Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 24 Apr 2019 13:02:59 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     Will Deacon <will.deacon@arm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-api <linux-api@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andy Lutomirski <luto@amacapital.net>,
        Dave Watson <davejwatson@fb.com>, Paul Turner <pjt@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Russell King <linux@arm.linux.org.uk>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Andi Kleen <andi@firstfloor.org>,
        Chris Lameter <cl@linux.com>, Ben Maurer <bmaurer@fb.com>,
        rostedt <rostedt@goodmis.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Joel Fernandes <joelaf@google.com>, shuah <shuah@kernel.org>,
        linux-kselftest <linux-kselftest@vger.kernel.org>
Message-ID: <2087640779.608.1556125379269.JavaMail.zimbra@efficios.com>
In-Reply-To: <697611694.604.1556125254852.JavaMail.zimbra@efficios.com>
References: <20190424152502.14246-1-mathieu.desnoyers@efficios.com> <20190424152502.14246-9-mathieu.desnoyers@efficios.com> <20190424164538.GC18611@fuggles.cambridge.arm.com> <20190424165150.GF21101@lakrids.cambridge.arm.com> <697611694.604.1556125254852.JavaMail.zimbra@efficios.com>
Subject: Re: [RFC PATCH for 5.2 08/10] rseq/selftests: aarch64 code
 signature: handle big-endian environment
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Thread-Topic: rseq/selftests: aarch64 code signature: handle big-endian environment
Thread-Index: OBjeHUeE7gQ5xyWKTP757DExutwbEyS+nxVk
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

----- On Apr 24, 2019, at 1:00 PM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:

> ----- On Apr 24, 2019, at 12:51 PM, Mark Rutland mark.rutland@arm.com wrote:
> 
>> On Wed, Apr 24, 2019 at 05:45:38PM +0100, Will Deacon wrote:
>>> On Wed, Apr 24, 2019 at 11:25:00AM -0400, Mathieu Desnoyers wrote:
>>> > +/*
>>> > + * aarch64 -mbig-endian generates mixed endianness code vs data:
>>> > + * little-endian code and big-endian data. Ensure the RSEQ_SIG signature
>>> > + * matches code endianness.
>>> > + */
>>> > +#define RSEQ_SIG_CODE	0xd428bc00	/* BRK #0x45E0.  */
>>> > +
>>> > +#ifdef __AARCH64EB__
>>> > +#define RSEQ_SIG_DATA	0x00bc28d4	/* BRK #0x45E0.  */
>>> 
>>> It would be neater to implement swab32 and use that with RSEQ_SIG_CODE,
>> 
>> If possible, marginally neater than that would be using
>> le32_to_cpu(RSEQ_SIG_CODE), without any ifdeffery necessary.
>> 
>> It looks like that's defined in tools/include/linux/kernel.h, but I'm
>> not sure if that gets pulled into your include path.
> 
> Considering that those RSEQ_SIG* define will end up in public bits/rseq.h
> headers within glibc, I'm tempted to keep the amount of dependencies on
> external headers to a minimum, if it's OK with you.

Also, I'm not sure the le32_to_cpu() approach would work in __ASSEMBLER__
builds.

Thanks,

Mathieu

> 
> Thanks,
> 
> Mathieu
> 
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com