Re: [PATCH v5 04/17] x86/acrn: Introduce hypercall interfaces

[Shuo A Liu]

On Mon 19.Oct'20 at 18:15:15 -0400, Arvind Sankar wrote:
> On Mon, Oct 19, 2020 at 02:17:50PM +0800, shuo.a.liu@xxxxxxxxx wrote:
> > From: Shuo Liu <shuo.a.liu@xxxxxxxxx>
> >
> > The Service VM communicates with the hypervisor via conventional
> > hypercalls. VMCALL instruction is used to make the hypercalls.
> >
> > ACRN hypercall ABI:
> >   * Hypercall number is in R8 register.
> >   * Up to 2 parameters are in RDI and RSI registers.
> >   * Return value is in RAX register.
> >
> > Introduce the ACRN hypercall interfaces. Because GCC doesn't support R8
> > register as direct register constraints, use supported constraint as
> > input with a explicit MOV to R8 in beginning of asm.
> >
> > +static inline long acrn_hypercall0(unsigned long hcall_id)
> > +{
> > +	long result;
> > +
> > +	asm volatile("movl %1, %%r8d\n\t"
> > +		     "vmcall\n\t"
> > +		     : "=a" (result)
> > +		     : "ir" (hcall_id)
>
> Is the hypercall id an unsigned long (64 bits) or an unsigned int (32
> bits)? This will generate broken assembly if the "r" option is chosen,
> eg something like
> 	movl %rdi, %r8d

Yes, it can be an unsigned long. So do MOV explicitly.

	asm volatile("movq %1, %%r8\n\t"
		     "vmcall\n\t"
		     : "=a" (result)
		     : "ir" (hcall_id)

Thanks