[PATCH v4 1/9] 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: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
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

Signed-off-by: Nadav Amit <namit@xxxxxxxxxx>
---
 Makefile                 |  9 +++++++--
 arch/x86/Makefile        | 11 +++++++++--
 arch/x86/kernel/Makefile |  6 ++++++
 arch/x86/kernel/macros.S |  7 +++++++
 scripts/Kbuild.include   |  4 +++-
 5 files changed, 32 insertions(+), 5 deletions(-)
 create mode 100644 arch/x86/kernel/macros.S

diff --git a/Makefile b/Makefile
index 554dcaddbce4..026586db2f26 100644
--- a/Makefile
+++ b/Makefile
@@ -1085,7 +1085,7 @@ scripts: scripts_basic include/config/auto.conf include/config/tristate.conf \
 # 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:
@@ -1109,7 +1109,9 @@ prepare1: prepare2 $(version_h) $(autoksyms_h) include/generated/utsrelease.h \
                    include/config/auto.conf
 	$(cmd_crmodverdir)
 
-archprepare: archheaders archscripts prepare1 scripts_basic
+macroprepare: prepare1 archmacros
+
+archprepare: archheaders archscripts macroprepare scripts_basic
 
 prepare0: archprepare gcc-plugins
 	$(Q)$(MAKE) $(build)=.
@@ -1214,6 +1216,9 @@ 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 60135cbd905c..6b82314776fd 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -235,8 +235,8 @@ ifdef CONFIG_X86_64
 LDFLAGS += $(call ld-option, -z max-page-size=0x200000)
 endif
 
-# Speed up the build
-KBUILD_CFLAGS += -pipe
+# We cannot use -pipe flag since we give an additional .s file to the compiler
+#KBUILD_CFLAGS += -pipe
 # Workaround for a gcc prelease that unfortunately was shipped in a suse release
 KBUILD_CFLAGS += -Wno-sign-compare
 #
@@ -258,11 +258,18 @@ archscripts: scripts_basic
 archheaders:
 	$(Q)$(MAKE) $(build)=arch/x86/entry/syscalls all
 
+archmacros:
+	$(Q)$(MAKE) $(build)=arch/x86/kernel macros
+
 archprepare:
 ifeq ($(CONFIG_KEXEC_FILE),y)
 	$(Q)$(MAKE) $(build)=arch/x86/purgatory arch/x86/purgatory/kexec-purgatory.c
 endif
 
+ASM_MACRO_FLAGS = -Wa,arch/x86/kernel/macros.s
+export ASM_MACRO_FLAGS
+KBUILD_CFLAGS += $(ASM_MACRO_FLAGS)
+
 ###
 # Kernel objects
 
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 02d6f5cf4e70..fdb6c5b2a922 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -9,6 +9,12 @@ extra-y	+= ebda.o
 extra-y	+= platform-quirks.o
 extra-y	+= vmlinux.lds
 
+$(obj)/macros.s: $(obj)/macros.S FORCE
+	$(call if_changed_dep,cpp_s_S)
+
+macros: $(obj)/macros.s
+	@:
+
 CPPFLAGS_vmlinux.lds += -U$(UTS_MACHINE)
 
 ifdef CONFIG_FUNCTION_TRACER
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 50cee534fd64..ad2c02062aa4 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -189,7 +189,9 @@ __cc-option = $(call try-run-cached,\
 
 # 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)
-- 
2.17.0