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

[Shuah Khan]

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@xxxxxxxxxxxxx>
> Cc: Stephen Boyd <sboyd@xxxxxxxxxx>
> Cc: Anna-Maria Behnsen <anna-maria@xxxxxxxxxxxxx>
> Cc: Frederic Weisbecker <frederic@xxxxxxxxxx>
> Cc: Shuah Khan <shuah@xxxxxxxxxx>
> Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
> Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Cc: Lee Jones <joneslee@xxxxxxxxxx>
> Cc: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
> Cc: linux-kselftest@xxxxxxxxxxxxxxx
> Reported-by: Lee Jones <joneslee@xxxxxxxxxx>
> Reported-by: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
> Link: https://lore.kernel.org/lkml/0c6d4f0d-2064-4444-986b-1d1ed782135f@xxxxxxxxxxxxx/
> Signed-off-by: John Stultz <jstultz@xxxxxxxxxx>
> ---

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

thanks,
-- Shuah