linux-kernel - Re: x86/boot: Avoid using Intel mnemonics in AT&T syntax asm

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Date:   Wed, 11 Jan 2023 14:59:02 -0800
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
CC:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...en8.de>
Subject: Re: x86/boot: Avoid using Intel mnemonics in AT&T syntax asm

On January 10, 2023 3:35:50 AM PST, Ingo Molnar <mingo@...nel.org> wrote:
>
>* Peter Zijlstra <peterz@...radead.org> wrote:
>
>> 
>> With 'GNU assembler (GNU Binutils for Debian) 2.39.90.20221231' the
>> build now reports:
>> 
>>   arch/x86/realmode/rm/../../boot/bioscall.S: Assembler messages:
>>   arch/x86/realmode/rm/../../boot/bioscall.S:35: Warning: found `movsd'; assuming `movsl' was meant
>>   arch/x86/realmode/rm/../../boot/bioscall.S:70: Warning: found `movsd'; assuming `movsl' was meant
>> 
>>   arch/x86/boot/bioscall.S: Assembler messages:
>>   arch/x86/boot/bioscall.S:35: Warning: found `movsd'; assuming `movsl' was meant
>>   arch/x86/boot/bioscall.S:70: Warning: found `movsd'; assuming `movsl' was meant
>> 
>> Which is due to:
>> 
>>   PR gas/29525
>> 
>>   Note that with the dropped CMPSD and MOVSD Intel Syntax string insn
>>   templates taking operands, mixed IsString/non-IsString template groups
>>   (with memory operands) cannot occur anymore. With that
>>   maybe_adjust_templates() becomes unnecessary (and is hence being
>>   removed).
>> 
>> More details: https://sourceware.org/bugzilla/show_bug.cgi?id=29525
>> 
>> Fixes: 7a734e7dd93b ("x86, setup: "glove box" BIOS calls -- infrastructure")
>> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>> ---
>>  arch/x86/boot/bioscall.S |    4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>> 
>> --- a/arch/x86/boot/bioscall.S
>> +++ b/arch/x86/boot/bioscall.S
>> @@ -32,7 +32,7 @@
>>  	movw	%dx, %si
>>  	movw	%sp, %di
>>  	movw	$11, %cx
>> -	rep; movsd
>> +	rep; movsl
>>  
>>  	/* Pop full state from the stack */
>>  	popal
>> @@ -67,7 +67,7 @@
>>  	jz	4f
>>  	movw	%sp, %si
>>  	movw	$11, %cx
>> -	rep; movsd
>> +	rep; movsl
>>  4:	addw	$44, %sp
>
>So I think the GAS change to introduce this warning was probably 
>unnecessary - these instructions weren't really causing any trouble and the 
>syntax was basically a legacy thing that shouldn't be touched - but I guess 
>that argument is water down the bridge now:
>
>   Reviewed-by: Ingo Molnar <mingo@...nel.org>
>
>Thanks,
>
>	Ingo

Yeah; looks like a gas bug/regression, but there isn't really any reason not to fix it.

The semicolon after rep isn't needed anymore either ;)

Acked-by: H. Peter Anvin (Intel) <hpa@...or.com>