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[PATCH v4] Makefile.debug: re-enable debug info for .S files

Nick Desaulniers posted 1 patch 3 years, 6 months ago 
lib/Kconfig.debug      |  4 +++-
scripts/Makefile.debug | 18 +++++++++---------
2 files changed, 12 insertions(+), 10 deletions(-)
[PATCH v4] Makefile.debug: re-enable debug info for .S files
Posted by Nick Desaulniers 3 years, 6 months ago 
Alexey reported that the fraction of unknown filename instances in
kallsyms grew from ~0.3% to ~10% recently; Bill and Greg tracked it down
to assembler defined symbols, which regressed as a result of:

commit b8a9092330da ("Kbuild: do not emit debug info for assembly with LLVM_IAS=1")

In that commit, I allude to restoring debug info for assembler defined
symbols in a follow up patch, but it seems I forgot to do so in

commit a66049e2cf0e ("Kbuild: make DWARF version a choice")

Link: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=31bf18645d98b4d3d7357353be840e320649a67d
Fixes: b8a9092330da ("Kbuild: do not emit debug info for assembly with LLVM_IAS=1")
Reported-by: Alexey Alexandrov <aalexand@google.com>
Reported-by: Bill Wendling <morbo@google.com>
Reported-by: Greg Thelen <gthelen@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
Changes v3 -> v4:
* Break out into its own patch.
* Move addition of debug-flags-y to DEBUG_CFLAGS and KBUILD_AFLAGS up
  grouping the -gdwarf-* handling together.

 lib/Kconfig.debug      |  4 +++-
 scripts/Makefile.debug | 18 +++++++++---------
 2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index bcbe60d6c80c..d3e5f36bb01e 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -264,8 +264,10 @@ config DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
 config DEBUG_INFO_DWARF4
 	bool "Generate DWARF Version 4 debuginfo"
 	select DEBUG_INFO
+	depends on !CC_IS_CLANG || (CC_IS_CLANG && (AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502)))
 	help
-	  Generate DWARF v4 debug info. This requires gcc 4.5+ and gdb 7.0+.
+	  Generate DWARF v4 debug info. This requires gcc 4.5+, binutils 2.35.2
+	  if using clang without clang's integrated assembler, and gdb 7.0+.
 
 	  If you have consumers of DWARF debug info that are not ready for
 	  newer revisions of DWARF, you may wish to choose this or have your
diff --git a/scripts/Makefile.debug b/scripts/Makefile.debug
index 26d6a9d97a20..d6aecd78b942 100644
--- a/scripts/Makefile.debug
+++ b/scripts/Makefile.debug
@@ -4,15 +4,15 @@ ifdef CONFIG_DEBUG_INFO_SPLIT
 DEBUG_CFLAGS	+= -gsplit-dwarf
 endif
 
-ifndef CONFIG_AS_IS_LLVM
-KBUILD_AFLAGS	+= -Wa,-gdwarf-2
-endif
-
-ifndef CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
-dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
-dwarf-version-$(CONFIG_DEBUG_INFO_DWARF5) := 5
-DEBUG_CFLAGS	+= -gdwarf-$(dwarf-version-y)
+debug-flags-$(CONFIG_DEBUG_INFO_DWARF4)	+= -gdwarf-4
+debug-flags-$(CONFIG_DEBUG_INFO_DWARF5)	+= -gdwarf-5
+ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_AS_IS_GNU),yy)
+# Clang does not pass -g or -gdwarf-* option down to GAS.
+# Add -Wa, prefix to explicitly specify the flags.
+KBUILD_AFLAGS	+= $(addprefix -Wa$(comma), $(debug-flags-y))
 endif
+DEBUG_CFLAGS	+= $(debug-flags-y)
+KBUILD_AFLAGS	+= $(debug-flags-y)
 
 ifdef CONFIG_DEBUG_INFO_REDUCED
 DEBUG_CFLAGS	+= -fno-var-tracking
@@ -27,5 +27,5 @@ KBUILD_AFLAGS	+= -gz=zlib
 KBUILD_LDFLAGS	+= --compress-debug-sections=zlib
 endif
 
