In this case, it's not actually that much of a bug: the segfault is entirely controlled. Threads' stacks are allocated with a guard page at the end that is mark

In this case, it's not actually that much of a bug: the segfault is entirely controlled. Threads' stacks are allocated with a guard page at the end that is marked as inaccessible (at the OS level), so any access---read or write---will make the OS kill the process, via a segfault. This particular type of segfault differs to typical segfaults in other languages because it is guaranteed to happen and guaranteed to be a segfault/kill the program. Segfaults in C code often hint at more serious bugs (e.g. use after free) that can be exploited for remote code execution etc. The bug is that the stack overflow detection isn't perfect: if writes to particularly large stack frames happen in just the wrong way, then a program can write beyond the guard page instead of being killed. This is obviously unfortunate, and the fix is ensuring LLVM has support for stack problems on all platforms (it currently has them on Windows).