For a namespace clean function, implement _kill, otherwise implement kill. The implementation of this functionality will be tightly bound to any operating infrastructure for handling multiple processes.

A minimal implementation has no concept of either signals, nor of processes to receive those signals. So this function should always fail with an appropriate value in errno.

#include <errno.h>

#undef errno
extern int  errno;

int
_kill (int  pid,
       int  sig)
{
  errno = EINVAL;
  return -1;                    /* Always fails */

}       /* _kill () */