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

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Date:	Fri, 06 Nov 2015 09:55:54 -0800
From:	"Shi, Yang" <yang.shi@...aro.org>
To:	Catalin Marinas <catalin.marinas@....com>
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 11/6/2015 9:51 AM, Catalin Marinas wrote:
> 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.

How about:

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 1d1521c..709255a 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -319,6 +319,7 @@ config DEBUG_SECTION_MISMATCH
  #
  config ARCH_WANT_FRAME_POINTERS
         bool
+       select FRAME_POINTER if ARM64
         help

  config FRAME_POINTER

If other architectures want the same behavior, they could easily append 
to the is statement. If all arches which selects 
ARCH_WANT_FRAME_POINTERS, the if statement could be just removed.

Yang

>
> 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
>

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