linux-kernel - Re: [tip:x86/urgent] x86/tools: Fix gcc-7 warning in relocs.c

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Message-ID: <c6f83231-9847-3f41-6743-325248ffc451@zytor.com>
Date:   Tue, 20 Dec 2016 01:30:48 -0800
From:   "H. Peter Anvin" <hpa@...or.com>
To:     markus@...ppelsdorf.de, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/urgent] x86/tools: Fix gcc-7 warning in relocs.c

I'd strongly prefer a non-data-dependent solution, specifically adding
at the top of sort_relocs():

if (!r->count)
	return;

However, by my reading of the C and POSIX standards, this is a gcc
error: qsort() should do nothing if the count is zero.

	-hpa

On 12/19/16 02:56, tip-bot for Markus Trippelsdorf wrote:
> Commit-ID:  7ebb916782949621ff6819acf373a06902df7679
> Gitweb:     http://git.kernel.org/tip/7ebb916782949621ff6819acf373a06902df7679
> Author:     Markus Trippelsdorf <markus@...ppelsdorf.de>
> AuthorDate: Thu, 15 Dec 2016 13:45:13 +0100
> Committer:  Thomas Gleixner <tglx@...utronix.de>
> CommitDate: Mon, 19 Dec 2016 11:50:24 +0100
> 
> x86/tools: Fix gcc-7 warning in relocs.c
> 
> gcc-7 warns:
> 
> In file included from arch/x86/tools/relocs_64.c:17:0:
> arch/x86/tools/relocs.c: In function ‘process_64’:
> arch/x86/tools/relocs.c:953:2: warning: argument 1 null where non-null expected [-Wnonnull]
>   qsort(r->offset, r->count, sizeof(r->offset[0]), cmp_relocs);
>   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> In file included from arch/x86/tools/relocs.h:6:0,
>                  from arch/x86/tools/relocs_64.c:1:
> /usr/include/stdlib.h:741:13: note: in a call to function ‘qsort’ declared here         
>  extern void qsort 
> 
> This happens because relocs16 is not used for ELF_BITS == 64, 
> so there is no point in trying to sort it.
> 
> Make the sort_relocs(&relocs16) call 32bit only.
> 
> Signed-off-by: Markus Trippelsdorf <markus@...ppelsdorf.de>
> Link: http://lkml.kernel.org/r/20161215124513.GA289@x4
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> 
> ---
>  arch/x86/tools/relocs.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
> index 0c2fae8..73eb7fd 100644
> --- a/arch/x86/tools/relocs.c
> +++ b/arch/x86/tools/relocs.c
> @@ -992,11 +992,12 @@ static void emit_relocs(int as_text, int use_real_mode)
>  		die("Segment relocations found but --realmode not specified\n");
>  
>  	/* Order the relocations for more efficient processing */
> -	sort_relocs(&relocs16);
>  	sort_relocs(&relocs32);
>  #if ELF_BITS == 64
>  	sort_relocs(&relocs32neg);
>  	sort_relocs(&relocs64);
> +#else
> +	sort_relocs(&relocs16);
>  #endif
>  
>  	/* Print the relocations */
> 
s