Subject: Re: [PATCH] Remove kretprobe_trampoline_holder.

From: Thiago Jung Bauermann <[email-masked]>
Date: Tue, 29 Mar 2016 15:34:22 -0300

Am Dienstag, 29 März 2016, 10:45:57 schrieb Michael Ellerman:
> On Mon, 2016-03-28 at 17:29 -0300, Thiago Jung Bauermann wrote:
> > If I do s/_do_fork/._do_fork/ in kprobe_ftrace.tc then all ftrace kprobe
> > tests pass:
> 
> OK. We fixed that in 'perf probe', but not if you're using the sysfs file
> directly.
> 
> Do you want to write a patch for ftracetest to try and handle it? I guess
> you'd try "_do_fork" and if that fails then try "._do_fork", and maybe
> only if uname -m says you're running on ppc64?

I did write a patch yesterday (included below for reference), but then I
noticed that the other ftrace tests use _do_fork and they work fine (I guess
because of the fix you mentioned). I think that ideally the ftrace filter
mechanism should work with dot symbols as well as regular symbols.

I think this could work by creating a mechanism analogous to the
ARCH_HAS_SYSCALL_MATCH_SYM_NAME one in trace_syscalls.c. Ftrace_match_record
could call it to adjust the symbol name (like kprobe_lookup_name) before
calling ftrace_match.

But I’m wondering if it’s really worth the effort and maybe patching the
testcase is enough? Also, I don’t know whether my idea would have any
side effects.

-- 
[]'s
Thiago Jung Bauermann
IBM Linux Technology Center

>>From 2ea9b3545906932b9aa213506ec0dff03cffdbe5 Mon Sep 17 00:00:00 2001
From: Thiago Jung Bauermann <[email-masked]>
Date: Mon, 28 Mar 2016 18:39:56 -0300
Subject: [PATCH] selftests: kprobe: Fix kprobe_ftrace.tc on ppc64

On ppc64 (but not ppc64le), symbols for function entry points start with
a dot. There's no _do_fork but there is a ._do_fork.

Signed-off-by: Thiago Jung Bauermann <[email-masked]>
---
 .../selftests/ftrace/test.d/kprobe/kprobe_ftrace.tc  | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_ftrace.tc b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_ftrace.tc
index d6f2f49..c3ec5c2 100644
--- a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_ftrace.tc
+++ b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_ftrace.tc
@@ -4,33 +4,39 @@
 [ -f kprobe_events ] || exit_unsupported # this is configurable
 grep function available_tracers || exit_unsupported # this is configurable
 
+if [ "$(uname -m)" = "ppc64" ]; then
+    FILTER_FUNCTION="._do_fork"
+else
+    FILTER_FUNCTION="_do_fork"
+fi
+
 # prepare
 echo nop > current_tracer
-echo _do_fork > set_ftrace_filter
+echo $FILTER_FUNCTION > set_ftrace_filter
 echo 0 > events/enable
 echo > kprobe_events
-echo 'p:testprobe _do_fork' > kprobe_events
+echo "p:testprobe $FILTER_FUNCTION" > kprobe_events
 
 # kprobe on / ftrace off
 echo 1 > events/kprobes/testprobe/enable
 echo > trace
 ( echo "forked")
 grep testprobe trace
-! grep '_do_fork <-' trace
+! grep "$FILTER_FUNCTION <-" trace
 
 # kprobe on / ftrace on
 echo function > current_tracer
 echo > trace
 ( echo "forked")
 grep testprobe trace
-grep '_do_fork <-' trace
+grep "$FILTER_FUNCTION <-" trace
 
 # kprobe off / ftrace on
 echo 0 > events/kprobes/testprobe/enable
 echo > trace
 ( echo "forked")
 ! grep testprobe trace
-grep '_do_fork <-' trace
+grep "$FILTER_FUNCTION <-" trace
 
 # kprobe on / ftrace on
 echo 1 > events/kprobes/testprobe/enable
@@ -38,14 +44,14 @@ echo function > current_tracer
 echo > trace
 ( echo "forked")
 grep testprobe trace
-grep '_do_fork <-' trace
+grep "$FILTER_FUNCTION <-" trace
 
 # kprobe on / ftrace off
 echo nop > current_tracer
 echo > trace
 ( echo "forked")
 grep testprobe trace
-! grep '_do_fork <-' trace
+! grep "$FILTER_FUNCTION <-" trace
 
 # cleanup
 echo nop > current_tracer
-- 
1.9.1