[cfe-dev] ARM Linux libc++ / libunwind — Exceptions not being caught

[Louis Dionne via cfe-dev]

> On Aug 30, 2018, at 17:03, Andrew Brownsword <andrew.e.brownsword at gmail.com> wrote:
> 
> I followed these steps with a couple of caveats:
> 	* used the (mostly) working clang toolchain I have in place (7.0.0rc2)
> 	* removed the -mcpu options (don’t know what valid list is)
> 	* had to prefix sub-project names with llvm/projects/*
> 	* created build directory in llvm/ (don’t normally like to do that)
> 	* ninja unwind (no lib prefix)
> 	* also tried using install-* target; built test program with paths to build dir as well as to the installed locations
> 
> Still doesn’t catch the stoul exception.
> 

I would suggest that you:

1. Use ldd to see exactly what shared objects are loaded by your program, and confirm that those are the ones you expect.
2. Run `nm --demangle` on libc++, libc++abi, libunwind and your program and look for the typeinfo of your exception class.
3. When building libcxxabi and libunwind, pass `-v` to ninja to see all the compilation commands, and then modify a command to preprocess `-E` the file instead and see exactly which headers are used to build. Confirm that you’re building libc++abi and libunwind against the correct headers.

Maybe you’ll find out that the exception class has typeinfo in more than one place, which could lead to the exception not being caught (if it’s thrown with a typeinfo different from the one used to catch). I’ve debugged very similar problems like that in the past. Another option is that your libunwind/libc++abi are somehow built against different headers or in a different configuration than you’re expecting, and that can lead to trouble (we’ve had one like that during the LLVM 7 release).

Louis

> 
>> My steps were:
>> 1.) Build trunk clang to use for building libc++ etc.
>> 2.) Using cmake
>> 
>> cmake -GNinja\
>>     /path/to/monorepo/llvm \
>>     -DLLVM_ENABLE_PROJECTS="libcxxabi;libcxx;libunwind" \
>>     -DCMAKE_BUILD_TYPE=Release \
>>     -DLLVM_ENABLE_ASSERTIONS=true\
>>     -DCMAKE_C_FLAGS='-mcpu=cortex-a57'\
>>     -DCMAKE_CXX_FLAGS='-mcpu=cortex-a57'\
>>     -DLLVM_TARGETS_TO_BUILD='ARM'\
>>     -DLIBCXXABI_USE_LLVM_UNWINDER=On
>> 3.) build
>> ninja libunwind
>> ninja cxxabi
>> ninja cxx
>> 
>> I was then able to run the example with:
>> clang++ --stdlib=libc++ -I ./include/c++/v1 t.cpp -o t.axf -L ./lib -v
>> --std=c++17
>> LD_LIBRARY_PATH=lib ./t.axf./t.axf
>> caught!
>