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      1 /* $NetBSD: makecontext.c,v 1.2 2018/11/16 10:51:08 ryo Exp $ */
      2 
      3 /*-
      4  * Copyright (c) 2014 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 of 3am Software Foundry.
      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 1.2 2018/11/16 10:51:08 ryo 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 * const gr = ucp->uc_mcontext.__gregs;
     48 	__uint64_t *sp;
     49 
     50 	/* Compute and align stack pointer. */
     51 	sp = (uint64_t *)
     52 	    (((uintptr_t)ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size) & -16LL);
     53 	/* Allocate necessary stack space for arguments exceeding x0-7. */
     54 	if (argc > 8)
     55 		sp -= argc - 8;
     56 	gr[_REG_SP] = (__greg_t)(uintptr_t)sp;
     57 	/* Wipe out frame pointer. */
     58 	gr[_REG_X29] = 0;
     59 	/* Arrange for return via the trampoline code. */
     60 	gr[_REG_X30] = (__greg_t)(uintptr_t)_resumecontext;
     61 	gr[_REG_PC] = (__greg_t)(uintptr_t)func;
     62 
     63 	va_list ap;
     64 	va_start(ap, argc);
     65 
     66 	/* Pass up to eight arguments in x0-x7. */
     67 	for (int i = 0; i < argc && i < 8; i++) {
     68 		gr[_REG_X0 + i] = va_arg(ap, __greg_t);
     69 	}
     70 
     71 	/* Pass any additional arguments on the stack. */
     72 	for (int i = 8; i < argc; i++) {
     73 		*sp++ = va_arg(ap, uint64_t);
     74 	}
     75 	va_end(ap);
     76 }
     77