Re: GDB single-step fails on alpha (Re: CVS commit: src/share/mk)

[Rin Okuyama <rokuyama%rk.phys.keio.ac.jp@localhost>]

Thank you very much for your kind explanation.

On 2016/12/07 13:26, Kamil Rytarowski wrote:
> On 07.12.2016 04:27, Rin Okuyama wrote:
> > However, before proceeding further, we need to discuss undocumented
> > details related to PT_STEP; What should we do when a process steps into
> > a RAS? How about the case where PT_STEP is used against a process which
> > is already in single stepping? And so on...
>
> According to my understanding RAS is intended to be atomic sequence of
> operations and tracer mustn't interrupt or preempt it.

process_sstep(9) should fail and return EFAULT in such a case?

> There might exist only single tracer attached to a process.
>
> I don't think PT_STEP called twice for the same process makes sense in
> real life, it might be undefined behavior on port-specific basis and/or
> return error (in other words just prevent panic(9) and vulnerabilities).
> If I remember correctly process sets MD-style PSL_T variable to indicate
> trap after at least single instruction - if so, we cannot set this bit
> twice.

Yes, it makes no sense. In my patch for powerpc/ibm4xx, process_sstep(9)
just returns 0 in that case. But I come to feel EFAULT more preferable.

rin