On Wed, May 28, 2025 at 06:30:35PM +0200, Peter Zijlstra wrote: > 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/[email protected]/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
This is the POP !drap and dest==base case. > ... > mov %rbp, %rsp # UNDEF > nop # FAIL > RESTORE > > Note that the MOV+NOP is the 4 bytes ERETS needs.
