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From:   Pingfan Liu <kernelfans@gmail.com>
Date:   Fri, 31 Jul 2020 17:36:34 +0800
Message-ID: <CAFgQCTsYTwpv6oCGLH5JTjt+1jPAZ7XjBm6sDoCPRnjrRPhvTQ@mail.gmail.com>
Subject: Re: [PATCH] x86/purgatory: strip debug info
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Hans de Goede <hdegoede@redhat.com>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        Steve Wahl <steve.wahl@hpe.com>,
        LKML <linux-kernel@vger.kernel.org>
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On Fri, Jul 31, 2020 at 7:11 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Thu, Jul 30, 2020 at 1:27 AM Pingfan Liu <kernelfans@gmail.com> wrote:
> >
> > It is useless to keep debug info in purgatory. And discarding them saves
> > about 200K space.
> >
> > Original:
> >   259080  kexec-purgatory.o
> > Stripped:
> >    29152  kexec-purgatory.o
> >
> > Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Ingo Molnar <mingo@redhat.com>
> > Cc: Borislav Petkov <bp@alien8.de>
> > Cc: "H. Peter Anvin" <hpa@zytor.com>
> > Cc: Hans de Goede <hdegoede@redhat.com>
> > Cc: Nick Desaulniers <ndesaulniers@google.com>
> > Cc: Arvind Sankar <nivedita@alum.mit.edu>
> > Cc: Steve Wahl <steve.wahl@hpe.com>
> > Cc: linux-kernel@vger.kernel.org
> > To: x86@kernel.org
>
> I don't see any code in
> arch/x86/purgatory/
> arch/x86/include/asm/purgatory.h
> include/linux/purgatory.h
> include/uapi/linux/kexec.h
> kernel/kexec*
> include/linux/kexec.h
> include/linux/crash_dump.h
> kernel/crash_dump.c
> arch/x86/kernel/crash*
> https://github.com/horms/kexec-tools/tree/master/kexec/arch/x86_64
> that mentions any kind of debug info section.  I'm not sure what you'd
> do with the debug info anyway for this binary.  So I suspect this
> information should ok to discard.
>
> This works, but it might be faster to build to not generate the
> compile info in the first place via compile flag `-g0`, which could be
> added `ifdef CONFIG_DEBUG_INFO` or even just unconditionally.  That
> way we're not doing additional work to generate debug info, then
> additional work to throw it away.
What about:
diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index 088bd76..7e1ad9e 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -32,7 +32,7 @@ KCOV_INSTRUMENT := n
 # make up the standalone purgatory.ro

 PURGATORY_CFLAGS_REMOVE := -mcmodel=kernel
-PURGATORY_CFLAGS := -mcmodel=large -ffreestanding -fno-zero-initialized-in-bss
+PURGATORY_CFLAGS := -mcmodel=large -ffreestanding
-fno-zero-initialized-in-bss -g0
 PURGATORY_CFLAGS += $(DISABLE_STACKLEAK_PLUGIN) -DDISABLE_BRANCH_PROFILING
 PURGATORY_CFLAGS += $(call cc-option,-fno-stack-protector)

Thanks,
Pingfan