Re: [RFC/PATCH] Implement new PTRACE_EVENT_SYSCALL_{ENTER,EXIT}

[Oleg Nesterov <oleg@redhat.com>]

On 01/19, Sergio Durigan Junior wrote:
>
> On Friday, January 10 2014, Oleg Nesterov wrote:
>
> > So suppose that gdb does ptrace(PTRACE_SINGLESTEP) and the tracee
> > executes the "syscall" insn. What it should report?
> [...]
> > But what should syscall-exit do? Should it still report SIGSEGV as
> > it currently does, or should it report _SYSCALL_EXIT instead (if
> > PTRACE_O_SYSCALL_EXIT of course), or should it report both?
>
> Both only if _SYSCALL_EXIT is set.  Otherwise, stick to the current
> behavior, I guess.

OK, both. In which order? Probably _EXIT first. But this looks a bit
strange. Suppose that the tracee reports _EXIT, then debugger does
ptrace(PTRACE_CONT), should the tracee report SIGTRAP?

SIGTRAP before _EXIT looks a bit strange too... Single-step trap should
be reported after insn, but we are still in syscall.

So perhaps _EXIT should win and do not report the step?

> Isn't it what my current patch does, by the way?

I forgot how this patch looks so I can be easily wrong, but iirc no.
Note that tracehook_report_syscall_exit() doesn't even call
ptrace_report_syscall() if step == T.

Btw, if you send v2, please CC Michael Kerrisk <mtk.manpages@gmail.com>.

Oleg.