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Date: Thu, 26 Feb 2015 19:41:00 -0000
From: Pedro Alves <palves@redhat.com>
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To: paul@mad-scientist.net
CC: Jack Howarth <howarth.mailing.lists@gmail.com>, pinskia@gmail.com,        Simon Marchi <simon.marchi@polymtl.ca>,        "Paul_Koning@dell.com" <Paul_Koning@dell.com>,        "gdb@sourceware.org" <gdb@sourceware.org>
Subject: Re: format string is not a string literal
References: <CADtEn-1ZT1uznxPzQxr_nBQya1AVrNLyE+ZSDmm2x_ux8qyzUQ@mail.gmail.com>		<0AB56024-875B-4724-8ED2-A9DDB237CBFF@dell.com>		<CADtEn-0txdtq6x6dAZZ5wew-VOvYU28fueT_kJ2cx7=H0=vdPg@mail.gmail.com>		<23CC7871-C616-436C-920C-4A635DC87189@dell.com>		<CAFXXi0=56gNf2GoSKkrx=bRArhjk+AhSbiu0crpdR3=df7B2BQ@mail.gmail.com>		<7A311B56-C424-4C4F-A0E4-B12B65131745@gmail.com>	 <CADtEn-1vHnay=ftK9Hq6ogYyDNPc_anNgLnwuUZSt4VjzF+7GQ@mail.gmail.com>	 <54EEECD9.4050909@redhat.com> <1424972642.824.33.camel@homebase>
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On 02/26/2015 05:44 PM, Paul Smith wrote:
> On Thu, 2015-02-26 at 09:52 +0000, Pedro Alves wrote:
>> +  /* Use FMT from here on instead of complaint->fmt, to avoid "format
>> +     string is not a string literal" warnings.  */
>> +  gdb_assert (complaint->fmt == fmt);
>> +
>>    if (complaint->file != NULL)
>> -    internal_vwarning (complaint->file, complaint->line, 
>> -                      complaint->fmt, args);
>> +    internal_vwarning (complaint->file, complaint->line, fmt, args);
> 
> Can someone quickly explain how using fmt instead of complaint->fmt here
> removes the warning?  fmt is not a "string literal" either...?
> 
> Just curious what the trick is...

Simon explained it, actually:

> If the function is vprintf-style, it's similar but the last argument
> should be 0. It will push the argument check a level higher, where
> eventually they are explicitely defined printf-style. The doc is
> somewhere here [2] in the middle.

That code is in this function:

> static void ATTRIBUTE_PRINTF (4, 0)
vcomplaint (struct complaints **c, const char *file,
	    int line, const char *fmt,
	    va_list args)
{

So here the compiler will check FMT in the caller.

Thanks,
Pedro Alves