Messages in this thread | | | Subject | Re: [PATCH 1/2] alpha/ptrace: Record and handle the absence of switch_stack | From | Michael Schmitz <> | Date | Mon, 21 Jun 2021 16:08:35 +1200 |
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Hi Linus,
I realized that the patch is still incomplete when answering Al...
Am 21.06.2021 um 15:37 schrieb Linus Torvalds: > On Sun, Jun 20, 2021 at 8:18 PM Michael Schmitz <schmitzmic@gmail.com> wrote: >> >> I hope that makes more sense? > > So the problem is in your debug patch: you don't set that > TIS_SWITCH_STACK in nearly enough places. > > In this particular example, I think it's that you don't set it in > do_trace_exit, so when you strace the process, the system call exit - > which is where the return value will be picked up - gets that warning. > > You did set TIS_SWITCH_STACK on trace_entry, but then it's cleared > again during the system call, and not set at the trace_exit path. > Oddly, your debug patch also _clears_ it on the exit path, but it > doesn't set it when do_trace_exit does the SAVE_SWITCH_STACK. > > You oddly also set it for __sys_exit, but not all the other special > system calls that also do that SAVE_SWITCH_STACK.
That's the one I used to test whether my debug patch had any ill side effects (i.e. smashing the stack) late yesterday. Forgot to add that to the other cases.
> > Really, pretty much every single case of SAVE_SWITCH_STACK would need > to set it. Not just do_trace_enter/exit
Yes - done that now and the warning is gone.
> It's why I didn't like Eric's debug patch either. It's quite expensive > to do, partly because you look up that curptr thing. All very nasty.
I need to talk to Geert and Andreas to find where register a1 is preserved, but if I have to reload a1 all the time, this won't be useful except for debugging.
> It would be *much* better to make the flag be part of the stack frame, > but sadly at least on alpha we had exported the format of that stack > frame to user space.
Same on m68k, but can we push a flag _after_ the switch stack?
> Anyway, I think these debug patches are not just expensive but the > m68k one most definitely is also very incomplete.
Yes, I've seen that in the meantime. Need to triple check my work next time.
Sorry for the extra noise!
Cheers,
Michael
> > Linus >
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