[PATCH -next v16 19/20] riscv: detect assembler support for .option arch

[Conor Dooley]

On Thu, Mar 23, 2023 at 02:59:23PM +0000, Andy Chiu wrote:
> Some extensions use .option arch directive to selectively enable certain
> extensions in parts of its assembly code. For example, Zbb uses it to
> inform assmebler to emit bit manipulation instructions. However,
> supporting of this directive only exist on GNU assembler and has not
> landed on clang at the moment, making TOOLCHAIN_HAS_ZBB depend on
> AS_IS_GNU.
> 
> While it is still under review at https://reviews.llvm.org/D123515, the
> upcoming Vector patch also requires this feature in assembler. Thus,
> provide Kconfig AS_HAS_OPTION_ARCH to detect such feature. Then
> TOOLCHAIN_HAS_XXX will be turned on automatically when the feature land.
> 
> Suggested-by: Nathan Chancellor <nathan at kernel.org>
> Signed-off-by: Andy Chiu <andy.chiu at sifive.com>
> ---
>  arch/riscv/Kconfig | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 36a5b6fed0d3..4f8fd4002f1d 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -244,6 +244,12 @@ config RISCV_DMA_NONCOHERENT
>  config AS_HAS_INSN
>  	def_bool $(as-instr,.insn r 51$(comma) 0$(comma) 0$(comma) t0$(comma) t0$(comma) zero)
>  
> +config AS_HAS_OPTION_ARCH
> +	# https://reviews.llvm.org/D123515
> +	def_bool y
> +	depends on $(as-instr, .option arch$(comma) +m)
> +	depends on !$(as-instr, .option arch$(comma) -i)

Oh cool, I didn't expect this to work given what Nathan said in his
mail, but I gave it a whirl and it does seem to.
I suppose:
Reviewed-by: Conor Dooley <conor.dooley at microchip.com>

I'd rather it be this way so that it is "hands off", as opposed to the
version check that would need updating in the future. And I guess it
means that support for V & IAS will automatically turn on for stable
kernels too once the LLVM change lands, which is nice ;)

Thanks Andy!

> +
>  source "arch/riscv/Kconfig.socs"
>  source "arch/riscv/Kconfig.errata"
>  
> @@ -442,7 +448,7 @@ config TOOLCHAIN_HAS_ZBB
>  	depends on !64BIT || $(cc-option,-mabi=lp64 -march=rv64ima_zbb)
>  	depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zbb)
>  	depends on LLD_VERSION >= 150000 || LD_VERSION >= 23900
> -	depends on AS_IS_GNU
> +	depends on AS_HAS_OPTION_ARCH
>  
>  config RISCV_ISA_ZBB
>  	bool "Zbb extension support for bit manipulation instructions"
> -- 
> 2.17.1
> 
> 
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