--- /dev/null
+/*
+ * Copyright (c) 2007 Apple Inc. All rights reserved.
+ *
+ * @APPLE_LICENSE_HEADER_START@
+ *
+ * This file contains Original Code and/or Modifications of Original Code
+ * as defined in and that are subject to the Apple Public Source License
+ * Version 2.0 (the 'License'). You may not use this file except in
+ * compliance with the License. Please obtain a copy of the License at
+ * http://www.opensource.apple.com/apsl/ and read it before using this
+ * file.
+ *
+ * The Original Code and all software distributed under the License are
+ * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
+ * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
+ * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
+ * Please see the License for the specific language governing rights and
+ * limitations under the License.
+ *
+ * @APPLE_LICENSE_HEADER_END@
+ */
+
+/*
+ * Copyright (c) 2001 Daniel M. Eischen <deischen@freebsd.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Neither the name of the author nor the names of its contributors
+ * may be used to endorse or promote products derived from this software
+ * without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#if defined(__i386__)
+
+#include <sys/cdefs.h>
+
+#include <sys/param.h>
+#include <sys/signal.h>
+#include <sys/ucontext.h>
+
+#include <errno.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <ucontext.h>
+#include <unistd.h>
+
+/* Prototypes */
+extern void _ctx_start(ucontext_t *, int argc, ...);
+
+void
+_ctx_done (ucontext_t *ucp)
+{
+ if (ucp->uc_link == NULL)
+ exit(0);
+ else {
+ /*
+ * Since this context has finished, don't allow it
+ * to be restarted without being reinitialized (via
+ * setcontext or swapcontext).
+ */
+ ucp->uc_mcsize = 0;
+
+ /* Set context to next one in link */
+ /* XXX - what to do for error, abort? */
+ setcontext((const ucontext_t *)ucp->uc_link);
+ abort(); /* should never get here */
+ }
+}
+
+void
+makecontext(ucontext_t *ucp, void (*start)(void), int argc, ...)
+{
+ va_list ap;
+ char *stack_top;
+ intptr_t *argp;
+ int i;
+
+ if (ucp == NULL)
+ return;
+ else if ((ucp->uc_stack.ss_sp == NULL) ||
+ (ucp->uc_stack.ss_size < MINSIGSTKSZ)) {
+ /*
+ * This should really return -1 with errno set to ENOMEM
+ * or something, but the spec says that makecontext is
+ * a void function. At least make sure that the context
+ * isn't valid so it can't be used without an error.
+ */
+ ucp->uc_mcsize = 0;
+ }
+ /* XXX - Do we want to sanity check argc? */
+ else if ((argc < 0) || (argc > NCARGS)) {
+ ucp->uc_mcsize = 0;
+ }
+ /* Make sure the context is valid. */
+ else {
+ /*
+ * Arrange the stack as follows:
+ *
+ * _ctx_start() - context start wrapper
+ * start() - user start routine
+ * arg1 - first argument, aligned(16)
+ * ...
+ * argn
+ * ucp - this context, %ebp points here
+ *
+ * When the context is started, control will return to
+ * the context start wrapper which will pop the user
+ * start routine from the top of the stack. After that,
+ * the top of the stack will be setup with all arguments
+ * necessary for calling the start routine. When the
+ * start routine returns, the context wrapper then sets
+ * the stack pointer to %ebp which was setup to point to
+ * the base of the stack (and where ucp is stored). It
+ * will then call _ctx_done() to swap in the next context
+ * (uc_link != 0) or exit the program (uc_link == 0).
+ */
+ mcontext_t mc;
+
+ stack_top = (char *)(ucp->uc_stack.ss_sp +
+ ucp->uc_stack.ss_size - sizeof(intptr_t));
+
+ /*
+ * Adjust top of stack to allow for 3 pointers (return
+ * address, _ctx_start, and ucp) and argc arguments.
+ * We allow the arguments to be pointers also. The first
+ * argument to the user function must be properly aligned.
+ */
+ stack_top = stack_top - (sizeof(intptr_t) * (1 + argc));
+ stack_top = (char *)((unsigned)stack_top & ~15);
+ stack_top = stack_top - (2 * sizeof(intptr_t));
+ argp = (intptr_t *)stack_top;
+
+ /*
+ * Setup the top of the stack with the user start routine
+ * followed by all of its aguments and the pointer to the
+ * ucontext. We need to leave a spare spot at the top of
+ * the stack because setcontext will move eip to the top
+ * of the stack before returning.
+ */
+ *argp = (intptr_t)_ctx_start; /* overwritten with same value */
+ argp++;
+ *argp = (intptr_t)start;
+ argp++;
+
+ /* Add all the arguments: */
+ va_start(ap, argc);
+ for (i = 0; i < argc; i++) {
+ *argp = va_arg(ap, intptr_t);
+ argp++;
+ }
+ va_end(ap);
+
+ /* The ucontext is placed at the bottom of the stack. */
+ *argp = (intptr_t)ucp;
+
+ /*
+ * Set the machine context to point to the top of the
+ * stack and the program counter to the context start
+ * wrapper. Note that setcontext() pushes the return
+ * address onto the top of the stack, so allow for this
+ * by adjusting the stack downward 1 slot. Also set
+ * %esi to point to the base of the stack where ucp
+ * is stored.
+ */
+ mc = ucp->uc_mcontext;
+
+ mc->__ss.__esi = (int)argp;
+ mc->__ss.__ebp = 0;
+ mc->__ss.__esp = (int)stack_top + sizeof(caddr_t);
+ mc->__ss.__eip = (int)_ctx_start;
+ }
+}
+
+#endif /* __i386__ */
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