Re: [Xen-devel] [PATCH RFC for-4.13 09/10] xen/arm: asm: Replace use of ALTERNATIVE with alternative_if

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 26 Sep 2019, Julien Grall wrote:
> Using alternative_if makes the code a bit more streamlined.
> 
> Take the opportunity to use the new auto-nop infrastructure to avoid
> counting the number of nop in the else part for arch/arm/arm64/entry.S
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> 
> ---
>     This is pretty much a matter of taste, but at least for arm64 this
>     allows us to use the auto-nop infrastructure. So the arm32 is more
>     to keep inline with arm64.
> ---
>  xen/arch/arm/arm32/entry.S | 9 ++++++---
>  xen/arch/arm/arm64/entry.S | 8 +++++---
>  2 files changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/xen/arch/arm/arm32/entry.S b/xen/arch/arm/arm32/entry.S
> index 0b4cd19abd..1428cd3583 100644
> --- a/xen/arch/arm/arm32/entry.S
> +++ b/xen/arch/arm/arm32/entry.S
> @@ -65,9 +65,12 @@ save_guest_regs:
>           * If the SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT has been set in the cpu
>           * feature, the checking of pending SErrors will be skipped.
>           */
> -        ALTERNATIVE("nop",
> -                    "b skip_check",
> -                    SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT)
> +        alternative_if SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT
> +        nop
> +        alternative_else
> +        b   skip_check
> +        alternative_endif

This could be written as:

alternative_if_not SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT
b   skip_check
alternative_else_nop_endif


>          /*
>           * Start to check pending virtual abort in the gap of Guest -> HYP
>           * world switch.
> diff --git a/xen/arch/arm/arm64/entry.S b/xen/arch/arm/arm64/entry.S
> index 458d12f188..91cf6ee6f4 100644
> --- a/xen/arch/arm/arm64/entry.S
> +++ b/xen/arch/arm/arm64/entry.S
> @@ -170,9 +170,11 @@
>           * is not set. If a vSError took place, the initial exception will be
>           * skipped. Exit ASAP
>           */
> -        ALTERNATIVE("bl check_pending_vserror; cbnz x0, 1f",
> -                    "nop; nop",
> -                    SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT)
> +        alternative_if SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT
> +        bl      check_pending_vserror
> +        cbnz    x0, 1f
> +        alternative_else_nop_endif
> +
>          mov     x0, sp
>          bl      enter_hypervisor_from_guest_noirq
>          msr     daifclr, \iflags
> -- 
> 2.11.0
> 

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