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

[Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>]

Julien Grall writes:

> 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
> +
for the arm32 code you can have my r-b:
Reviewed-By: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>

>          /*
>           * 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
> +
You asked other people to do not introduce new code in one patch and
rewrite it in the following patch. But there you are doing exactly the
same. I believe, it is possible to move all "alternative" patches to the
very beginning of the patch series and only then introduce macro
guest_vector.

>          mov     x0, sp
>          bl      enter_hypervisor_from_guest_noirq
>          msr     daifclr, \iflags


--
Volodymyr Babchuk at EPAM
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