linux-kernel - Re: [RFC PATCH for 5.2 08/10] rseq/selftests: aarch64 code signature: handle big-endian environment

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Message-ID: <2087640779.608.1556125379269.JavaMail.zimbra@efficios.com>
Date:   Wed, 24 Apr 2019 13:02:59 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Will Deacon <will.deacon@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>, Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@....linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
        Chris Lameter <cl@...ux.com>, Ben Maurer <bmaurer@...com>,
        rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Joel Fernandes <joelaf@...gle.com>, shuah <shuah@...nel.org>,
        linux-kselftest <linux-kselftest@...r.kernel.org>
Subject: Re: [RFC PATCH for 5.2 08/10] rseq/selftests: aarch64 code
 signature: handle big-endian environment

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

> ----- On Apr 24, 2019, at 12:51 PM, Mark Rutland mark.rutland@....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