powerpc: unrel_branch_check.sh: use nm to find symbol value

This is considerably faster then parsing the objdump asm output.  It will
also make the enabling of llvm-objdump a little easier.
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200812081036.7969-2-sfr@canb.auug.org.au

arch/powerpc/Makefile.postlink

@@ -18,7 +18,7 @@ quiet_cmd_relocs_check = CHKREL  $@
 ifdef CONFIG_PPC_BOOK3S_64
       cmd_relocs_check =						\
 	$(CONFIG_SHELL) $(srctree)/arch/powerpc/tools/relocs_check.sh "$(OBJDUMP)" "$(NM)" "$@" ; \
-	$(BASH) $(srctree)/arch/powerpc/tools/unrel_branch_check.sh "$(OBJDUMP)" "$@"
+	$(BASH) $(srctree)/arch/powerpc/tools/unrel_branch_check.sh "$(OBJDUMP)" "$(NM)" "$@"
 else
       cmd_relocs_check =						\
 	$(CONFIG_SHELL) $(srctree)/arch/powerpc/tools/relocs_check.sh "$(OBJDUMP)" "$(NM)" "$@"

arch/powerpc/tools/unrel_branch_check.sh

@@ -5,18 +5,15 @@
 # This script checks the unrelocated code of a vmlinux for "suspicious"
 # branches to relocated code (head_64.S code).
 
-# Have Kbuild supply the path to objdump so we handle cross compilation.
+# Have Kbuild supply the path to objdump and nm so we handle cross compilation.
 objdump="$1"
-vmlinux="$2"
+nm="$2"
+vmlinux="$3"
 
-#__end_interrupts should be located within the first 64K
 kstart=0xc000000000000000
-printf -v kend '0x%x' $(( kstart + 0x10000 ))
 
-end_intr=0x$(
-$objdump -R -d --start-address="$kstart" --stop-address="$kend" "$vmlinux" 2>/dev/null |
-awk '$2 == "<__end_interrupts>:" { print $1 }'
-)
+end_intr=0x$($nm -p "$vmlinux" |
+	sed -E -n '/\s+[[:alpha:]]\s+__end_interrupts\s*$/{s///p;q}')
 if [ "$end_intr" = "0x" ]; then
 	exit 0
 fi