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

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Message-ID: <7cb1285a-42e6-2b67-664f-7d206bc9fd80@csgroup.eu>
Date:   Wed, 7 Sep 2022 19:21:35 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Mathieu Malaterre <malat@...ian.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
        Joel Stanley <joel@....id.au>, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] powerpc/lib/xor_vmx: Relax frame size for clang



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@....id.au>
> Signed-off-by: Mathieu Malaterre <malat@...ian.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)