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      1 /*	$NetBSD: makecontext.c,v 1.10 2025/04/24 23:54:13 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 1.10 2025/04/24 23:54:13 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 __resumecontext(void) __dead;
     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;
     53 	int i;
     54 	va_list ap;
     55 
     56 	/* LINTED uintptr_t is safe */
     57 	sp  = (__greg_t *)
     58 	    ((uintptr_t)ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
     59 #if defined(__mips_o32) || defined(__mips_o64)
     60 	sp -= (argc >= 4 ? argc : 4);	/* Make room for >=4 arguments. */
     61 #elif defined(__mips_n32) || defined(__mips_n64)
     62 	sp -= (argc > 8 ? argc - 8 : 0); /* Make room for > 8 arguments. */
     63 #endif
     64 	/* LINTED uintptr_t is safe */
     65 	sp  = (__greg_t *)((uintptr_t)sp & ~STACK_ALIGNBYTES);
     66 
     67 	gr[_REG_SP]  = (intptr_t)sp;
     68 	gr[_REG_RA]  = (intptr_t)__resumecontext;
     69 	gr[_REG_T9]  = (intptr_t)func;		/* required for .abicalls */
     70 	gr[_REG_EPC] = (intptr_t)func;
     71 
     72 	/* Construct argument list. */
     73 	va_start(ap, argc);
     74 #if defined(__mips_o32) || defined(__mips_o64)
     75 	/* Up to the first four arguments are passed in $a0-3. */
     76 	for (i = 0; i < argc && i < 4; i++)
     77 		/* LINTED __greg_t is safe */
     78 		gr[_REG_A0 + i] = va_arg(ap, __greg_t);
     79 	/* Pass remaining arguments on the stack above the $a0-3 gap. */
     80 	sp += i;
     81 #endif
     82 #if defined(__mips_n32) || defined(__mips_n64)
     83 	/* Up to the first 8 arguments are passed in $a0-7. */
     84 	for (i = 0; i < argc && i < 8; i++)
     85 		/* LINTED __greg_t is safe */
     86 		gr[_REG_A0 + i] = va_arg(ap, __greg_t);
     87 	/* Pass remaining arguments on the stack */
     88 #endif
     89 	for (; i < argc; i++)
     90 		/* LINTED uintptr_t is safe */
     91 		*sp++ = va_arg(ap, __greg_t);
     92 	va_end(ap);
     93 }
     94