CPU_LWP_FORK(9) BSD Kernel Developer's Manual CPU_LWP_FORK(9)
cpu_lwp_fork, child_return, proc_trampoline -- finish a fork operation
cpu_lwp_fork(struct lwp *l1, struct lwp *l2, void *stack, size_t stacksize,
void (*func)(void *), void *arg);
cpu_lwp_fork() is the machine-dependent portion of fork1() which finishes a fork operation,
with child lwp l2 nearly set up. It copies and updates the PCB and trap frame from the par-
ent l1, making the child ready to run.
cpu_lwp_fork() rigs the child's kernel stack so that it will start in proc_trampoline().
proc_trampoline() does not have a normal calling sequence and is entered by cpu_switch().
If an alternate user-level stack is requested (with non-zero values in both the stack and
stacksize arguments), the user stack pointer is set up accordingly.
After being entered by cpu_switch() and while running in user context (within the kernel)
proc_trampoline() will invoke the function func with the argument arg. If a kernel thread
is being created, the return path and argument are specified with func and arg. If a user
process is being created, fork1() will pass child_return() and l2 to cpu_lwp_fork() as func
and arg respectively. This causes the newly-created child process to go directly to user
level with an apparent return value of 0 from fork(2), while the parent process returns nor-
fork(2), cpu_switchto(9), fork1(9)
BSD April 13, 2010 BSD