-KBUILD_CFLAGS += $(DEBUG_CFLAGS)
+KBUILD_CFLAGS	+= $(DEBUG_CFLAGS)
 export DEBUG_CFLAGS
-- 
2.37.3.968.ga6b4b080e4-goog
Re: [PATCH v4] Makefile.debug: re-enable debug info for .S files
Posted by Masahiro Yamada 3 years, 6 months ago 
On Tue, Sep 20, 2022 at 2:45 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> Alexey reported that the fraction of unknown filename instances in
> kallsyms grew from ~0.3% to ~10% recently; Bill and Greg tracked it down
> to assembler defined symbols, which regressed as a result of:
>
> commit b8a9092330da ("Kbuild: do not emit debug info for assembly with LLVM_IAS=1")
>
> In that commit, I allude to restoring debug info for assembler defined
> symbols in a follow up patch, but it seems I forgot to do so in
>
> commit a66049e2cf0e ("Kbuild: make DWARF version a choice")
>
> Link: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=31bf18645d98b4d3d7357353be840e320649a67d
> Fixes: b8a9092330da ("Kbuild: do not emit debug info for assembly with LLVM_IAS=1")
> Reported-by: Alexey Alexandrov <aalexand@google.com>
> Reported-by: Bill Wendling <morbo@google.com>
> Reported-by: Greg Thelen <gthelen@google.com>
> Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> ---
> Changes v3 -> v4:
> * Break out into its own patch.
> * Move addition of debug-flags-y to DEBUG_CFLAGS and KBUILD_AFLAGS up
>   grouping the -gdwarf-* handling together.
>
>  lib/Kconfig.debug      |  4 +++-
>  scripts/Makefile.debug | 18 +++++++++---------
>  2 files changed, 12 insertions(+), 10 deletions(-)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index bcbe60d6c80c..d3e5f36bb01e 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -264,8 +264,10 @@ config DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
>  config DEBUG_INFO_DWARF4
>         bool "Generate DWARF Version 4 debuginfo"
>         select DEBUG_INFO
> +       depends on !CC_IS_CLANG || (CC_IS_CLANG && (AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502)))
>         help
> -         Generate DWARF v4 debug info. This requires gcc 4.5+ and gdb 7.0+.
> +         Generate DWARF v4 debug info. This requires gcc 4.5+, binutils 2.35.2
> +         if using clang without clang's integrated assembler, and gdb 7.0+.
>
>           If you have consumers of DWARF debug info that are not ready for
>           newer revisions of DWARF, you may wish to choose this or have your
> diff --git a/scripts/Makefile.debug b/scripts/Makefile.debug
> index 26d6a9d97a20..d6aecd78b942 100644
> --- a/scripts/Makefile.debug
> +++ b/scripts/Makefile.debug
> @@ -4,15 +4,15 @@ ifdef CONFIG_DEBUG_INFO_SPLIT
>  DEBUG_CFLAGS   += -gsplit-dwarf
>  endif
>
> -ifndef CONFIG_AS_IS_LLVM
> -KBUILD_AFLAGS  += -Wa,-gdwarf-2
> -endif
> -
> -ifndef CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
> -dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
> -dwarf-version-$(CONFIG_DEBUG_INFO_DWARF5) := 5
> -DEBUG_CFLAGS   += -gdwarf-$(dwarf-version-y)
> +debug-flags-$(CONFIG_DEBUG_INFO_DWARF4)        += -gdwarf-4
> +debug-flags-$(CONFIG_DEBUG_INFO_DWARF5)        += -gdwarf-5
> +ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_AS_IS_GNU),yy)
> +# Clang does not pass -g or -gdwarf-* option down to GAS.




This patch still misses the debug info for *.S files
for the combination of LLVM_IAS=0 and
CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
because, as the comment says, Clang does not pass -g down to GAS.


