-fsanitize=signed-integer-overflow causes linker errors

[ngg]

If I compile with -fsanitize=signed-integer-overflow flag the binaries try to call the __mulodi4 function and it will give an undefined reference linker error. This happens both on ARM and x86 archs. Most of the other similar sanitizers work well.

[DanAlbert]

Sorry, somehow I didn't see this bug until now.

__mulodi4 isn't provided by libgcc which is needed to implement the trapping integer overflow arithmetic. We need to start using compiler-rt for the NDK to provide support for this. It's something that we have people looking in to, but I don't have an estimate on the timeline (though @stephenhines might).

[stephenhines]

https://llvm.org/bugs/show_bug.cgi?id=28629 is the upstream bug for this. The truth is that we want to switch to compiler-rt, but just haven't had the ability to complete the transition. It is something we are looking at doing, however I don't have a great estimate on when it will be completed. You can add your own weak versions of those symbols in the meantime to get unblocked.

[sitsofe]

(For others who might end up here via a search: if you're trying to compile using clang's undefined sanitizer on a regular 32 bit Linux distro and you're hitting the "undefined reference to `__mulodi4'" a workaround might be to link against the appropriate libclang_rt.builtins* :

$ cat <<EOF > mulodi4.c 
int main(void) {
	long long ll = 1;
	int i1 = 2;
	return (ll * i1);
}
EOF
$ clang-4.0 -fsanitize=undefined mulodi4.c
/tmp/foo-605e44.o: In function `main':
foo.c:(.text+0x5a): undefined reference to `__mulodi4'
clang: error: linker command failed with exit code 1 (use -v to see invocation)
$ clang-4.0 -fsanitize=undefined mulodi4.c /usr/lib/llvm-4.0/lib/clang/4.0.0/lib/linux/libclang_rt.builtins-i686.a 
$ echo $?
0

See ldc-developers/ldc#813 for an example of a project that works around the problem)

[DanAlbert]

This no longer happens for this particular case in r17. Seems Clang isn't generating this call for signed-integer-overflow any more.

Closing in favor of #294 as the root cause rather than the symptom.

[AstralStorm]

Happens again in r18 on armv7, 18.1.5063045:
ndk-bundle/sources/cxx-stl/llvm-libc++/include/chrono:388: error: undefined reference to '__mulodi4'

[DanAlbert]

It's fixed in r19 though, so nothing to do here: #294.