[cfe-users] Trouble adding leak sanitizer suppressions with --fsanitizer-blacklist option

Alexey Samsonov vonosmas at gmail.com
Fri Oct 3 15:28:22 PDT 2014

Hi Andrew,

Blacklist file and suppressions file are different, and have different
Here's the description of blacklist file format for ASan:

Blacklist file is only used during the compilation. Compiler just doesn't
insert ASan checks for blacklisted items, so
if you have a bug in a blacklisted function, its code will not have ASan
checks, and this the bug has no chance of being reported in runtime.

Suppression file is used in runtime - when the error actually happens, it
is matched against the suppressions, and is not reported in case of a match.

Note that:
1) There's no way to "suppress" ASan errors. Currently all ASan errors are
fatal and immediately crash your executable. This is done on purpose -
we believe ASan-detected errors are critical and definitely needs to be
fixed, and making the errors unrecoverable improves tool performance

2) There's currently no way to "blacklist" memory leaks. They can only be
suppressed. The reason is - LSan doesn't modify the program at compile time
all. It just replaces the memory allocator at link time, plugging in custom
functions instead of malloc/free from standard library. So, in order to
blacklist contents to LSan, we'd have to bake it into the executable, which
we don't really want to do.

Now this problem is solved with __lsan_default_suppressions, so I don't
really know what to advise you, assuming you're bound to the old version of

On Thu, Oct 2, 2014 at 10:58 AM, Andrew C. Morrow <andrew.c.morrow at gmail.com
> wrote:

> Hi cfe-users -
> I'm using clang-3.4 from Ubuntu Trusty and trying to get leak
> sanitizer integrated with a project. The project builds with
> -fsanitize=address passed to all compile and link lines, and reports
> various memory errors, so I know it is working. When run with
> ASAN_OPTIONS="detect_leaks=1" in the environment leaks are reported at
> exit, so that is working as well.
> I have a suppressions file that works correctly when
> LSAN_OPTIONS="suppressions=etc/asan.suppressions" is set in the shell
> environment. The expected suppressions are applied and the suppressed
> leaks are not reported at exit. The file looks like this:
> $ cat ./etc/asan.suppressions
> # ignore v8 for now
> leak:v8::
> However, if I try to set this file as the suppressions file with
> --fsanitize-blacklist=etc/asan.suppressions, then the suppressions are
> not applied, and all of the leaks I would expect to have been
> suppressed are still reported. I know that clang actually is consuming
> the file, because if I put a malformed line into the suppressions file
> the build fails with:
> clang: error: malformed sanitizer blacklist: 'Malformed line 1:
> 'aslaskdfj''
> I'm passing both -fsanitize=address and
> -fsanitize-blacklist=etc/asan.suppressions to both the compile and
> link stages of the build.
> Obviously, I can just use LSAN_OPTIONS, but the blacklist would I
> think be preferable if I could get it to work.
> What am I doing wrong?
> Also, a question about the blacklist that does not seem to be answered
> in the docs:
> Does the blacklist file get read on each execution of the binary built
> with -fsanitize-blacklist, and therefore needs to be kept with the
> binary? Or are the contents of the blacklist file read at compile time
> and baked into the executable so that the binary can be used
> standalone? I'm hoping the latter, as what I would really like to use
> is __lsan_default_suppressions, but it appears that that is not
> available until clang-3.5 (it is mentioned in
> sanitizer/lsan_interface.h for clang-3.5, but not for clang-3.4), and
> unfortunately I need this integration to work with clang-3.4.
> Thanks,
> Andrew
> $ uname -a
> Linux workstation 3.13.0-35-generic #62-Ubuntu SMP Fri Aug 15 01:58:42
> UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
> $ clang++ --version
> Ubuntu clang version 3.4-1ubuntu3 (tags/RELEASE_34/final) (based on LLVM
> 3.4)
> Target: x86_64-pc-linux-gnu
> Thread model: posix
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Alexey Samsonov
vonosmas at gmail.com
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