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      1 /*	$NetBSD: makecontext.c,v 1.4 2012/03/22 17:32:22 christos Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2003 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Matt Thomas.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     29  * POSSIBILITY OF SUCH DAMAGE.
     30  */
     31 
     32 #include <sys/cdefs.h>
     33 #if defined(LIBC_SCCS) && !defined(lint)
     34 __RCSID("$NetBSD: makecontext.c,v 1.4 2012/03/22 17:32:22 christos Exp $");
     35 #endif
     36 
     37 #include <stddef.h>
     38 #include <inttypes.h>
     39 #include <ucontext.h>
     40 #include "extern.h"
     41 
     42 #include <stdarg.h>
     43 
     44 void
     45 makecontext(ucontext_t *ucp, void (*func)(void), int argc, ...)
     46 {
     47 	__greg_t *gr = ucp->uc_mcontext.__gregs;
     48 	va_list ap;
     49 	int *sp;
     50 	int i;
     51 
     52 	/* Compute and align stack pointer. */
     53 	sp = (int *)
     54 	    (((uintptr_t)ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size) & ~0x3);
     55 
     56 	/*
     57 	 * Allocate necessary stack space for arguments including arg count
     58 	 * and call frame
     59 	 */
     60 	sp -= argc + 1 + 5;
     61 
     62 	va_start(ap, argc);
     63 	sp[5] = argc;
     64 	for (i = 1; argc > 0; argc--, i++)
     65 		sp[5 + i] = va_arg(ap, int);
     66 	va_end(ap);
     67 
     68 	sp[0] = 0;			/* condition handler is null */
     69 	sp[1] = 0x20000000;		/* make this a CALLS frame */
     70 	sp[2] = 0;			/* saved argument pointer */
     71 	sp[3] = 0;			/* saved frame pointer */
     72 	sp[4] = (int)(uintptr_t)_resumecontext+2;/* return via trampoline code */
     73 
     74 	gr[_REG_AP] = (__greg_t)(uintptr_t)(sp + 5);
     75 	gr[_REG_SP] = (__greg_t)(uintptr_t)sp;
     76 	gr[_REG_FP] = (__greg_t)(uintptr_t)sp;
     77 	gr[_REG_PC] = (__greg_t)(uintptr_t)func+2;
     78 
     79 }
     80