linux-kernel - Re: [ARCH question] Do syscall_get_nr and syscall_get

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Message-ID: <1392752362.2165.31.camel@flatline.rdu.redhat.com>
Date:	Tue, 18 Feb 2014 14:39:22 -0500
From:	Eric Paris <eparis@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Jonas Bonn <jonas.bonn@...il.com>, Oleg Nesterov <oleg@...hat.com>,
	linux-arch <linux-arch@...r.kernel.org>, linux-audit@...hat.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Steve Grubb <sgrubb@...hat.com>
Subject: Re: [ARCH question] Do syscall_get_nr and syscall_get_arguments
 always work?

On Fri, 2014-02-07 at 08:40 -0800, Andy Lutomirski wrote:
> On Fri, Feb 7, 2014 at 4:58 AM, Jonas Bonn <jonas.bonn@...il.com> wrote:
> > Hi Andy,
> >
> > On 5 February 2014 00:50, Andy Lutomirski <luto@...capital.net> wrote:
> >>
> >> I can't even find the system call entry point on mips.
> >>
> >>
> >> Is there a semi-official answer here?
> >
> > I don't have an official answer for you, but when I wanted to do
> > something with these entry points a couple of years back I discovered
> > that they aren't very thoroughly implemented across the various
> > architectures.  I started cleaning this up and can probably dig up
> > some of this for you if you need it.
> 
> The syscall_get_xyz functions are certainly implemented and functional
> in all relevant architectures -- the audit code is already using them.
>  The thing I'm uncertain about is whether they are usable with no
> syscall slow path bits set.
> 
> I guess that, if the syscall restart logic needs to read the argument
> registers, then they're probably reliably saved...

Al just indicated to me that on at least ia64, syscall_get_arguments()
is really expensive.  So maybe not a deal breaker, but sounds like we'd
lose a lot of performance trying to get them at syscall exit...

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