Here's the LLVM code that clang-3.0-6ubuntu3 emits: define i64 @crash() nounwind uwtable readnone optsize { ret i64 undef } In machine code term

Here's the LLVM code that clang-3.0-6ubuntu3 emits: define i64 @crash() nounwind uwtable readnone optsize { ret i64 undef } In machine code terms, on x86-64 this turns into a function composed entirely of the ret opcode. gcc-4.6 adds an xor eax, eax before the ret.