linux-kernel - Re: [PATCH] lib/zlib_inflate/inffast: Check config in C to avoid unused function warning

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Date:   Fri, 17 Sep 2021 07:17:00 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Paul Menzel <pmenzel@...gen.mpg.de>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     llvm@...ts.linux.dev, Zhen Lei <thunder.leizhen@...wei.com>,
        linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] lib/zlib_inflate/inffast: Check config in C to avoid
 unused function warning



Le 16/09/2021 à 16:22, Paul Menzel a écrit :
> Building Linux for ppc64le with Ubuntu clang version 12.0.0-3ubuntu1~21.04.1
> shows the warning below.
> 
>      arch/powerpc/boot/inffast.c:20:1: warning: unused function 'get_unaligned16' [-Wunused-function]
>      get_unaligned16(const unsigned short *p)
>      ^
>      1 warning generated.
> 
> Fix it, by moving the check from the preprocessor to C, so the compiler
> sees the use.
> 
> Signed-off-by: Paul Menzel <pmenzel@...gen.mpg.de>
> ---
>   lib/zlib_inflate/inffast.c | 6 +-----
>   1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/lib/zlib_inflate/inffast.c b/lib/zlib_inflate/inffast.c
> index f19c4fbe1be7..444ad3c3ccd3 100644
> --- a/lib/zlib_inflate/inffast.c
> +++ b/lib/zlib_inflate/inffast.c
> @@ -254,11 +254,7 @@ void inflate_fast(z_streamp strm, unsigned start)
>   			sfrom = (unsigned short *)(from);
>   			loops = len >> 1;
>   			do
> -#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
> -			    *sout++ = *sfrom++;
> -#else
> -			    *sout++ = get_unaligned16(sfrom++);
> -#endif
> +			    *sout++ = CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS ? *sfrom++ : get_unaligned16(sfrom++);

You can't do that, CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS is not 
something that have value 0 or 1, it is something which is either 
defined or not. You have to use IS_ENABLED() macro, so it should become 
something like:

	if (IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
		*sout++ = *sfrom++;
	else
		*sout++ = get_unaligned16(sfrom++);


>   			while (--loops);
>   			out = (unsigned char *)sout;
>   			from = (unsigned char *)sfrom;
>