selftests/ftrace: Add new test case which adds multiple consecutive probes in a function

Commit 97f88a3d ("powerpc/kprobes: Fix null pointer reference in
arch_prepare_kprobe()") fixed a recent kernel oops that was caused as
ftrace-based kprobe does not generate kprobe::ainsn::insn and it gets
set to NULL.
Add new test case kprobe_insn_boundary.tc which adds a
kprobe at every byte within $FUNCTION_FORK up to an offset of 256 bytes,
to be able to test potential issues with kprobes on
successive instructions.
The '|| continue' is added with the echo statement to ignore errors that
are caused by trying to add kprobes to non probeable lines and continue
with the test.

Link: https://lore.kernel.org/linux-trace-kernel/20230428163842.95118-2-akanksha@linux.ibm.comSigned-off-by: Akanksha J N <akanksha@linux.ibm.com>
Acked-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

tools/testing/selftests/ftrace/test.d/kprobe/kprobe_insn_boundary.tc

+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Copyright (C) 2023 Akanksha J N, IBM corporation
+# description: Register multiple kprobe events in a function
+# requires: kprobe_events
+
+for i in `seq 0 255`; do
+  echo p $FUNCTION_FORK+${i} >> kprobe_events || continue
+done
+
+cat kprobe_events >> $testlog
+
+echo 1 > events/kprobes/enable
+( echo "forked" )
+echo 0 > events/kprobes/enable
+echo > kprobe_events
+echo "Waiting for unoptimizing & freeing"
+sleep 5
+echo "Done"