linux-kernel - Re: [PATCH] LoongArch: Define the symbol fault as a local label in fpu.S

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Date:   Tue, 29 Aug 2023 14:45:42 +0800
From:   Xi Ruoyao <xry111@...111.site>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Huacai Chen <chenhuacai@...nel.org>
Cc:     loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org,
        loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH] LoongArch: Define the symbol fault as a local label in
 fpu.S

On Tue, 2023-08-29 at 14:28 +0800, Tiezhu Yang wrote:
> The initial aim is to silence the following objtool warnings:
> 
>   arch/loongarch/kernel/fpu.o: warning: objtool: _save_fp_context() falls through to next function fault()
>   arch/loongarch/kernel/fpu.o: warning: objtool: _restore_fp_context() falls through to next function fault()
>   arch/loongarch/kernel/fpu.o: warning: objtool: _save_lsx_context() falls through to next function fault()
>   arch/loongarch/kernel/fpu.o: warning: objtool: _restore_lsx_context() falls through to next function fault()
>   arch/loongarch/kernel/fpu.o: warning: objtool: _save_lasx_context() falls through to next function fault()
>   arch/loongarch/kernel/fpu.o: warning: objtool: _restore_lasx_context() falls through to next function fault()
> 
> Obviously, the symbol fault is not a function, it is just a local label,

Hmm why?  To me this seems a function.  We don't branch to it but store
its address (a "function pointer") in the extable.

And these warnings do not make any sense to me:

/* snip */

> diff --git a/arch/loongarch/kernel/fpu.S b/arch/loongarch/kernel/fpu.S
> index b4032de..7defe50 100644
> --- a/arch/loongarch/kernel/fpu.S
> +++ b/arch/loongarch/kernel/fpu.S
> @@ -521,7 +521,7 @@ SYM_FUNC_START(_restore_lasx_context)
>         jr      ra

_restore_lasx_context returns with this instruction.  How can it fall
through into fault?

>  SYM_FUNC_END(_restore_lasx_context)

> -SYM_FUNC_START(fault)
> +SYM_CODE_START_LOCAL(fault)
>         li.w    a0, -EFAULT                             # failure
>         jr      ra
> -SYM_FUNC_END(fault)
> +SYM_CODE_END(fault)

-- 
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University