From Fedora Project Wiki

ABI variants

Some architectures have binary-incompatible sub-architecture variants. Historic examples are non-executable stacks (handled with the GNU_STACK program header and the .note.GNU-stack section) and 16-byte stack alignment on i386 (which did not receive any markup).

Potential such changes are:

MIPS executables already have a PT_ABIFLAGS segment, as well as PT_REGINFO.