linux-kernel - [PATCH AUTOSEL 5.15 09/10] selftests: timers: Fix valid-adjtimex signed left-shift undefined behavior

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Message-ID: <20240422231929.1611680-9-sashal@kernel.org>
Date: Mon, 22 Apr 2024 19:19:22 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: John Stultz <jstultz@...gle.com>,
	Lee Jones <joneslee@...gle.com>,
	Muhammad Usama Anjum <usama.anjum@...labora.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sasha Levin <sashal@...nel.org>,
	shuah@...nel.org,
	nathan@...nel.org,
	linux-kselftest@...r.kernel.org,
	llvm@...ts.linux.dev
Subject: [PATCH AUTOSEL 5.15 09/10] selftests: timers: Fix valid-adjtimex signed left-shift undefined behavior

From: John Stultz <jstultz@...gle.com>

[ Upstream commit 076361362122a6d8a4c45f172ced5576b2d4a50d ]

The struct adjtimex freq field takes a signed value who's units are in
shifted (<<16) parts-per-million.

Unfortunately for negative adjustments, the straightforward use of:

  freq = ppm << 16 trips undefined behavior warnings with clang:

valid-adjtimex.c:66:6: warning: shifting a negative signed value is undefined [-Wshift-negative-value]
        -499<<16,
        ~~~~^
valid-adjtimex.c:67:6: warning: shifting a negative signed value is undefined [-Wshift-negative-value]
        -450<<16,
        ~~~~^
.

Fix it by using a multiply by (1 << 16) instead of shifting negative values
in the valid-adjtimex test case. Align the values for better readability.

Reported-by: Lee Jones <joneslee@...gle.com>
Reported-by: Muhammad Usama Anjum <usama.anjum@...labora.com>
Signed-off-by: John Stultz <jstultz@...gle.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@...labora.com>
Link: https://lore.kernel.org/r/20240409202222.2830476-1-jstultz@google.com
Link: https://lore.kernel.org/lkml/0c6d4f0d-2064-4444-986b-1d1ed782135f@collabora.com/
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 .../testing/selftests/timers/valid-adjtimex.c | 73 +++++++++----------
 1 file changed, 36 insertions(+), 37 deletions(-)

diff --git a/tools/testing/selftests/timers/valid-adjtimex.c b/tools/testing/selftests/timers/valid-adjtimex.c
index 48b9a803235a8..d13ebde203221 100644
--- a/tools/testing/selftests/timers/valid-adjtimex.c
+++ b/tools/testing/selftests/timers/valid-adjtimex.c
@@ -21,9 +21,6 @@
  *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  *   GNU General Public License for more details.
  */
-
-
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <time.h>
@@ -62,45 +59,47 @@ int clear_time_state(void)
 #define NUM_FREQ_OUTOFRANGE 4
 #define NUM_FREQ_INVALID 2
 
+#define SHIFTED_PPM (1 << 16)
+
 long valid_freq[NUM_FREQ_VALID] = {
-	-499<<16,
-	-450<<16,
-	-400<<16,
-	-350<<16,
-	-300<<16,
-	-250<<16,
-	-200<<16,
-	-150<<16,
-	-100<<16,
-	-75<<16,
-	-50<<16,
-	-25<<16,
-	-10<<16,
-	-5<<16,
-	-1<<16,
+	 -499 * SHIFTED_PPM,
+	 -450 * SHIFTED_PPM,
+	 -400 * SHIFTED_PPM,
+	 -350 * SHIFTED_PPM,
+	 -300 * SHIFTED_PPM,
+	 -250 * SHIFTED_PPM,
+	 -200 * SHIFTED_PPM,
+	 -150 * SHIFTED_PPM,
+	 -100 * SHIFTED_PPM,
+	  -75 * SHIFTED_PPM,
+	  -50 * SHIFTED_PPM,
+	  -25 * SHIFTED_PPM,
+	  -10 * SHIFTED_PPM,
+	   -5 * SHIFTED_PPM,
+	   -1 * SHIFTED_PPM,
 	-1000,
-	1<<16,
-	5<<16,
-	10<<16,
-	25<<16,
-	50<<16,
-	75<<16,
-	100<<16,
-	150<<16,
-	200<<16,
-	250<<16,
-	300<<16,
-	350<<16,
-	400<<16,
-	450<<16,
-	499<<16,
+	    1 * SHIFTED_PPM,
+	    5 * SHIFTED_PPM,
+	   10 * SHIFTED_PPM,
+	   25 * SHIFTED_PPM,
+	   50 * SHIFTED_PPM,
+	   75 * SHIFTED_PPM,
+	  100 * SHIFTED_PPM,
+	  150 * SHIFTED_PPM,
+	  200 * SHIFTED_PPM,
+	  250 * SHIFTED_PPM,
+	  300 * SHIFTED_PPM,
+	  350 * SHIFTED_PPM,
+	  400 * SHIFTED_PPM,
+	  450 * SHIFTED_PPM,
+	  499 * SHIFTED_PPM,
 };
 
 long outofrange_freq[NUM_FREQ_OUTOFRANGE] = {
-	-1000<<16,
-	-550<<16,
-	550<<16,
-	1000<<16,
+	-1000 * SHIFTED_PPM,
+	 -550 * SHIFTED_PPM,
+	  550 * SHIFTED_PPM,
+	 1000 * SHIFTED_PPM,
 };
 
 #define LONG_MAX (~0UL>>1)
-- 
2.43.0