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Date:   Sun,  7 Jul 2019 01:25:08 +0900
From:   Masahiro Yamada <>
Cc:     Sam Ravnborg <>,
        Masahiro Yamada <>,,,
        Jonathan Corbet <>,
        Michal Marek <>
Subject: [PATCH v2] kbuild: get rid of misleading $(AS) from documents

The assembler files in the kernel are *.S instead of *.s, so they must
be preprocessed. Since 'as' of GNU binutils is not able to preprocess,
we always use $(CC) as an assembler driver.

$(AS) is almost unused in Kbuild. As of writing, there is just one place
that directly invokes $(AS).

  $ git grep -e '$(AS)' -e '${AS}' -e '$AS' -e '$(AS:' -e '${AS:' -- :^Documentation
  drivers/net/wan/Makefile:  AS68K = $(AS)

The documentation about *_AFLAGS* sounds like the flags were passed
to $(AS). This is somewhat misleading.

Signed-off-by: Masahiro Yamada <>
Reviewed-by: Nathan Chancellor <>

Changes in v2:
  - Rephrase without using "assembling"

 Documentation/kbuild/kbuild.txt    |  5 ++---
 Documentation/kbuild/makefiles.txt | 12 ++++++------
 2 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/Documentation/kbuild/kbuild.txt b/Documentation/kbuild/kbuild.txt
index 9c230ea71963..2c6188abb213 100644
--- a/Documentation/kbuild/kbuild.txt
+++ b/Documentation/kbuild/kbuild.txt
@@ -31,12 +31,11 @@ Additional options to the assembler (for built-in and modules).
-Additional module specific options to use for $(AS).
+Additional assembler options for modules.
-Additional options for $(AS) when used for assembler
-code for code that is compiled as built-in.
+Additional assembler options for built-in.
diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
index d65ad5746f94..895bbbf38a0c 100644
--- a/Documentation/kbuild/makefiles.txt
+++ b/Documentation/kbuild/makefiles.txt
@@ -306,7 +306,7 @@ more details, with real examples.
 	variable $(KBUILD_CFLAGS) and uses it for compilation flags for the
 	entire tree.
-	asflags-y specifies options for assembling with $(AS).
+	asflags-y specifies assembler options.
@@ -441,7 +441,7 @@ more details, with real examples.
 	as-instr checks if the assembler reports a specific instruction
 	and then outputs either option1 or option2
 	C escapes are supported in the test instruction
-	Note: as-instr-option uses KBUILD_AFLAGS for $(AS) options
+	Note: as-instr-option uses KBUILD_AFLAGS for assembler options
 	cc-option is used to check if $(CC) supports a given option, and if
@@ -814,7 +814,7 @@ When kbuild executes, the following steps are followed (roughly):
 	In this example, the binary $(obj)/image is a binary version of
 	vmlinux. The usage of $(call if_changed,xxx) will be described later.
-    KBUILD_AFLAGS		$(AS) assembler flags
+    KBUILD_AFLAGS		assembler flags
 	Default value - see top level Makefile
 	Append or modify as required per architecture.
@@ -853,15 +853,15 @@ When kbuild executes, the following steps are followed (roughly):
 	The first example utilises the trick that a config option expands
 	to 'y' when selected.
-    KBUILD_AFLAGS_KERNEL	$(AS) options specific for built-in
+    KBUILD_AFLAGS_KERNEL	Assembler options specific for built-in
 	$(KBUILD_AFLAGS_KERNEL) contains extra C compiler flags used to compile
 	resident kernel code.
-    KBUILD_AFLAGS_MODULE   Options for $(AS) when building modules
+    KBUILD_AFLAGS_MODULE   Assembler options specific for modules
 	$(KBUILD_AFLAGS_MODULE) is used to add arch-specific options that
-	are used for $(AS).
+	are used for assembler.
 	From commandline AFLAGS_MODULE shall be used (see kbuild.txt).
     KBUILD_CFLAGS_KERNEL	$(CC) options specific for built-in

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