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