kconfig: allow to pass optional flag into as-instr macro
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Message ID 20200323215732.13339-1-masahiroy@kernel.org
State New
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Series
  • kconfig: allow to pass optional flag into as-instr macro
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Commit Message

Masahiro Yamada March 23, 2020, 9:57 p.m. UTC
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@kernel.org>
---

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

Comments

Jason A. Donenfeld March 23, 2020, 10:20 p.m. UTC | #1
On Mon, Mar 23, 2020 at 3:58 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> 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@kernel.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

This looks fine to me, and might be useful down the line in the
future. But for the ADX situation, I wound up just going with the
bicompatible register:

https://git.zx2c4.com/linux-dev/commit/?h=jd/kconfig-assembler-support&id=c81d9c743d058ef9013fbf8661d071ac9d574472

+# binutils >= 2.23
+config AS_ADX
+ def_bool $(as-instr,adox %eax$(comma)%eax)

This seems to work. But it also doesn't matter much, as it gets
removed anyway during the binutils 2.23 bump:

https://git.zx2c4.com/linux-dev/commit/?h=jd/kconfig-assembler-support&id=c95d6f2ce88722eeb86d54f206bd7599bdc51e1d

Patch
diff mbox series

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)