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From:   Florian Weimer <fw@deneb.enyo.de>
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc:     Michael Kerrisk <mtk.manpages@gmail.com>,
        libc-alpha <libc-alpha@sourceware.org>,
        carlos <carlos@redhat.com>, Rich Felker <dalias@libc.org>,
        linux-api <linux-api@vger.kernel.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Will Deacon <will.deacon@arm.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ben Maurer <bmaurer@fb.com>, Dave Watson <davejwatson@fb.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Paul <paulmck@linux.vnet.ibm.com>, Paul Turner <pjt@google.com>,
        Joseph Myers <joseph@codesourcery.com>,
        Szabolcs Nagy <szabolcs.nagy@arm.com>
Subject: Re: [PATCH glibc 5/9] glibc: Perform rseq(2) registration at C startup and thread creation (v17)
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Date:   Wed, 29 Apr 2020 14:19:38 +0200
In-Reply-To: <1862775654.72437.1588078588989.JavaMail.zimbra@efficios.com>
        (Mathieu Desnoyers's message of "Tue, 28 Apr 2020 08:56:28 -0400
        (EDT)")
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* Mathieu Desnoyers:

> ----- On Apr 28, 2020, at 8:33 AM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:
>
>> ----- On Apr 28, 2020, at 8:02 AM, Florian Weimer fw@deneb.enyo.de wrote:
>> 
> [...]
>>> 
>>>> x32 should not be an issue as explained above, so I'm very open to
>>>> add this "uptr" for user-space only.
>>> 
>>> Okay, then please use anonymous unions and structs as necessary, to
>>> ensure that the uptr field can be reached on all platforms in the same
>>> way.
>> 
>> OK, will do!
>
> What I came up with looks like this. User-space can use rseq_cs.uptr.ptr
> both on 32-bit and 64-bit to update the pointer:

Agreed, this should work.