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

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Message-ID: <4F206420.5080200@redhat.com>
Date:	Wed, 25 Jan 2012 20:20:48 +0000
From:	Pedro Alves <palves@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Indan Zupancic <indan@....nu>,
	Andi Kleen <andi@...stfloor.org>,
	Jamie Lokier <jamie@...reable.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>,
	Denys Vlasenko <vda.linux@...glemail.com>
Subject: Re: Compat 32-bit syscall entry from 64-bit task!?

On 01/25/2012 07:36 PM, Oleg Nesterov wrote:
> 
> Not sure this is really better, but there is another idea. Currently we
> have PTRACE_O_TRACESYSGOOD to avoid the confusion with the real SIGTRAP.
> Perhaps we can add PTRACE_O_TRACESYS_VERY_GOOD (or we can look at
> PT_SEIZED instead) and report TS_COMPAT via ptrace_report_syscall ?

May I beg to don't rely on PTRACE_SYSCALL for anything new?
You can't PTRACE_SINGLESTEP and PTRACE_SYSCALL simultaneously.  Think of
gdb single-stepping all the way for some reason (software watchpoints, for ex.),
while at the same time wanting to catch syscalls.

As Roland suggested, replacing PTRACE_SYSCALL with PTRACE_O_TRACE_SYSCALL_{ENTRY,EXIT}
and PTRACE_EVENT_SYSCALL_{ENTRY,EXIT} would be superior, syscall tracing wise.

-- 
Pedro Alves
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