diff options
Diffstat (limited to 'lib/libc/i386/gen/makecontext.c')
| -rw-r--r-- | lib/libc/i386/gen/makecontext.c | 159 |
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 000000000000..1334b5af430c --- /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; + } +} |