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

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

Posted by Heiko Carstens 10 months ago

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@linux.ibm.com>
---
 .../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

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

Posted by Steven Rostedt 9 months, 3 weeks ago

On Thu, 20 Feb 2025 14:01:02 +0100
Heiko Carstens <hca@linux.ibm.com> wrote:

> 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@linux.ibm.com>

Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Shuah,

Can you take this in your tree?

-- Steve

> ---
>  .../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

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

Posted by Shuah Khan 9 months, 3 weeks ago

On 2/26/25 10:13, Steven Rostedt wrote:
> On Thu, 20 Feb 2025 14:01:02 +0100
> Heiko Carstens <hca@linux.ibm.com> wrote:
> 
>> 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@linux.ibm.com>
> 
> Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> 
> Shuah,
> 
> Can you take this in your tree?
> 
> -- Steve

Applied to linux_kselftest next for Linux 6.15-rc1.

thanks,
-- Shuah