linux-kernel - Re: [PATCH glibc 5/9] glibc: Perform rseq(2) registration at C startup and thread creation (v17)

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Message-ID: <87368mcwmd.fsf@mid.deneb.enyo.de>
Date:   Wed, 29 Apr 2020 14:19:38 +0200
From:   Florian Weimer <fw@...eb.enyo.de>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Michael Kerrisk <mtk.manpages@...il.com>,
        libc-alpha <libc-alpha@...rceware.org>,
        carlos <carlos@...hat.com>, Rich Felker <dalias@...c.org>,
        linux-api <linux-api@...r.kernel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ben Maurer <bmaurer@...com>, Dave Watson <davejwatson@...com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul <paulmck@...ux.vnet.ibm.com>, Paul Turner <pjt@...gle.com>,
        Joseph Myers <joseph@...esourcery.com>,
        Szabolcs Nagy <szabolcs.nagy@....com>
Subject: Re: [PATCH glibc 5/9] glibc: Perform rseq(2) registration at C startup and thread creation (v17)

* Mathieu Desnoyers:

> ----- On Apr 28, 2020, at 8:33 AM, Mathieu Desnoyers mathieu.desnoyers@...icios.com wrote:
>
>> ----- On Apr 28, 2020, at 8:02 AM, Florian Weimer fw@...eb.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.