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Subject[PATCH v3] x86, kconfig: Default to ARCH=x86 to avoid overriding CONFIG_64BIT
I *frequently* waste a bunch of time when I take a 32-bit .config from a
test machine and try to build it on a faster 64-bit system, and its
existing setting of CONFIG_64BIT=n gets *changed* to match the build host.

This is because the default setting for $ARCH when discovered from
'uname' is one of the legacy pre-x86-merge values (i386 or x86_64),
which effectively force the setting of CONFIG_64BIT to match. We should
default to ARCH=x86 instead, finally completing the merge that we
started so long ago.

This patch preserves the behaviour of the legacy ARCH settings for commands
such as:

make ARCH=x86_64 randconfig
make ARCH=i386 randconfig

... although since my commit "Enable 'make CONFIG_FOO=y oldconfig'" those
would be better expressed as:

make CONFIG_64BIT=y randconfig
make CONFIG_64BIT=n randconfig

... since that is a more generic way to set *any* config option, and
there's no other technical reason to keep the legacy ARCH values around
any more just to achieve that purpose; they could be removed at any

Signed-off-by: David Woodhouse <>
v2: Explicitly turn off CONFIG_64BIT in i386_defconfig. The default for
CONFIG_64BIT has *changed* (from n to y) for ARCH=x86, so it needs to
be explicitly turned off or 'make i386_defconfig' will give you 64-bit.
v3: Same patch as before; just updated changelog.

Makefile | 3 ++-
arch/x86/Kconfig | 2 +-
arch/x86/Makefile | 4 ++++
arch/x86/configs/i386_defconfig | 1 +
4 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index d018956..303df9b 100644
--- a/Makefile
+++ b/Makefile
@@ -165,7 +165,8 @@ export srctree objtree VPATH
# then ARCH is assigned, getting whatever value it gets normally, and
# SUBARCH is subsequently ignored.

-SUBARCH := $(shell uname -m | sed -e s/i.86/i386/ -e s/sun4u/sparc64/ \
+SUBARCH := $(shell uname -m | sed -e s/i.86/x86/ -e s/x86_64/x86/ \
+ -e s/sun4u/sparc64/ \
-e s/arm.*/arm/ -e s/sa110/arm/ \
-e s/s390x/s390/ -e s/parisc64/parisc/ \
-e s/ppc.*/powerpc/ -e s/mips.*/mips/ \
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 153aa6f..9467fdd 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1,7 +1,7 @@
# Select 32 or 64 bit
config 64BIT
bool "64-bit kernel" if ARCH = "x86"
- default ARCH = "x86_64"
+ default ARCH != "i386"
Say yes to build a 64-bit kernel - formerly known as x86_64
Say no to build a 32-bit kernel - formerly known as i386
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index b02e509..94c2d8c 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -2,7 +2,11 @@

# select defconfig based on actual architecture
ifeq ($(ARCH),x86)
+ ifeq ($(shell uname -m),x86_64)
+ KBUILD_DEFCONFIG := x86_64_defconfig
+ else
KBUILD_DEFCONFIG := i386_defconfig
+ endif
diff --git a/arch/x86/configs/i386_defconfig b/arch/x86/configs/i386_defconfig
index 2bf18059f..5f96c1c 100644
--- a/arch/x86/configs/i386_defconfig
+++ b/arch/x86/configs/i386_defconfig
@@ -1,3 +1,4 @@
+# CONFIG_64BIT is not set


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