With "[v4] Makefile.debug: set -g unconditional on CONFIG_DEBUG_INFO_SPLIT"
and this one applied,



$ grep CONFIG_DEBUG_INFO_DWARF .config
CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
# CONFIG_DEBUG_INFO_DWARF4 is not set
# CONFIG_DEBUG_INFO_DWARF5 is not set
$ make LLVM=1 LLVM_IAS=0 arch/x86/kernel/irqflags.o
  SYNC    include/config/auto.conf.cmd
  SYSHDR  arch/x86/include/generated/asm/unistd_32_ia32.h
  SYSHDR  arch/x86/include/generated/asm/unistd_64_x32.h
  SYSTBL  arch/x86/include/generated/asm/syscalls_64.h
  HOSTCC  arch/x86/tools/relocs_32.o
  [snip]
  AS      arch/x86/kernel/irqflags.o
$ objdump  -h arch/x86/kernel/irqflags.o | grep debug
$








I think the following fix-up is needed on top.




diff --git a/scripts/Makefile.debug b/scripts/Makefile.debug
index d6aecd78b942..8cf1cb22dd93 100644
--- a/scripts/Makefile.debug
+++ b/scripts/Makefile.debug
@@ -1,4 +1,5 @@
-DEBUG_CFLAGS   := -g
+DEBUG_CFLAGS   :=
+debug-flags-y  := -g

 ifdef CONFIG_DEBUG_INFO_SPLIT
 DEBUG_CFLAGS   += -gsplit-dwarf




Then, I can see the debug sections.



$ make LLVM=1 LLVM_IAS=0 arch/x86/kernel/irqflags.o
  CALL    scripts/checksyscalls.sh
  DESCEND objtool
  AS      arch/x86/kernel/irqflags.o
$ objdump -h arch/x86/kernel/irqflags.o | grep debug
  6 .debug_line   00000050  0000000000000000  0000000000000000  0000008f  2**0
  7 .debug_info   0000002e  0000000000000000  0000000000000000  000000f8  2**0
  8 .debug_abbrev 00000014  0000000000000000  0000000000000000  000001d0  2**0
  9 .debug_aranges 00000030  0000000000000000  0000000000000000  000001f0  2**4
 10 .debug_str    0000004d  0000000000000000  0000000000000000  00000250  2**0





If you agree, I can locally fix it up as such.





--
Best Regards
Masahiro Yamada
Re: [PATCH v4] Makefile.debug: re-enable debug info for .S files
Posted by Nick Desaulniers 3 years, 6 months ago 
On Fri, Sep 23, 2022 at 7:12 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> This patch still misses the debug info for *.S files
> for the combination of LLVM_IAS=0 and
> CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
> because, as the comment says, Clang does not pass -g down to GAS.
>
>
> With "[v4] Makefile.debug: set -g unconditional on CONFIG_DEBUG_INFO_SPLIT"
> and this one applied,
>
>
>
> $ grep CONFIG_DEBUG_INFO_DWARF .config
> CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
> # CONFIG_DEBUG_INFO_DWARF4 is not set
> # CONFIG_DEBUG_INFO_DWARF5 is not set
> $ make LLVM=1 LLVM_IAS=0 arch/x86/kernel/irqflags.o
>   SYNC    include/config/auto.conf.cmd
>   SYSHDR  arch/x86/include/generated/asm/unistd_32_ia32.h
>   SYSHDR  arch/x86/include/generated/asm/unistd_64_x32.h
>   SYSTBL  arch/x86/include/generated/asm/syscalls_64.h
>   HOSTCC  arch/x86/tools/relocs_32.o
>   [snip]
>   AS      arch/x86/kernel/irqflags.o
> $ objdump  -h arch/x86/kernel/irqflags.o | grep debug
> $
>
>
>
>
>
>
>
>
> I think the following fix-up is needed on top.
>
>
>
>
> diff --git a/scripts/Makefile.debug b/scripts/Makefile.debug
> index d6aecd78b942..8cf1cb22dd93 100644
> --- a/scripts/Makefile.debug
> +++ b/scripts/Makefile.debug
> @@ -1,4 +1,5 @@
> -DEBUG_CFLAGS   := -g
> +DEBUG_CFLAGS   :=
> +debug-flags-y  := -g
>
>  ifdef CONFIG_DEBUG_INFO_SPLIT
>  DEBUG_CFLAGS   += -gsplit-dwarf
>
>
>
>
> Then, I can see the debug sections.
>
>
>
> $ make LLVM=1 LLVM_IAS=0 arch/x86/kernel/irqflags.o
>   CALL    scripts/checksyscalls.sh
>   DESCEND objtool
>   AS      arch/x86/kernel/irqflags.o
> $ objdump -h arch/x86/kernel/irqflags.o | grep debug
>   6 .debug_line   00000050  0000000000000000  0000000000000000  0000008f  2**0
>   7 .debug_info   0000002e  0000000000000000  0000000000000000  000000f8  2**0
>   8 .debug_abbrev 00000014  0000000000000000  0000000000000000  000001d0  2**0
>   9 .debug_aranges 00000030  0000000000000000  0000000000000000  000001f0  2**4
>  10 .debug_str    0000004d  0000000000000000  0000000000000000  00000250  2**0
>
>
>
>
>
> If you agree, I can locally fix it up as such.

