linux-kernel - Re: Compat 32-bit syscall entry from 64-bit task!?

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Date:	Thu, 26 Jan 2012 15:02:21 +0100
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Jamie Lokier <jamie@...reable.org>
Cc:	Indan Zupancic <indan@....nu>, Oleg Nesterov <oleg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Lutomirski <luto@....edu>,
	Will Drewry <wad@...omium.org>, linux-kernel@...r.kernel.org,
	keescook@...omium.org, john.johansen@...onical.com,
	serge.hallyn@...onical.com, coreyb@...ux.vnet.ibm.com,
	pmoore@...hat.com, eparis@...hat.com, djm@...drot.org,
	segoon@...nwall.com, rostedt@...dmis.org, jmorris@...ei.org,
	scarybeasts@...il.com, avi@...hat.com, penberg@...helsinki.fi,
	viro@...iv.linux.org.uk, mingo@...e.hu, akpm@...ux-foundation.org,
	khilman@...com, borislav.petkov@....com, amwang@...hat.com,
	ak@...ux.intel.com, eric.dumazet@...il.com, gregkh@...e.de,
	dhowells@...hat.com, daniel.lezcano@...e.fr,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, olofj@...omium.org,
	mhalcrow@...gle.com, dlaor@...hat.com,
	Roland McGrath <mcgrathr@...omium.org>
Subject: Re: Compat 32-bit syscall entry from 64-bit task!?

On Thu, Jan 26, 2012 at 12:01 PM, Jamie Lokier <jamie@...reable.org> wrote:
> Denys Vlasenko wrote:
>> On Thu, Jan 26, 2012 at 11:31 AM, Jamie Lokier <jamie@...reable.org> wrote:
>> >> It's still unclear if the PTRACE_EVENT_EXEC comes before or after
>> >> or instead of the post-execve ptrace event.
>>
>> Denis <- confused.
>> Was ist das "post-execve ptrace event"? I know no such thing.
>> I know about PTRACE_EVENT_EXEC, and "post-execve SIGTRAP".
>
> Sorry, I meant to write execve-syscall-exit event.

PTRACE_EVENT_EXEC happens before syscall exit. syscall exit
is not lost. Basically, the sequence is:

tracer               tracee with tid N, tgid M
   <------------- syscall entry for execve, pid=N
PTRACE_SYSCALL--->
   <------------- PTRACE_EVENT_EXEC, pid=M
PTRACE_GETEVENTMSG-->
   <------------- returns N ("I used to be tid N")
PTRACE_SYSCALL--->
   <------------- syscall exit for execve, pid=M
...

-- 
vda
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