File:  [DragonFly] / src / sys / kern / kern_exec.c
Revision 1.20: download - view: text, annotated - select for diffs
Mon Mar 1 06:33:17 2004 UTC (10 years, 9 months ago) by dillon
Branches: MAIN
CVS tags: HEAD
Newtoken commit.  Change the token implementation as follows:  (1) Obtaining
a token no longer enters a critical section.  (2) tokens can be held through
schedular switches and blocking conditions and are effectively released and
reacquired on resume.  Thus tokens serialize access only while the thread
is actually running.  Serialization is not broken by preemptive interrupts.
That is, interrupt threads which preempt do no release the preempted thread's
tokens.  (3) Unlike spl's, tokens will interlock w/ interrupt threads on
the same or on a different cpu.

The vnode interlock code has been rewritten and the API has changed.  The
mountlist vnode scanning code has been consolidated and all known races have
been fixed.  The vnode interlock is now a pool token.

The code that frees unreferenced vnodes whos last VM page has been freed has
been moved out of the low level vm_page_free() code and moved to the
periodic filesystem sycer code in vfs_msycn().

The SMP startup code and the IPI code has been cleaned up considerably.
Certain early token interactions on AP cpus have been moved to the BSP.

The LWKT rwlock API has been cleaned up and turned on.

Major testing by: David Rhodus

/*
 * Copyright (c) 1993, David Greenman
 * 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. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * 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.
 *
 * $FreeBSD: src/sys/kern/kern_exec.c,v 1.107.2.15 2002/07/30 15:40:46 nectar Exp $
 * $DragonFly: src/sys/kern/kern_exec.c,v 1.20 2004/03/01 06:33:17 dillon Exp $
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/sysproto.h>
#include <sys/kernel.h>
#include <sys/mount.h>
#include <sys/filedesc.h>
#include <sys/fcntl.h>
#include <sys/acct.h>
#include <sys/exec.h>
#include <sys/imgact.h>
#include <sys/imgact_elf.h>
#include <sys/kern_syscall.h>
#include <sys/wait.h>
#include <sys/malloc.h>
#include <sys/proc.h>
#include <sys/signalvar.h>
#include <sys/pioctl.h>
#include <sys/namei.h>
#include <sys/sysent.h>
#include <sys/shm.h>
#include <sys/sysctl.h>
#include <sys/vnode.h>
#include <sys/aio.h>

#include <vm/vm.h>
#include <vm/vm_param.h>
#include <sys/lock.h>
#include <vm/pmap.h>
#include <vm/vm_page.h>
#include <vm/vm_map.h>
#include <vm/vm_kern.h>
#include <vm/vm_extern.h>
#include <vm/vm_object.h>
#include <vm/vm_pager.h>

#include <sys/user.h>
#include <machine/reg.h>

MALLOC_DEFINE(M_PARGS, "proc-args", "Process arguments");

static register_t *exec_copyout_strings (struct image_params *);

/* XXX This should be vm_size_t. */
static u_long ps_strings = PS_STRINGS;
SYSCTL_ULONG(_kern, KERN_PS_STRINGS, ps_strings, CTLFLAG_RD, &ps_strings, 0, "");

/* XXX This should be vm_size_t. */
static u_long usrstack = USRSTACK;
SYSCTL_ULONG(_kern, KERN_USRSTACK, usrstack, CTLFLAG_RD, &usrstack, 0, "");

u_long ps_arg_cache_limit = PAGE_SIZE / 16;
SYSCTL_LONG(_kern, OID_AUTO, ps_arg_cache_limit, CTLFLAG_RW, 
    &ps_arg_cache_limit, 0, "");

int ps_argsopen = 1;
SYSCTL_INT(_kern, OID_AUTO, ps_argsopen, CTLFLAG_RW, &ps_argsopen, 0, "");

void print_execve_args(struct image_args *args);
int debug_execve_args = 0;
SYSCTL_INT(_kern, OID_AUTO, debug_execve_args, CTLFLAG_RW, &debug_execve_args,
    0, "");

void
print_execve_args(struct image_args *args)
{
	char *cp;
	int ndx;

	cp = args->begin_argv;
	for (ndx = 0; ndx < args->argc; ndx++) {
		printf("\targv[%d]: %s\n", ndx, cp);
		while (*cp++ != '\0');
	}
	for (ndx = 0; ndx < args->envc; ndx++) {
		printf("\tenvv[%d]: %s\n", ndx, cp);
		while (*cp++ != '\0');
	}
}

/*
 * Each of the items is a pointer to a `const struct execsw', hence the
 * double pointer here.
 */
static const struct execsw **execsw;

int
kern_execve(struct nameidata *ndp, struct image_args *args)
{
	struct thread *td = curthread;
	struct proc *p = td->td_proc;
	register_t *stack_base;
	int error, len, i;
	struct image_params image_params, *imgp;
	struct vattr attr;
	int (*img_first) (struct image_params *);

	if (debug_execve_args) {
		printf("%s()\n", __func__);
		print_execve_args(args);
	}

