Re: [PATCH] powerpc/lib/xor_vmx: Relax frame size for clang

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 21/06/2019 à 10:58, Mathieu Malaterre a écrit :
> When building with clang-8 the frame size limit is hit:
> 
>    ../arch/powerpc/lib/xor_vmx.c:119:6: error: stack frame size of 1200 bytes in function '__xor_altivec_5' [-Werror,-Wframe-larger-than=]
> 
> Follow the same approach as commit 9c87156cce5a ("powerpc/xmon: Relax
> frame size for clang") until a proper fix is implemented upstream in
> clang and relax requirement for clang.

With Clang 14 I get the following errors, but only with KASAN selected.

   CC      arch/powerpc/lib/xor_vmx.o
arch/powerpc/lib/xor_vmx.c:95:6: error: stack frame size (1040) exceeds 
limit (1024) in '__xor_altivec_4' [-Werror,-Wframe-larger-than]
void __xor_altivec_4(unsigned long bytes,
      ^
arch/powerpc/lib/xor_vmx.c:124:6: error: stack frame size (1312) exceeds 
limit (1024) in '__xor_altivec_5' [-Werror,-Wframe-larger-than]
void __xor_altivec_5(unsigned long bytes,
      ^


Is this patch still relevant ?

Or should frame size be relaxed when KASAN is selected ? After all the 
stack size is multiplied by 2 when we have KASAN, so maybe the warning 
limit should be increased as well ?

Thanks
Christophe

> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/563
> Cc: Joel Stanley <joel@jms.id.au>
> Signed-off-by: Mathieu Malaterre <malat@debian.org>
> ---
>   arch/powerpc/lib/Makefile | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
> index c55f9c27bf79..b3f7d64caaf0 100644
> --- a/arch/powerpc/lib/Makefile
> +++ b/arch/powerpc/lib/Makefile
> @@ -58,5 +58,9 @@ obj-$(CONFIG_FTR_FIXUP_SELFTEST) += feature-fixups-test.o
>   
>   obj-$(CONFIG_ALTIVEC)	+= xor_vmx.o xor_vmx_glue.o
>   CFLAGS_xor_vmx.o += -maltivec $(call cc-option,-mabi=altivec)
> +ifdef CONFIG_CC_IS_CLANG
> +# See https://github.com/ClangBuiltLinux/linux/issues/563
> +CFLAGS_xor_vmx.o += -Wframe-larger-than=4096
> +endif
>   
>   obj-$(CONFIG_PPC64) += $(obj64-y)