perf probe: Fix failure to probe events on arm

Fix failure to probe events on arm, the problem was introduced by commit
5a51fcd1f30c ("perf probe: Skip kernel symbols which is out of .text").

For some architectures, the '_etext' label is not in the .text section
(in the .notes section for arm/arm64).  Labels out of the .text section
are not loaded as symbols and we get a zero value when looking up its
addresses, which causes all events to be wrongly skipped.

This patch skips checking the text address range when failing to get the
address of '_etext' and thus fixes the problem.

The problem can be reproduced on arm as follows:

  # perf probe --add='generic_perform_write'
  generic_perform_write+0 is out of .text, skip it.
  Probe point 'generic_perform_write' not found.
    Error: Failed to add events.

After this patch:

  # perf probe --add='generic_perform_write'
  Added new event:
    probe:generic_perform_write (on generic_perform_write)

  You can now use it in all perf tools, such as:

    perf record -e probe:generic_perform_write -aR sleep 1

Signed-off-by: He Kuang <hekuang@huawei.com>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1434595750-129791-1-git-send-email-hekuang@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/probe-event.c

@@ -249,8 +249,12 @@ static void clear_probe_trace_events(struct probe_trace_event *tevs, int ntevs)
 static bool kprobe_blacklist__listed(unsigned long address);
 static bool kprobe_warn_out_range(const char *symbol, unsigned long address)
 {
+	u64 etext_addr;
+
 	/* Get the address of _etext for checking non-probable text symbol */
-	if (kernel_get_symbol_address_by_name("_etext", false) < address)
+	etext_addr = kernel_get_symbol_address_by_name("_etext", false);
+
+	if (etext_addr != 0 && etext_addr < address)
 		pr_warning("%s is out of .text, skip it.\n", symbol);
 	else if (kprobe_blacklist__listed(address))
 		pr_warning("%s is blacklisted function, skip it.\n", symbol);