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Date:   Thu, 18 Apr 2019 14:48:34 +0000
From:   Joseph Myers <joseph@codesourcery.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC:     Will Deacon <will.deacon@arm.com>, carlos <carlos@redhat.com>,
        Florian Weimer <fweimer@redhat.com>,
        Szabolcs Nagy <szabolcs.nagy@arm.com>,
        libc-alpha <libc-alpha@sourceware.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ben Maurer <bmaurer@fb.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        Dave Watson <davejwatson@fb.com>, Paul Turner <pjt@google.com>,
        Rich Felker <dalias@libc.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-api <linux-api@vger.kernel.org>
Subject: Re: [PATCH 1/5] glibc: Perform rseq(2) registration at C startup
 and thread creation (v8)
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On Thu, 18 Apr 2019, Mathieu Desnoyers wrote:

> The approach above should work for arm32 be8 vs be32 linker weirdness.
> 
> For aarch64, I think we can simply do:
> 
> /*
>  * 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 __ARM_BIG_ENDIAN
> #define RSEQ_SIG_DATA   0x00bc28d4      /* BRK #0x45E0.  */
> #else
> #define RSEQ_SIG_DATA   RSEQ_SIG_CODE
> #endif
> 
> #define RSEQ_SIG        RSEQ_SIG_DATA
> 
> Feedback is most welcome,

You'll also need __ASSEMBLER__ conditionals in the installed sys/rseq.h 
header so that it only defines constants and doesn't include any C 
declarations in that case, if RSEQ_SIG_CODE is meant to be usable in .S 
files rather than just inline asm in C files.

-- 
Joseph S. Myers
joseph@codesourcery.com