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

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Date:	Fri, 10 Feb 2012 22:19:29 +0100
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	"Indan Zupancic" <indan@....nu>
Cc:	"Jamie Lokier" <jamie@...reable.org>,
	"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 Friday 10 February 2012 04:37, Indan Zupancic wrote:
> > I read somewhere about a bug report where syscall-exit was seen after
> > attach, but I don't remember where now.
> 
> Well, if you attach at a random moment you can get a syscall-exit first,
> I guess. I suppose you have to wait till you get the SIGSTOP notification
> before you can be sure that the next syscall event will be an entry one.

No. After PTRACE_ATTACH, next reported waitpid result will be either
a ptrace-stop of signal-delivery-stop variety,
or death (WIFEXITED/WIFSIGNALED). Syscall exit notification
is not possible (modulo kernel bugs). For one, syscall entry/exit
notifications must be explicitly requested by PTRACE_SYSCALL, which
wasn't yet done!

-- 
vda
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