linux-kernel - Re: Random crashes with 2.6.27-rc3 on PPC

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Message-Id: <200808241700.22815.mb@bu3sch.de>
Date:	Sun, 24 Aug 2008 17:00:22 +0200
From:	Michael Buesch <mb@...sch.de>
To:	Andreas Schwab <schwab@...e.de>
Cc:	benh@...nel.crashing.org, linuxppc-dev@...abs.org,
	Linus Torvalds <torvalds@...l.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Random crashes with 2.6.27-rc3 on PPC

On Sunday 24 August 2008 16:46:38 Andreas Schwab wrote:
> Michael Buesch <mb@...sch.de> writes:
> 
> > The following workaround seems to fix the crashes on powerpc.
> > However, this patch is clearly not what we want for other architectures,
> > as they might need -fno-omit-frame-pointer to function properly.
> 
> This has a better chance to be accepted. :-)
> 
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 8b5a7d3..f9a2e48 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -394,7 +394,7 @@ config LOCKDEP
>  	bool
>  	depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
>  	select STACKTRACE
> -	select FRAME_POINTER if !X86 && !MIPS
> +	select FRAME_POINTER if !X86 && !MIPS && !PPC
>  	select KALLSYMS
>  	select KALLSYMS_ALL

This is not what my patch is doing.
Your patch always forces FRAME_POINTER off. At least as far as lockdep is concerned.
What about other parts of the kernel that enable FRAME_POINTER?

I think this should be fixed in the makefile by substitution of
-fno-omit-frame-pointer on PPC (and probably depending on the compiler
version).

Otherwise, if somebody else decides to do select FRAME_POINTER in some other
code, the bug will reappear.
I'm also not sure if it's desired to always force FRAME_POINTER off.

-- 
Greetings Michael.
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