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From: hch@infradead.org (Christoph Hellwig)
To: linux-riscv@lists.infradead.org
Subject: On Supporting no-FPU machines
Date: Wed, 13 Jun 2018 00:20:12 -0700	[thread overview]
Message-ID: <20180613072012.GA5293@infradead.org> (raw)
In-Reply-To: <CAK8P3a1bC1PgkV6n=HkSB7EnbEWGZYUo8CsDWtUh-xoLWg+rpA@mail.gmail.com>

On Wed, Jun 13, 2018 at 08:47:00AM +0200, Arnd Bergmann wrote:
> > A separate CONFIG_FPU to not build the FPU code sounds fine to me
> > as long as it defaults to on.
> 
> If we do this, that option must also take care to disable the FPU hardware
> if it exists. Otherwise you might run into the situation of having a system
> intended to run without FPU access but a task uses FPU registers anyway
> (e.g. because the compiler decides it is faster that way on the
> microarchitecture it is optimizing for) and we fail to save/restore the FPU
> state between task switches.

I'm not sure we can force this.  It would require a write to misa,
which requires M-mode privileges.

  reply	other threads:[~2018-06-13  7:20 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-13  6:26 On Supporting no-FPU machines Alan Kao
2018-06-13  6:32 ` Christoph Hellwig
2018-06-13  6:47   ` Arnd Bergmann
2018-06-13  7:20     ` Christoph Hellwig [this message]
2018-06-13  7:20       ` Christoph Hellwig
2018-06-13 12:29         ` Arnd Bergmann
2018-06-13 16:49           ` Darius Rad
2018-06-14  0:25           ` Alan Kao
2018-06-15 20:38 ` Palmer Dabbelt
2018-06-15 23:42   ` Andrew Waterman

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