On Wed, Aug 22, 2012 at 1:33 PM, Oleg Pekar (olpekar) <olpe...@cisco.com> wrote:
>>On Wed, Aug 22, 2012 at 12:38 PM, Oleg Pekar (olpekar) <olpe...@cisco.com>
>>wrote:
>>> I'm using gcc 4.1.2, it supports -D_FORTIFY_SOURCE option for c files but
>>> not for c++. I'm looking for gcc version number where support for this
>>> option in c++ files was added.
>
>>I'm not sure how to answer your question, because -D_FORTIFY_SOURCE is not a
>>GCC feature. It is a glibc feature. It causes glibc to change some function
>>definitions to use features that are provided by GCC.
>>As far as I know, all the _FORTIFY_SOURCE features that GCC provides are
>>available in both C and C++.
>
>>So, please give us an example of something that fails with g++ and
>>-D_FORTIFY_SOURCE that you expect to work.
>
>>Ian
>
> I created a tiny program test.c:
> #include <memory.h>
> int main()
> {
> char buf[4];
> memcpy(buf, "1234", 5);
> return 0;
> }
>
> Then I compile it with gcc 4.1.2 on Red Hat Linux 5.5. When I compile it as c
> file - gcc performs the check specified by FORTIFY_SOURCE, when I compile it
> as c++ file - it doesn't.
>
> dev /tmp>gcc -x c -D_FORTIFY_SOURCE=2 -O2 -o test.exe -lstdc++ test.c
> test.c: In function \u2018main\u2019:
> test.c:6: warning: call to __builtin___memcpy_chk will always overflow
> destination buffer
>
> dev /tmp>gcc -x c++ -D_FORTIFY_SOURCE=2 -O2 -o test.exe -lstdc++ test.c
> dev /tmp>
Thanks for the example. I could recreate the problem with GCC 4.1 on
my system. It doesn't have anything to do with GCC, though, at least
not directly; it has to do with glibc. In the version of glibc on my
system, it works with g++ 4.3 or later.
I won't go into all the details, but it's because of these lines in
<sys/cdefs.h>:
/* GCC 4.3 and above with -std=c99 or -std=gnu99 implements ISO C99
inline semantics, unless -fgnu89-inline is used. */
#if !defined __cplusplus || __GNUC_PREREQ (4,3)
# if defined __GNUC_STDC_INLINE__ || defined __cplusplus
# define __extern_inline extern __inline __attribute__ ((__gnu_inline__))
# if __GNUC_PREREQ (4,3)
...
Basically, the feature is only available if not C++ or if GCC 4.3 or later.
Ian
