linux-kernel - Re: [PATCH v2] spi: bcm2835: Enable shared interrupt support

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200605152739.GH5413@sirena.org.uk>
Date:   Fri, 5 Jun 2020 16:27:39 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Scott Branden <sbranden@...adcom.com>, lukas@...ner.de,
        Ray Jui <rjui@...adcom.com>, linux-kernel@...r.kernel.org,
        "open list:SPI SUBSYSTEM" <linux-spi@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "maintainer:BROADCOM BCM281XX/BCM11XXX/BCM216XX ARM ARCHITE..." 
        <bcm-kernel-feedback-list@...adcom.com>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>,
        Martin Sperl <kernel@...tin.sperl.org>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Subject: Re: [PATCH v2] spi: bcm2835: Enable shared interrupt support

On Fri, Jun 05, 2020 at 03:41:27PM +0100, Robin Murphy wrote:

> Ha, and in fact having checked a build out of curiosity, this patch as-is
> actually stands to make things considerably worse. At least with GCC 8.3 and
> bcm2835_defconfig, bcm2835_spi_interrupt_common() doesn't get inlined, which
> means bcm2835_spi_interrupt() pushes/pops a stack frame and makes an
> out-of-line call to bcm2835_spi_interrupt_common(), resulting in massively
> *more* work than the extra two instructions of simply inlining the test.

Whichever compiler I was using (clang-11 probably) did manage to inline
the tail call so it really was the two instructions but yeah, in general
this approach is going to be fragile.

> So yes, the overhead of inlining the test vs. the alternative is indeed
> non-zero. It's just also negative :D

And variable!

Download attachment "signature.asc" of type "application/pgp-signature" (489 bytes)