add an optional config option for stripping all unnecessary symbol exports from the kernel image

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@17181 3c298f89-4303-0410-b956-a3cf2f4a3e73

include/kernel-build.mk

@@ -54,6 +54,28 @@ define BuildKernel
 	$(Kernel/Prepare)
 	touch $$@
 
+  $(KERNEL_BUILD_DIR)/symtab.txt: FORCE
+	find $(LINUX_DIR) $(STAGING_DIR_ROOT)/lib/modules -name \*.ko | \
+		xargs $(TARGET_CROSS)nm | \
+		awk '$$$$1 == "U" { print $$$$2 } ' | \
+		sort -u > $$@
+
+  $(KERNEL_BUILD_DIR)/symtab.h: $(KERNEL_BUILD_DIR)/symtab.txt
+	( \
+		echo '#define SYMTAB_KEEP \'; \
+		cat $(KERNEL_BUILD_DIR)/symtab.txt | \
+			awk '{print "*(__ksymtab." $$$$1 ") \\" }'; \
+		echo; \
+		echo '#define SYMTAB_KEEP_GPL \'; \
+		cat $(KERNEL_BUILD_DIR)/symtab.txt | \
+			awk '{print "*(__ksymtab_gpl." $$$$1 ") \\" }'; \
+		echo; \
+		echo '#define SYMTAB_KEEP_STR \'; \
+		cat $(KERNEL_BUILD_DIR)/symtab.txt | \
+			awk '{print "*(__ksymtab_strings." $$$$1 ") \\" }'; \
+		echo; \
+	) > $$@
+
   $(STAMP_CONFIGURED): $(STAMP_PREPARED) $(LINUX_CONFIG) $(GENERIC_LINUX_CONFIG) $(TOPDIR)/.config
 	$(Kernel/Configure)
 	touch $$@
@@ -62,7 +84,7 @@ define BuildKernel
 	$(Kernel/CompileModules)
 	touch $$@
 
-  $(LINUX_DIR)/.image: $(STAMP_CONFIGURED) FORCE
+  $(LINUX_DIR)/.image: $(STAMP_CONFIGURED) $(if $(CONFIG_STRIP_KERNEL_EXPORTS),$(KERNEL_BUILD_DIR)/symtab.h) FORCE
 	$(Kernel/CompileImage)
 	touch $$@
 	

include/kernel-defaults.mk

@@ -22,6 +22,11 @@ KERNEL_MAKEOPTS := -C $(LINUX_DIR) \
 	KBUILD_HAVE_NLS=no \
 	CONFIG_SHELL="$(BASH)"
 
+ifdef CONFIG_STRIP_KERNEL_EXPORTS
+  KERNEL_MAKEOPTS += \
+	EXTRA_LDSFLAGS="-I$(KERNEL_BUILD_DIR) -include symtab.h"
+endif
+
 INITRAMFS_EXTRA_FILES ?= $(GENERIC_PLATFORM_DIR)/image/initramfs-base-files.txt
 
 ifneq (,$(KERNEL_CC))