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: <20190424164536.GE21101@lakrids.cambridge.arm.com>
Date:   Wed, 24 Apr 2019 17:45:37 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        linux-kernel@...r.kernel.org, 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>,
        Steven Rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org
Subject: Re: [RFC PATCH for 5.2 08/10] rseq/selftests: aarch64 code
 signature: handle big-endian environment

On Wed, Apr 24, 2019 at 05:40:33PM +0100, Mark Rutland 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.  */
> > +#else
> > +#define RSEQ_SIG_DATA	RSEQ_SIG_CODE
> > +#endif
> > +
> > +#define RSEQ_SIG	RSEQ_SIG_DATA
> >  
> >  #define rseq_smp_mb()	__asm__ __volatile__ ("dmb ish" ::: "memory")
> >  #define rseq_smp_rmb()	__asm__ __volatile__ ("dmb ishld" ::: "memory")
> > @@ -121,7 +134,7 @@ do {										\
> >  
> >  #define RSEQ_ASM_DEFINE_ABORT(label, abort_label)				\
> >  	"	b	222f\n"							\
> > -	"	.inst 	"	__rseq_str(RSEQ_SIG) "\n"			\
> > +	"	.inst 	"	__rseq_str(RSEQ_SIG_CODE) "\n"			\
> 
> I don't think this is right; the .inst directive _should_ emit the value
> in the instruction stream endianness (i.e. LE, regardless of the data
> endianness).

Now I see the RSEQ_CODE value isn't endian-swapped as teh RSEQ_DATA
value is, so the code above is fine.

Sory for the noise.

Thanks,
Mark.