Re: Using the perf python module with address sanitizer

[Namhyung Kim <namhyung@kernel.org>]

On Thu, Oct 17, 2024 at 09:20:07AM -0700, Ian Rogers wrote:
> Hi,
> 
> I just wanted to capture/share the steps I used for getting the perf
> python module working with address sanitizer. The process isn't ideal
> so hopefully others can suggest improvements and possibly how we can
> make this more automatic in the build, or use for automated testing,
> etc.
> 
> To build perf with address sanitizer you add to the CFLAGS by passing to make:
> EXTRA_CFLAGS="-fsanitize=address"
> 
> However, this yields a python module that fails with an undefined symbol:
> ```
> $ perf test python -v
> --- start ---
> test child forked, pid 712715
> python usage test: "echo "import sys ; sys.path.insert(0,
> '/tmp/perf/python'); import perf" | '/usr/bin/python3' "
> Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
> ImportError: /tmp/perf/python/perf.cpython-311-x86_64-linux-gnu.so:
> undefined symbol: __asan_option_detect_stack_use_after_return
> ---- end(-1) ----
> 18: 'import perf' in python                                         : FAILED!
> ```
> 
> To resolve this issue add "-shared-libasan" to the CFLAGS:
> EXTRA_CFLAGS="-fsanitize=address -shared-libasan"
> 
> The build needs to find (on x86) libclang_rt.asan-x86_64.so which for
> me on a Debian derived OS wasn't on the LD_LIBRARY_PATH. I found it
> with:
> ```
> $ dpkg -L libclang-rt-16-dev|grep libclang_rt.asan-x86_64.so
> /usr/lib/llvm-16/lib/clang/16/lib/linux/libclang_rt.asan-x86_64.so
> ```

I think we can use llvm-config like below.

  $ find $(llvm-config --libdir) -name libclang_rt.asan-$(uname -m).so
  /usr/lib/llvm-16/lib/clang/16/lib/linux/libclang_rt.asan-x86_64.so

Thanks,
Namhyung


> I then built with:
> ```
> $ LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/lib/llvm-16/lib/clang/16/lib/linux
> make EXTRA_CFLAGS="-fsanitize=address -shared-libasan"
> ```
> 
> However, still using the module wasn't successful:
> ```
> $ LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/lib/llvm-16/lib/clang/16/lib/linux
> perf test python -v
> --- start ---
> test child forked, pid 720500
> python usage test: "echo "import sys ; sys.path.insert(0,
> '/tmp/perf/python'); import perf" | '/usr/bin/python3' "
> ==720503==ASan runtime does not come first in initial library list;
> you should either link runtime to your application or manually preload
> it with LD_PRELOAD.
> ---- end(-1) ----
> 18: 'import perf' in python                                         : FAILED!
> ```
> 
> I resolved this with LD_PRELOAD but there is a leak sanitizer issue
> that doesn't relate to importing the perf module:
> ```
> $ LD_PRELOAD=/usr/lib/llvm-16/lib/clang/16/lib/linux/libclang_rt.asan-x86_64.so
> perf test python -v
> --- start ---
> test child forked, pid 720967
> python usage test: "echo "import sys ; sys.path.insert(0,
> '/tmp/perf/python'); import perf" | '/usr/bin/python3' "
> 
> =================================================================
> ==720971==ERROR: LeakSanitizer: detected memory leaks
> 
> Direct leak of 13628 byte(s) in 6 object(s) allocated from:
>    #0 0x7fda504e8b42 in __interceptor_malloc
> (/usr/lib/llvm-16/lib/clang/16/lib/linux/libclang_rt.asan-x86_64.so+0xe8b42)
>    #1 0x4de57f in PyMem_RawMalloc build-static/../Objects/obmalloc.c:586:12
>    #2 0x4de57f in _PyObject_Malloc build-static/../Objects/obmalloc.c:2003:11
>    #3 0x4de57f in _PyObject_Malloc build-static/../Objects/obmalloc.c:1996:1
> 
> SUMMARY: AddressSanitizer: 13628 byte(s) leaked in 6 allocation(s).
> ---- end(-1) ----
> 18: 'import perf' in python
> ```
> 
> To clean that up I added "ASAN_OPTIONS=detect_leaks=0":
> ```
> $ LD_PRELOAD=/usr/lib/llvm-16/lib/clang/16/lib/linux/libclang_rt.asan-x86_64.so
> ASAN_OPTIONS=detect_leaks=0 perf test python -v
> 18: 'import perf' in python                                         : Ok
> ```
> 
> So somewhat convoluted but it is possible.
> 
> Thanks,
> Ian