1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21 
  22 /*
  23  * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
  24  * Use is subject to license terms.
  25  */
  26 
  27 /*      Copyright (c) 1988 AT&T     */
  28 /*        All Rights Reserved   */
  29 
  30 #pragma weak _makecontext = makecontext
  31 
  32 #include "lint.h"
  33 #include <stdarg.h>
  34 #include <ucontext.h>
  35 #include <sys/stack.h>
  36 
  37 /*
  38  * The ucontext_t that the user passes in must have been primed with a
  39  * call to getcontext(2), have the uc_stack member set to reflect the
  40  * stack which this context will use, and have the uc_link member set
  41  * to the context which should be resumed when this context returns.
  42  * When makecontext() returns, the ucontext_t will be set to run the
  43  * given function with the given parameters on the stack specified by
  44  * uc_stack, and which will return to the ucontext_t specified by uc_link.
  45  */
  46 
  47 static void resumecontext(void);
  48 
  49 void
  50 makecontext(ucontext_t *ucp, void (*func)(), int argc, ...)
  51 {
  52         long *sp;
  53         long *tsp;
  54         va_list ap;
  55         size_t size;
  56         int pusharg = (argc > 6 ? argc - 6 : 0);
  57         greg_t tmp;
  58         int i;
  59 
  60         ucp->uc_mcontext.gregs[REG_PC] = (greg_t)func;
  61 
  62         size = sizeof (long) * (pusharg + 1);
  63 
  64         /*
  65          * Calculate new value for %rsp. On entry to a function,
  66          * %rsp must be STACK_ENTRY_ALIGNed but not STACK_ALIGNed.
  67          * This is because the pushq %rbp will correct the alignment.
  68          */
  69 
  70         sp = (long *)(((uintptr_t)ucp->uc_stack.ss_sp +
  71             ucp->uc_stack.ss_size - size) & ~(STACK_ENTRY_ALIGN - 1));
  72 
  73         if (((uintptr_t)sp & (STACK_ALIGN - 1ul)) == 0)
  74                 sp -= STACK_ENTRY_ALIGN / sizeof (*sp);
  75 
  76         tsp = sp + 1;
  77 
  78         va_start(ap, argc);
  79 
  80         for (i = 0; i < argc; i++) {
  81                 tmp = va_arg(ap, long);
  82                 switch (i) {
  83                 case 0:
  84                         ucp->uc_mcontext.gregs[REG_RDI] = tmp;
  85                         break;
  86                 case 1:
  87                         ucp->uc_mcontext.gregs[REG_RSI] = tmp;
  88                         break;
  89                 case 2:
  90                         ucp->uc_mcontext.gregs[REG_RDX] = tmp;
  91                         break;
  92                 case 3:
  93                         ucp->uc_mcontext.gregs[REG_RCX] = tmp;
  94                         break;
  95                 case 4:
  96                         ucp->uc_mcontext.gregs[REG_R8] = tmp;
  97                         break;
  98                 case 5:
  99                         ucp->uc_mcontext.gregs[REG_R9] = tmp;
 100                         break;
 101                 default:
 102                         *tsp++ = tmp;
 103                         break;
 104                 }
 105         }
 106 
 107         va_end(ap);
 108 
 109         *sp = (long)resumecontext;              /* return address */
 110 
 111         ucp->uc_mcontext.gregs[REG_SP] = (greg_t)sp;
 112 }
 113 
 114 
 115 static void
 116 resumecontext(void)
 117 {
 118         ucontext_t uc;
 119 
 120         (void) getcontext(&uc);
 121         (void) setcontext(uc.uc_link);
 122 }