Re: [PATCH v9 00/24] ILP32 for ARM64

From: Eugene Syromiatnikov <esyr@redhat.com>
To: Yury Norov <ynorov@caviumnetworks.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Arnd Bergmann <arnd@arndb.de>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-arch@vger.kernel.org, linux-api@vger.kernel.org,
	Adam Borowski <kilobyte@angband.pl>,
	Alexander Graf <agraf@suse.de>,
	Alexey Klimov <klimov.linux@gmail.com>,
	Andreas Schwab <schwab@suse.de>,
	Andrew Pinski <pinskia@gmail.com>,
	Bamvor Zhangjian <bamv2005@gmail.com>,
	Chris Metcalf <cmetcalf@mellanox.com>,
	Christoph Muellner <christoph.muellner@theobroma-systems.com>,
	Dave Martin <Dave.Martin@arm.com>,
	"David S . Miller" <davem@davemloft.net>,
	Florian Weimer <fweimer@redhat.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	James Hogan <james.hogan@imgtec.com>,
	James Morse <james.morse@arm.com>,
	Joseph Myers <joseph@codesourcery.com>,
	Lin Yongting <linyongting@huawei.com>,
	Manuel Montezelo <manuel.montezelo@gmail.com>,
	Mark Brown <broonie@kernel.org>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Maxim Kuvyrkov <maxim.kuvyrkov@linaro.org>,
	Nathan_Lynch <Nathan_Lynch@mentor.com>,
	Philipp Tomsich <philipp.tomsich@theobroma-systems.com>,
	Prasun Kapoor <Prasun.Kapoor@caviumnetworks.com>,
	Ramana Radhakrishnan <ramana.gcc@googlemail.com>,
	Steve Ellcey <sellcey@caviumnetworks.com>,
	Szabolcs Nagy <szabolcs.nagy@arm.com>,
	Pavel Machek <pavel@ucw.cz>, Palmer Dabbelt <palmer@sifive.com>,
	Wookey <wookey@wookware.org>
Subject: Re: [PATCH v9 00/24] ILP32 for ARM64
Date: Wed, 10 Oct 2018 16:10:21 +0200	[thread overview]
Message-ID: <20181010141017.GA2881@asgard.redhat.com> (raw)
In-Reply-To: <20180724173957.GA22106@yury-thinkpad>

On Tue, Jul 24, 2018 at 08:39:57PM +0300, Yury Norov wrote:
> Hi all,
> 
> + Pavel Machek, Palmer Dabbelt, Wookey.
> 
> On Wed, May 16, 2018 at 11:18:45AM +0300, Yury Norov wrote:
> > This series enables AARCH64 with ILP32 mode.
> > 
> > As supporting work, it introduces ARCH_32BIT_OFF_T configuration
> > option that is enabled for existing 32-bit architectures but disabled
> > for new arches (so 64-bit off_t userspace type is used by new userspace).
> > Also it deprecates getrlimit and setrlimit syscalls prior to prlimit64.
> > 
> > Based on kernel v4.16. Tested with LTP, glibc testsuite, trinity, lmbench,
> > CPUSpec.

> This is the update of the series based on 4.17 kernel
> https://github.com/norov/linux/tree/ilp32-4.17

Hello.

I have some questions regarding AArch64 ILP32 implementation for which I
failed to find an answer myself:
 * How ptrace() tracer is supposed to distinguish between ILP32 and LP64
   tracees? For MIPS N32 and x32 this is possible based on syscall
   number, but for AArch64 ILP32 I do not see such a sign. There's also
   ARM_ip is employed for signalling entering/exiting, I wonder whether
   it's possible to employ it also for signalling tracee's personality.
 * What's the reasoning behind capping syscall arguments to 32 bit? x32
   and MIPS N32 do not have such a restriction (and do not need special
   wrappers for syscalls that pass 64-bit values as a result, except
   when they do,  as it is the case for preadv2 on x32); moreover, that
   would lead to insurmountable difficulties for AArch64 ILP32 tracers
   that try to trace LP64 tracees, as it would be impossible to pass
   64-bit addresses to process_vm_{read,write} or ptrace PEEK/POKE.

Thank you.