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

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Date:   Fri, 23 Sep 2022 19:20:03 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Michal Marek <michal.lkml@...kovi.net>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <llvm@...ts.linux.dev>,
        Bill Wendling <morbo@...gle.com>,
        Greg Thelen <gthelen@...gle.com>,
        Alexey Alexandrov <aalexand@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH v4] Makefile.debug: re-enable debug info for .S files

On Fri, Sep 23, 2022 at 7:12 PM Masahiro Yamada <masahiroy@...nel.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