selftests/ftrace: Use readelf to find entry point in uprobe test

The uprobe events test fails on s390, but also on x86 (Fedora 41). The
problem appears to be that there is an assumption that adding a uprobe to
the beginning of the executable mapping of /bin/sh is sufficient to trigger
a uprobe event when /bin/sh is executed.

This assumption is not necessarily true. Therefore use "readelf -h" to find
the entry point address of /bin/sh and use this address when adding the
uprobe event.

This adds a dependency to readelf which is not always installed. Therefore
add a check and exit with exit_unresolved if it is not installed.

Link: https://lore.kernel.org/r/20250220130102.2079179-1-hca@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

diff --git a/tools/testing/selftests/ftrace/test.d/dynevent/add_remove_uprobe.tc b/tools/testing/selftests/ftrace/test.d/dynevent/add_remove_uprobe.tc
index 86c76679c56e940737ceb02d62d4d3a316b163f3..f2048c24452615f09ed54a1e185001e639c5d049 100644 (file)
--- a/tools/testing/selftests/ftrace/test.d/dynevent/add_remove_uprobe.tc
+++ b/tools/testing/selftests/ftrace/test.d/dynevent/add_remove_uprobe.tc
@@ -3,14 +3,18 @@
 # description: Generic dynamic event - add/remove/test uprobe events
 # requires: uprobe_events
 
+if ! which readelf > /dev/null 2>&1 ; then
+  echo "No readelf found. skipped."
+  exit_unresolved
+fi
+
 echo 0 > events/enable
 echo > dynamic_events
 
 REALBIN=`readlink -f /bin/sh`
+ENTRYPOINT=`readelf -h ${REALBIN} | grep Entry | sed -e 's/[^0]*//'`
 
-echo 'cat /proc/$$/maps' | /bin/sh | \
-       grep "r-xp .*${REALBIN}$" | \
-       awk '{printf "p:myevent %s:0x%s\n", $6,$3 }' >> uprobe_events
+echo "p:myevent ${REALBIN}:${ENTRYPOINT}" >> uprobe_events
 
 grep -q myevent uprobe_events
 test -d events/uprobes/myevent