ ld -v
GNU ld (GNU Binutils) 2.18
$ objcopy --version
GNU objcopy (GNU Binutils) 2.18
Copyright 2007 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of the GNU General Public License version 3 or (at your option) any later version.
This program has absolutely no warranty.

Regards,
Wenji