On Thu, May 29, 2025 at 11:30:17AM +0200, Peter Zijlstra wrote: > > > So the sequence of fail is: > > > > > > push %rbp > > > mov %rsp, %rbp # cfa.base = BP > > > > > > SAVE > > sub $0x40,%rsp > and $0xffffffffffffffc0,%rsp > > This hits the 'older GCC, drap with frame pointer' case in OP_SRC_AND. > Which means we then hard rely on the frame pointer to get things right. > > However, per all the PUSH/POP_REGS nonsense, BP can get clobbered. > Specifically the code between the CALL and POP %rbp below are up in the > air. I don't think it can currently unwind properly there.
RBP is callee saved, so there's no need to pop it or any of the other callee-saved regs. If they were to change, that would break C ABI pretty badly. Maybe add a skip_callee=1 arg to POP_REGS? -- Josh
