[PATCH v2 8/9] x86: add comments about the binutils version to support code in as-instr

[Masahiro Yamada <masahiroy@kernel.org>]

We raise the minimal supported binutils version from time to time.
The last bump was commit 1fb12b35e5ff ("kbuild: Raise the minimum
required binutils version to 2.21").

We need to keep these as-instr checks because binutils 2.21 does not
support them.

I hope this will be a good hint which one can be dropped when we
bump the minimal binutils version next time.

As for the Clang/LLVM builds, we require very new LLVM version,
so the LLVM integrated assembler supports all of them.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Jason A. Donenfeld <Jason@zx2c4.com>
---

Changes in v2: None

 arch/x86/Makefile | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index f32ef7b8d5ca..4c57cb3018fb 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -178,10 +178,15 @@ ifeq ($(ACCUMULATE_OUTGOING_ARGS), 1)
 endif
 
 # does binutils support specific instructions?
+# binutils >= 2.22
 avx2_instr :=$(call as-instr,vpbroadcastb %xmm0$(comma)%ymm1,-DCONFIG_AS_AVX2=1)
+# binutils >= 2.25
 avx512_instr :=$(call as-instr,vpmovm2b %k1$(comma)%zmm5,-DCONFIG_AS_AVX512=1)
+# binutils >= 2.24
 sha1_ni_instr :=$(call as-instr,sha1msg1 %xmm0$(comma)%xmm1,-DCONFIG_AS_SHA1_NI=1)
+# binutils >= 2.24
 sha256_ni_instr :=$(call as-instr,sha256msg1 %xmm0$(comma)%xmm1,-DCONFIG_AS_SHA256_NI=1)
+# binutils >= 2.23
 adx_instr := $(call as-instr,adox %r10$(comma)%r10,-DCONFIG_AS_ADX=1)
 
 KBUILD_AFLAGS += $(avx2_instr) $(avx512_instr) $(sha1_ni_instr) $(sha256_ni_instr) $(adx_instr)
-- 
2.17.1