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