linux-kernel - [PATCH] kconfig: allow to pass optional flag into as-instr macro

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Date:   Tue, 24 Mar 2020 06:57:31 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        "Jason A . Donenfeld" <Jason@...c4.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        clang-built-linux@...glegroups.com
Subject: [PATCH] kconfig: allow to pass optional flag into as-instr macro

Commit 42d519e3d0c0 ("kbuild: Add support for 'as-instr' to be used in
Kconfig files") introduced the Kconfig variant of as-instr.

It is currently used in arch/arm64/Kconfig.

arm and arm64 are simple cases because they are separated by directory,
and GCC also provides a single architecture.

Such architectures as x86, powerpc, sparc, etc. support both 32 and
64 bit kernel in the unified arch directory, and GCC can be biarch.
On such architectures, Kbuild passes -m32 / -m64 flag (or a proper
target triple for Clang) to select the target machine bit.

This commit adds the second parameter to as-instr so you can optionally
pass a compiler flag to evaluate the instruction with.

One example usage of this is for the conversion of the following code
in arch/x86/Makefile:

  adx_instr := $(call as-instr,adox %r10$(comma)%r10,-DCONFIG_AS_ADX=1)

This instruction code should be evaluated by the 64-bit assembler
(r10 is a 64-bit register).

If you use compiler that defaults to 32-bit for building the 64-bit
kernel, -m64 should be passed to invoke the 64-bit assembler.

  config AS_ADX
          def_bool $(as-instr,adox %r10$(comma)%r10,$(m64-flags))

Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
---

 scripts/Kconfig.include | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include
index 496d11c92c97..9b8c98168ba9 100644
--- a/scripts/Kconfig.include
+++ b/scripts/Kconfig.include
@@ -31,9 +31,10 @@ cc-option = $(success,$(CC) -Werror $(CLANG_FLAGS) $(1) -S -x c /dev/null -o /de
 # Return y if the linker supports <flag>, n otherwise
 ld-option = $(success,$(LD) -v $(1))

-# $(as-instr,<instr>)
+# $(as-instr,<instr>,[<flag>])
 # Return y if the assembler supports <instr>, n otherwise
-as-instr = $(success,printf "%b\n" "$(1)" | $(CC) $(CLANG_FLAGS) -c -x assembler -o /dev/null -)
+# You can pass optional <flag> to evaluate <instr> with
+as-instr = $(success,printf "%b\n" "$(1)" | $(CC) $(CLANG_FLAGS) $(2) -c -x assembler -o /dev/null -)

 # check if $(CC) and $(LD) exist
 $(error-if,$(failure,command -v $(CC)),compiler '$(CC)' not found)
-- 
2.17.1