Thanks, is there any reference for this at least to add in the PR?

Is there any program you tried and is failing on openbsd without this patch?

The compiler will crash when compiling:

./bin/crystal build  -o .build/std_spec spec/std_spec.cr
Using compiled compiler at `.build/crystal'
Invalid memory access (signal 11) at address 0x0
[0xbff7b532456] *CallStack::print_backtrace:Int32 +118
[0xbff7b514f5b] __crystal_sigfault_handler +75
[0xbff7c206a30] sigfault_handler +48
gmake: *** [Makefile:112: .build/std_spec] Error 11

And a kernel message logged:

trap [crystal]753/414181 type 262: sp 187f8632fbe0 not inside 7f7fffbf6000-7f7fffff5000

This is due to a change in OpenBSD 6.3 which required similar changes in Go and other language ports.

Does STACK_MAP exists in previous, still supported, openbsd releases? Such as 6.2?

Oops, it will be required for OpenBSD 6.4 (and 6.3-current now). The flag was added for 6.3 but was ignored under the hood, but using the flag in previous versions will return an error. Is there a proper way to check a system .h header when compiling to toggle a flag?

I am getting other crashes when trying to compile the compiler or when running 'make spec', which I am looking into.

I believe the target triple is amd64-unknown-openbsd6.X, right? If so, You can try:

{% if flag?(:openbsd) && !flag?(:"openbsd6.2") %}

I've updated the commit to skip openbsd6.2.

I've also run crystal tool format on mman.cr since the CI tests appear to require this to pass.

Thank you!