[PATCH v1 2/2] RISC-V: make TOOLCHAIN_NEEDS_SPEC_20191213 gas only

[Conor Dooley <conor@kernel.org>]

From: Conor Dooley <conor.dooley@microchip.com>

Quoting the llvm docs:
> Between versions 2.0 and 2.1 of the base I specification, a backwards
> incompatible change was made to remove selected instructions and CSRs
> from the base ISA. These instructions were grouped into a set of new
> extensions, but were no longer required by the base ISA. (snip) LLVM
> currently implements version 2.0 of the base specification. Thus,
> instructions from these extensions are accepted as part of the base
> ISA.

There is therefore no need (at present!) to carry out a $cc-option
check, and instead just gate presence of zicsr and zifencei in march
on the version of binutils that commit 6df2a016c0c8 ("riscv: fix build
with binutils 2.38") highlights as the introduction of the requirement.

In fact, the status quo creates some issues with mixed llvm/binutils
builds, specifically building with llvm-17 and ld from binutils-2.35.
Odd combo you may think, but this is what tuxsuite's debian stable uses
while testing 5.10 stable kernels as doesn't support LLD.

CC: stable@vger.kernel.org # needs RISC-V: move zicsr/zifencei spec version check to Kconfi
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Link: https://lore.kernel.org/all/CA+G9fYt9T=ELCLaB9byxaLW2Qf4pZcDO=huCA0D8ug2V2+irJQ@mail.gmail.com/
Suggested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
---
 arch/riscv/Kconfig | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 4eb0ef8314b3..c6902f4c5650 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -291,8 +291,7 @@ endchoice
 config TOOLCHAIN_NEEDS_SPEC_20191213
 	bool
 	default y
-	depends on !64BIT || $(cc-option,-mabi=lp64 -march=rv64ima_zicsr_zifencei)
-	depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zicsr_zifencei)
+	depends on AS_IS_GNU && AS_VERSION >= 23800
 	help
 	  Newer binutils versions default to ISA spec version 20191213 which
 	  moves some instructions from the I extension to the Zicsr and Zifencei
-- 
2.39.1