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@bootlin.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

Quoting Luca Ceresoli (2024-03-11 08:24:54)
> 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

s/identlcally/identically/

> 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@bootlin.com>
> ---

Reviewed-by: Stephen Boyd <swboyd@chromium.org>

Hello Stephen,

On Wed, 8 May 2024 17:35:53 -0400
Stephen Boyd <swboyd@chromium.org> wrote:

> Quoting Luca Ceresoli (2024-03-11 08:24:54)
> > 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  
> 
> s/identlcally/identically/

Well spotted!

Thanks for reviewing, v2 on its way.

Luca

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com