	KKASSERT(p);
	imgp = &image_params;

	/*
	 * Lock the process and set the P_INEXEC flag to indicate that
	 * it should be left alone until we're done here.  This is
	 * necessary to avoid race conditions - e.g. in ptrace() -
	 * that might allow a local user to illicitly obtain elevated
	 * privileges.
	 */
	p->p_flag |= P_INEXEC;

	/*
	 * Initialize part of the common data
	 */
	imgp->proc = p;
	imgp->args = args;
	imgp->attr = &attr;
	imgp->entry_addr = 0;
	imgp->resident = 0;
	imgp->vmspace_destroyed = 0;
	imgp->interpreted = 0;
	imgp->interpreter_name[0] = 0;
	imgp->auxargs = NULL;
	imgp->vp = NULL;
	imgp->firstpage = NULL;
	imgp->ps_strings = 0;

	/*
	 * Allocate temporary demand zeroed space for argument and
	 *	environment strings
	 */
	imgp->image_header = (char *)kmem_alloc_wait(exec_map, PAGE_SIZE);
	if (imgp->image_header == NULL) {
		error = ENOMEM;
		goto exec_fail;
	}

interpret:

	/*
	 * Translate the file name. namei() returns a vnode pointer
	 *	in ni_vp amoung other things.
	 */
	error = namei(ndp);
	if (error) {
		kmem_free_wakeup(exec_map, (vm_offset_t)imgp->image_header,
		    PAGE_SIZE);
		goto exec_fail;
	}

	imgp->vp = ndp->ni_vp;

	/*
	 * Check file permissions (also 'opens' file)
	 */
	error = exec_check_permissions(imgp);
	if (error) {
		VOP_UNLOCK(imgp->vp, NULL, 0, td);
		goto exec_fail_dealloc;
	}

	error = exec_map_first_page(imgp);
	VOP_UNLOCK(imgp->vp, NULL, 0, td);
	if (error)
		goto exec_fail_dealloc;

	if (debug_execve_args && imgp->interpreted) {
		printf("    target is interpreted -- recursive pass\n");
		printf("    interpreter: %s\n", imgp->interpreter_name);
		print_execve_args(args);
	}

	/*
	 *	If the current process has a special image activator it
	 *	wants to try first, call it.   For example, emulating shell 
	 *	scripts differently.
	 */
	error = -1;
	if ((img_first = imgp->proc->p_sysent->sv_imgact_try) != NULL)
		error = img_first(imgp);

	/*
	 *	If the vnode has a registered vmspace, exec the vmspace
	 */
	if (error == -1 && imgp->vp->v_resident) {
		error = exec_resident_imgact(imgp);
	}

	/*
	 *	Loop through the list of image activators, calling each one.
	 *	An activator returns -1 if there is no match, 0 on success,
	 *	and an error otherwise.
	 */
	for (i = 0; error == -1 && execsw[i]; ++i) {
		if (execsw[i]->ex_imgact == NULL ||
		    execsw[i]->ex_imgact == img_first) {
			continue;
		}
		error = (*execsw[i]->ex_imgact)(imgp);
	}

	if (error) {
		if (error == -1)
			error = ENOEXEC;
		goto exec_fail_dealloc;
	}

	/*
	 * Special interpreter operation, cleanup and loop up to try to
	 * activate the interpreter.
	 */
	if (imgp->interpreted) {
		exec_unmap_first_page(imgp);
		/* free name buffer and old vnode */
		NDFREE(ndp, NDF_ONLY_PNBUF);
		vrele(ndp->ni_vp);
		/* set new name to that of the interpreter */
		NDINIT(ndp, NAMEI_LOOKUP, 
		    CNP_LOCKLEAF | CNP_FOLLOW | CNP_SAVENAME,
		    UIO_SYSSPACE, imgp->interpreter_name, td);
		goto interpret;
	}

	/*
	 * Copy out strings (args and env) and initialize stack base
	 */
	stack_base = exec_copyout_strings(imgp);
	p->p_vmspace->vm_minsaddr = (char *)stack_base;

	/*
	 * If custom stack fixup routine present for this process
	 * let it do the stack setup.  If we are running a resident
	 * image there is no auxinfo or other image activator context
	 * so don't try to add fixups to the stack.
	 *
	 * Else stuff argument count as first item on stack
	 */
	if (p->p_sysent->sv_fixup && imgp->resident == 0)
		(*p->p_sysent->sv_fixup)(&stack_base, imgp);
	else
		suword(--stack_base, imgp->args->argc);

	/*
	 * For security and other reasons, the file descriptor table cannot
	 * be shared after an exec.
	 */
	if (p->p_fd->fd_refcnt > 1) {
		struct filedesc *tmp;

		tmp = fdcopy(p);
		fdfree(p);
		p->p_fd = tmp;
	}

	/*
	 * For security and other reasons, signal handlers cannot
	 * be shared after an exec. The new proces gets a copy of the old
	 * handlers. In execsigs(), the new process will have its signals
	 * reset.
	 */
	if (p->p_procsig->ps_refcnt > 1) {
		struct procsig *newprocsig;

