[PATCH v3 04/18] arm64: assembler: user_alt label optional

[Mark Rutland]

On Thu, May 20, 2021 at 01:43:52PM +0100, Fuad Tabba wrote:
> Make the label for the extable entry in user_alt optional, only
> generating an extable entry if provided.
> 
> This is needed later in the series, to avoid instruction
> duplication in the assembly code.
> 
> While at it, clean up the label used to be globally unique using
> \@ as for other macros.

Nice; thanks for cleaning up the labels too!

> 
> Signed-off-by: Fuad Tabba <tabba at google.com>
> ---
>  arch/arm64/include/asm/alternative-macros.h | 9 ++++++---
>  arch/arm64/mm/cache.S                       | 2 +-
>  2 files changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/alternative-macros.h b/arch/arm64/include/asm/alternative-macros.h
> index 8a078fc662ac..01ef954c9b2d 100644
> --- a/arch/arm64/include/asm/alternative-macros.h
> +++ b/arch/arm64/include/asm/alternative-macros.h
> @@ -197,9 +197,12 @@ alternative_endif
>  #define _ALTERNATIVE_CFG(insn1, insn2, cap, cfg, ...)	\
>  	alternative_insn insn1, insn2, cap, IS_ENABLED(cfg)
>  
> -.macro user_alt, label, oldinstr, newinstr, cond
> -9999:	alternative_insn "\oldinstr", "\newinstr", \cond
> -	_asm_extable 9999b, \label
> +.macro user_alt, oldinstr, newinstr, cond, label
> +.Lextable_\@:
> +	alternative_insn "\oldinstr", "\newinstr", \cond
> +	.ifnc \label,
> +	_asm_extable .Lextable_\@, \label
> +	.endif
>  .endm

We can use _cond_extable here to simplify this to:

| .macro user_alt, oldinstr, newinstr, cond, label
| .Lextable_\@:
| 	alternative_insn "\oldinstr", "\newinstr", \cond
| 	_cond_extable .Lextable_\@, \label
| .endm

However, since we only use user_alt in __flush_icache_range /
__flush_cache_user_range, I reckon it would be simpler overall to have
those use alternative_insn and _cond_extable directly. Then that would
align with the style of the *_by_line macros, and we could delete
user_alt.

Either way, this looks good, so:

Acked-by: Mark Rutland <mark.rutland at arm.com>

>  
>  #endif  /*  __ASSEMBLY__  */
> diff --git a/arch/arm64/mm/cache.S b/arch/arm64/mm/cache.S
> index 2d881f34dd9d..5ff8dfa86975 100644
> --- a/arch/arm64/mm/cache.S
> +++ b/arch/arm64/mm/cache.S
> @@ -47,7 +47,7 @@ alternative_else_nop_endif
>  	sub	x3, x2, #1
>  	bic	x4, x0, x3
>  1:
> -user_alt 9f, "dc cvau, x4",  "dc civac, x4",  ARM64_WORKAROUND_CLEAN_CACHE
> +user_alt "dc cvau, x4",  "dc civac, x4",  ARM64_WORKAROUND_CLEAN_CACHE, 9f
>  	add	x4, x4, x2
>  	cmp	x4, x1
>  	b.lo	1b
> -- 
> 2.31.1.751.gd2f1c929bd-goog
>