[steerablesafe]

It's well defined in the system V ABI, isn't it? Compilers do follow that. Otherwise no layout is defined by the C and C++ standards, even outside of bitfields.

edit: It's under "Bit-Fields" in [1]. I'm not entirely happy with the wording, but it's there.

[1] https://raw.githubusercontent.com/wiki/hjl-tools/x86-psABI/x...