linux-kernel - Re: [PATCH] arm64: remove redundant FRAME

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Message-ID: <20151106175119.GD7637@e104818-lin.cambridge.arm.com>
Date:	Fri, 6 Nov 2015 17:51:20 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	"Shi, Yang" <yang.shi@...aro.org>
Cc:	Mark Rutland <mark.rutland@....com>,
	linaro-kernel@...ts.linaro.org, Will Deacon <will.deacon@....com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64: remove redundant FRAME_POINTER kconfig option

On Fri, Nov 06, 2015 at 09:39:07AM -0800, Shi, Yang wrote:
> On 11/6/2015 9:35 AM, Catalin Marinas wrote:
> >On Fri, Nov 06, 2015 at 09:23:38AM -0800, Shi, Yang wrote:
> >>On 11/6/2015 8:25 AM, Will Deacon wrote:
> >>>However, the patch would allow one to
> >>>disable FRAME_POINTERS (not sure it has any effect on the aarch64 gcc
> >>>though).
> >>
> >>No, it doesn't. Actually, FRAME_POINTER could be disabled regardless of the
> >>patch.
> >
> >In which case I suggest that we always select it just as a clearer
> >statement that the feature cannot be disabled (and you never know what
> >the compiler people decide to do in the future).
> 
> Do you mean select FRAME_POINTER in ARCH_WANT_FRAME_POINTERS?
> 
> Yes, we could, but this may cause other architectures which select
> ARCH_WANT_FRAME_POINTERS to have FRAME_POINTER selected too.

This would have been the ideal option, something like:

--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -322,7 +322,7 @@ config ARCH_WANT_FRAME_POINTERS
 	help
 
 config FRAME_POINTER
-	bool "Compile the kernel with frame pointers"
+	bool "Compile the kernel with frame pointers" if !ARCH_WANT_FRAME_POINTERS
 	depends on DEBUG_KERNEL && \
 		(CRIS || M68K || FRV || UML || \
 		 AVR32 || SUPERH || BLACKFIN || MN10300 || METAG) || \

But, as you said, we would need to check the other architectures
selecting ARCH_WANT_FRAME_POINTERS.

In the meantime:

--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -27,6 +27,7 @@ config ARM64
 	select CPU_PM if (SUSPEND || CPU_IDLE)
 	select DCACHE_WORD_ACCESS
 	select EDAC_SUPPORT
+	select FRAME_POINTER
 	select GENERIC_ALLOCATOR
 	select GENERIC_CLOCKEVENTS
 	select GENERIC_CLOCKEVENTS_BROADCAST

-- 
Catalin
--
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