[llvm-dev] [cfe-dev] Buildling with/without AddressSanitizer causes divergent execution behaviour

[Yury Gribov via llvm-dev]

On 02/09/2016 09:57 PM, Dan Liew via cfe-dev wrote:
> Hi,
>
> # TL;DR
>
> I've been building an application with and without the address
> sanitizer (with gcc 5.3 and clang 3.7.1) and I've observed that the
> application's behaviour changes (assertion hit/ not hit). I'm
> wondering if this could be a bug in address sanitizer or if the
> application I'm running is just buggy (e.g. doing bad things like
> relying on memory layout, etc.).

We've experienced such situations as well. Usually this was caused by 
some wild memory write which was unnoticed before but started to corrupt 
something important due to changed stack/heap layout.

You can try to apply ASan selectively to parts of your program to 
isolate the problem.

> I'm also observing ASan reporting a
> heap-use-after-free which Valgrind is not reporting, which makes me
> wonder if it is a false positive.
>
> Any hints on how I might determine this? Building with UBSan doesn't
> turn up anything.
>
> # Longer version (if you are interested in the specific details)
>
> The application of interest is the Z3 constraint solver [1].
>
> Much of what I'm going to say is covered in [2] which is a bug report
> I opened (including a heap-use-after-free AddressSanitizer finds, I'm
> not sure if this a false positive or not) but here are the basics of
> what I found.
>
> Build Z3 as follows
>
> ```
> git clone https://github.com/Z3Prover/z3.git
> cd z3
>
> # Now apply the attached patch.
> # Basically this makes it so that in ``examples/c/test_capi.c``
> # the main() function only calls two functions.
> # Note if you build without the patch when running ``c_example``
> program AddressSanitizer
> # reports a heap-use-after-free. I'm not sure if this a false positive
> or not. Valgrind doesn't
> # seem to think there's a problem.
>
> # Build with ASan, Assertion will be hit when running the example
> CXX=clang++ CC=clang CXXFLAGS="-fno-omit-frame-pointer
> -fsanitize=address" LDFLAGS="-fsanitize=address" python
> scripts/mk_make.py --debug --noomp --build build_asan
> cd build_asan
> make
> make c_examples
> LD_LIBRARY_PATH=`pwd` ./c_example
> ...
> ASSERTION VIOLATION
> File: ../src/sat/sat_clause.h
> Line: 59
>
> # Now build without ASan
> cd ../
> CXX=clang++ CC=clang python scripts/mk_make.py --debug --noomp --build
> build_noasan
> cd build_noasan
> make
> make c_example
> LD_LIBRARY_PATH=`pwd` ./c_example
>
> # No assertion is hit
> ```
>
> Any insights/suggestions on how I could debug what I'm seeing further
> would be appreciated.
>
> [1] https://github.com/z3prover/z3
> [2] https://github.com/Z3Prover/z3/issues/436
>
> Thanks,
> Dan.
>
>
>
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