[PATCH] kbuild: use ?= to assign CROSS_COMPILE by arch-Makefile

[Masahiro Yamada <masahiroy@kernel.org>]

Use ?= operator to let arch/*/Makefile to assign CROSS_COMPILE only
when CROSS_COMPILE is undefined.

This allows arch-Makefiles to drop the ifeq ($(CROSS_COMPILE),)
conditional.

This slightly changes the behavior; the arch-Makefile previously
overrode CROSS_COMPILE when CROSS_COMPILE has already been made empty
via an environment variable as in 'export CROSS_COMPILE='.

With this commit, arch-Makefle will respect the user's environment
set-up, which seems to be a more correct behavior.

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

 arch/arc/Makefile    | 4 +---
 arch/h8300/Makefile  | 4 +---
 arch/m68k/Makefile   | 4 +---
 arch/mips/Makefile   | 4 +---
 arch/parisc/Makefile | 6 ++----
 arch/sh/Makefile     | 4 +---
 6 files changed, 7 insertions(+), 19 deletions(-)

diff --git a/arch/arc/Makefile b/arch/arc/Makefile
index 4392c9c189c4..bd5a9daa3461 100644
--- a/arch/arc/Makefile
+++ b/arch/arc/Makefile
@@ -5,9 +5,7 @@
 
 KBUILD_DEFCONFIG := haps_hs_smp_defconfig
 
-ifeq ($(CROSS_COMPILE),)
-CROSS_COMPILE := $(call cc-cross-prefix, arc-linux- arceb-linux-)
-endif
+CROSS_COMPILE ?= $(call cc-cross-prefix, arc-linux- arceb-linux-)
 
 cflags-y	+= -fno-common -pipe -fno-builtin -mmedium-calls -D__linux__
 
diff --git a/arch/h8300/Makefile b/arch/h8300/Makefile
index ba0f26cfad61..d6e466dbfc00 100644
--- a/arch/h8300/Makefile
+++ b/arch/h8300/Makefile
@@ -26,9 +26,7 @@ KBUILD_LDFLAGS += $(ldflags-y)
 
 CHECKFLAGS += -msize-long
 
-ifeq ($(CROSS_COMPILE),)
-CROSS_COMPILE := $(call cc-cross-prefix, h8300-unknown-linux- h8300-linux-)
-endif
+CROSS_COMPILE ?= $(call cc-cross-prefix, h8300-unknown-linux- h8300-linux-)
 
 core-y	+= arch/$(ARCH)/kernel/ arch/$(ARCH)/mm/
 core-y	+= arch/$(ARCH)/boot/dts/
diff --git a/arch/m68k/Makefile b/arch/m68k/Makefile
index ea14f2046fb4..79208ad7a355 100644
--- a/arch/m68k/Makefile
+++ b/arch/m68k/Makefile
@@ -17,10 +17,8 @@
 KBUILD_DEFCONFIG := multi_defconfig
 
 ifneq ($(SUBARCH),$(ARCH))
-	ifeq ($(CROSS_COMPILE),)
-		CROSS_COMPILE := $(call cc-cross-prefix, \
+	CROSS_COMPILE ?= $(call cc-cross-prefix, \
 			m68k-linux-gnu- m68k-linux- m68k-unknown-linux-gnu-)
-	endif
 endif
 
 #
diff --git a/arch/mips/Makefile b/arch/mips/Makefile
index e71d587af49c..75e4e46532a4 100644
--- a/arch/mips/Makefile
+++ b/arch/mips/Makefile
@@ -51,9 +51,7 @@ UTS_MACHINE		:= mips64
 endif
 
 ifneq ($(SUBARCH),$(ARCH))
-  ifeq ($(CROSS_COMPILE),)
-    CROSS_COMPILE := $(call cc-cross-prefix, $(tool-archpref)-linux-  $(tool-archpref)-linux-gnu-  $(tool-archpref)-unknown-linux-gnu-)
-  endif
+  CROSS_COMPILE ?= $(call cc-cross-prefix, $(tool-archpref)-linux-  $(tool-archpref)-linux-gnu-  $(tool-archpref)-unknown-linux-gnu-)
 endif
 
 ifdef CONFIG_FUNCTION_GRAPH_TRACER
diff --git a/arch/parisc/Makefile b/arch/parisc/Makefile
index 7d9f71aa829a..62272cb3513c 100644
--- a/arch/parisc/Makefile
+++ b/arch/parisc/Makefile
@@ -42,12 +42,10 @@ endif
 export LD_BFD
 
 ifneq ($(SUBARCH),$(UTS_MACHINE))
-	ifeq ($(CROSS_COMPILE),)
-		CC_SUFFIXES = linux linux-gnu unknown-linux-gnu
-		CROSS_COMPILE := $(call cc-cross-prefix, \
+	CC_SUFFIXES = linux linux-gnu unknown-linux-gnu
+	CROSS_COMPILE ?= $(call cc-cross-prefix, \
 			$(foreach a,$(CC_ARCHES), \
 			$(foreach s,$(CC_SUFFIXES),$(a)-$(s)-)))
-	endif
 endif
 
 ifdef CONFIG_DYNAMIC_FTRACE
diff --git a/arch/sh/Makefile b/arch/sh/Makefile
index 3bcbf52fb30e..0e8277be362e 100644
--- a/arch/sh/Makefile
+++ b/arch/sh/Makefile
@@ -10,9 +10,7 @@
 # for more details.
 #
 ifneq ($(SUBARCH),$(ARCH))
-  ifeq ($(CROSS_COMPILE),)
-    CROSS_COMPILE := $(call cc-cross-prefix, sh-linux- sh-linux-gnu- sh-unknown-linux-gnu-)
-  endif
+  CROSS_COMPILE ?= $(call cc-cross-prefix, sh-linux- sh-linux-gnu- sh-unknown-linux-gnu-)
 endif
 
 KBUILD_DEFCONFIG	:= shx3_defconfig
-- 
2.27.0