minimal.cc example fails on ARM

[slyon]

Describe the bug
ptl-minimal crashes with SIGFPE, Arithmetic exception on 32bit ARM. If commit 4e230f6 is reverted, the problem disappears. Especially the following line seems to introduce the Floating point exception:
static intmax_t nincr = std::max<intmax_t>(ncores / ncpus, 1);

See also: https://bugs.debian.org/1001237

(gdb) run
Starting program: /root/ptl-2.3.0/examples/build/minimal/ptl-minimal 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/arm-linux-gnueabihf/libthread_db.so.1".


          ##############################
          !!! Backtrace is activated !!!
          ##############################

[ptl-minimal]> Number of threads: 1
[New Thread 0xf7c259a0 (LWP 17519)]

Thread 1 "ptl-minimal" received signal SIGFPE, Arithmetic exception.
__libc_do_syscall () at ../sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:47
47	../sysdeps/unix/sysv/linux/arm/libc-do-syscall.S: No such file or directory.
(gdb) bt
#0  __libc_do_syscall () at ../sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:47
#1  0xf7cac3e0 in __pthread_kill_implementation (threadid=4160618512, signo=signo@entry=8, no_tid=no_tid@entry=0)
    at pthread_kill.c:43
#2  0xf7cac424 in __pthread_kill_internal (signo=<optimized out>, threadid=<optimized out>) at pthread_kill.c:80
#3  0xf7c7b690 in __GI_raise (sig=8) at ../sysdeps/posix/raise.c:26
#4  0xf7d8201e in __aeabi_ldiv0 () from /lib/arm-linux-gnueabihf/libgcc_s.so.1
#5  0x00407e5c in main::{lambda(long long)#3}::operator()(long long) const ()
#6  0x0040d49e in long long std::__invoke_impl<long long, main::{lambda(long long)#3}&, long long>(std::__invoke_other, main::{lambda(long long)#3}&, long long&&) ()
#7  0x0040ca6e in std::enable_if<is_invocable_r_v<long long, main::{lambda(long long)#3}&, long long>, long long>::type std::__invoke_r<long long, main::{lambda(long long)#3}&, long long>(main::{lambda(long long)#3}&, long long&&) ()
#8  0x0040baf6 in std::_Function_handler<long long (long long), main::{lambda(long long)#3}>::_M_invoke(std::_Any_data const&, long long&&) ()
#9  0xf7f9f620 in PTL::ThreadPool::set_affinity(long long, std::thread&) const ()
   from /lib/arm-linux-gnueabihf/libptl.so.2
#10 0xf7fa1234 in PTL::ThreadPool::initialize_threadpool(unsigned int) () from /lib/arm-linux-gnueabihf/libptl.so.2
#11 0xf7fa22d8 in PTL::ThreadPool::ThreadPool(PTL::ThreadPool::Config const&) ()
   from /lib/arm-linux-gnueabihf/libptl.so.2
#12 0x00408ada in main ()

To Reproduce
Steps to reproduce the behavior:

1. apt install libptl-dev (v2.3.0-1)
2. cd examples && mkdir build && cd build
3. cmake .. && make
4. ./minimal/ptl-minimal (Observe crash)

Expected behavior
Test should be run successfully.

Desktop (please complete the following information):

• OS: Ubuntu Jammy (devel)
• Version 22.04

Additional context
Does not seem to happen on other architectures but armhf (32bit ARM)

[slyon]

On further investigation I think the problem is in the new Threading::GetNumberOfPhysicalCpus() function.

It reads /proc/cpuinfo and checks for core id lines, that is (for some reason) not available on armhf, returning 0 and producing a division by zero:

$ uname -a
Linux deciding-barnacle 5.4.0-54-generic #60-Ubuntu SMP Fri Nov 6 10:42:16 UTC 2020 armv8l armv8l armv8l GNU/Linux
$ cat /proc/cpuinfo 
processor	: 0
BogoMIPS	: 100.00
Features	: fp asimd evtstrm cpuid
CPU implementer	: 0x50
CPU architecture: 8
CPU variant	: 0x0
CPU part	: 0x000
CPU revision	: 1