On Mon, Apr 14, 2025 at 03:36:50PM -0700, Josh Poimboeuf wrote: > On Mon, Apr 14, 2025 at 01:11:43PM +0200, Peter Zijlstra wrote: > > Since there is only a single fastop() function, convert the FASTOP > > stuff from CALL_NOSPEC+RET to JMP_NOSPEC+JMP, avoiding the return > > thunks and all that jazz. > > > > Specifically FASTOPs rely on the return thunk to preserve EFLAGS, > > which not all of them can trivially do (call depth tracing suffers > > here). > > > > Objtool strenuously complains about things, therefore fix up the > > various problems: > > > > - indirect call without a .rodata, fails to determine JUMP_TABLE, > > add an annotation for this. > > - fastop functions fall through, create an exception for this case > > - unreachable instruction after fastop_return, save/restore > > I think this breaks unwinding. Each of the individual fastops inherits > fastop()'s stack but the ORC doesn't reflect that. I'm not sure I understand. There is only the one location, and we simply save/restore the state around the one 'call'.
