[compiler-rt] Build custom libc++abi without exceptions.

[morehouse]

Summary

Since neither compiler-rt nor the libc++ we build use exceptions, we
don't need libc++abi to have them either.

This resolves an issue where libFuzzer's private libc++ contains
implementations for __cxa_throw and friends, causing fuzz targets built
with their own C++ library to segfault during exception unwinding.

See https://github.com/google/oss-fuzz/issues/2328.

[kcc]

a test maybe?

[phosek]

LGTM

Related to this does anything in libFuzzer uses RTTI? If not we could also consider disabling RTTI to save extra space.

[morehouse]

• Add test.

[morehouse]

In D61053#1477178, @phosek wrote:

Related to this does anything in libFuzzer uses RTTI? If not we could also consider disabling RTTI to save extra space.

I'll look into this and mail a followup patch if possible.

[morehouse]

In D61053#1477275, @morehouse wrote:

In D61053#1477178, @phosek wrote:

Related to this does anything in libFuzzer uses RTTI? If not we could also consider disabling RTTI to save extra space.

I'll look into this and mail a followup patch if possible.

It doesn't look like we need RTTI, but I tried building libc++ without it and started getting link errors:

llvm-build/projects/compiler-rt/lib/fuzzer/tests/libRTFuzzerTest.x86_64.a(FuzzerDriver.cpp.o):(.data.rel.ro._ZTINSt6Fuzzer18basic_stringstreamIcNS_11char_traitsIcEENS_9allocatorIcEEEE[_ZTINSt6Fuzzer18basic_stringstreamIcNS_11char_traitsIcEENS_9allocatorIcEEEE]+0x10): undefined reference to `typeinfo for std::Fuzzer::basic_iostream<char, std::Fuzzer::char_traits<char> >'

llvm-build/projects/compiler-rt/lib/fuzzer/tests/libRTFuzzerTest.x86_64.a(FuzzerDriver.cpp.o):(.data.rel.ro._ZTINSt6Fuzzer15basic_stringbufIcNS_11char_traitsIcEENS_9allocatorIcEEEE[_ZTINSt6Fuzzer15basic_stringbufIcNS_11char_traitsIcEENS_9allocatorIcEEEE]+0x10): undefined reference to `typeinfo for std::Fuzzer::basic_streambuf<char, std::Fuzzer::char_traits<char> >'

llvm-build/projects/compiler-rt/lib/fuzzer/tests/libRTFuzzerTest.x86_64.a(FuzzerFork.cpp.o):(.data.rel.ro._ZTCNSt6Fuzzer19basic_istringstreamIcNS_11char_traitsIcEENS_9allocatorIcEEEE0_NS_13basic_istreamIcS2_EE[_ZTCNSt6Fuzzer19basic_istringstreamIcNS_11char_traitsIcEENS_9allocatorIcEEEE0_NS_13basic_istreamIcS2_EE]+0x10): undefined reference to `typeinfo for std::Fuzzer::basic_istream<char, std::Fuzzer::char_traits<char> >'

cmake/Modules/CustomLibcxx/CMakeLists.txt

 cmake_minimum_required(VERSION 3.4.3)
 project(custom-libcxx C CXX)
 
 # Build static libcxxabi.
 set(LIBCXXABI_STANDALONE_BUILD 1)
 set(LIBCXXABI_ENABLE_SHARED OFF CACHE BOOL "")
+set(LIBCXXABI_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
 set(LIBCXXABI_HERMETIC_STATIC_LIBRARY ON CACHE STRING "")
 set(LIBCXXABI_LIBCXX_PATH ${COMPILER_RT_LIBCXX_PATH} CACHE PATH "")
 set(LIBCXXABI_INCLUDE_TESTS OFF CACHE BOOL "")
 add_subdirectory(${COMPILER_RT_LIBCXXABI_PATH} ${CMAKE_CURRENT_BINARY_DIR}/cxxabi)
 
 # Build static libcxx without exceptions.
 set(LIBCXX_STANDALONE_BUILD 1)
 set(LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY OFF CACHE BOOL "")

test/fuzzer/libcxx.test

+# Ensures that the libFuzzer library does not export exceptions.
+
+RUN: %cpp_compiler %S/SimpleTest.cpp -o %t
+RUN: nm %t 2>&1 | FileCheck %s
+
+CHECK-NOT: t __cxa_allocate_dependent_exception
+CHECK-NOT: t __cxa_allocate_exception
+CHECK-NOT: t __cxa_begin_catch
+CHECK-NOT: t __cxa_call_unexpected
+CHECK-NOT: t __cxa_current_exception_type
+CHECK-NOT: t __cxa_end_catch
+CHECK-NOT: t __cxa_free_dependent_exception
+CHECK-NOT: t __cxa_free_exception
+CHECK-NOT: t __cxa_get_exception_ptr
+CHECK-NOT: t __cxa_throw