[v1] selftests: timers: Fix valid-adjtimex signed left-shift undefined behavior

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

Posted by John Stultz 1 year, 10 months ago

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 <tglx@linutronix.de>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Anna-Maria Behnsen <anna-maria@linutronix.de>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Lee Jones <joneslee@google.com>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: linux-kselftest@vger.kernel.org
Reported-by: Lee Jones <joneslee@google.com>
Reported-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Link: https://lore.kernel.org/lkml/0c6d4f0d-2064-4444-986b-1d1ed782135f@collabora.com/
Signed-off-by: John Stultz <jstultz@google.com>
---
 .../testing/selftests/timers/valid-adjtimex.c | 69 ++++++++++---------
 1 file changed, 35 insertions(+), 34 deletions(-)

diff --git a/tools/testing/selftests/timers/valid-adjtimex.c b/tools/testing/selftests/timers/valid-adjtimex.c
index 48b9a803235a..9606d45767e7 100644
--- a/tools/testing/selftests/timers/valid-adjtimex.c
+++ b/tools/testing/selftests/timers/valid-adjtimex.c
@@ -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)
-- 
2.44.0.478.gd926399ef9-goog

Re: [PATCH] selftests: timers: Fix valid-adjtimex signed left-shift undefined behavior

Posted by Shuah Khan 1 year, 10 months ago

On 4/9/24 14:22, John Stultz wrote:
> 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 <tglx@linutronix.de>
> Cc: Stephen Boyd <sboyd@kernel.org>
> Cc: Anna-Maria Behnsen <anna-maria@linutronix.de>
> Cc: Frederic Weisbecker <frederic@kernel.org>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Nathan Chancellor <nathan@kernel.org>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Cc: Lee Jones <joneslee@google.com>
> Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
> Cc: linux-kselftest@vger.kernel.org
> Reported-by: Lee Jones <joneslee@google.com>
> Reported-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
> Link: https://lore.kernel.org/lkml/0c6d4f0d-2064-4444-986b-1d1ed782135f@collabora.com/
> Signed-off-by: John Stultz <jstultz@google.com>
> ---

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

thanks,
-- Shuah

Re: [PATCH] selftests: timers: Fix valid-adjtimex signed left-shift undefined behavior

Posted by Thomas Gleixner 1 year, 10 months ago

Shuah!

On Thu, Apr 11 2024 at 15:01, Shuah Khan wrote:
>
> 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

Re: [PATCH] selftests: timers: Fix valid-adjtimex signed left-shift undefined behavior

Posted by Muhammad Usama Anjum 1 year, 10 months ago

On 4/10/24 1:22 AM, John Stultz wrote:
> 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 <tglx@linutronix.de>
> Cc: Stephen Boyd <sboyd@kernel.org>
> Cc: Anna-Maria Behnsen <anna-maria@linutronix.de>
> Cc: Frederic Weisbecker <frederic@kernel.org>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Nathan Chancellor <nathan@kernel.org>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Cc: Lee Jones <joneslee@google.com>
> Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
> Cc: linux-kselftest@vger.kernel.org
> Reported-by: Lee Jones <joneslee@google.com>
> Reported-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
> Link: https://lore.kernel.org/lkml/0c6d4f0d-2064-4444-986b-1d1ed782135f@collabora.com/
> Signed-off-by: John Stultz <jstultz@google.com>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>

> ---
>  .../testing/selftests/timers/valid-adjtimex.c | 69 ++++++++++---------
>  1 file changed, 35 insertions(+), 34 deletions(-)
> 
> diff --git a/tools/testing/selftests/timers/valid-adjtimex.c b/tools/testing/selftests/timers/valid-adjtimex.c
> index 48b9a803235a..9606d45767e7 100644
> --- a/tools/testing/selftests/timers/valid-adjtimex.c
> +++ b/tools/testing/selftests/timers/valid-adjtimex.c
> @@ -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)

-- 
BR,
Muhammad Usama Anjum

[tip: timers/urgent] selftests: timers: Fix valid-adjtimex signed left-shift undefined behavior

Posted by tip-bot2 for John Stultz 1 year, 10 months ago

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 <jstultz@google.com>
AuthorDate:    Tue, 09 Apr 2024 13:22:12 -07:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
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 <joneslee@google.com>
Reported-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.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/
---
 tools/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 48b9a80..d13ebde 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)