Re: [PATCH] Kbuild: generate debug info in building

Re: [PATCH] Kbuild: generate debug info in building

[Wenji Huang]

Sam Ravnborg wrote:
> On Tue, Nov 18, 2008 at 10:08:12AM +0800, Wenji Huang wrote:
>> 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.
>>
>> Signed-off-by: Wenji Huang <wenji.huang@oracle.com>
> 
> Hi Wenji.
> 
> Can you tell a bit more why we need this?
> I do not see anyone really asking for this.

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

Please see updated one.

Regards,
Wenji

diff --git a/Makefile b/Makefile
index 7b1f238..4151f53 100644
--- a/Makefile
+++ b/Makefile
@@ -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)'
diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index f4053dc..6e630e6 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -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.
  # 
---------------------------------------------------------------------------

Re: [PATCH] Kbuild: generate debug info in building

[Wenji Huang]

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

Building error of 2.6.29-rc1 using old binutils

[Wenji Huang]

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

Re: Building error of 2.6.29-rc1 using old binutils

[Wenji Huang]

Wenji Huang wrote:
> 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