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

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Message-ID: <20170106143619.GC12863@e104818-lin.cambridge.arm.com>
Date:   Fri, 6 Jan 2017 14:36:19 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Yury Norov <ynorov@...iumnetworks.com>
Cc:     Arnd Bergmann <arnd@...db.de>, 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 Fri, Jan 06, 2017 at 02:10:03AM +0530, Yury Norov wrote:
> 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.

This looks better to me (and even better if you no longer need to touch
the generic ptrace code).

-- 
Catalin