linux-kernel - Re: [PATCH 16/18] arm64: ptrace: handle ptrace_request differently for aarch32 and ilp32

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Message-ID: <20170105204003.GA7437@yury-N73SV>
Date:   Fri, 6 Jan 2017 02:10:03 +0530
From:   Yury Norov <ynorov@...iumnetworks.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Catalin Marinas <catalin.marinas@....com>,
        <linux-doc@...r.kernel.org>, <szabolcs.nagy@....com>,
        <heiko.carstens@...ibm.com>, <cmetcalf@...hip.com>,
        <philipp.tomsich@...obroma-systems.com>, <joseph@...esourcery.com>,
        <linux-arch@...r.kernel.org>, <zhouchengming1@...wei.com>,
        <Prasun.Kapoor@...iumnetworks.com>, <agraf@...e.de>,
        <geert@...ux-m68k.org>, <kilobyte@...band.pl>,
        <manuel.montezelo@...il.com>, <pinskia@...il.com>,
        <linyongting@...wei.com>, <klimov.linux@...il.com>,
        <broonie@...nel.org>, <bamvor.zhangjian@...wei.com>,
        Bamvor Zhang Jian <bamvor.zhangjian@...aro.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <maxim.kuvyrkov@...aro.org>, <Nathan_Lynch@...tor.com>,
        <linux-kernel@...r.kernel.org>, <schwidefsky@...ibm.com>,
        <davem@...emloft.net>, <christoph.muellner@...obroma-systems.com>
Subject: Re: [PATCH 16/18] arm64: ptrace: handle ptrace_request differently
 for aarch32 and ilp32

On Wed, Dec 07, 2016 at 09:40:13PM +0100, Arnd Bergmann wrote:
> On Wednesday, December 7, 2016 4:59:13 PM CET Catalin Marinas wrote:
> > On Tue, Dec 06, 2016 at 11:55:08AM +0530, Yury Norov wrote:
> > > On Mon, Dec 05, 2016 at 04:34:23PM +0000, Catalin Marinas wrote:
> > > > On Fri, Oct 21, 2016 at 11:33:15PM +0300, Yury Norov wrote:
> > > > > New aarch32 ptrace syscall handler is introduced to avoid run-time
> > > > > detection of the task type.
> > > > 
> > > > What's wrong with the run-time detection? If it's just to avoid a
> > > > negligible overhead, I would rather keep the code simpler by avoiding
> > > > duplicating the generic compat_sys_ptrace().
> > > 
> > > Nothing wrong. This is how Arnd asked me to do. You already asked this
> > > question: http://lkml.iu.edu/hypermail/linux/kernel/1604.3/00930.html
> > 
> > Hmm, I completely forgot about this ;). There is still an advantage to
> > doing run-time checking if we avoid touching core code (less acks to
> > gather and less code duplication).
> > 
> > Let's see what Arnd says but the initial patch looked simpler.
> 
> I don't currently have either version of the patch in my inbox
> (the archive is on a different machine), but in general I'd still
> think it's best to avoid the runtime check for aarch64-ilp32
> altogether. I'd have to look at the overall kernel source to
> see if it's worth avoiding one or two instances though, or
> if there are an overwhelming number of other checks that we
> can't avoid at all.
> 
> Regarding ptrace, I notice that arch/tile doesn't even use
> the compat entry point for its ilp32 user space on 64-bit
> kernels, it just calls the regular 64-bit one. Would that
> help here?

ILP32 tasks has unique context that is not like aarch64 or aarch32,
so we have to have unique ptrace handler. I prepared the patch for
ptrace with runtime ABI detection, as Catalin said, see there:
https://github.com/norov/linux/commit/1f66dc22a4450b192e83458f2c3cc0e79f53e670

If it's OK, I'd like to update submission.

Yury