Messages in this thread | | | Date | Fri, 06 Nov 2015 09:23:38 -0800 | From | "Shi, Yang" <> | Subject | Re: [PATCH] arm64: remove redundant FRAME_POINTER kconfig option |
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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@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 arch/arm64/Kconfig.debug.
The lib/Kconfig.debug one looks like:
config FRAME_POINTER bool "Compile the kernel with frame pointers" depends on DEBUG_KERNEL && \ (CRIS || M68K || FRV || UML || \ AVR32 || SUPERH || BLACKFIN || MN10300 || METAG) || \ ARCH_WANT_FRAME_POINTERS default y if (DEBUG_INFO && UML) || ARCH_WANT_FRAME_POINTERS help 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 > though).
No, it doesn't. Actually, FRAME_POINTER could be disabled regardless of the patch.
Thanks, Yang
> > Will >
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