sparc: Validate VDSO for undefined symbols.

There should be no undefined symbols in the resulting VDSO image(s).

On sparc, fixed register usage can result in undefined symbols ending
up in the image.  To combat this, we do two things:

1) Define current_thread_info() specially when BUILD_DSO.

2) Ignore "#scratch" register undefined symbols in the output.
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc/include/asm/thread_info_64.h

@@ -121,8 +121,12 @@ struct thread_info {
 }
 
 /* how to get the thread information struct from C */
+#ifndef BUILD_VDSO
 register struct thread_info *current_thread_info_reg asm("g6");
 #define current_thread_info()	(current_thread_info_reg)
+#else
+extern struct thread_info *current_thread_info(void);
+#endif
 
 /* thread information allocation */
 #if PAGE_SHIFT == 13

arch/sparc/vdso/Makefile

@@ -111,7 +111,8 @@ $(obj)/vdso32.so.dbg: FORCE \
 quiet_cmd_vdso = VDSO    $@
       cmd_vdso = $(LD) -nostdlib -o $@ \
 		       $(VDSO_LDFLAGS) $(VDSO_LDFLAGS_$(filter %.lds,$(^F))) \
-		       -T $(filter %.lds,$^) $(filter %.o,$^)
+		       -T $(filter %.lds,$^) $(filter %.o,$^) && \
+		sh $(srctree)/$(src)/checkundef.sh '$(OBJDUMP)' '$@'
 
 VDSO_LDFLAGS = -shared $(call ld-option, --hash-style=both) \
 	$(call ld-option, --build-id) -Bsymbolic

arch/sparc/vdso/checkundef.sh

+#!/bin/sh
+objdump="$1"
+file="$2"
+$objdump -t "$file" | grep '*UUND*' | grep -v '#scratch' > /dev/null 2>&1
+if [ $? -eq 1 ]; then
+    exit 0
+else
+    echo "$file: undefined symbols found" >&2
+    exit 1
+fi