linux-kernel - Re: [PATCH] x86/alternatives: fixup alternative_call

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Date:   Sun, 14 Jan 2018 12:54:52 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Alexey Dobriyan <adobriyan@...il.com>
cc:     mingo@...hat.com, hpa@...or.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/alternatives: fixup alternative_call_2

On Mon, 25 Dec 2017, Alexey Dobriyan wrote:

> The following pattern fails to compile while the same pattern
> with alternative_call() does.
> 
> 	if (...)
> 		alternative_call_2(...);
> 	else
> 		alternative_call_2(...);

Sigh. Can we get an explanation WHY it fails ?

> 
> Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
> ---
> 
>  arch/x86/include/asm/alternative.h |    4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> --- a/arch/x86/include/asm/alternative.h
> +++ b/arch/x86/include/asm/alternative.h
> @@ -218,13 +218,11 @@ static inline int alternatives_text_reserved(void *start, void *end)
>   */
>  #define alternative_call_2(oldfunc, newfunc1, feature1, newfunc2, feature2,   \
>  			   output, input...)				      \
> -{									      \
>  	asm volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
>  		"call %P[new2]", feature2)				      \
>  		: output, ASM_CALL_CONSTRAINT				      \
>  		: [old] "i" (oldfunc), [new1] "i" (newfunc1),		      \
> -		  [new2] "i" (newfunc2), ## input);			      \
> -}
> +		  [new2] "i" (newfunc2), ## input)
>  
>  /*
>   * use this macro(s) if you need more than one output parameter
>