[PATCH v9 02/10] Makefile: Prepare for using macros for inline asm

[Nadav Amit]

Using macros for inline assembly improves both readability and
compilation decisions that are distorted by big assembly blocks that use
alternative sections. Compile macros.S and use it to assemble all C
files. Currently, only x86 will use it.

Cc: Sam Ravnborg <sam@xxxxxxxxxxxx>
Cc: Michal Marek <michal.lkml@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-kbuild@xxxxxxxxxxxxxxx
Acked-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Tested-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Nadav Amit <namit@xxxxxxxxxx>
---
 Makefile                 | 9 +++++++--
 arch/x86/Makefile        | 7 +++++++
 arch/x86/kernel/macros.S | 7 +++++++
 scripts/Kbuild.include   | 4 +++-
 scripts/mod/Makefile     | 2 ++
 5 files changed, 26 insertions(+), 3 deletions(-)
 create mode 100644 arch/x86/kernel/macros.S

diff --git a/Makefile b/Makefile
index 6c3da3e10f07..6c40d547513c 100644
--- a/Makefile
+++ b/Makefile
@@ -1071,7 +1071,7 @@ scripts: scripts_basic asm-generic gcc-plugins $(autoksyms_h)
 # version.h and scripts_basic is processed / created.
 
 # Listed in dependency order
-PHONY += prepare archprepare prepare0 prepare1 prepare2 prepare3
+PHONY += prepare archprepare macroprepare prepare0 prepare1 prepare2 prepare3
 
 # prepare3 is used to check if we are building in a separate output directory,
 # and if so do:
@@ -1094,7 +1094,9 @@ prepare2: prepare3 outputmakefile asm-generic
 prepare1: prepare2 $(version_h) $(autoksyms_h) include/generated/utsrelease.h
 	$(cmd_crmodverdir)
 
-archprepare: archheaders archscripts prepare1 scripts_basic
+macroprepare: prepare1 archmacros
+
+archprepare: archheaders archscripts macroprepare scripts_basic
 
 prepare0: archprepare gcc-plugins
 	$(Q)$(MAKE) $(build)=.
@@ -1162,6 +1164,9 @@ archheaders:
 PHONY += archscripts
 archscripts:
 
+PHONY += archmacros
+archmacros:
+
 PHONY += __headers
 __headers: $(version_h) scripts_basic uapi-asm-generic archheaders archscripts
 	$(Q)$(MAKE) $(build)=scripts build_unifdef
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 8f6e7eb8ae9f..18a0084f134b 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -237,6 +237,13 @@ archscripts: scripts_basic
 archheaders:
 	$(Q)$(MAKE) $(build)=arch/x86/entry/syscalls all
 
+archmacros:
+	$(Q)$(MAKE) $(build)=arch/x86/kernel arch/x86/kernel/macros.s
+
+ASM_MACRO_FLAGS = -Wa,arch/x86/kernel/macros.s -Wa,-
+export ASM_MACRO_FLAGS
+KBUILD_CFLAGS += $(ASM_MACRO_FLAGS)
+
 ###
 # Kernel objects
 
diff --git a/arch/x86/kernel/macros.S b/arch/x86/kernel/macros.S
new file mode 100644
index 000000000000..cfc1c7d1a6eb
--- /dev/null
+++ b/arch/x86/kernel/macros.S
@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * This file includes headers whose assembly part includes macros which are
+ * commonly used. The macros are precompiled into assmebly file which is later
+ * assembled together with each compiled file.
+ */
diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index ce53639a864a..8aeb60eb6ee3 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -115,7 +115,9 @@ __cc-option = $(call try-run,\
 
 # Do not attempt to build with gcc plugins during cc-option tests.
 # (And this uses delayed resolution so the flags will be up to date.)
-CC_OPTION_CFLAGS = $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS))
+# In addition, do not include the asm macros which are built later.
+CC_OPTION_FILTERED = $(GCC_PLUGINS_CFLAGS) $(ASM_MACRO_FLAGS)
+CC_OPTION_CFLAGS = $(filter-out $(CC_OPTION_FILTERED),$(KBUILD_CFLAGS))
 
 # cc-option
 # Usage: cflags-y += $(call cc-option,-march=winchip-c6,-march=i586)
diff --git a/scripts/mod/Makefile b/scripts/mod/Makefile
index 42c5d50f2bcc..a5b4af47987a 100644
--- a/scripts/mod/Makefile
+++ b/scripts/mod/Makefile
@@ -4,6 +4,8 @@ OBJECT_FILES_NON_STANDARD := y
 hostprogs-y	:= modpost mk_elfconfig
 always		:= $(hostprogs-y) empty.o
 
+CFLAGS_REMOVE_empty.o := $(ASM_MACRO_FLAGS)
+
 modpost-objs	:= modpost.o file2alias.o sumversion.o
 
 devicetable-offsets-file := devicetable-offsets.h
-- 
2.17.1