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From: Richard Henderson <richard.henderson@linaro.org>
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Date: Wed, 1 Aug 2018 09:54:48 -0400
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Subject: Re: [Qemu-devel] [RFC] target/mips: Initial support for MIPS R5900
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To: Fredrik Noring <noring@nocrew.org>, "Maciej W. Rozycki" <macro@linux-mips.org>, Aurelien Jarno <aurelien@aurel32.net>, Aleksandar Markovic <aleksandar.markovic@mips.com>
Cc: =?UTF-8?Q?J=c3=bcrgen_Urban?= <JuergenUrban@gmx.de>, qemu-devel@nongnu.org

On 08/01/2018 09:39 AM, Fredrik Noring wrote:
>  Can QEMU be instructed to emulate
> the FPU only for Linux user space programs as opposed to hardware emulation?

Yes, that can be done.  I would suggest something like

/*
 * Hardware traps to the operating system for emulation.
 * For user-only, qemu is the operating system, so we
 * emulate the trap and emulate by simply emulating the
 * instruction directly.
 */
#ifdef CONFIG_USER_ONLY
# define CP0C1_FP_USER_ONLY  (1 << CP0C1_FP)
#else
# define CP0C1_FP_USER_ONLY  0
#endif

and include that in your initialization of CP0_Config1.


r~