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

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Message-ID: <5373BACB.9090807@redhat.com>
Date:	Wed, 14 May 2014 19:49:47 +0100
From:	Pedro Alves <palves@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>,
	Sergio Durigan Junior <sergiodj@...hat.com>
CC:	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}

I realized now that I responded to this.  Sorry about that.

On 01/19/2014 03:29 PM, Oleg Nesterov wrote:
> 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?

Seems to me that this should be very much the same as fork/vfork/clone
event handling.  Those are triggered by a syscall anyway.  So, say:

- ptrace(PTRACE_SINGLESTEP)
- the tracee executes the "syscall" insn, and the syscall is "clone".
- PTRACE_EVENT_FORK is reported.
- The debugger does ptrace(PTRACE_CONT).

What should be reported?  What is reported now?

-- 
Pedro Alves

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