feat(runtime): Add an OpenBSD implementation for rss() (denoland#19221)

In case you would consider including specific implementations and not
only build fixes, here's the implementation of the ```rss()``` function
for OpenBSD.

runtime/ops/os/mod.rs

@@ -380,6 +380,53 @@ fn rss() -> usize {
  task_info.resident_size as usize
 }
 
+#[cfg(target_os = "openbsd")]
+fn rss() -> usize {
+ // Uses OpenBSD's KERN_PROC_PID sysctl(2)
+ // to retrieve information about the current
+ // process, part of which is the RSS (p_vm_rssize)
+
+ // SAFETY: libc call (get PID of own process)
+ let pid = unsafe { libc::getpid() };
+ // SAFETY: libc call (get system page size)
+ let pagesize = unsafe { libc::sysconf(libc::_SC_PAGESIZE) } as usize;
+ // KERN_PROC_PID returns a struct libc::kinfo_proc
+ let mut kinfoproc = std::mem::MaybeUninit::<libc::kinfo_proc>::uninit();
+ let mut size = std::mem::size_of_val(&kinfoproc) as libc::size_t;
+ let mut mib = [
+ libc::CTL_KERN,
+ libc::KERN_PROC,
+ libc::KERN_PROC_PID,
+ pid,
+ // mib is an array of integers, size is of type size_t
+ // conversion is safe, because the size of a libc::kinfo_proc
+ // structure will not exceed i32::MAX
+ size.try_into().unwrap(),
+ 1,
+ ];
+ // SAFETY: libc call, mib has been statically initialized,
+ // kinfoproc is a valid pointer to a libc::kinfo_proc struct
+ let res = unsafe {
+ libc::sysctl(
+ mib.as_mut_ptr(),
+ mib.len() as _,
+ kinfoproc.as_mut_ptr() as *mut libc::c_void,
+ &mut size,
+ std::ptr::null_mut(),
+ 0,
+ )
+ };
+
+ if res == 0 {
+ // SAFETY: sysctl returns 0 on success and kinfoproc is initialized
+ // p_vm_rssize contains size in pages -> multiply with pagesize to
+ // get size in bytes.
+ pagesize * unsafe { (*kinfoproc.as_mut_ptr()).p_vm_rssize as usize }
+ } else {
+ 0
+ }
+}
+
 #[cfg(windows)]
 fn rss() -> usize {
  use winapi::shared::minwindef::DWORD;