scripts/decode_stacktrace.sh: fix build ID and PC source parsing

commit 7d9f7d390f6af3a29614e81e802e2b9c238eb7b2 upstream.

Support for parsing PC source info in stacktraces (e.g.  '(P)') was added
in commit 2bff77c ("scripts/decode_stacktrace.sh: fix decoding of
lines with an additional info").  However, this logic was placed after the
build ID processing.  This incorrect order fails to parse lines containing
both elements, e.g.:

  drm_gem_mmap_obj+0x114/0x200 [drm 03d0564e0529947d67bb2008c3548be77279fd27] (P)

This patch fixes the problem by extracting the PC source info first and
then processing the module build ID.  With this change, the line above is
now properly parsed as such:

  drm_gem_mmap_obj (./include/linux/mmap_lock.h:212 ./include/linux/mm.h:811 drivers/gpu/drm/drm_gem.c:1177) drm (P)

While here, also add a brief explanation the build ID section.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 2bff77c ("scripts/decode_stacktrace.sh: fix decoding of lines with an additional info")
Signed-off-by: Carlos Llamas <[email protected]>
Reviewed-by: Matthieu Baerts (NGI0) <[email protected]>
Reviewed-by: Luca Ceresoli <[email protected]>
Cc: Breno Leitao <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Marc Rutland <[email protected]>
Cc: Mark Brown <[email protected]>
Cc: Matthieu Baerts <[email protected]>
Cc: Miroslav Benes <[email protected]>
Cc: Puranjay Mohan <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Carlos Llamas

scripts/decode_stacktrace.sh

@@ -275,12 +275,6 @@ handle_line() {
 		fi
 	done
 
-	if [[ ${words[$last]} =~ ^[0-9a-f]+\] ]]; then
-		words[$last-1]="${words[$last-1]} ${words[$last]}"
-		unset words[$last] spaces[$last]
-		last=$(( $last - 1 ))
-	fi
-
 	# Extract info after the symbol if present. E.g.:
 	# func_name+0x54/0x80 (P)
 	#                     ^^^
@@ -293,6 +287,14 @@ handle_line() {
 		last=$(( $last - 1 ))
 	fi
 
+	# Join module name with its build id if present, as these were
+	# split during tokenization (e.g. "[module" and "modbuildid]").
+	if [[ ${words[$last]} =~ ^[0-9a-f]+\] ]]; then
+		words[$last-1]="${words[$last-1]} ${words[$last]}"
+		unset words[$last] spaces[$last]
+		last=$(( $last - 1 ))
+	fi
+
 	if [[ ${words[$last]} =~ \[([^]]+)\] ]]; then
 		module=${words[$last]}
 		# some traces format is "(%pS)", which like "(foo+0x0/0x1 [bar])"