kbuild: make it possible for the linker to discard local symbols from vmlinux

Make it possible for the linker to discard local symbols from vmlinux as
they cause vmlinux to balloon when CONFIG_KALLSYMS=y and they cause
dump_stack() and get_wchan() to produce useless information under some
circumstances.

With this we add a config option (CONFIG_STRIP_ASM_SYMS) that will cause
the build to supply -X to the linker to tell it to strip temporary local
symbols.

This doesn't seem to cause gdb any problems.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Makefile

@@ -597,6 +597,10 @@ LDFLAGS_BUILD_ID = $(patsubst -Wl$(comma)%,%,\
 LDFLAGS_MODULE += $(LDFLAGS_BUILD_ID)
 LDFLAGS_vmlinux += $(LDFLAGS_BUILD_ID)
 
+ifeq ($(CONFIG_STRIP_ASM_SYMS),y)
+LDFLAGS_vmlinux	+= -X
+endif
+
 # Default kernel image to build when no specific target is given.
 # KBUILD_IMAGE may be overruled on the command line or
 # set in the environment

init/Kconfig

@@ -808,6 +808,14 @@ config KALLSYMS_EXTRA_PASS
 	   you wait for kallsyms to be fixed.
 
 
+config STRIP_ASM_SYMS
+	bool "Strip assembler-generated symbols during link"
+	default n
+	help
+	  Strip internal assembler-generated symbols during a link (symbols
+	  that look like '.Lxxx') so they don't pollute the output of
+	  get_wchan() and suchlike.
+
 config HOTPLUG
 	bool "Support for hot-pluggable devices" if EMBEDDED
 	default y