linux-kernel - Re: [RFC v5 47/57] arm64: assembler: Add macro to annotate asm function having non standard stack-frame.

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Message-ID: <20200121103005.GA11154@willie-the-truck>
Date:   Tue, 21 Jan 2020 10:30:06 +0000
From:   Will Deacon <will@...nel.org>
To:     Julien Thierry <jthierry@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        jpoimboe@...hat.com, peterz@...radead.org, raphael.gault@....com,
        catalin.marinas@....com
Subject: Re: [RFC v5 47/57] arm64: assembler: Add macro to annotate asm
 function having non standard stack-frame.

On Thu, Jan 09, 2020 at 04:02:50PM +0000, Julien Thierry wrote:
> From: Raphael Gault <raphael.gault@....com>
> 
> Some functions don't have standard stack-frames but are intended
> this way. In order for objtool to ignore those particular cases
> we add a macro that enables us to annotate the cases we chose
> to mark as particular.
> 
> Signed-off-by: Raphael Gault <raphael.gault@....com>
> Signed-off-by: Julien Thierry <jthierry@...hat.com>
> ---
>  include/linux/frame.h | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/frame.h b/include/linux/frame.h
> index 02d3ca2d9598..1e35e58ab259 100644
> --- a/include/linux/frame.h
> +++ b/include/linux/frame.h
> @@ -11,14 +11,31 @@
>   *
>   * For more information, see tools/objtool/Documentation/stack-validation.txt.
>   */
> +#ifndef __ASSEMBLY__
>  #define STACK_FRAME_NON_STANDARD(func) \
>  	static void __used __section(.discard.func_stack_frame_non_standard) \
>  		*__func_stack_frame_non_standard_##func = func
> +#else
> +	/*
> +	 * This macro is the arm64 assembler equivalent of the
> +	 * macro STACK_FRAME_NON_STANDARD define at
> +	 * ~/include/linux/frame.h
> +	 */
> +	.macro	asm_stack_frame_non_standard	func
> +	.pushsection ".discard.func_stack_frame_non_standard"
> +	.quad	\func
> +	.popsection
> +	.endm
> 
> +#endif /* __ASSEMBLY__ */
>  #else /* !CONFIG_STACK_VALIDATION */
> 
> +#ifndef __ASSEMBLY__
>  #define STACK_FRAME_NON_STANDARD(func)
> -
> +#else
> +	.macro	asm_stack_frame_non_standard	func
> +	.endm
> +#endif /* __ASSEMBLY__ */

Hmm. Given that we're currently going through the exercise of converting
a bunch of ENTRY/ENDPROC macros to use the new SYM_{CODE,FUNC}_{START,END}
macros, I would much prefer for this to be a new flavour of those.

In fact, can you just use SYM_CODE_* for this?

Will