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

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Date:   Thu, 23 Jan 2020 13:45:58 +0000
From:   Julien Thierry <jthierry@...hat.com>
To:     Will Deacon <will@...nel.org>
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 1/21/20 10:30 AM, Will Deacon wrote:
> 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?
> 

You mean to not introduce the STACK_FRAME_NON_STANDARD() macro and just 
mark the asm callable symbols that don't set up a stackframe as SYM_CODE_* ?

-- 
Julien Thierry