scripts/decode_stacktrace.sh: remove find_module recursion and improve error reporting

Patch series "scripts/decode_stacktrace.sh: improve error reporting and
usability", v2.

This small series improves usability of scripts/decode_stacktrace.sh by
improving the usage text and correctly reporting when modules are built
without debugging symbols.

This patch (of 3):

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 debuginfo code at the beginning of find_module() is executed
identically 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.

Link: https://lkml.kernel.org/r/20240823-decode_stacktrace-find_module-improvements-v2-0-d7a57d35558b@bootlin.com
Link: https://lkml.kernel.org/r/20240823-decode_stacktrace-find_module-improvements-v2-1-d7a57d35558b@bootlin.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Cc: Alexis Lothoré (eBPF Foundation) <alexis.lothore@bootlin.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Luca Ceresoli <luca.ceresoli@bootlin.com>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/scripts/decode_stacktrace.sh b/scripts/decode_stacktrace.sh
index ed9f914334cc32ff4d483e18d78bcad3359198cd..e6b38ab7c8c5a4f728b6e11f1e2a0f773ae42f6c 100755 (executable)
--- a/scripts/decode_stacktrace.sh
+++ b/scripts/decode_stacktrace.sh
@@ -89,31 +89,32 @@ 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
 }
 
@@ -131,7 +132,6 @@ 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