Ah, sorry I missed testing that combination. Thanks for your
thoroughness. Yes please apply that diff on top.
-- 
Thanks,
~Nick Desaulniers
Re: [PATCH v4] Makefile.debug: re-enable debug info for .S files
Posted by Masahiro Yamada 3 years, 6 months ago 
On Sat, Sep 24, 2022 at 11:20 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Fri, Sep 23, 2022 at 7:12 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > This patch still misses the debug info for *.S files
> > for the combination of LLVM_IAS=0 and
> > CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
> > because, as the comment says, Clang does not pass -g down to GAS.
> >
> >
> > With "[v4] Makefile.debug: set -g unconditional on CONFIG_DEBUG_INFO_SPLIT"
> > and this one applied,
> >
> >
> >
> > $ grep CONFIG_DEBUG_INFO_DWARF .config
> > CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
> > # CONFIG_DEBUG_INFO_DWARF4 is not set
> > # CONFIG_DEBUG_INFO_DWARF5 is not set
> > $ make LLVM=1 LLVM_IAS=0 arch/x86/kernel/irqflags.o
> >   SYNC    include/config/auto.conf.cmd
> >   SYSHDR  arch/x86/include/generated/asm/unistd_32_ia32.h
> >   SYSHDR  arch/x86/include/generated/asm/unistd_64_x32.h
> >   SYSTBL  arch/x86/include/generated/asm/syscalls_64.h
> >   HOSTCC  arch/x86/tools/relocs_32.o
> >   [snip]
> >   AS      arch/x86/kernel/irqflags.o
> > $ objdump  -h arch/x86/kernel/irqflags.o | grep debug
> > $
> >
> >
> >
> >
> >
> >
> >
> >
> > I think the following fix-up is needed on top.
> >
> >
> >
> >
> > diff --git a/scripts/Makefile.debug b/scripts/Makefile.debug
> > index d6aecd78b942..8cf1cb22dd93 100644
> > --- a/scripts/Makefile.debug
> > +++ b/scripts/Makefile.debug
> > @@ -1,4 +1,5 @@
> > -DEBUG_CFLAGS   := -g
> > +DEBUG_CFLAGS   :=
> > +debug-flags-y  := -g
> >
> >  ifdef CONFIG_DEBUG_INFO_SPLIT
> >  DEBUG_CFLAGS   += -gsplit-dwarf
> >
> >
> >
> >
> > Then, I can see the debug sections.
> >
> >
> >
> > $ make LLVM=1 LLVM_IAS=0 arch/x86/kernel/irqflags.o
> >   CALL    scripts/checksyscalls.sh
> >   DESCEND objtool
> >   AS      arch/x86/kernel/irqflags.o
> > $ objdump -h arch/x86/kernel/irqflags.o | grep debug
> >   6 .debug_line   00000050  0000000000000000  0000000000000000  0000008f  2**0
> >   7 .debug_info   0000002e  0000000000000000  0000000000000000  000000f8  2**0
> >   8 .debug_abbrev 00000014  0000000000000000  0000000000000000  000001d0  2**0
> >   9 .debug_aranges 00000030  0000000000000000  0000000000000000  000001f0  2**4
> >  10 .debug_str    0000004d  0000000000000000  0000000000000000  00000250  2**0
> >
> >
> >
> >
> >
> > If you agree, I can locally fix it up as such.
>
> Ah, sorry I missed testing that combination. Thanks for your
> thoroughness. Yes please apply that diff on top.
> --
> Thanks,
> ~Nick Desaulniers



Applied to linux-kbuild with the fixup.



-- 
Best Regards
Masahiro Yamada

Patchew 2.1-devel-ea86937

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