On Tue, Dec 12, 2006 at 03:26:34PM +0000, Andrew Haley wrote: > Ulrich Drepper writes: > > Andrew Haley wrote: > > > Null-terminating the call stack is too well-established practice to be > > > changed now. > > > > Which does not mean that the mistake should hold people back. > > Sure it does. Not breaking things is an excellent reason, probably > one of the the best reasons you can have.
Well, libgcc unwinder handles neither %rbp 0 termination (even if that would be rephrased as outermost frame on x86-64 is determined by %rbp == 0 if CFA is %rbp + offset (that would handle the -fomit-frame-pointer routines where CFA is %rsp + offset)), nor DW_CFA_undefined %rip termination ATM. Things worked until now simply because the outermost routine (_start resp. thread_start hunk in clone in glibc) so far didn't have any unwind info. What would work with stock libgcc unwinder would probably be if _start or clone's child hunk had %rip point to memory containing 0 or DW_CFA_val_expression returning 0 (well, on SPARC that would need to be -8, as RETURN_ADDR_OFFSET is added to it). Jakub