2. Save the following bash script, fixing LLVM_ROOT to point to your installation.
#! /bin/sh if [ -z $1 ] ; then echo "usage: $0 <dirname>" elif [ -d $1 ] ; then echo "directory $1 already exists" else autoconf2.13 autoconf213 mkdir $1 cd $1 LLVM_ROOT="$HOME/llvm" SANFLAG="-fsanitize=undefined -fno-sanitize=alignment,float-cast-overflow,float-divide-by-zero,vptr -Dxmalloc=myxmalloc" \ CC="$LLVM_ROOT/build/Release+Asserts/bin/clang" \ CXX="$LLVM_ROOT/build/Release+Asserts/bin/clang++" \ CFLAGS="$SANFLAG" \ CXXFLAGS="$SANFLAG" \ MOZ_LLVM_HACKS=1 \ ../configure --enable-debug --disable-optimize make -j 8 fi
3. Use the script to compile SpiderMonkey.
This enables all the cheap undefined behavior checks other than:
- alignment, which hits known bugs in SpiderMonkey, and is more implementation-defined (slow on x86 / crash on ARM) than undefined behavior
- float-cast-overflow, which hits known bugs in SpiderMonkey, and isn't exploited by today's compilers
- float-divide-by-zero, which Jesse doesn't think is actually undefined behavior (aside from the question of whether CPU overflow flags are set)
- vptr, a check that requires RTTI, which is disabled by default in SpiderMonkey
4. When you hit a bug and want a stack trace, run under gdb with a breakpoint at the end of __ubsan::Diag::~Diag(). The stack trace should show a function such as __ubsan_handle_load_invalid_value or __ubsan_handle_type_mismatch being called by the buggy C++ code. (For automated testing outside of gdb, you can instead build with -fsanitize=undefined-trap -fsanitize-undefined-trap-on-error, but then you lose UBSan's diagnostics and the ability to continue past errors.)
Known bugs. Please file new bugs with e.g. [-fsanitize=float-cast-overflow] in the status whiteboard.