Re: [Qemu-trivial] [Qemu-devel] [PATCH] configure: Undefine _FORTIFY_SOURCE prior using it

[Stefan Hajnoczi <stefanha@gmail.com>]

On Fri, Feb 01, 2013 at 04:18:23PM +0100, Michal Privoznik wrote:
> On 01.02.2013 10:54, Andreas Färber wrote:
> > Am 31.01.2013 11:15, schrieb Michal Privoznik:
> >> Currently, we are enforcing the _FORTIFY_SOURCE=2 without any
> >> previous detection if the macro has been already defined, e.g.
> >> by environment, or is just enabled by compiler by default.
> >>
> >> Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
> >> ---
> >>  configure | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/configure b/configure
> >> index b7635e4..97070eb 100755
> >> --- a/configure
> >> +++ b/configure
> >> @@ -3159,7 +3159,7 @@ if test "$gcov" = "yes" ; then
> >>    CFLAGS="-fprofile-arcs -ftest-coverage -g $CFLAGS"
> >>    LDFLAGS="-fprofile-arcs -ftest-coverage $LDFLAGS"
> >>  elif test "$debug" = "no" ; then
> >> -  CFLAGS="-O2 -D_FORTIFY_SOURCE=2 $CFLAGS"
> >> +  CFLAGS="-O2 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 $CFLAGS"
> >>  fi
> >>  
> >>  
> > 
> > Should we maybe instead add a compile-test?
> > 
> > #ifdef _FORTIFY_SOURCE
> > #if _FORTIFY_SOURCE >= 2
> > #error Environment already has _FORTIFY_SOURCE
> > #endif
> > #endif
> > 
> > I admit I have no clue what the number means and whether there are more
> > fortified levels.
> > 
> > Cheers,
> > Andreas
> > 
> 
> I don't think that's necessary. The 2nd level is the highest one [1] or [2].
> It seems like in my case it's compiler who's defining the macro:
> 
> $ echo "int main() {return 0;}" | gcc -D_FORTIFY_SOURCE=2 -x c -
> <command-line>:0:0: warning: "_FORTIFY_SOURCE" redefined [enabled by default]
> <stdin>:1:0: note: this is the location of the previous definition
> 
> in which case we must undefine it. However, if the _FORTIFY_SOURCE is
> defined by environment, I think we should not override it. So maybe need
> a different approach. Anyway, with current state I cannot compile. I am using
> gcc version 4.7.2 (Gentoo 4.7.2 p1.3, pie-0.5.5)

It would be nice to fix this for QEMU 1.4 but my gcc FORTIFY_SOURCE foo
is not strong enough to know what the best approach is here.

Reviews from anyone else?

Stefan