linux-kernel - Re: [RFC PATCH 2/4] rseq: Allow extending struct rseq

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Date:   Wed, 15 Jul 2020 10:54:06 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Florian Weimer <fweimer@...hat.com>
Cc:     carlos <carlos@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        paulmck <paulmck@...ux.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        "H. Peter Anvin" <hpa@...or.com>, Paul Turner <pjt@...gle.com>,
        linux-api <linux-api@...r.kernel.org>,
        Christian Brauner <christian.brauner@...ntu.com>
Subject: Re: [RFC PATCH 2/4] rseq: Allow extending struct rseq

----- On Jul 15, 2020, at 9:42 AM, Florian Weimer fweimer@...hat.com wrote:
> * Mathieu Desnoyers:
> 
[...]
>> How would this allow early-rseq-adopter libraries to interact with
>> glibc ?
> 
> Under all extension proposals I've seen so far, early adopters are
> essentially incompatible with glibc rseq registration.  I don't think
> you can have it both ways.

The basic question I'm not sure about is whether we are allowed to increase
the size and alignement of __rseq_abi from e.g. glibc 2.32 to glibc 2.33.
If not, then we just need to find another way to extend struct rseq, e.g. by
adding a pointer to another extended structure in the padding space we
have at the end of struct rseq.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com