linux-kernel - [PATCH 1/3] scripts/decode_stacktrace.sh: remove find_module recursion and improve error reporting

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Message-Id: <20240311-decode_stacktrace-find_module-improvements-v1-1-8bea42b421aa@bootlin.com>
Date: Mon, 11 Mar 2024 16:24:54 +0100
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: Konstantin Khlebnikov <koct9i@...il.com>, 
 Stephen Boyd <swboyd@...omium.org>, Sasha Levin <sashal@...nel.org>, 
 Alexis Lothoré <alexis.lothore@...tlin.com>, 
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 linux-kernel@...r.kernel.org, Luca Ceresoli <luca.ceresoli@...tlin.com>
Subject: [PATCH 1/3] scripts/decode_stacktrace.sh: remove find_module
 recursion and improve error reporting

The find_module() function can fail for two reasons:

 * the module was not found
 * the module was found but without debugging info

In both cases the user is reported the same error:

   WARNING! Modules path isn't set, but is needed to parse this symbol

This is misleading in case the modules path is set correctly.

find_module() is currently implemented as a recursive function based on
global variables in order to check up to 4 different paths. This is not
straightforward to read and even less to modify.

Besides, the debuginfod code at the beginning of find_module() is executed
identlcally every time the function is entered, i.e. up to 4 times per each
module search due to recursion.

To be able to improve error reporting, first rewrite the find_module()
function to remove recursion. The new version of the function iterates over
all the same (up to 4) paths as before and for each of them does the same
checks as before. At the end of the iteration it is now able to print an
appropriate error message, so that has been moved from the caller into
find_module().

Finally, when the module is found but without debugging info, mention the
two Kconfig variables one needs to set in order to have the needed
debugging symbols.

Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
---
 scripts/decode_stacktrace.sh | 40 ++++++++++++++++++++--------------------
 1 file changed, 20 insertions(+), 20 deletions(-)

diff --git a/scripts/decode_stacktrace.sh b/scripts/decode_stacktrace.sh
index fa5be6f57b00..7f3fb5e82707 100755
--- a/scripts/decode_stacktrace.sh
+++ b/scripts/decode_stacktrace.sh
@@ -88,31 +88,32 @@ find_module() {
 		fi
 	fi
 
-	if [[ "$modpath" != "" ]] ; then
-		for fn in $(find "$modpath" -name "${module//_/[-_]}.ko*") ; do
-			if ${READELF} -WS "$fn" | grep -qwF .debug_line ; then
-				echo $fn
-				return
-			fi
-		done
-		return 1
-	fi
-
-	modpath=$(dirname "$vmlinux")
-	find_module && return
-
-	if [[ $release == "" ]] ; then
+	if [ -z $release ] ; then
 		release=$(gdb -ex 'print init_uts_ns.name.release' -ex 'quit' -quiet -batch "$vmlinux" 2>/dev/null | sed -n 's/\$1 = "\(.*\)".*/\1/p')
 	fi
+	if [ -n "${release}" ] ; then
+		release_dirs="/usr/lib/debug/lib/modules/$release /lib/modules/$release"
+	fi
 
-	for dn in {/usr/lib/debug,}/lib/modules/$release ; do
-		if [ -e "$dn" ] ; then
-			modpath="$dn"
-			find_module && return
+	found_without_debug_info=false
+	for dir in "$modpath" "$(dirname "$vmlinux")" ${release_dirs}; do
+		if [ -n "${dir}" ] && [ -e "${dir}" ]; then
+			for fn in $(find "$dir" -name "${module//_/[-_]}.ko*") ; do
+				if ${READELF} -WS "$fn" | grep -qwF .debug_line ; then
+					echo $fn
+					return
+				fi
+				found_without_debug_info=true
+			done
 		fi
 	done
 
-	modpath=""
+	if [[ ${found_without_debug_info} == true ]]; then
+		echo "WARNING! No debugging info in module ${module}, rebuild with DEBUG_KERNEL and DEBUG_INFO" >&2
+	else
+		echo "WARNING! Cannot find .ko for module ${module}, please pass a valid module path" >&2
+	fi
+
 	return 1
 }
 
@@ -130,7 +131,6 @@ parse_symbol() {
 	else
 		local objfile=$(find_module)
 		if [[ $objfile == "" ]] ; then
-			echo "WARNING! Modules path isn't set, but is needed to parse this symbol" >&2
 			return
 		fi
 		if [[ $aarray_support == true ]]; then

-- 
2.34.1