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

[Shuo A Liu]

On Mon 19.Oct'20 at 22:08:51 -0400, Arvind Sankar wrote:
> On Tue, Oct 20, 2020 at 09:38:09AM +0800, Shuo A Liu wrote:
> > 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
>
> All the hypercall ID's defined seem to be only 32 bits though?

Yes, they are.
The paramter is unsigned long, use movq to align it.