Add getcontext, setcontext, makecontext, and swapcontext. These

functions are defined in SUSv2 and the latest POSIX spec.

Thanks to Bernd Walter <ticso@cicely8.cicely.de> for helping debug my
alpha assembly.

Approved by:	-arch

1 files changed, 159 insertions, 0 deletions

diff --git a/lib/libc/i386/gen/makecontext.c b/lib/libc/i386/gen/makecontext.c
new file mode 100644
index 0000000..1334b5a
--- /dev/null
+++ b/lib/libc/i386/gen/makecontext.c
@@ -0,0 +1,159 @@
+/*
+ * 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.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/signal.h>
+
+#include <errno.h>
+#include <stdarg.h>
+#include <ucontext.h>
+#include <unistd.h>
+
+/* Prototypes */
+extern void _ctx_start(ucontext_t *, int argc, ...);
+
+
+__weak_reference(__makecontext, makecontext);
+
+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_mcontext.mc_flags = 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_mcontext.mc_flags = 0;
+	}
+	/* XXX - Do we want to sanity check argc? */
+	else if ((argc < 0) || (argc > NCARGS)) {
+		ucp->uc_mcontext.mc_flags = 0;
+	}
+	/* Make sure the context is valid. */
+	else if ((ucp->uc_mcontext.mc_flags & __UC_MC_VALID) != 0) {
+		/*
+		 * Arrange the stack as follows:
+		 *
+		 *	_ctx_start()	- context start wrapper
+		 *	start()		- user start routine
+		 * 	arg1
+		 *	...
+		 *	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).
+		 */
+		stack_top = (char *)(ucp->uc_stack.ss_sp +
+		    ucp->uc_stack.ss_size - sizeof(double));
+		stack_top = (char *)ALIGN(stack_top);
+
+		/*
+		 * 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.
+		 */
+		stack_top = stack_top - (sizeof(intptr_t) * (3 + argc));
+		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
+		 * %ebp to point to the base of the stack where ucp
+		 * is stored.
+		 */
+		ucp->uc_mcontext.mc_ebp = (int)argp;
+		ucp->uc_mcontext.mc_esp = (int)stack_top + sizeof(caddr_t);
+		ucp->uc_mcontext.mc_eip = (int)_ctx_start;
+	}
+}