selftests: timers: Fix valid-adjtimex signed left-shift undefined behavior

PATCH Applied John Stultz 5 participants 5 messages Apr 9, 2024 – Apr 12, 2024

Subsystems (3)

Kselftest Timekeeping, clocksource core, NTP, alarmtimer High-resolution timers, timer wheel, clockevents

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John Stultz

author maintainer

2024-04-09 20:22 UTC #0 lore raw

PATCH 1/1 selftests: timers: Fix valid-adjtimex signed left-shift undefined behavior

So, 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

will trip 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,
        ~~~~^

...

So fix our use of shifting negative values in the valid-adjtimex test case to use multiply by (1<<16) to avoid this.

The patch also aligns the values a bit to make it look nicer.

Cc Thomas Gleixner <[email protected]>

Cc Stephen Boyd <[email protected]>

Cc Anna-Maria Behnsen <[email protected]>

Cc Frederic Weisbecker <[email protected]>

Cc Shuah Khan <[email protected]>

Cc Nathan Chancellor <[email protected]>

Cc Nick Desaulniers <[email protected]>

Cc Lee Jones <[email protected]>

Cc Muhammad Usama Anjum <[email protected]>

Cc [email protected]

Reported-by Lee Jones <[email protected]>

Reported-by Muhammad Usama Anjum <[email protected]>

Link https://lore.kernel.org/lkml/[email protected]/ open here

Signed-off-by John Stultz <[email protected]>

---
 .../testing/selftests/timers/valid-adjtimex.c | 69 ++++++++++---------
 1 file changed, 35 insertions(+), 34 deletions(-)

tools/testing/selftests/timers/valid-adjtimex.c +35 ~~-34~~

index 48b9a803235a..9606d45767e7 100644
@@ -62,45 +62,46 @@ 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)

Signature · 1 line

2.44.0.478.gd926399ef9-goog

Muhammad Usama Anjum

Reviewed-by on v1 1/1

2024-04-10 19:13 UTC #1 lore raw

Quoted 21 lines · John Stultz

So, 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
will trip 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,
        ~~~~^
...
So fix our use of shifting negative values in the valid-adjtimex test case to use multiply by (1<<16) to avoid this.
The patch also aligns the values a bit to make it look nicer.

Quoted 14 lines

Cc Thomas Gleixner <[email protected]>
Cc Stephen Boyd <[email protected]>
Cc Anna-Maria Behnsen <[email protected]>
Cc Frederic Weisbecker <[email protected]>
Cc Shuah Khan <[email protected]>
Cc Nathan Chancellor <[email protected]>
Cc Nick Desaulniers <[email protected]>
Cc Lee Jones <[email protected]>
Cc Muhammad Usama Anjum <[email protected]>
Cc [email protected]
Reported-by Lee Jones <[email protected]>
Reported-by Muhammad Usama Anjum <[email protected]>
Link https://lore.kernel.org/lkml/[email protected]/ open here
Signed-off-by John Stultz <[email protected]>

Reviewed-by Muhammad Usama Anjum <[email protected]>

Quoted 89 lines

---
 .../testing/selftests/timers/valid-adjtimex.c | 69 ++++++++++---------
 1 file changed, 35 insertions(+), 34 deletions(-)

tools/testing/selftests/timers/valid-adjtimex.c +35 ~~-34~~

index 48b9a803235a..9606d45767e7 100644
@@ -62,45 +62,46 @@ 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)

Signature · 2 lines

BR,
Muhammad Usama Anjum

tip-bot2 for John Stultz

merge bot Applied

2024-04-10 20:14 UTC #2 lore raw

In reply to John Stultz

The following commit has been merged into the timers/urgent branch of tip:

Commit-ID:     076361362122a6d8a4c45f172ced5576b2d4a50d
Gitweb:        https://git.kernel.org/tip/076361362122a6d8a4c45f172ced5576b2d4a50d
Author:        John Stultz <[email protected]>
AuthorDate:    Tue, 09 Apr 2024 13:22:12 -07:00
Committer:     Thomas Gleixner <[email protected]>
CommitterDate: Wed, 10 Apr 2024 22:07:42 +02:00

selftests: timers: Fix valid-adjtimex signed left-shift undefined behavior

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 <[email protected]>

Reported-by Muhammad Usama Anjum <[email protected]>

Signed-off-by John Stultz <[email protected]>

Signed-off-by Thomas Gleixner <[email protected]>

Reviewed-by Muhammad Usama Anjum <[email protected]>

Link https://lore.kernel.org/r/[email protected] open here

Link https://lore.kernel.org/lkml/[email protected]/ open here

---
 tools/testing/selftests/timers/valid-adjtimex.c | 73 +++++++---------
 1 file changed, 36 insertions(+), 37 deletions(-)

tools/testing/selftests/timers/valid-adjtimex.c +36 ~~-37~~

index 48b9a80..d13ebde 100644
@@ -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)

Shuah Khan

maintainer

2024-04-11 21:01 UTC #3 lore raw

In reply to John Stultz

Quoted 35 lines · John Stultz

So, 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
will trip 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,
         ~~~~^
...
So fix our use of shifting negative values in the valid-adjtimex test case to use multiply by (1<<16) to avoid this.
The patch also aligns the values a bit to make it look nicer.
Cc Thomas Gleixner <[email protected]>
Cc Stephen Boyd <[email protected]>
Cc Anna-Maria Behnsen <[email protected]>
Cc Frederic Weisbecker <[email protected]>
Cc Shuah Khan <[email protected]>
Cc Nathan Chancellor <[email protected]>
Cc Nick Desaulniers <[email protected]>
Cc Lee Jones <[email protected]>
Cc Muhammad Usama Anjum <[email protected]>
Cc [email protected]
Reported-by Lee Jones <[email protected]>
Reported-by Muhammad Usama Anjum <[email protected]>
Link https://lore.kernel.org/lkml/[email protected]/ open here
Signed-off-by John Stultz <[email protected]>

Quoted 1 line

---

Applied to linux-kselftest next for Linux6.10-rc1.

thanks,
-- Shuah

Thomas Gleixner

2024-04-12 10:01 UTC #4 lore raw

Shuah!

Quoted 2 lines · Shuah Khan

Applied to linux-kselftest next for Linux6.10-rc1.

I took this already through my tree as I have more timer selftest related stuff pending and coming up soon along with actual kernel changes.

Thanks,

tglx