Re: [Xen-devel] [PATCH v5 08/12] x86/hyperv: provide Hyper-V hypercall functions

[Wei Liu <wl@xxxxxxx>]

On Fri, Jan 31, 2020 at 04:35:23PM +0100, Jan Beulich wrote:
> On 31.01.2020 15:37, Wei Liu wrote:
> > On Fri, Jan 31, 2020 at 03:24:07PM +0100, Jan Beulich wrote:
> >> On 29.01.2020 21:20, Wei Liu wrote:
> >>> I tried using the asm(".equ ..") trick but hit a problem with %c again.
> >>>
> >>> mm.c:5736:5: error: invalid 'asm': operand is not a condition code, 
> >>> invalid operand code 'c'
> >>>                asm ( ".equ HV_HCALL_PAGE, %c0; .global HV_HCALL_PAGE"
> >>
> >> Would you mind also indicating what the input operand actually
> >> was? According to my looking at gcc sources when you first
> >> mentioned this (on irc iirc), much depends on it actually be
> >> recognizable as a constant by the compiler.
> > 
> > Something along the line:
> > 
> >   asm ( ".equ HV_HCALL_PAGE, %c0; .global HV_HCALL_PAGE"
> >        :: "i" (__fix_x_to_virt(FIX_X_HV...))
> 
> Quite a bit of playing later, %P0 is documented, supported
> already in gcc 4.1.x, and also used in a few cases by Linux.
> %p0 would be another documented alternative, but support for
> this looks to have been introduced later. Not being able to use
> %c0 here still smells like a bug (and I guess I'll enter one.)

OK. Let me try that.

If that turns out successful, do you want me to change the other
instance to %P0 too?

Wei.

> 
> Jan

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