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      1 /*	$NetBSD: _lwp.c,v 1.10 2025/04/24 23:56:25 riastradh Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2002 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * Redistribution and use in source and binary forms, with or without
      8  * modification, are permitted provided that the following conditions
      9  * are met:
     10  * 1. Redistributions of source code must retain the above copyright
     11  *    notice, this list of conditions and the following disclaimer.
     12  * 2. Redistributions in binary form must reproduce the above copyright
     13  *    notice, this list of conditions and the following disclaimer in the
     14  *    documentation and/or other materials provided with the distribution.
     15  *
     16  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     17  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     18  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     19  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     20  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     21  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     22  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     23  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     24  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     25  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     26  * POSSIBILITY OF SUCH DAMAGE.
     27  */
     28 
     29 #include <sys/cdefs.h>
     30 #if defined(LIBC_SCCS) && !defined(lint)
     31 __RCSID("$NetBSD: _lwp.c,v 1.10 2025/04/24 23:56:25 riastradh Exp $");
     32 #endif /* LIBC_SCCS and not lint */
     33 
     34 #include "namespace.h"
     35 
     36 #include <sys/param.h>
     37 #include <sys/types.h>
     38 
     39 #include <lwp.h>
     40 #include <stdlib.h>
     41 #include <ucontext.h>
     42 
     43 void
     44 _lwp_makecontext(ucontext_t *u, void (*start)(void *), void *arg,
     45 		 void *private, caddr_t stack_base, size_t stack_size)
     46 {
     47 	__greg_t *gr;
     48 	unsigned long *sp;
     49 
     50 	getcontext(u);
     51 	gr = u->uc_mcontext.__gregs;
     52 
     53 	u->uc_link = NULL;
     54 
     55 	u->uc_stack.ss_sp = stack_base;
     56 	u->uc_stack.ss_size = stack_size;
     57 
     58 
     59 	sp = (void *)(stack_base + stack_size);
     60 	sp = (ulong *)((ulong)sp & ~STACK_ALIGNBYTES);
     61 
     62 	/* Make room for the fake caller stack frame (CCFSZ, only in words) */
     63 	sp -= 8 + 8 + 1 + 6 + 1;
     64 
     65 	/* Entering (*start)(arg), return is to _lwp_exit */
     66 	gr[_REG_PC] = (ulong) start;
     67 	gr[_REG_nPC] = (ulong) start + 4;
     68 	gr[_REG_O0] = (ulong)arg;
     69 	gr[_REG_O6] = (ulong)sp;
     70 	gr[_REG_O7] = (ulong)_lwp_exit - 8;
     71 	gr[_REG_G7] = (ulong)private;
     72 
     73 	/* XXX: uwe: why do we need this? */
     74 	/* create loopback in the window save area on the stack? */
     75 	sp[8+6] = (ulong)sp;		/* %i6 */
     76 	sp[8+7] = (ulong)_lwp_exit - 8;	/* %i7 */
     77 }
     78