[FFmpeg-devel] [PATCH] configure: add -fPIE instead of -pie to C flags for ThreadSanitizer

Wan-Teh Chang wtc at google.com
Mon Dec 12 21:55:05 EET 2016

On Mon, Dec 12, 2016 at 6:42 AM, Carl Eugen Hoyos <ceffmpeg at gmail.com> wrote:
> 2016-12-02 23:04 GMT+01:00 Wan-Teh Chang <wtc-at-google.com at ffmpeg.org>:
>> -pie was added to C flags for ThreadSanitizer in commit
>> 19f251a2882a8d0779b432e63bf282e4d9c443bb. Under clang 3.8.0, the -pie
>> flag causes a compiler warning and a linker error when running configure
>> --toolchain=clang-tsan.
> Does the patch have any effect when using gcc?

Hi Carl,

Yes, the patch modifies the code shared by --toolchain=clang-tsan and

I am using Ubuntu 14.04 LTS, which comes with gcc 4.8.4. gcc 4.8.4
does NOT work with and without my patch. I got an error in config.log
like this:

BEGIN /tmp/ffconf.jceENASz.c
    1   int main(void){ return 0; }
END /tmp/ffconf.jceENASz.c
gcc -fsanitize=thread -fPIE -fPIC -c -o /tmp/ffconf.LuPWPOJB.o
gcc -fsanitize=thread -pie -fPIC -o /tmp/ffconf.03RtebJv /tmp/ffconf.LuPWPOJB.o
/tmp/ffconf.LuPWPOJB.o: In function `_GLOBAL__sub_I_00099_0_ffconf.jceENASz.c':
ffconf.jceENASz.c:(.text+0x10): undefined reference to `__tsan_init'
collect2: error: ld returned 1 exit status
C compiler test failed.

This looks like the gcc 4.9.2 bug described in
Unfortunately, I can't fix the undefined reference to __tsan_init even
if I add -ltsan to the linker flags.

I then built gcc 6.2.0 from sources and tested it. gcc 6.2.0 works
with and without my patch. So I consider my patch safe for gcc. If
there is any other gcc version I should test my patch with, please let
me know.

Wan-Teh Chang

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