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Re: [PATCH] MIPS: Emulate 64-bit FPU on 64-bit CPUs.

To: David Daney <ddaney@caviumnetworks.com>
Subject: Re: [PATCH] MIPS: Emulate 64-bit FPU on 64-bit CPUs.
From: Ralf Baechle <ralf@linux-mips.org>
Date: Tue, 3 Nov 2009 05:27:12 +0100
Cc: linux-mips@linux-mips.org
In-reply-to: <1257190426-29346-1-git-send-email-ddaney@caviumnetworks.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <1257190426-29346-1-git-send-email-ddaney@caviumnetworks.com>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mutt/1.5.19 (2009-01-05)
On Mon, Nov 02, 2009 at 11:33:46AM -0800, David Daney wrote:

> Running a 64-bit kernel on a 64-bit CPU without an FPU would cause the
> emulator to run in 32-bit mode.  The c0_Status.FR bit is wired to zero
> on systems without an FPU, so using that bit to decide how the
> emulator behaves doesn't allow for proper emulation on 64-bit FPU-less
> processors.
> 
> Instead, we need to select the emulator mode based on the user-space
> ABI.  Since the thread flag TIF_32BIT_REGS is used to set
> c0_Status.FR, we can just use it to decide if the emulator should be
> in 32-bit or 64-bit mode.

Thanks, applied!

  Ralf

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