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

[Paolo Bonzini]

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