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      1 /*	$NetBSD: makecontext.c,v 1.6 2025/04/24 23:56:25 riastradh 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 1.6 2025/04/24 23:56:25 riastradh Exp $");
     35 #endif
     36 
     37 #include <sys/param.h>
     38 
     39 #include <inttypes.h>
     40 #include <stdarg.h>
     41 #include <stddef.h>
     42 #include <ucontext.h>
     43 
     44 #include "extern.h"
     45 
     46 void
     47 makecontext(ucontext_t *ucp, void (*func)(void), int argc, ...)
     48 {
     49 	__greg_t *gr = ucp->uc_mcontext.__gregs;
     50 	int i;
     51 	unsigned long *sp;
     52 	va_list ap;
     53 
     54 	sp = (unsigned long *)
     55 	    ((unsigned long)ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
     56 	/* Make room for: rwindow, struct return pointer, argd, argx */
     57 	sp -= 8 + 8 + 1 + 6 + 1; /* CCFSZ, only in words */
     58 	/* CCFSZ provides space for up to 7 arguments, add more if necessary */
     59 	if (argc > 7)
     60 		sp -= argc - 7;
     61 	/* Align on double-word boundary. */
     62 	sp = (unsigned long *)((unsigned long)sp & ~STACK_ALIGNBYTES);
     63 
     64 	gr[_REG_O6] = (__greg_t)sp;
     65 	gr[_REG_PC] = (__greg_t)func;
     66 	gr[_REG_nPC] = (__greg_t)func + 4;
     67 	gr[_REG_O7] = (__greg_t)_resumecontext - 8;
     68 
     69 	va_start(ap, argc);
     70 	/* Pass up to 6 arguments in %o0..%o5. */
     71 	for (i = 0; i < argc && i < 6; i++)
     72 		gr[_REG_O0 + i] = va_arg(ap, unsigned long);
     73 	/* Pass any additional arguments on the stack. */
     74 	for (/* i = 6 */; i < argc; i++)
     75 		sp[8 + 8 + 1 + 6 + (i - 6)] = va_arg(ap, unsigned long);
     76 	va_end(ap);
     77 }
     78