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 $
36 #include <machine/asmacros.h>
37 #include <machine/segments.h>
38 #include <machine/lock.h>
39 #include <machine/psl.h>
40 #include <machine/trap.h>
46 .globl lwkt_switch_return
49 * This function is what cpu_heavy_restore jumps to after a new process
50 * is created. The LWKT subsystem switches while holding a critical
51 * section and we maintain that abstraction here (e.g. because
52 * cpu_heavy_restore needs it due to PCB_*() manipulation), then get out of
53 * it before calling the initial function (typically fork_return()) and/or
54 * returning to user mode.
56 * The MP lock is not held at any point but the critcount is bumped
57 * on entry to prevent interruption of the trampoline at a bad point.
59 * This is effectively what td->td_switch() returns to. It 'returns' the
60 * old thread in %eax and since this is not returning to a td->td_switch()
61 * call from lwkt_switch() we must handle the cleanup for the old thread
62 * by calling lwkt_switch_return().
64 * fork_trampoline(%eax:otd, %esi:func, %ebx:arg)
66 ENTRY(fork_trampoline)
68 call lwkt_switch_return
70 movl PCPU(curthread),%eax
71 decl TD_CRITCOUNT(%eax)
74 * cpu_set_fork_handler intercepts this function call to
75 * have this call a non-return function to stay in kernel mode.
77 * initproc has its own fork handler, start_init(), which DOES
80 * The function (set in pcb_esi) gets passed two arguments,
81 * the primary parameter set in pcb_ebx and a pointer to the
83 * void (func)(int arg, struct trapframe *frame);
85 pushl %esp /* pass frame by reference */
87 call *%esi /* function */
89 /* cut from syscall */
94 * Return via doreti to handle ASTs.
99 pushl %esp /* pass by reference */