siginfo_t: si_pid, si_status on OpenBSD/NetBSD

[LunarLambda]

POSIX defines the following fields on siginfo_t link:

int           si_signo  Signal number. 
int           si_code   Signal code. 
int           si_errno  If non-zero, an errno value associated with 
                        this signal, as described in <errno.h>. 
pid_t         si_pid    Sending process ID. 
uid_t         si_uid    Real user ID of sending process. 
void         *si_addr   Address of faulting instruction. 
int           si_status Exit value or signal. 
long          si_band   Band event for SIGPOLL. 
union sigval  si_value  Signal value.

Of particular interest to me are si_signo, si_code (which are already exposed everywhere), as well as si_pid and si_status. These allow asynchronously receiving the exit status of a child process via SIGCHLD.

However, on x86_64-unknown-netbsd (documented here) and x86_64-unknown-openbsd (undocumented but exists here) , these fields are not exposed in any way. on x86_64-unknown-linux-gnu they are exposed as unsafe methods, and on x86_64-unknown-freebsd, as regular struct fields and unsafe methods.

I understand that this is due to some implementations choosing to use unions, or having different struct field orders. It would be very helpful if there was a consistent, portable way to access them, or at the very least, expose them on those two targets.