GCC

After quite the lengthy tread through GCC and C-land (mind you everything discussed before was written in C), we finally find ourselves back at C++. C++ exception semantics seem simple, but actually hide many surprising edge cases. Functions Like before, let’s discuss the API of the C++ exception handling regime. Note that while you’re not supposed to call these functions directly, these functions are called in compiler generated code anyways, so are a part of the public ABI....

Last time I mentioned libunwind, but now I’m going to go over the implementation of libunwind in GCC. As mentioned before, libunwind used to be a library developed by HP, but it got vendored into GCC as a part of libgcc. libgcc itself is a small library containing, besides libunwind, various intrinsics for floating point and integer math. libunwind One might reasonably ask the question of how one can unwind a stack while using functions that modify the stack?...

As it turns out there’s not really a good in depth explanation of how exceptions work. There are disparate explanations of how separate parts of exceptions in C++ work, but not really the whole picture. So I’m writing this down here as a reference to how everything in C++ exceptions work. Disclaimer My experiences are exclusively in GCC. Broadly, Clang should follow the same Architecture as GCC, but may vary in implementation details....

Quite a while ago, I’ve integrated my exceptions work into a fork of GCC. At that point, I was already modifying GCC to suppress the libunwind symbols, so putting all of my code into GCC was a no brainer. Moreover, it isn’t actually that hard to build GCC. Editing GCC GCC is built via the autoconf build system. Autoconf is a collection of scripts that is somewhat like CMake, but written entirely in shell script and is intended to be portable for any system that runs shell scripts and has a C compiler....