[3/3] trace-cmd traceevent: Add handler for __builtin_expect()

Commit Message

Tzvetomir Stoyanov (VMware) June 25, 2020, 10:04 a.m. UTC

From: Steven Rostedt (VMware) <[e-mail]>

In order to move pointer checks like IS_ERR_VALUE() out of the hotpath
and into the reader path of a trace event, user space tools need to be
able to parse that. IS_ERR_VALUE() is defined as:

 #define IS_ERR_VALUE() unlikely((unsigned long)(void *)(x) >= (unsigned long)-MAX_ERRNO)

Which eventually turns into:

  __builtin_expect(!!((unsigned long)(void *)(x) >= (unsigned long)-4095), 0)

Now the traceevent parser can handle most of that except for the
__builtin_expect(), which needs to be added.

Link: https://lore.kernel.org/linux-mm/[e-mail]/

Signed-off-by: Steven Rostedt (VMware) <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Jaewon Kim <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Kees Kook <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Link: http://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>
Signed-off-by: Tzvetomir Stoyanov (VMware) <[e-mail]>
---
 lib/traceevent/event-parse.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

Patch

diff --git a/lib/traceevent/event-parse.c b/lib/traceevent/event-parse.c
index 7e9cd9bb..ee16be96 100644
--- a/lib/traceevent/event-parse.c
+++ b/lib/traceevent/event-parse.c
@@ -3084,6 +3084,37 @@  err:
 	return TEP_EVENT_ERROR;
 }
 
+static enum tep_event_type
+process_builtin_expect(struct tep_event *event, struct tep_print_arg *arg, char **tok)
+{
+	enum tep_event_type type;
+	char *token = NULL;
+
+	/* Handle __builtin_expect( cond, #) */
+	type = process_arg(event, arg, &token);
+
+	if (type != TEP_EVENT_DELIM || token[0] != ',')
+		goto out_free;
+
+	free_token(token);
+
+	/* We don't care what the second parameter is of the __builtin_expect() */
+	if (read_expect_type(TEP_EVENT_ITEM, &token) < 0)
+		goto out_free;
+
+	if (read_expected(TEP_EVENT_DELIM, ")") < 0)
+		goto out_free;
+
+	free_token(token);
+	type = read_token_item(tok);
+	return type;
+
+out_free:
+	free_token(token);
+	*tok = NULL;
+	return TEP_EVENT_ERROR;
+}
+
 static enum tep_event_type
 process_function(struct tep_event *event, struct tep_print_arg *arg,
 		 char *token, char **tok)
@@ -3128,6 +3159,10 @@  process_function(struct tep_event *event, struct tep_print_arg *arg,
 		free_token(token);
 		return process_dynamic_array_len(event, arg, tok);
 	}
+	if (strcmp(token, "__builtin_expect") == 0) {
+		free_token(token);
+		return process_builtin_expect(event, arg, tok);
+	}
 
 	func = find_func_handler(event->tep, token);
 	if (func) {