2 * Copyright (c) 1990 The Regents of the University of California.
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33 * $FreeBSD: src/sys/i386/i386/exception.s,v 1.65.2.3 2001/08/15 01:23:49 peter Exp $
34 * $DragonFly: src/sys/platform/vkernel/i386/fork_tramp.s,v 1.3 2007/01/22 19:37:04 corecode Exp $
37 #include <machine/asmacros.h>
38 #include <machine/segments.h>
39 #include <machine/lock.h>
40 #include <machine/psl.h>
41 #include <machine/trap.h>
48 * This function is what cpu_heavy_restore jumps to after a new process
49 * is created. The LWKT subsystem switches while holding a critical
50 * section and we maintain that abstraction here (e.g. because
51 * cpu_heavy_restore needs it due to PCB_*() manipulation), then get out of
52 * it before calling the initial function (typically fork_return()) and/or
53 * returning to user mode.
55 * The MP lock is held on entry, but for processes fork_return(esi)
56 * releases it. 'doreti' always runs without the MP lock.
58 ENTRY(fork_trampoline)
59 movq PCPU(curthread),%rax
60 subl $TDPRI_CRIT,TD_PRI(%rax)
63 * cpu_set_fork_handler intercepts this function call to
64 * have this call a non-return function to stay in kernel mode.
66 * initproc has its own fork handler, start_init(), which DOES
69 * %rbx - chaining function (typically fork_return)
70 * %r12 -> %rdi (argument)
71 * frame-> %rsi (trap frame)
73 * void (func:rbx)(arg:rdi, trapframe:rsi)
75 movq %rsp, %rsi /* pass trapframe by reference */
76 movq %r12, %rdi /* arg1 */
77 call *%rbx /* function */
79 /* cut from syscall */
83 #if defined(INVARIANTS) && defined(SMP)
84 movq PCPU(curthread),%rax
85 cmpl $0,TD_MPCOUNT(%rax)
88 movl TD_MPCOUNT(%rax), %esi
92 pmsg4: .asciz "fork_trampoline mpcount %d after calling %p"
93 /* JG what's the purpose of this alignment and is it enough on amd64? */
98 * Return via doreti to handle ASTs.
100 * trapframe is at the top of the stack.
103 pushq $0 /* if_vec */
104 movq %rsp,%rdi /* pass by reference */