[PATCH] perf probe: Show correct error about @symbol for uprobe

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

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

Reported-by: Arnaldo Carvalho de Melo <acme@kernel.org>
Closes: https://lore.kernel.org/all/ZLWDEjvFjrrEJODp@kernel.org/
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 tools/perf/util/probe-event.c |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 6e2110d605fb..c1ded85fe859 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);
 }