AddressSanitizer

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1

Hi lists,

I am encountering a large number of check-clang failures after building Clang/LLVM with -DLLVM_USE_SANITIZER=Address. I have reported the issue on Bugzilla (https://bugs.llvm.org/show_bug.cgi?id=47678). I cannot even compile helloworld.c with the resulting clang tool without a lot of false positives from ASan. Is it because I am not supposed to use GCC’s AddressSanitizer when building Clang?

2

Hi Bryan,

Yes, building LLVM with GCC+ASAN is a warranty void zone.
It can probably be made to work with some effort, but unless someone is willing to
maintain a public bot with this build, it will remain unsupported.

Building LLVM with LLVM+ASAN is fully supported, and the bots are maintained.

thanks!

–kcc

3

Thanks Kostya, using Clang to build itself with ASan enabled, and running my

build container in privileged mode, helped solve a lot of the problems. But I
now encounter a lot of link errors while testing my stage-2 build:

FAIL: libomp :: api/has_openmp.c (52345 of 54886)
******************** TEST ‘libomp :: api/has_openmp.c’ FAILED ********************
Script:

4

+Vitaly Buka to help with the links to build bots.

Not sure if any of those cover OpenMP.

5

Can you please share the full cmake command line?

6

Hi Vitaly,

This is the CMake command line I used:

cmake -G Ninja -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=$HOME/stage2
-DCMAKE_C_COMPILER=$HOME/stage1/bin/clang
-DCMAKE_CXX_COMPILER=$HOME/stage1/bin/clang++
-DCOMPILER_RT_BUILD_BUILTINS=off -DCOMPILER_RT_BUILD_PROFILE=on
-DCOMPILER_RT_BUILD_SANITIZERS=on -DCOMPILER_RT_BUILD_XRAY=off
-DLLVM_ENABLE_PROJECTS=“clang;compiler-rt;lld;openmp”
-DLLVM_ENABLE_ASSERTIONS=on -DLLVM_OPTIMIZED_TABLEGEN=on
-DLLVM_STATIC_LINK_CXX_STDLIB=on -DLLVM_TARGETS_TO_BUILD=“AArch64;X86”
-DLLVM_USE_LINKER=gold -DLLVM_USE_SANITIZER=Address …/llvm

Stage 1 was built from the same source using the same CMake command, without
-DLLVM_USE_SANITIZER. CMAKE_C_FLAGS and CMAKE_CXX_FLAGS contained some
hardening options like “-fstack-protector-strong -D_FORTIFY_SOURCE=2” which
I omitted for brevity. I am building on an AArch64 CentOS system.

The Builtins-aarch64-linux test failures have disappeared after I set the
PATH and LD_LIBRARY_PATH environment variables to point to $HOME/stage1/bin
and $HOME/stage1/lib. But I still see the tools/gold/X86 and OpenMP test
failures.

Thanks,

7

I guess the problem is the following:
Stage2 builds libomp.so instrumented with AddressSanitizer. Then omp tests are compiled without -fsanitize=address and load instrumented libomp.so which fails on missing symbols.

You can try to solve this in two ways:

  1. Disable sanitizers on libomp.so even -DLLVM_USE_SANITIZER= is set. That can be hard if it uses some part of llvm as dependency. If so, you can try to build non-instrumented libomp.so using ExternalProject_Add.
    Should work but sanitizer will cover only the compiler binary not libomp.so.

  2. Use asan in all tests e.g. with -DOPENMP_TEST_FLAGS=-fsanitize=address (better to do so in cmake file). Problem here is that stage2 does not build asan because it uses LLVM_USE_SANITIZER. We can just use stage1 compiler which contains asan libs. With a hack like this:

if(LLVM_USE_SANITIZER)
set(OPENMP_TEST_C_COMPILER ${CMAKE_C_COMPILER})
set(OPENMP_TEST_CXX_COMPILER ${CMAKE_CXX_COMPILER})

set(saved_CMAKE_C_FLAGS ${CMAKE_C_FLAGS})
set(saved_CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})

unset(CMAKE_C_FLAGS)
append_common_sanitizer_flags()
set(OPENMP_TEST_FLAGS “${CMAKE_C_FLAGS} -fsanitize=address ${OPENMP_TEST_FLAGS}”)

set(CMAKE_C_FLAGS ${saved_CMAKE_C_FLAGS})
set(CMAKE_CXX_FLAGS ${saved_CMAKE_CXX_FLAGS})
endif()

I can run most of the test:

Unsupported : 39

Passed : 241
Expectedly Failed: 2
Failed : 33 (it was 270+ before)

then you can fix or disable failing tests

8

Hi Bryan,

Clang doesn't seem to play nicely when using GCC ASAN, It should work
fine using clang as the host compiler though.

~Nathan

9

Disregard that, Didn't reaslise this had already been answered