utrace —
insert user record in ktrace log
Standard C Library (libc, -lc)
Adds a record to the process trace with information supplied by user. The record
  is identified by label and contains
  len bytes from memory pointed to by
  addr. This call only has an effect if the calling
  process is being traced.
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1
  is returned and errno is set to indicate the error.
  - [ENOSYS]
- Currently running kernel was compiled without
      ktrace(2) support (option
      KTRACE).
- [EINVAL]
- Specified data length len was bigger than
      KTR_USER_MAXLEN.
Theutrace() system call first appeared in
  FreeBSD 2.2. It was added to
  NetBSD in NetBSD 1.6. The
  label argument is a NetBSD
  extension.