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      1 /*	$NetBSD: makecontext.c,v 1.3 2008/04/28 20:22:57 martin Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2001 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Klaus Klein.
      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 1.3 2008/04/28 20:22:57 martin Exp $");
     35 #endif
     36 
     37 #include <inttypes.h>
     38 #include <stddef.h>
     39 #include <ucontext.h>
     40 #include "extern.h"
     41 
     42 #if __STDC__
     43 #include <stdarg.h>
     44 #else
     45 #include <varargs.h>
     46 #endif
     47 
     48 void
     49 makecontext(ucontext_t *ucp, void (*func)(void), int argc, ...)
     50 {
     51 	__greg_t *gr = ucp->uc_mcontext.__gregs;
     52 	__greg_t sp, *spp;
     53 	int i;
     54 	va_list ap;
     55 
     56 	sp  = (__greg_t) ((uintptr_t)ucp->uc_stack.ss_sp
     57 	    + ucp->uc_stack.ss_size);
     58 	sp -= 2 + (argc > 8 ? argc - 8: 0); /* Make room for call frame. */
     59 	sp  = (__greg_t) ((uintptr_t)sp & ~0xf);
     60 
     61 	/*
     62 	 * Start executing at <func> -- when <func> completes, return to
     63 	 * <_resumecontext>.
     64 	 */
     65 	gr[_REG_R1]  = sp;
     66 	gr[_REG_LR] = (__greg_t)_resumecontext;
     67 	gr[_REG_PC] = (__greg_t)func; // XXX -- this is the descriptor address!
     68 
     69 	/* Wipe out stack frame backchain pointer. */
     70 	spp = (__greg_t *)sp;
     71 	*spp = 0;
     72 
     73 	/* Construct argument list. */
     74 	va_start(ap, argc);
     75 	/* Up to the first eight arguments are passed in r3-10. */
     76 	for (i = 0; i < argc && i < 8; i++)
     77 		gr[_REG_R3 + i] = va_arg(ap, long);
     78 	/* Pass remaining arguments on the stack above the backchain/lr gap. */
     79 	for (spp += 2; i < argc; i++)
     80 		*spp++ = va_arg(ap, long);
     81 	va_end(ap);
     82 }
     83