kbuild: Add target debug_kallsyms

From: Keith Owens <kaos@ocs.com.au>

Make it easier to generate maps for debugging kallsyms problems.
debug_kallsyms is only a debugging target so no help or silent mode.
Signed-off-by: Keith Owens <kaos@ocs.com.au>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Makefile

@@ -722,6 +722,16 @@ quiet_cmd_kallsyms = KSYM    $@
 # Needs to visit scripts/ before $(KALLSYMS) can be used.
 $(KALLSYMS): scripts ;
 
+# Generate some data for debugging strange kallsyms problems
+debug_kallsyms: .tmp_map$(last_kallsyms)
+
+.tmp_map%: .tmp_vmlinux% FORCE
+	($(OBJDUMP) -h $< | $(AWK) '/^ +[0-9]/{print $$4 " 0 " $$2}'; $(NM) $<) | sort > $@
+
+.tmp_map3: .tmp_map2
+
+.tmp_map2: .tmp_map1
+
 endif # ifdef CONFIG_KALLSYMS
 
 # vmlinux image - including updated kernel symbols