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

[Michal Privoznik <mprivozn@redhat.com>]

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)

Michal

1: http://gcc.gnu.org/ml/gcc-patches/2004-09/msg02055.html
2: http://gcc.gnu.org/git/?p=gcc.git;a=blob;f=libssp/ssp/ssp.h.in