scripts/decode_stacktrace.sh: skip missing symbols

For now script turns missing symbols into '0' and make bogus decode.  Skip
them instead.  Also simplify parsing output of 'nm'.

Before:

$ echo 'xxx+0x0/0x0' | ./scripts/decode_stacktrace.sh vmlinux ""
xxx (home/khlebnikov/src/linux/./arch/x86/include/asm/processor.h:398)

After:

$ echo 'xxx+0x0/0x0' | ./scripts/decode_stacktrace.sh vmlinux ""
xxx+0x0/0x0

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Sasha Levin <sashal@kernel.org>
Link: http://lkml.kernel.org/r/159282922499.248444.4883465570858385250.stgit@buzz
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/scripts/decode_stacktrace.sh b/scripts/decode_stacktrace.sh
index 0869def..b157037 100755 (executable)
--- a/scripts/decode_stacktrace.sh
+++ b/scripts/decode_stacktrace.sh
@@ -56,7 +56,11 @@ parse_symbol() {
        if [[ "${cache[$module,$name]+isset}" == "isset" ]]; then
                local base_addr=${cache[$module,$name]}
        else
-               local base_addr=$(nm "$objfile" | grep -i ' t ' | awk "/ $name\$/ {print \$1}" | head -n1)
+               local base_addr=$(nm "$objfile" | awk '$3 == "'$name'" && ($2 == "t" || $2 == "T") {print $1; exit}')
+               if [[ $base_addr == "" ]] ; then
+                       # address not found
+                       return
+               fi
                cache[$module,$name]="$base_addr"
        fi
        # Let's start doing the math to get the exact address into the