perf probe: Show correct error message about @symbol usage for uprobe

Since @symbol variable access is not supported by uprobe event, it must be
correctly warn user instead of kernel version update.

Committer testing:

With/without the patch:

  [root@quaco ~]# perf probe -x ~/bin/perf -L sigtrap_handler
  <sigtrap_handler@/home/acme/git/perf-tools-next/tools/perf/tests/sigtrap.c:0>
        0  sigtrap_handler(int signum __maybe_unused, siginfo_t *info, void *ucontext __maybe_unused)
        1  {
        2         if (!__atomic_fetch_add(&ctx.signal_count, 1, __ATOMIC_RELAXED))
        3                 ctx.first_siginfo = *info;
        4         __atomic_fetch_sub(&ctx.tids_want_signal, syscall(SYS_gettid), __ATOMIC_RELAXED);
        5  }

           static void *test_thread(void *arg)
           {

  [root@quaco ~]# perf probe -x ~/bin/perf sigtrap_handler:4 "ctx.signal_count"

Without the patch:

  [root@quaco ~]# perf probe -x ~/bin/perf sigtrap_handler:4 "ctx.signal_count"
  Failed to write event: Invalid argument
  Please upgrade your kernel to at least 3.14 to have access to feature @ctx
    Error: Failed to add events.
  [root@quaco ~]#

With the patch:

  [root@quaco ~]#
  Failed to write event: Invalid argument
  @ctx accesses a variable by symbol name, but that is not supported for user application probe.
    Error: Failed to add events.
  [root@quaco ~]#

Reported-by: Arnaldo Carvalho de Melo <acme@kernel.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Closes: https://lore.kernel.org/all/ZLWDEjvFjrrEJODp@kernel.org/
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: https://lore.kernel.org/r/169055397023.67089.12693645664676964310.stgit@devnote2
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 9 insertions, 4 deletions

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 16822a8a540f..2d056f02ae40 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -2800,13 +2800,18 @@ static void warn_uprobe_event_compat(struct probe_trace_event *tev)
 	if (!tev->uprobes || tev->nargs == 0 || !buf)
 		goto out;
 
-	for (i = 0; i < tev->nargs; i++)
-		if (strglobmatch(tev->args[i].value, "[$@+-]*")) {
-			pr_warning("Please upgrade your kernel to at least "
-				   "3.14 to have access to feature %s\n",
+	for (i = 0; i < tev->nargs; i++) {
+		if (strchr(tev->args[i].value, '@')) {
+			pr_warning("%s accesses a variable by symbol name, but that is not supported for user application probe.\n",
+				   tev->args[i].value);
+			break;
+		}
+		if (strglobmatch(tev->args[i].value, "[$+-]*")) {
+			pr_warning("Please upgrade your kernel to at least 3.14 to have access to feature %s\n",
 				   tev->args[i].value);
 			break;
 		}
+	}
 out:
 	free(buf);
 }