https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88662
Vincent Lefèvre <vincent-gcc at vinc17 dot net> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |vincent-gcc at vinc17 dot net --- Comment #14 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> --- IMHO, this is implementation-defined, thus needs to be documented. 6.2.6.1p2 says "Except for bit-fields, objects are composed of contiguous sequences of one or more bytes, the number, order, and encoding of which are either explicitly specified or implementation-defined." And the combination of valid padding bits is part of the encoding. If you fear that there may be any issue with a future change of GCC, you could still say that this may change in the future.