Re: [PATCH -next v21 23/27] riscv: detect assembler support for .option arch

Nathan Chancellor
2023-06-05T15:49:22Z

Hi Andy,

On Mon, Jun 05, 2023 at 11:07:20AM +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.

Just an FYI, this change has landed in LLVM main, so it should be in
LLVM 17 in a few months:

https://github.com/llvm/llvm-project/commit/9e8ed3403c191ab9c4903e8eeb8f732ff8a43cb4

If you have to spin another revision for some reason, consider updating
the Phabricator link to that one, as I expect that link to remain more
stable in the long run over the Phabricator one, as LLVM is planning to
eventually move away from Phabricator to GitHub pull requests. I don't
think this is worth respinning on its own (obviously, heh).

The rest of the change still looks good to me, thanks again for taking
this up.

> Suggested-by: Nathan Chancellor <nathan@kernel.org>
> Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
> Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
> Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> Reviewed-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
> Tested-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
> ---
> arch/riscv/Kconfig | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 348c0fa1fc8c..1019b519d590 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -262,6 +262,12 @@ 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)
> +
> source "arch/riscv/Kconfig.socs"
> source "arch/riscv/Kconfig.errata"
>
> @@ -466,7 +472,7 @@ 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
>