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

From: Catalin Marinas <catalin.marinas@arm.com>
To: Yury Norov <ynorov@caviumnetworks.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
	linux-doc@vger.kernel.org, szabolcs.nagy@arm.com,
	heiko.carstens@de.ibm.com, cmetcalf@ezchip.com,
	philipp.tomsich@theobroma-systems.com, joseph@codesourcery.com,
	linux-arch@vger.kernel.org, zhouchengming1@huawei.com,
	Prasun.Kapoor@caviumnetworks.com, agraf@suse.de,
	geert@linux-m68k.org, kilobyte@angband.pl,
	manuel.montezelo@gmail.com, pinskia@gmail.com,
	linyongting@huawei.com, klimov.linux@gmail.com,
	broonie@kernel.org, bamvor.zhangjian@huawei.com,
	Bamvor Zhang Jian <bamvor.zhangjian@linaro.org>,
	linux-arm-kernel@lists.infradead.org, maxim.kuvyrkov@linaro.org,
	Nathan_Lynch@mentor.com, linux-kernel@vger.kernel.org,
	schwidefsky@de.ibm.com, davem@davemloft.net,
	christoph.muellner@theobroma-systems.com
Subject: Re: [PATCH 16/18] arm64: ptrace: handle ptrace_request differently for aarch32 and ilp32
Date: Fri, 6 Jan 2017 14:36:19 +0000	[thread overview]
Message-ID: <20170106143619.GC12863@e104818-lin.cambridge.arm.com> (raw)
Message-ID: <20170106143619.CtCpM9X02JBTdEhheGAVBfzU35cj8989y6sUF0U3-7k@z> (raw)
In-Reply-To: <20170105204003.GA7437@yury-N73SV>

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