kbuild: Check for undefined symbols in vmlinux

At least one bin-utils version for ARM is know to ignore undefined
symbols when performing the final link of vmlinux.
Add an explicit check for undefined symbols to catch this.
The check is made in combination with generating the System.map file
and the actual algorithm is moved to a small shell script - mksysmap.

External symbols with three leading underscores are ignored - sparc
uses them for the BTFIXUP logic.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Makefile

@@ -538,7 +538,8 @@ define rule_vmlinux__
 	echo 'cmd_$@ := $(cmd_vmlinux__)' > $(@D)/.$(@F).cmd
 endef
 
-do_system_map = $(NM) $(1) | grep -v '\(compiled\)\|\(\.o$$\)\|\( [aUw] \)\|\(\.\.ng$$\)\|\(LASH[RL]DI\)' | sort > $(2)
+quiet_cmd_sysmap = SYSMAP 
+      cmd_sysmap = $(CONFIG_SHELL) $(srctree)/scripts/mksysmap
 		   
 LDFLAGS_vmlinux += -T arch/$(ARCH)/kernel/vmlinux.lds.s
 
@@ -570,8 +571,10 @@ endif
 kallsyms.o := .tmp_kallsyms$(last_kallsyms).o
 
 define rule_verify_kallsyms
-	@$(call do_system_map, .tmp_vmlinux$(last_kallsyms), .tmp_System.map)
-	@cmp -s System.map .tmp_System.map || \
+	$(Q)$(if $($(quiet)cmd_sysmap),                       \
+	  echo '  $($(quiet)cmd_sysmap) .tmp_System.map' &&)  \
+	  $(cmd_sysmap) .tmp_vmlinux$(last_kallsyms) .tmp_System.map
+	$(Q)cmp -s System.map .tmp_System.map || \
 		(echo Inconsistent kallsyms data, try setting CONFIG_KALLSYMS_EXTRA_PASS ; rm .tmp_kallsyms* ; false)
 endef
 
@@ -596,10 +599,18 @@ cmd_kallsyms = $(NM) -n $< | $(KALLSYMS) $(foreach x,$(CONFIG_KALLSYMS_ALL),--al
 endif
 
 # Finally the vmlinux rule
+# This rule is also used to generate System.map
+# and to verify that the content of kallsyms are consistent
 
 define rule_vmlinux
-	$(rule_vmlinux__); \
-	$(call do_system_map, $@, System.map)
+	$(rule_vmlinux__);
+	$(Q)$(if $($(quiet)cmd_sysmap),          \
+	  echo '  $($(quiet)cmd_sysmap) $@' &&)  \
+	$(cmd_sysmap) $@ System.map;             \
+	if [ $$? -ne 0 ]; then                   \
+		rm -f $@;                        \
+		/bin/false;                      \
+	fi;
 	$(rule_verify_kallsyms)
 endef
 

scripts/mksysmap

+#!/bin/sh -x
+# Based on the vmlinux file create the System.map file
+# System.map is used by module-init tools and some debugging
+# tools to retreive the actual addresses of symbols in the kernel.
+#
+# Before creating the System.map file as a sideeffect check for
+# undefined symbols.
+# At least one version of the ARM bin-utils did not error out on
+# undefined symbols, so catch them here instead.
+
+# Usage
+# mksysmap vmlinux System.map
+
+
+#####
+# Check for undefined symbols.
+# Undefined symbols with three leading underscores are ignored since
+# they are used by the sparc BTFIXUP logic - and is assumed to be undefined.
+
+
+if [ "`$NM -u $1 | grep -v ' ____'`" != "" ]; then
+	echo "$1: error: undefined symbol(s) found:"
+	$NM -u $1 | grep -v ' ___'
+	exit 1
+fi
+
+#####
+# Generate System.map (actual filename passed as second argument)
+
+# $NM produces the following output:
+# f0081e80 T alloc_vfsmnt
+
+#   The second row specify the type of the symbol:
+#   A = Absolute
+#   B = Uninitialised data (.bss)
+#   C = Comon symbol
+#   D = Initialised data
+#   G = Initialised data for small objects
+#   I = Indirect reference to another symbol
+#   N = Debugging symbol
+#   R = Read only
+#   S = Uninitialised data for small objects
+#   T = Text code symbol
+#   U = Undefined symbol
+#   V = Weak symbol
+#   W = Weak symbol
+#   Corresponding small letters are local symbols
+
+# For System.map filter away:
+#   a - local absolute symbols
+#   U - undefined global symbols
+#   w - local weak symbols
+
+nm $1 | grep -v ' [aUw] ' > $2