[PATCH] detect uninitialised per-cpu storage

So poor old Dave spent days hunting down memory corruption because the
`kstat' per-cpu storage is not initialised (it needs to be, it's a workaround
for ancient gcc's).

The same problem had me hunting for a day too.

This patch, based on an initial version from Rusty will
parse System.map at final link and will fail the build if
any per-cpu symbols are found to be not in the percpu section.

Makefile

@@ -299,6 +299,8 @@ define cmd_vmlinux__
 endef
 
 #	set -e makes the rule exit immediately on error
+#	Final awk script makes sure per-cpu vars are in per-cpu section, as
+#	old gcc (eg egcs 2.92.11) ignores section attribute if uninitialized.
 
 define rule_vmlinux__
 	set -e
@@ -312,11 +314,22 @@ define rule_vmlinux__
 	echo 'cmd_$@ := $(cmd_vmlinux__)' > $(@D)/.$(@F).cmd
 endef
 
-define rule_vmlinux
+define rule_vmlinux_no_percpu
 	$(rule_vmlinux__)
 	$(NM) $@ | grep -v '\(compiled\)\|\(\.o$$\)\|\( [aUw] \)\|\(\.\.ng$$\)\|\(LASH[RL]DI\)' | sort > System.map
 endef
 
+ifdef CONFIG_SMP
+define rule_vmlinux
+	$(rule_vmlinux_no_percpu)
+	$(AWK) -f scripts/per-cpu-check.awk < System.map
+endef
+else
+define rule_vmlinux
+	$(rule_vmlinux_no_percpu)
+endef
+endif
+
 LDFLAGS_vmlinux += -T arch/$(ARCH)/vmlinux.lds.s
 
 #	Generate section listing all symbols and add it into vmlinux

scripts/per-cpu-check.awk

+/ __per_cpu_start$$/ {
+	IN_PER_CPU=1
+}
+
+/ __per_cpu_end$$/ {
+	IN_PER_CPU=0
+}
+
+/__per_cpu$$/ && ! / __ksymtab_/ {
+	if (!IN_PER_CPU) {
+		print $$3 " not in per-cpu section" > "/dev/stderr";
+		FOUND=1;
+	}
+}
+
+END {
+	exit FOUND;
+}
+