Re: [PATCH v2 3/6] xen/riscv: introduce function for physical offset calculation

[Julien Grall <julien@xxxxxxx>]

On 07/07/2023 10:12, Oleksii wrote:
> On Thu, 2023-07-06 at 13:18 +0200, Jan Beulich wrote:
> > On 19.06.2023 15:34, Oleksii Kurochko wrote:
> > > --- a/xen/arch/riscv/riscv64/head.S
> > > +++ b/xen/arch/riscv/riscv64/head.S
> > > @@ -29,6 +29,8 @@ ENTRY(start)
> > >   
> > >           jal     reset_stack
> > >   
> > > +        jal     calc_phys_offset
> > > +
> > >           tail    start_xen
> > >   
> > >           .section .text, "ax", %progbits
> > Since you call a C function, the code to save/restore a0/a1 needs to
> > move here (from patch 4).
> Thanks. It makes sense.
> It would be better to move save/restore a0/a1 ( from patch 4 )code
> here.
>
> The only one reason I didn't do that before that calc_phys_offset
> doesn't touch that and it is guaranteed that it will not ( as it
> doesn't have arguments )
IIUC, the calling convention requires a0/a1 to be caller saved. So even 
if they are not used for arguments, such callee is still free to use 
them for internal purpose.
Cheers,

--
Julien Grall