https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103699
--- Comment #2 from Petr <kobalicek.petr at gmail dot com> --- If you compile this with clang the function test_u32() will corretly return the expected 0xBBCCDDEE and not 0x0708090A. If you compile with older GCC, like GCC 10, the test would also return 0xBBCCDDEE. Only GCC-11 and upward return 0x0708090A. Based on the documentation here: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#Common-Variable-Attributes It's stated that "When used as part of a typedef, the aligned attribute can both increase and decrease alignment, and specifying the packed attribute generates a warning." - it explicitly allows to create a type with lower alignment, so I don't consider this undefined behavior - in general UBSAN is fine with this construct.
