Re: [PATCH] kbuild: Disable extra debugging info in .s output

Masahiro Yamada
2019-02-19T23:56:05Z

On Mon, Feb 18, 2019 at 11:32 PM Borislav Petkov <bp@alien8.de> wrote:
>
> On Mon, Feb 18, 2019 at 06:10:57PM +0900, Masahiro Yamada wrote:
> > Could you send v2 as I suggested?
> > Your commit log describes your motivation perfectly.
> >
> > (I lost the applicable patch because
> > I just modified the code locally and pasted it
> > into the previous email.)
>
> Sure, here it is.
>
> Thx.

Applied to linux-kbuild.

Thanks.

> ---
> From: Masahiro Yamada <yamada.masahiro@socionext.com>
> Date: Sun, 25 Nov 2018 23:58:00 +0100
> Subject: [PATCH] kbuild: Disable extra debugging info in .s output
>
> Modern gcc adds view assignments, reset assertion checking in .loc
> directives and a couple more additional debug markers, which clutters
> the asm output unnecessarily:
>
> For example:
>
> bsp_resume:
> .LFB3466:
> .loc 1 1868 1 is_stmt 1 view -0
> .cfi_startproc
> .loc 1 1869 2 view .LVU73
> # arch/x86/kernel/cpu/common.c:1869: if (this_cpu->c_bsp_resume)
> .loc 1 1869 14 is_stmt 0 view .LVU74
> movq this_cpu(%rip), %rax # this_cpu, this_cpu
> movq 64(%rax), %rax # this_cpu.94_1->c_bsp_resume, _2
> # arch/x86/kernel/cpu/common.c:1869: if (this_cpu->c_bsp_resume)
> .loc 1 1869 5 view .LVU75
> testq %rax, %rax # _2
> je .L8 #,
> .loc 1 1870 3 is_stmt 1 view .LVU76
> movq $boot_cpu_data, %rdi #,
> jmp __x86_indirect_thunk_rax
>
> or
> .loc 2 57 9 view .LVU478
> .loc 2 57 9 view .LVU479
> .loc 2 57 9 view .LVU480
> .loc 2 57 9 view .LVU481
> .LBB1385:
> .LBB1383:
> .LBB1379:
> .LBB1377:
> .LBB1375:
> .loc 2 57 9 view .LVU482
> .loc 2 57 9 view .LVU483
> movl %edi, %edx # cpu, cpu
> .LVL87:
> .loc 2 57 9 is_stmt 0 view .LVU484
>
> That MOV in there is drowned in debugging information and latter makes
> it hard to follow the asm. And that DWARF info is not really needed for
> asm output staring.
>
> Disable the debug information generation which clutters the asm output
> unnecessarily:
>
> bsp_resume:
> # arch/x86/kernel/cpu/common.c:1869: if (this_cpu->c_bsp_resume)
> movq this_cpu(%rip), %rax # this_cpu, this_cpu
> movq 64(%rax), %rax # this_cpu.94_1->c_bsp_resume, _2
> # arch/x86/kernel/cpu/common.c:1869: if (this_cpu->c_bsp_resume)
> testq %rax, %rax # _2
> je .L8 #,
> # arch/x86/kernel/cpu/common.c:1870: this_cpu->c_bsp_resume(&boot_cpu_data);
> movq $boot_cpu_data, %rdi #,
> jmp __x86_indirect_thunk_rax
> .L8:
> # arch/x86/kernel/cpu/common.c:1871: }
> rep ret
> .size bsp_resume, .-bsp_resume
>
> [ bp: write commit message. ]
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> Signed-off-by: Borislav Petkov <bp@suse.de>
> Cc: Michal Marek <michal.lkml@markovi.net>
> Cc: linux-kbuild@vger.kernel.org
> ---
> Makefile | 13 ++++++++-----
> scripts/Makefile.build | 2 +-
> 2 files changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 96c5335e7ee4..c5e7d3ac8bd2 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -729,25 +729,28 @@ KBUILD_CFLAGS += -fomit-frame-pointer
> endif
> endif
>
> -KBUILD_CFLAGS += $(call cc-option, -fno-var-tracking-assignments)
> +DEBUG_CFLAGS := $(call cc-option, -fno-var-tracking-assignments)
>
> ifdef CONFIG_DEBUG_INFO
> ifdef CONFIG_DEBUG_INFO_SPLIT
> -KBUILD_CFLAGS += $(call cc-option, -gsplit-dwarf, -g)
> +DEBUG_CFLAGS += $(call cc-option, -gsplit-dwarf, -g)
> else
> -KBUILD_CFLAGS += -g
> +DEBUG_CFLAGS += -g
> endif
> KBUILD_AFLAGS += -Wa,-gdwarf-2
> endif
> ifdef CONFIG_DEBUG_INFO_DWARF4
> -KBUILD_CFLAGS += $(call cc-option, -gdwarf-4,)
> +DEBUG_CFLAGS += $(call cc-option, -gdwarf-4,)
> endif
>
> ifdef CONFIG_DEBUG_INFO_REDUCED
> -KBUILD_CFLAGS += $(call cc-option, -femit-struct-debug-baseonly) \
> +DEBUG_CFLAGS += $(call cc-option, -femit-struct-debug-baseonly) \
> $(call cc-option,-fno-var-tracking)
> endif
>
> +KBUILD_CFLAGS += $(DEBUG_CFLAGS)
> +export DEBUG_CFLAGS
> +
> ifdef CONFIG_FUNCTION_TRACER
> ifdef CONFIG_FTRACE_MCOUNT_RECORD
> # gcc 5 supports generating the mcount tables directly
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index fd03d60f6c5a..8f5c86da77b1 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -104,7 +104,7 @@ modkern_cflags = \
> quiet_modtag = $(if $(part-of-module),[M], )
>
> quiet_cmd_cc_s_c = CC $(quiet_modtag) $@
> -cmd_cc_s_c = $(CC) $(c_flags) $(DISABLE_LTO) -fverbose-asm -S -o $@ $<
> +cmd_cc_s_c = $(CC) $(filter-out $(DEBUG_CFLAGS), $(c_flags)) $(DISABLE_LTO) -fverbose-asm -S -o $@ $<
>
> $(obj)/%.s: $(src)/%.c FORCE
> $(call if_changed_dep,cc_s_c)
> --
> 2.19.1
>
> --
> Regards/Gruss,
> Boris.
>
> Good mailing practices for 400: avoid top-posting and trim the reply.

--
Best Regards
Masahiro Yamada