[Qemu-devel] Re: [PATCH] Suppress warning: zero-length gnu_printf format string

[Paolo Bonzini <pbonzini@redhat.com>]

On 10/14/2010 07:59 PM, Blue Swirl wrote:
>> It is even more hypothetical when empty-format printfs are optimized away by
>> GCC:
>>
>> $ gcc -x c - -O2 -S -o -
>> #include<stdio.h>
>> main() { printf (""); }
>>
>>         .file   ""
>>         .text
>>         .p2align 4,,15
>> .globl main
>>         .type   main, @function
>> main:
>> .LFB11:
>>         .cfi_startproc
>>         rep
>>         ret
>>         .cfi_endproc
>>
>> and other attribute-printf-marked functions are probably not noop when the
>> format argument is empty.
>
> How is that? Does the warning message from qobject_from_json("") mean
> that GCC may optimize that call away?

I meant, the warning is likely bogus for most functions that do 
"something like printf" but it is not printf (like qobject_from_json, or 
asprintf).  If the only good reason to have the warning is a 
hypothetical performance degradation, let's please turn it off, because 
this performance degradation isn't even there.

Paolo