[PATCH 53-55] (Was: Q: what user_enable_single_step() actually means?)

[Oleg Nesterov]

On 09/25, Oleg Nesterov wrote:
>
> On 09/25, Roland McGrath wrote:
> >
> > > > it being after the syscall insn, but (in vanilla ptrace, and at the
> > > > time of report_clone callbacks at utrace level) without the return
> > > > value register having been written yet.
> > >
> > > And how we can implement this?
> > >
> > > regs->ax is updated right after "call *sys_call_table[]", and we
> > > report PTRACE_EVENT_FORK or PTRACE_EVENT_EXEC much later.
> >
> > I didn't intend to.  This is a change I think is more desireable than the
> > bug-compatibility.  In today's ptrace these extra stops are the sole
> > exceptions where the register state you fiddle with ptrace gets clobbered
> > later.  I've never thought that was useful.
>
> Ah, good! I misunderstood you.
>
> Let's ignore this minor incompatibility then.

OK, but I'd like to clarify one thing, just to be absolutely sure I
understand what do you think.

> It's a further oddity that you can single-step (or not) "into" the
> system call and then get a ptrace stop "inside" it, that being for
> PTRACE_EVENT_FORK et al.

And utrace-ptrace should be compatible here, yes?

Oleg.