Re: [PATCH] i386: fix merge mistake in i387.c

[Ingo Molnar <mingo@elte.hu>]

* Jan Beulich <jbeulich@novell.com> wrote:

> convert_fxsr_to_user() in 2.6.24's i387_32.c did this, and 
> convert_to_fxsr() also does the inverse, so I assume it's an oversight 
> that it is no longer being done.

thanks Jan, applied.

> -	env->fcs = fxsave->fcs;
> +	env->fcs = (u16) fxsave->fcs | ((u32) fxsave->fop << 16);

we encode it this way because there's no space for the 'FPU Last 
Instruction Opcode' (->fop) field in the legacy user_i387_ia32_struct 
that ptrace PTRACE_GETFPREGS/PTRACE_SETFPREGS uses.

it's probably pure legacy - i'd be surprised if any user-space relied on 
the FPU Last Opcode in any way. But indeed we used to do it previously 
so the most conservative thing is to preserve that piece of information.

FXRESTORE ignores the FOP field so the "restore" direction is 
meaningless:

    fxsave->fop = (u16) ((u32) env->fcs >> 16);

	Ingo