linux-kernel - Re: [PATCH v4 1/1] x86, relocs: add printf attribute to die()

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Date:   Tue, 7 Mar 2017 10:16:11 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Nicolas Iooss <nicolas.iooss_linux@....org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/1] x86, relocs: add printf attribute to die()


* Nicolas Iooss <nicolas.iooss_linux@....org> wrote:

> Adding such an attribute helps to detect errors in the format string at
> build time. After doing this, the compiler complains about some issues:
> 
>     arch/x86/tools/relocs.c:460:5: error: format specifies type 'int'
>     but the argument has type 'Elf64_Xword' (aka 'unsigned long')
>     [-Werror,-Wformat]
>                                     sec->shdr.sh_size);
>                                     ^~~~~~~~~~~~~~~~~
>     arch/x86/tools/relocs.c:464:5: error: format specifies type 'int'
>     but the argument has type 'Elf64_Off' (aka 'unsigned long')
>     [-Werror,-Wformat]
>                                     sec->shdr.sh_offset, strerror(errno));
>                                     ^~~~~~~~~~~~~~~~~~~
> 
> When relocs.c is included by relocs_32.c, sec->shdr.sh_size and
> sec->shdr.sh_offset are 32-bit unsigned integers. When the file is
> included by relocs_64.c, these expressions are 64-bit unsigned integers.
> 
> Add casts to unsigned long long, which length is always 64-bit, and use
> %llu to format sec->shdr.sh_size and sec->shdr.sh_offset in relocs.c.
> 
> While at it, constify the format attribute of die().
> 
> Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@....org>
> ---
>  arch/x86/tools/relocs.c        | 31 +++++++++++++++++--------------
>  arch/x86/tools/relocs.h        |  3 ++-
>  arch/x86/tools/relocs_common.c |  2 +-
>  3 files changed, 20 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
> index 73eb7fd4aec4..3cc02065c677 100644
> --- a/arch/x86/tools/relocs.c
> +++ b/arch/x86/tools/relocs.c
> @@ -397,8 +397,8 @@ static void read_shdrs(FILE *fp)
>  		    ehdr.e_shnum);
>  	}
>  	if (fseek(fp, ehdr.e_shoff, SEEK_SET) < 0) {
> -		die("Seek to %d failed: %s\n",
> -			ehdr.e_shoff, strerror(errno));
> +		die("Seek to %llu failed: %s\n",
> +			(unsigned long long)ehdr.e_shoff, strerror(errno));

Isn't "(u64)" shorter to write?

Thanks,

	Ingo