linux-kernel - Re: [RFC PATCH v2 04/10] lib: vdso: get pointer to vdso data from the arch

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Message-ID: <20191224144621.GG4505@gate.crashing.org>
Date:   Tue, 24 Dec 2019 08:46:21 -0600
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     christophe leroy <christophe.leroy@....fr>,
        Arnd Bergmann <arnd@...db.de>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:MIPS" <linux-mips@...r.kernel.org>,
        Paul Mackerras <paulus@...ba.org>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH v2 04/10] lib: vdso: get pointer to vdso data from the arch

On Tue, Dec 24, 2019 at 08:15:11PM +0800, Andy Lutomirski wrote:
> Does power have PC-relative data access?  If so, I wonder if the code can be arranged so that even the array accesses don’t require computing an absolute address at any point.

Not before ISA 3.0 (that is Power9).

The bcl/mflr dance isn't *that* expensive, if you use it sparingly.


Segher