linux-kernel - Re: [PATCH 2/7] tracing: Change strlen to sizeof for hist trigger static strings

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Date:   Wed, 19 Dec 2018 15:27:05 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Tom Zanussi <zanussi@...nel.org>
Cc:     tglx@...utronix.de, mhiramat@...nel.org, namhyung@...nel.org,
        vedang.patel@...el.com, bigeasy@...utronix.de,
        joel@...lfernandes.org, mathieu.desnoyers@...icios.com,
        julia@...com, linux-kernel@...r.kernel.org,
        linux-rt-users@...r.kernel.org
Subject: Re: [PATCH 2/7] tracing: Change strlen to sizeof for hist trigger
 static strings

On Wed, 19 Dec 2018 13:46:49 -0600
Tom Zanussi <zanussi@...nel.org> wrote:


> Yeah, I had considered it but wasn't sure it was worth it.  Since
> you're suggesting it is, I can send another patch on top of these, or
> feel free if you want to too.  ;-)
> 

Here, want to ack/review it?

-- Steve


>From 664457f5cc776aa624502bc628285ea6d70ac8c9 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
Date: Wed, 19 Dec 2018 15:13:33 -0500
Subject: [PATCH] tracing: Add strncmp_const() macro to prevent typos and cut
 paste errors

The trace_events_hist.c file has a lot of strncmp()s of the form:

   if (strncmp(str, "constant", sizeof("constant") - 1) == 0)

To prevent typos and errors with the constant string being different from
the string use in sizeof(), and also to condense the code, add a macro that
does this:

 #define strncmp_const(str, str_const) \
   strncmp(str, str_const, sizeof(str_const) - 1)

Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 kernel/trace/trace_events_hist.c | 32 ++++++++++++++++++--------------
 1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index c5448c103770..40e76053d3d7 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -22,6 +22,10 @@
 
 #define STR_VAR_LEN_MAX		32 /* must be multiple of sizeof(u64) */
 
+/* Safe way to compare string constants (from typos and cut and paste errors) */
+#define strncmp_const(str, str_const)			\
+	strncmp(str, str_const, sizeof(str_const) - 1)
+
 struct hist_field;
 
 typedef u64 (*hist_field_fn_t) (struct hist_field *field,
@@ -1881,8 +1885,8 @@ static int parse_action(char *str, struct hist_trigger_attrs *attrs)
 	if (attrs->n_actions >= HIST_ACTIONS_MAX)
 		return ret;
 
-	if ((strncmp(str, "onmatch(", sizeof("onmatch(") - 1) == 0) ||
-	    (strncmp(str, "onmax(", sizeof("onmax(") - 1) == 0)) {
+	if ((strncmp_const(str, "onmatch(") == 0) ||
+	    (strncmp_const(str, "onmax(") == 0)) {
 		attrs->action_str[attrs->n_actions] = kstrdup(str, GFP_KERNEL);
 		if (!attrs->action_str[attrs->n_actions]) {
 			ret = -ENOMEM;
@@ -1899,34 +1903,34 @@ static int parse_assignment(char *str, struct hist_trigger_attrs *attrs)
 {
 	int ret = 0;
 
-	if ((strncmp(str, "key=", sizeof("key=") - 1) == 0) ||
-	    (strncmp(str, "keys=", sizeof("keys=") - 1) == 0)) {
+	if ((strncmp_const(str, "key=") == 0) ||
+	    (strncmp_const(str, "keys=") == 0)) {
 		attrs->keys_str = kstrdup(str, GFP_KERNEL);
 		if (!attrs->keys_str) {
 			ret = -ENOMEM;
 			goto out;
 		}
-	} else if ((strncmp(str, "val=", sizeof("val=") - 1) == 0) ||
-		 (strncmp(str, "vals=", sizeof("vals=") - 1) == 0) ||
-		 (strncmp(str, "values=", sizeof("values=") - 1) == 0)) {
+	} else if ((strncmp_const(str, "val=") == 0) ||
+		   (strncmp_const(str, "vals=") == 0) ||
+		   (strncmp_const(str, "values=") == 0)) {
 		attrs->vals_str = kstrdup(str, GFP_KERNEL);
 		if (!attrs->vals_str) {
 			ret = -ENOMEM;
 			goto out;
 		}
-	} else if (strncmp(str, "sort=", sizeof("sort=") - 1) == 0) {
+	} else if (strncmp_const(str, "sort=") == 0) {
 		attrs->sort_key_str = kstrdup(str, GFP_KERNEL);
 		if (!attrs->sort_key_str) {
 			ret = -ENOMEM;
 			goto out;
 		}
-	} else if (strncmp(str, "name=", sizeof("name=") - 1) == 0) {
+	} else if (strncmp_const(str, "name=") == 0) {
 		attrs->name = kstrdup(str, GFP_KERNEL);
 		if (!attrs->name) {
 			ret = -ENOMEM;
 			goto out;
 		}
-	} else if (strncmp(str, "clock=", sizeof("clock=") - 1) == 0) {
+	} else if (strncmp_const(str, "clock=") == 0) {
 		strsep(&str, "=");
 		if (!str) {
 			ret = -EINVAL;
@@ -1939,7 +1943,7 @@ static int parse_assignment(char *str, struct hist_trigger_attrs *attrs)
 			ret = -ENOMEM;
 			goto out;
 		}
-	} else if (strncmp(str, "size=", sizeof("size=") - 1) == 0) {
+	} else if (strncmp_const(str, "size=") == 0) {
 		int map_bits = parse_map_size(str);
 
 		if (map_bits < 0) {
@@ -3558,7 +3562,7 @@ static struct action_data *onmax_parse(char *str)
 	if (!onmax_fn_name || !str)
 		goto free;
 
-	if (strncmp(onmax_fn_name, "save", sizeof("save") - 1) == 0) {
+	if (strncmp_const(onmax_fn_name, "save") == 0) {
 		char *params = strsep(&str, ")");
 
 		if (!params) {
@@ -4346,7 +4350,7 @@ static int parse_actions(struct hist_trigger_data *hist_data)
 	for (i = 0; i < hist_data->attrs->n_actions; i++) {
 		str = hist_data->attrs->action_str[i];
 
-		if (strncmp(str, "onmatch(", sizeof("onmatch(") - 1) == 0) {
+		if (strncmp_const(str, "onmatch(") == 0) {
 			char *action_str = str + sizeof("onmatch(") - 1;
 
 			data = onmatch_parse(tr, action_str);
@@ -4355,7 +4359,7 @@ static int parse_actions(struct hist_trigger_data *hist_data)
 				break;
 			}
 			data->fn = action_trace;
-		} else if (strncmp(str, "onmax(", sizeof("onmax(") - 1) == 0) {
+		} else if (strncmp_const(str, "onmax(") == 0) {
 			char *action_str = str + sizeof("onmax(") - 1;
 
 			data = onmax_parse(action_str);
-- 
2.19.1