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

[Heiko Carstens]

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.

Signed-off-by: Heiko Carstens <hca@xxxxxxxxxxxxx>
---
 .../ftrace/test.d/dynevent/add_remove_uprobe.tc        | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

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 86c76679c56e..f2048c244526 100644
--- 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
-- 
2.45.2