[cfe-dev] -fsanitize=undefined and shared libraries

[Richard Smith]

On Sun, Jan 27, 2013 at 4:56 PM, Will Dietz <willdtz at gmail.com> wrote:

> See: http://llvm.org/bugs/show_bug.cgi?id=14469 , which I can
> reproduce locally using -fsanitize=integer -m32 and by multiplying two
> 64bit integers together.
>
> The issue is we emit overflow intrinsics that aren't neatly supported
> on the platform and so a call to the supporting runtime is emitted
> instead.  Unfortunately libgcc doesn't implement __mulodi4
> (compiler-rt does) resulting in the undefined reference you're seeing.
>
> Unfortunately I don't know a good way to convince clang that
> compiler-rt is available and to use that instead of libgcc, and it
> seems Motsak in the bug report has the same question.  As a kludge of
> a workaround, you can manually add the libclang_rt library for your
> architecture to your linker invocation (like:
> /path/to/libclang_rt.i386.a), which I've used myself to get around
> this issue in the past.
>
> Perhaps someone more familiar with the issue can comment on the
> challenges in resolving the linked bug?
>

Yes, I've seen this too. The easiest solution might be to include
compiler-rt's mulodi4.o in libclang_rt.ubsan.*.a. -- that's the approach
I've been using when testing UBSan -- although this doesn't fix the problem
for code not using UBSan.


> Hope this helps,
>
> ~Will
>
> On Sun, Jan 27, 2013 at 4:22 PM, zapadinsky <zapadinsky at gmail.com> wrote:
> > Sorry for bringing this thread up again...
> > I've updated clang and compiler-rt to current trunk. Now I have this
> error
> > trying to link against libMyLib.so which was linked with
> -fsanitize=integer
> > switch:
> >
> > clang++ -fsanitize=integer ... -lMyLib -o ...
> > /.../libMyLib.so: undefined reference to `__mulodi4'
> > clang: error: linker command failed with exit code 1 (use -v to see
> > invocation)
> >
> > I'm trying to localize the problem but have no big progress for now. It
> is
> > not reproduced on a simple shared lib project. Any ideas? Without
> -fsanitize
> > all works fine
> >
> >
> >
> > --
> > View this message in context:
> http://clang-developers.42468.n3.nabble.com/fsanitize-undefined-and-shared-libraries-tp4029561p4030098.html
> > Sent from the Clang Developers mailing list archive at Nabble.com.
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