linux-kernel - Re: [RFC/PATCH] Implement new PTRACE_EVENT_SYSCALL

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Date:	Fri, 10 Jan 2014 14:58:02 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Pedro Alves <palves@...hat.com>
Cc:	Sergio Durigan Junior <sergiodj@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Roland McGrath <roland@...k.frob.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Tom Tromey <tromey@...hat.com>,
	Jan Kratochvil <jan.kratochvil@...hat.com>,
	Tejun Heo <tj@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC/PATCH] Implement new PTRACE_EVENT_SYSCALL_{ENTER,EXIT}

On 01/09, Pedro Alves wrote:
>
> On 01/07/2014 03:30 PM, Oleg Nesterov wrote:
> >
> > This way PTRACE_O_SYSCALL_* will work like other ptrace options which
> > ask to report an event.
>
> +10^6.  With PTRACE_SYSCALL/sysgood, we don't have a way to trace
> syscalls when single-stepping, which isn't much of a problem for
> strace, but of course is for GDB.  That is one of the things the
> new API should definitely sort out.

Hmm. I think this is a good point, but this needs more discussion.

So suppose that gdb does ptrace(PTRACE_SINGLESTEP) and the tracee
executes the "syscall" insn. What it should report?

syscall-entry looks obvious, PTRACE_EVENT_SYSCALL_ENTER should be
reported if PTRACE_O_SYSCALL_ENTER was set.

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?

Oleg.

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