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/*-
* SPDX-License-Identifier: BSD-2-Clause
*
* 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/param.h>
#include <sys/signal.h>
#include <sys/ucontext.h>
#include <errno.h>
#include <stdarg.h>
#include <stdlib.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_len = 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_len = 0;
}
/* XXX - Do we want to sanity check argc? */
else if (argc < 0) {
ucp->uc_mcontext.mc_len = 0;
}
/* Make sure the context is valid. */
else if (ucp->uc_mcontext.mc_len == sizeof(mcontext_t)) {
/*
* 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).
*/
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.
*/
ucp->uc_mcontext.mc_esi = (int)argp;
ucp->uc_mcontext.mc_ebp = 0;
ucp->uc_mcontext.mc_esp = (int)stack_top + sizeof(caddr_t);
ucp->uc_mcontext.mc_eip = (int)_ctx_start;
}
}
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