https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102953
--- Comment #20 from Andrew Cooper <andrew.cooper3 at citrix dot com> --- (In reply to H.J. Lu from comment #19) > (In reply to Andrew Cooper from comment #17) > > I think I've found a bug in the -fcf-check-attribute implementation. > > Please try the v5 patch. Thanks. That does fix the issue. > BTW, do you have a testcase to show how > -fcf-check-attribute=yes is used? So, this was something I was going to leave until I'd got CET-IBT working, so as to have time to consider all parts before proposing improvements. I don't have a usecase for -fcf-check-attribute=yes, because it is almost totally redundant with regular -fcf-protection in the first place. When you are are applying control flow checks, every function is either checked or not checked. But GCC currently has a 3-way model of {unknown, explicit yes, explicit no} on which it builds its typechecking. Furthermore, -mmanual-endbr is a gross hack which by default leaves you with a broken binary. If I were building this from scratch, I'd not have -mmanual-endbr or -fcf-check-attribute at all, because they're exposing complexity which ought not to exist. I get why the default for -fcf-protection=branch puts an ENDBR* instruction everywhere. It is the quick, easy and non-invasive way to make libraries compatible with CET, which is a net improvement, even if not ideal. The ideal way, and definitely future work, is for GCC to calculate the minimum set of required ENDBR*. At a guess, all non-local symbols (except those LTO can determine are not publicly visible), and any local symbols used by function pointers. What I'm trying to do is a stopgap in the middle. No ENDBR*'s by default, but have the compiler tell me where I've got function pointers to a non-ENDBR'd function, so when the result compiles, it stands a reasonable chance of functioning correctly. Personally, I'd suggest having these as sub-modes of -fcf-protection=branch, instead of exposing all the internals on the command line.