[PATCH v2 3/4] kconfig: get target architecture from config file

From: Konstantin Khlebnikov
Date: Mon Sep 01 2014 - 03:16:57 EST

This patch makes kernel cross-compilation little bit easier.
After initial configuration no special environment variables
are required because default ARCH is saved in .config file:

# make ARCH=arm defconfig
# make menuconfig
# make

To solve chicken and egg problem ARCH is read directly from config file.

Signed-off-by: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
Documentation/kbuild/makefiles.txt | 3 ++-
Makefile | 15 ++++++++++-----
2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
index 764f599..92cf95b 100644
--- a/Documentation/kbuild/makefiles.txt
+++ b/Documentation/kbuild/makefiles.txt
@@ -1365,7 +1365,8 @@ The top Makefile exports the following variables:
"arm", or "sparc". Some kbuild Makefiles test $(ARCH) to
determine which files to compile.

- By default, the top Makefile sets $(ARCH) to be the same as the
+ By default $(ARCH) is set by option CONFIG_ARCH in .config,
+ default for it is set by top Makefile to be the same as the
host system architecture. For a cross build, a user may
override the value of $(ARCH) on the command line:

diff --git a/Makefile b/Makefile
index 2893d7f..f648405 100644
--- a/Makefile
+++ b/Makefile
@@ -220,6 +220,8 @@ VPATH := $(srctree)$(if $(KBUILD_EXTMOD),:$(KBUILD_EXTMOD))

export srctree objtree VPATH

+KCONFIG_CONFIG ?= .config

# SUBARCH tells the usermode build what the underlying arch is. That is set
# first, and if a usermode build is happening, the "ARCH=um" on the command
@@ -242,7 +244,14 @@ SUBARCH := $(shell uname -m | sed -e s/i.86/x86/ -e s/x86_64/x86/ \
# ARCH can be set during invocation of make:
# make ARCH=ia64
# Another way is to have ARCH set in the environment.
-# The default ARCH is the host where make is executed.
+# Usually default value is saved in .config as CONFIG_ARCH.
+# If this option is undefined or config file does not exist
+# ARCH is set to the host where make is executed.
+ifndef ARCH
+ ARCH := $(shell $(srctree)/scripts/config \
+ --if-undef "$(SUBARCH)" --state "ARCH")

# CROSS_COMPILE specify the prefix used for all executables used
# during compilation. Only gcc and related bin-utils executables
@@ -254,7 +263,6 @@ SUBARCH := $(shell uname -m | sed -e s/i.86/x86/ -e s/x86_64/x86/ \
# "make" in the configured kernel build directory always uses that.
# Default value for CROSS_COMPILE is not to prefix executables
# Note: Some architectures assign CROSS_COMPILE in their arch/*/Makefile

# Architecture as present in compile.h
@@ -293,9 +301,6 @@ endif
# Where to locate arch specific headers
hdr-arch := $(SRCARCH)

-KCONFIG_CONFIG ?= .config
# SHELL used by kbuild
CONFIG_SHELL := $(shell if [ -x "$$BASH" ]; then echo $$BASH; \
else if [ -x /bin/bash ]; then echo /bin/bash; \

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