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

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Message-ID: <20250226121316.7653ae38@gandalf.local.home>
Date: Wed, 26 Feb 2025 12:13:16 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Heiko Carstens <hca@...ux.ibm.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Shuah Khan <shuah@...nel.org>,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org, Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] selftests/ftrace: Use readelf to find entry point in
 uprobe test

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

Acked-by: Steven Rostedt (Google) <rostedt@...dmis.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