linux-kernel - Re: [PATCH v3 1/1] x86, relocs: add printf attribute to die()

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Message-ID: <53bd203b-c006-fb7c-0bd6-54a6a926fd1e@m4x.org>
Date:   Wed, 1 Feb 2017 23:42:37 +0100
From:   Nicolas Iooss <nicolas.iooss_linux@....org>
To:     Ingo Molnar <mingo@...nel.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 v3 1/1] x86, relocs: add printf attribute to die()

On 01/02/17 10:04, Ingo Molnar wrote:
> 
> * 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 such 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.
>>
>> Introduce a PRIuELF macro to define the right format to use when
>> printing sh_size and sh_offset values.
>>
>> While at it, constify the format attribute of die().
>>
>> Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@....org>
>> ---
>> I sent the first versions of this patch in September (cf.
>> https://patchwork.kernel.org/patch/9312665/) but it has not been
>> applied.
>>
>> As commit adee8705d251 ("x86/build: Annotate die() with noreturn to fix
>> build warning on clang") introduced the noreturn attribute to die(),
>> this patch now only adds the printf attribute.
>>
>>  arch/x86/tools/relocs.c        | 14 +++++++-------
>>  arch/x86/tools/relocs.h        |  3 ++-
>>  arch/x86/tools/relocs_32.c     |  3 +++
>>  arch/x86/tools/relocs_64.c     |  3 +++
>>  arch/x86/tools/relocs_common.c |  2 +-
>>  5 files changed, 16 insertions(+), 9 deletions(-)
>>
>> diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
>> index 0c2fae8d929d..4cad603b8d58 100644
>> --- a/arch/x86/tools/relocs.c
>> +++ b/arch/x86/tools/relocs.c
>> @@ -397,7 +397,7 @@ 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",
>> +		die("Seek to %"PRIuELF" failed: %s\n",
> 
> Doesn't a simple "%Ld" work as well?

With %Ld, my compiler (gcc 6.3.1 on x86_64) complains:

arch/x86/tools/relocs.c:400:7: error: format ‘%Ld’ expects argument of
type ‘long long int’, but argument 2 has type ‘Elf64_Off {aka long
unsigned int}’ [-Werror=format=]

Thanks,
Nicolas