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

Borislav Petkov
2019-01-31T11:58:30Z

Ping?

On Mon, Jan 21, 2019 at 10:53:38AM +0100, Borislav Petkov wrote:
> From: Borislav Petkov <bp@suse.de>
>
> 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:
> .LFB3466:
> .loc 1 1868 1
> # arch/x86/kernel/cpu/common.c:1869: if (this_cpu->c_bsp_resume)
> .loc 1 1869 14
> 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
> testq %rax, %rax # _2
> je .L8 #,
> # arch/x86/kernel/cpu/common.c:1870: this_cpu->c_bsp_resume(&boot_cpu_data);
> .loc 1 1870 3
> movq $boot_cpu_data, %rdi #,
> jmp __x86_indirect_thunk_rax
>
> Signed-off-by: Borislav Petkov <bp@suse.de>
> Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
> Cc: Michal Marek <michal.lkml@markovi.net>
> Cc: linux-kbuild@vger.kernel.org
> ---
> scripts/Makefile.build | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index fd03d60f6c5a..4f33fdab89d2 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -103,8 +103,12 @@ modkern_cflags = \
> $(KBUILD_CFLAGS_KERNEL) $(CFLAGS_KERNEL))
> quiet_modtag = $(if $(part-of-module),[M], )
>
> +disable_extra_cc_dbg := $(call cc-option,-gno-as-locview-support)
> +disable_extra_cc_dbg += $(call cc-option,-fno-dwarf2-cfi-asm)
> +disable_extra_cc_dbg += $(call cc-option,-feliminate-unused-debug-symbols)
> +disable_extra_cc_dbg += $(call cc-option,-gno-statement-frontiers)
> 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) $(c_flags) $(DISABLE_LTO) $(disable_extra_cc_dbg) -fverbose-asm -S -o $@ $<
>
> $(obj)/%.s: $(src)/%.c FORCE
> $(call if_changed_dep,cc_s_c)
> --
> 2.19.1