/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License (the "License").
* You may not use this file except in compliance with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* or http://www.opensolaris.org/os/licensing.
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright 2008 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
*/
/* Copyright (c) 1988 AT&T */
/* All Rights Reserved */
#pragma weak _makecontext = makecontext
#include "lint.h"
#include <stdarg.h>
#include <ucontext.h>
#include <sys/stack.h>
/*
* The ucontext_t that the user passes in must have been primed with a
* call to getcontext(2), have the uc_stack member set to reflect the
* stack which this context will use, and have the uc_link member set
* to the context which should be resumed when this context returns.
* When makecontext() returns, the ucontext_t will be set to run the
* given function with the given parameters on the stack specified by
* uc_stack, and which will return to the ucontext_t specified by uc_link.
*/
/*
* The original i386 ABI said that the stack pointer need be only 4-byte
* aligned before a function call (STACK_ALIGN == 4). The ABI supplement
* version 1.0 changed the required alignment to 16-byte for the benefit of
* floating point code compiled using sse2. The compiler assumes this
* alignment and maintains it for calls it generates. If the stack is
* initially properly aligned, it will continue to be so aligned. If it is
* not initially so aligned, it will never become so aligned.
*
* One slightly confusing detail to keep in mind is that the 16-byte
* alignment (%esp & 0xf == 0) is true just *before* the call instruction.
* The call instruction will then push a return value, decrementing %esp by
* 4. Therefore, if one dumps %esp at the at the very first instruction in
* a function, it will end with a 0xc. The compiler expects this and
* compensates for it properly.
*
* Note: If you change this value, you need to change it in the following
* files as well:
*
* - lib/libc/i386/threads/machdep.c
* - lib/common/i386/crti.s
* - lib/common/i386/crt1.s
*/
#undef STACK_ALIGN
#define STACK_ALIGN 16
static void resumecontext(void);
void
makecontext(ucontext_t *ucp, void (*func)(), int argc, ...)
{
long *sp;
long *tsp;
va_list ap;
size_t size;
ucp->uc_mcontext.gregs[EIP] = (greg_t)func;
size = sizeof (long) * (argc + 1);
tsp = (long *)(((uintptr_t)ucp->uc_stack.ss_sp +
ucp->uc_stack.ss_size - size) & ~(STACK_ALIGN - 1));
/*
* Since we're emulating the call instruction, we must push the
* return address (which involves adjusting the stack pointer to
* have the proper 4-byte bias).
*/
sp = tsp - 1;
*sp = (long)resumecontext; /* return address */
ucp->uc_mcontext.gregs[UESP] = (greg_t)sp;
/*
* "push" all the arguments
*/
va_start(ap, argc);
while (argc-- > 0)
*tsp++ = va_arg(ap, long);
va_end(ap);
}
static void
resumecontext(void)
{
ucontext_t uc;
(void) getcontext(&uc);
(void) setcontext(uc.uc_link);
}