[PATCH] arm64: remove redundant FRAME_POINTER kconfig option
yang.shi at linaro.org
Fri Nov 6 09:23:38 PST 2015
On 11/6/2015 8:25 AM, Will Deacon wrote:
> On Fri, Nov 06, 2015 at 04:21:09PM +0000, Catalin Marinas wrote:
>> On Fri, Nov 06, 2015 at 12:50:02PM +0000, Mark Rutland wrote:
>>> On Fri, Nov 06, 2015 at 12:30:09PM +0000, Will Deacon wrote:
>>>> On Wed, Nov 04, 2015 at 09:37:51AM -0800, Yang Shi wrote:
>>>>> FRAME_POINTER is defined in lib/Kconfig.debug, it is unnecessary to redefine
>>>>> it in arch/arm64/Kconfig.debug.
>>>> It might be worth noting that this adds a dependency on DEBUG_KERNEL
>>>> for building with frame pointers. I'm ok with that (it appears to be
>>>> enabled in defconfig and follows the vast majority of other archs) but
>>>> it is a change in behaviour.
>>>> With that:
>>>> Acked-by: Will Deacon <will.deacon at arm.com>
>>> The code in arch/arm64/kernel/stacktrace.c assumes we have frame
>>> pointers regardless of FRAME_POINTER. Depending on what the compiler
>>> decides to use x29 for, we could get some weird fake unwinding and/or
>>> dodgy memory accesses.
>>> I think we should first audit the uses of frame pointers to ensure that
>>> they are guarded for !FRAME_POINTER.
>> Or we just select FRAME_POINTER in the ARM64 Kconfig entry.
> Yang, did you see any benefit disabling frame pointers, or was this patch
> purely based on you spotting a duplicate Kconfig entry?
It just spots a duplicate Kconfig entry.
FRAME_POINTER is defined in both lib/Kconfig.debug and
The lib/Kconfig.debug one looks like:
bool "Compile the kernel with frame pointers"
depends on DEBUG_KERNEL && \
(CRIS || M68K || FRV || UML || \
AVR32 || SUPERH || BLACKFIN || MN10300 || METAG) || \
default y if (DEBUG_INFO && UML) || ARCH_WANT_FRAME_POINTERS
If you say Y here the resulting kernel image will be slightly
larger and slower, but it gives very useful debugging information
in case of kernel bugs. (precise oopses/stacktraces/warnings)
The common one just depends on DEBUG_KERNEL && ARCH_WANT_FRAME_POINTERS.
ARCH_WANT_FRAME_POINTERS is selected by ARM64 kconfig entry.
To answer Catalin's question about:
> However, the patch would allow one to
> disable FRAME_POINTERS (not sure it has any effect on the aarch64 gcc
No, it doesn't. Actually, FRAME_POINTER could be disabled regardless of
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