On Sun, Jan 04, 2026 at 03:17:24PM +0000, Richard Kojedzinszky wrote: > Package: mawk > Version: 1.3.4.20250131-1 > Severity: normal > X-Debbugs-Cc: [email protected], [email protected] > User: [email protected] > Usertags: arm64 > > Running `mawk 'BEGIN {print rand()}'` on Debian Trixie on arm64, > produces the same results. It is expected (and documented) that srand() > is called implicitly. And on Bookworm or on amd64, this works as > expected. Easy to reproduce using docker:
I see the problem.
Initially I assumed that the initial_seed function is returning
values that are much less than Max_UInt, and since they're close
together, the fmod gives the same result:
(with inactive ifdef's removed):
static double
initial_seed(void)
{
double result;
struct timespec data;
if (clock_gettime(CLOCK_REALTIME, &data) == 0)
result = (((double) data.tv_sec * 1e9) + (double) data.tv_nsec);
else
result = 0.0;
return result;
}
double seed32;
...
cseed.dval = initial_seed();
...
seed32 = fmod(cseed.dval, (double) Max_UInt);
srandom((unsigned) seed32);
Max_UInt is a 64-bit number, while unsigned is not.
However, the actual problem is this:
With my aarch64 machine, the unsigned cast on seed32 gives 0xffffffff,
(in the call to srandom) while it does not with x86_64
Changing that to a 32-bit value, e.g., UINT_MAX
seed32 = fmod(cseed.dval, (double) 0xffffffff);
makes it work.
>
> ```
> $ docker run -it --rm --platform linux/arm64 debian:trixie sh -c 'for i in 1
> 2 3 4; do mawk "BEGIN {print rand()}"; sleep 1; done'
> 0.118709
> 0.118709
> 0.118709
> 0.118709
> ```
>
> ```
> $ docker run -it --rm --platform linux/amd64 debian:trixie sh -c 'for i in 1
> 2 3 4; do mawk "BEGIN {print rand()}"; sleep 1; done'
> 0.301452
> 0.968917
> 0.975551
> 0.0758413
> ```
>
> ```
> $ docker run -it --rm --platform linux/amd64 debian:bookworm sh -c 'for i in
> 1 2 3 4; do mawk "BEGIN {print rand()}"; sleep 1; done'
> 0.133928
> 0.991352
> 0.852069
> 0.211199
> ```
>
> ```
> $ docker run -it --rm --platform linux/arm64 debian:bookworm sh -c 'for i in
> 1 2 3 4; do mawk "BEGIN {print rand()}"; sleep 1; done'
> 0.5202
> 0.878447
> 0.73942
> 0.956202
> ```
>
>
> -- System Information:
> Debian Release: 13.2
> APT prefers stable-updates
> APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500,
> 'stable')
> Architecture: arm64 (aarch64)
>
> Kernel: Linux 6.12.57+deb13-amd64 (SMP w/16 CPU threads; PREEMPT)
> Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_WARN, TAINT_OOT_MODULE,
> TAINT_UNSIGNED_MODULE
> Locale: LANG=C, LC_CTYPE=C.UTF-8 (charmap=UTF-8), LANGUAGE not set
> Shell: /bin/sh linked to /usr/bin/dash
> Init: unable to detect
>
> Versions of packages mawk depends on:
> ii libc6 2.41-12
>
> mawk recommends no packages.
>
> mawk suggests no packages.
>
> -- no debconf information
>
--
Thomas E. Dickey <[email protected]>
https://invisible-island.net
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