[PATCH] x86: Add "make tinyconfig" to configure the tiniest possible kernel

[Josh Triplett <josh@joshtriplett.org>]

Since commit 5d2acfc7b974bbd3858b4dd3f2cdc6362dd8843a ("kconfig: make
allnoconfig disable options behind EMBEDDED and EXPERT") in 3.15-rc1,
"make allnoconfig" disables every possible config option.

However, a few configuration options (CC_OPTIMIZE_FOR_SIZE,
OPTIMIZE_INLINING) produce a smaller kernel when turned on, and a few
choices exist (compression, highmem, allocator) for which a non-default
option produces a smaller kernel.

Add a "tinyconfig" target, which starts from allnoconfig and then sets
these options to configure the tiniest possible kernel.  This provides a
better baseline for embedded systems or efforts to reduce kernel size.

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
---
 arch/x86/Makefile            | 6 ++++++
 arch/x86/configs/tiny.config | 5 +++++
 2 files changed, 11 insertions(+)
 create mode 100644 arch/x86/configs/tiny.config

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index c65fd96..f20abcd 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -253,6 +253,11 @@ kvmconfig:
 	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/kconfig/merge_config.sh -m -O $(objtree) $(objtree)/.config $(srctree)/arch/x86/configs/kvm_guest.config
 	$(Q)yes "" | $(MAKE) -f $(srctree)/Makefile oldconfig
 
+PHONY += tinyconfig
+tinyconfig: allnoconfig
+	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/kconfig/merge_config.sh -m -O $(objtree) $(objtree)/.config $(srctree)/arch/x86/configs/tiny.config
+	$(Q)yes "" | $(MAKE) -f $(srctree)/Makefile oldconfig
+
 define archhelp
   echo  '* bzImage      - Compressed kernel image (arch/x86/boot/bzImage)'
   echo  '  install      - Install kernel using'
@@ -267,4 +272,5 @@ define archhelp
   echo  '                  FDARGS="..."  arguments for the booted kernel'
   echo  '                  FDINITRD=file initrd for the booted kernel'
   echo  '  kvmconfig	- Enable additional options for guest kernel support'
+  echo  '  tinyconfig   - Configure the tiniest possible kernel'
 endef
diff --git a/arch/x86/configs/tiny.config b/arch/x86/configs/tiny.config
new file mode 100644
index 0000000..8f0e54c
--- /dev/null
+++ b/arch/x86/configs/tiny.config
@@ -0,0 +1,5 @@
+CONFIG_CC_OPTIMIZE_FOR_SIZE=y
+CONFIG_KERNEL_XZ=y
+CONFIG_NOHIGHMEM=y
+CONFIG_OPTIMIZE_INLINING=y
+CONFIG_SLOB=y
-- 
2.0.1