linux-kernel - [PATCH 2/5] kcsan: Simplify constant string handling

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Message-Id: <20200731081723.2181297-3-elver@google.com>
Date:   Fri, 31 Jul 2020 10:17:20 +0200
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com, paulmck@...nel.org
Cc:     dvyukov@...gle.com, glider@...gle.com, andreyknvl@...gle.com,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org
Subject: [PATCH 2/5] kcsan: Simplify constant string handling

Simplify checking prefixes and length calculation of constant strings.
For the former, the kernel provides str_has_prefix(), and the latter we
should just use strlen("..") because GCC and Clang have optimizations
that optimize these into constants.

No functional change intended.

Signed-off-by: Marco Elver <elver@...gle.com>
---
 kernel/kcsan/debugfs.c | 8 ++++----
 kernel/kcsan/report.c  | 4 ++--
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/kcsan/debugfs.c b/kernel/kcsan/debugfs.c
index 3a9566addeff..116bdd8f050c 100644
--- a/kernel/kcsan/debugfs.c
+++ b/kernel/kcsan/debugfs.c
@@ -300,16 +300,16 @@ debugfs_write(struct file *file, const char __user *buf, size_t count, loff_t *o
 		WRITE_ONCE(kcsan_enabled, true);
 	} else if (!strcmp(arg, "off")) {
 		WRITE_ONCE(kcsan_enabled, false);
-	} else if (!strncmp(arg, "microbench=", sizeof("microbench=") - 1)) {
+	} else if (str_has_prefix(arg, "microbench=")) {
 		unsigned long iters;
 
-		if (kstrtoul(&arg[sizeof("microbench=") - 1], 0, &iters))
+		if (kstrtoul(&arg[strlen("microbench=")], 0, &iters))
 			return -EINVAL;
 		microbenchmark(iters);
-	} else if (!strncmp(arg, "test=", sizeof("test=") - 1)) {
+	} else if (str_has_prefix(arg, "test=")) {
 		unsigned long iters;
 
-		if (kstrtoul(&arg[sizeof("test=") - 1], 0, &iters))
+		if (kstrtoul(&arg[strlen("test=")], 0, &iters))
 			return -EINVAL;
 		test_thread(iters);
 	} else if (!strcmp(arg, "whitelist")) {
diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
index d05052c23261..15add93ff12e 100644
--- a/kernel/kcsan/report.c
+++ b/kernel/kcsan/report.c
@@ -279,8 +279,8 @@ static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries
 
 		cur = strnstr(buf, "kcsan_", len);
 		if (cur) {
-			cur += sizeof("kcsan_") - 1;
-			if (strncmp(cur, "test", sizeof("test") - 1))
+			cur += strlen("kcsan_");
+			if (!str_has_prefix(cur, "test"))
 				continue; /* KCSAN runtime function. */
 			/* KCSAN related test. */
 		}
-- 
2.28.0.163.g6104cc2f0b6-goog