On Wed, May 28, 2025 at 09:44:52AM +0200, Peter Zijlstra wrote: > On Tue, May 06, 2025 at 12:18:49PM -0700, Josh Poimboeuf wrote: > > > Weird, I'm not seeing that. > > I Ate'nt Crazeh... > > https://lore.kernel.org/all/202505280410.2qfTQCRt-lkp@xxxxxxxxx/T/#u > > I'll go poke at it, see if today is the day I can figure out WTF > happens. It manages to trip the CFI_UNDEFINED case in op->dest.reg == cfa->base in update_cfi_state(). I figured it ought to tickle the regular 'mov %rbp, %rsp' case above there, but it doesn't, for some reason it has cfa.base == SP at this point. This happens... /me looks in scrollback ... at POP_REGS 'pop %rbp'. ARGH!! So the sequence of fail is: push %rbp mov %rsp, %rbp # cfa.base = BP SAVE ... push %rbp ... pop %rbp # cfa.base = SP ... mov %rbp, %rsp # UNDEF nop # FAIL RESTORE Note that the MOV+NOP is the 4 bytes ERETS needs.
