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Re: reverse-next doing repeated reverse-stepi's ?


Greg Law wrote:
Michael Snyder wrote:
Julian Smith wrote:
I've been trying out reverse-next with UndoDB as a remote debug server,
and it looks like reverse-next works by doing repeated
`bs' (reverse-stepi) commands.

I was expecting it to set breakpoints and do `bc' (reverse-continue)
commands, by analogy with normal forwards step etc.

Am i doing something wrong here ? Or is this the expected behaviour ?
Short answer: this is expected behavior.

Forward-next works the same way, in general.
Both forward-next and reverse-next will set breakpoints
under some circumstances, but will often work by
singlestepping.

If I understand correctly, when doing a 'next' gdb does something like:


while (PC in current line) {
  ptrace (PTRACE_SINGLESTEP)
  if (PC outside current function) {
    plant breakpoint at return address
    ptrace (PTRACE_CONT)
    remove breakpoint
  }
}

however, when doing a reverse-next, we don't see this. We just see repeated reverse single-steps. If trying to do a reverse-next over a non-trivial function, this can take a very long time. Is this expected?

No, it should work similarly to forward next. When you have stepped backward into a function, it should place a breakpoint at the entry point, run backward to that, and then step back into the caller.


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