linux-kernel - RE: [RFC PATCH v2 1/2] rseq: x86: implement abort-at-ip extension

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Date:   Wed, 12 Jan 2022 14:58:14 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Mathieu Desnoyers' <mathieu.desnoyers@...icios.com>,
        Christian Brauner <christian.brauner@...ntu.com>
CC:     Christian Brauner <brauner@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        paulmck <paulmck@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
        "H. Peter Anvin" <hpa@...or.com>, Paul Turner <pjt@...gle.com>,
        linux-api <linux-api@...r.kernel.org>,
        Florian Weimer <fw@...eb.enyo.de>, carlos <carlos@...hat.com>
Subject: RE: [RFC PATCH v2 1/2] rseq: x86: implement abort-at-ip extension

>  * [*] The openrisc, powerpc64 and x86-64 architectures define a "redzone" as a
>  *     stack area beyond the stack pointer which can be used by the compiler
>  *     to store local variables in leaf functions.

I wonder if that is really worth the trouble it causes!
By the time a function is spilling values to stack the cost
of a %sp update is almost certainly noise.

Someone clearly thought it was a 'good idea (tm)'.

	David

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