Re: [Xen-devel] [PATCH 2/3] mini-os: cleanup x86_64.S

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 26/08/16 15:35, Juergen Gross wrote:
> arch/x86/x86_64.S contains some unnecessary macros. Remove them.
>
> Add a SAVE_PARAVIRT macro for saving %rcx and %r11 on the stack in
> case of CONFIG_PARAVIRT defined.
>
> Remove the parameter from HYPERVISOR_IRET macro as it is used with
> 0 only.
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
>   arch/x86/x86_64.S | 44 ++++++++++++++++----------------------------
>   1 file changed, 16 insertions(+), 28 deletions(-)
>
> diff --git a/arch/x86/x86_64.S b/arch/x86/x86_64.S
> index 2046187..3a7116f 100644
> --- a/arch/x86/x86_64.S
> +++ b/arch/x86/x86_64.S
> @@ -45,21 +45,10 @@ hypercall_page:
>   
>   
>   #define XEN_GET_VCPU_INFO(reg)	movq HYPERVISOR_shared_info,reg
> -#define XEN_PUT_VCPU_INFO(reg)
> -#define XEN_PUT_VCPU_INFO_fixup
>   #define XEN_LOCKED_BLOCK_EVENTS(reg)  movb $1,evtchn_upcall_mask(reg)
>   #define XEN_LOCKED_UNBLOCK_EVENTS(reg)        movb $0,evtchn_upcall_mask(reg)
>   #define XEN_TEST_PENDING(reg) testb $0xFF,evtchn_upcall_pending(reg)
>   
> -#define XEN_BLOCK_EVENTS(reg)	XEN_GET_VCPU_INFO(reg)			; \
> -                                       XEN_LOCKED_BLOCK_EVENTS(reg)    ; \
> -                                           XEN_PUT_VCPU_INFO(reg)
> -
> -#define XEN_UNBLOCK_EVENTS(reg)        XEN_GET_VCPU_INFO(reg)                  
> ; \
> -                                               XEN_LOCKED_UNBLOCK_EVENTS(reg)  
> ; \
> -                                       XEN_PUT_VCPU_INFO(reg)
> -
> -
>   /* Offsets into shared_info_t. */
>   #define evtchn_upcall_pending         /* 0 */
>   #define evtchn_upcall_mask            1
> @@ -77,12 +66,16 @@ KERNEL_CS_MASK = 0xfc
>   
>   
>   /* Macros */
> +.macro SAVE_PARAVIRT
> +#ifdef CONFIG_PARAVIRT
> +       movq (%rsp),%rcx
> +       movq 8(%rsp),%r11
> +       addq $0x10,%rsp /* rsp points to the error code */iwt
I know this is just moving code, but I would recommend switching to a 
pop %rcx; pop %r11, which is shorter and more efficient.
It also plays better in the stack engine with the adjacent pushes/pops.

~Andrew

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