Subject: Re: [PATCH RFC 1/2] Makefile: Never use -fno-omit-frame-pointer

From: Anton Vorontsov <[email-masked]>
Date: Tue, 14 Jul 2009 17:37:16 +0400

On Wed, Jun 17, 2009 at 12:16:30AM +0400, Anton Vorontsov wrote:
> According to Segher Boessenkool and GCC manual, -fomit-frame-pointer
> is only the default when optimising on archs/ABIs where it doesn't
> hinder debugging and -pg. So, we do not get it by default on x86,
> not at any optimisation level.
> 
> On the other hand, *using* -fno-omit-frame-pointer causes gcc to
> produce buggy code on PowerPC targets.
> 
> If Segher and GCC manual are right, this patch should be a no-op
> for all arches except PowerPC, where the patch fixes gcc issues.
> 
> Signed-off-by: Anton Vorontsov <[email-masked]>
> ---
> 
> See this thread for more discussion:
> http://osdir.com/ml/linux-kernel/2009-05/msg01754.html
> 
> p.s.
> Obviously, I didn't test this patch on anything else but PPC32. ;-)
> 
> Segher, do you know if all GCC versions that we support for
> building Linux are behaving the way that GCC manual describe?

No news is good news... Ingo, can we merge this into -tip for testing?

Thanks,

>  Makefile |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index ea63667..70ad1ff 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -535,7 +535,7 @@ KBUILD_CFLAGS += $(call cc-option, -fno-stack-protector)
>  endif
>  
>  ifdef CONFIG_FRAME_POINTER
> -KBUILD_CFLAGS	+= -fno-omit-frame-pointer -fno-optimize-sibling-calls
> +KBUILD_CFLAGS	+= -fno-optimize-sibling-calls
>  else
>  KBUILD_CFLAGS	+= -fomit-frame-pointer
>  endif
> -- 
> 1.6.3.1
> 
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> [email-masked]
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-- 
Anton Vorontsov
email: [email-masked]
irc://irc.freenode.net/bd2