		MALLOC(newprocsig, struct procsig *, sizeof(struct procsig),
		       M_SUBPROC, M_WAITOK);
		bcopy(p->p_procsig, newprocsig, sizeof(*newprocsig));
		p->p_procsig->ps_refcnt--;
		p->p_procsig = newprocsig;
		p->p_procsig->ps_refcnt = 1;
		if (p->p_sigacts == &p->p_addr->u_sigacts)
			panic("shared procsig but private sigacts?");

		p->p_addr->u_sigacts = *p->p_sigacts;
		p->p_sigacts = &p->p_addr->u_sigacts;
	}

	/* Stop profiling */
	stopprofclock(p);

	/* close files on exec */
	fdcloseexec(p);

	/* reset caught signals */
	execsigs(p);

	/* name this process - nameiexec(p, ndp) */
	len = min(ndp->ni_cnd.cn_namelen,MAXCOMLEN);
	bcopy(ndp->ni_cnd.cn_nameptr, p->p_comm, len);
	p->p_comm[len] = 0;

	/*
	 * mark as execed, wakeup the process that vforked (if any) and tell
	 * it that it now has its own resources back
	 */
	p->p_flag |= P_EXEC;
	if (p->p_pptr && (p->p_flag & P_PPWAIT)) {
		p->p_flag &= ~P_PPWAIT;
		wakeup((caddr_t)p->p_pptr);
	}

	/*
	 * Implement image setuid/setgid.
	 *
	 * Don't honor setuid/setgid if the filesystem prohibits it or if
	 * the process is being traced.
	 */
	if ((((attr.va_mode & VSUID) && p->p_ucred->cr_uid != attr.va_uid) ||
	     ((attr.va_mode & VSGID) && p->p_ucred->cr_gid != attr.va_gid)) &&
	    (imgp->vp->v_mount->mnt_flag & MNT_NOSUID) == 0 &&
	    (p->p_flag & P_TRACED) == 0) {
		/*
		 * Turn off syscall tracing for set-id programs, except for
		 * root.  Record any set-id flags first to make sure that
		 * we do not regain any tracing during a possible block.
		 */
		setsugid();
		if (p->p_tracep && suser(td)) {
			struct vnode *vtmp;

			if ((vtmp = p->p_tracep) != NULL) {
				p->p_tracep = NULL;
				p->p_traceflag = 0;
				vrele(vtmp);
			}
		}
		/* Close any file descriptors 0..2 that reference procfs */
		setugidsafety(p);
		/* Make sure file descriptors 0..2 are in use. */
		error = fdcheckstd(p);
		if (error != 0)
			goto exec_fail_dealloc;
		/*
		 * Set the new credentials.
		 */
		cratom(&p->p_ucred);
		if (attr.va_mode & VSUID)
			change_euid(attr.va_uid);
		if (attr.va_mode & VSGID)
			p->p_ucred->cr_gid = attr.va_gid;

		/*
		 * Clear local varsym variables
		 */
		varsymset_clean(&p->p_varsymset);
	} else {
		if (p->p_ucred->cr_uid == p->p_ucred->cr_ruid &&
		    p->p_ucred->cr_gid == p->p_ucred->cr_rgid)
			p->p_flag &= ~P_SUGID;
	}

	/*
	 * Implement correct POSIX saved-id behavior.
	 */
	if (p->p_ucred->cr_svuid != p->p_ucred->cr_uid ||
	    p->p_ucred->cr_svgid != p->p_ucred->cr_gid) {
		cratom(&p->p_ucred);
		p->p_ucred->cr_svuid = p->p_ucred->cr_uid;
		p->p_ucred->cr_svgid = p->p_ucred->cr_gid;
	}

	/*
	 * Store the vp for use in procfs
	 */
	if (p->p_textvp)		/* release old reference */
		vrele(p->p_textvp);
	VREF(ndp->ni_vp);
	p->p_textvp = ndp->ni_vp;

        /*
         * Notify others that we exec'd, and clear the P_INEXEC flag
         * as we're now a bona fide freshly-execed process.
         */
	KNOTE(&p->p_klist, NOTE_EXEC);
	p->p_flag &= ~P_INEXEC;

	/*
	 * If tracing the process, trap to debugger so breakpoints
	 * 	can be set before the program executes.
	 */
	STOPEVENT(p, S_EXEC, 0);

	if (p->p_flag & P_TRACED)
		psignal(p, SIGTRAP);

	/* clear "fork but no exec" flag, as we _are_ execing */
	p->p_acflag &= ~AFORK;

	/* Set values passed into the program in registers. */
	setregs(p, imgp->entry_addr, (u_long)(uintptr_t)stack_base,
	    imgp->ps_strings);

	/* Free any previous argument cache */
	if (p->p_args && --p->p_args->ar_ref == 0)
		FREE(p->p_args, M_PARGS);
	p->p_args = NULL;

	/* Cache arguments if they fit inside our allowance */
	i = imgp->args->begin_envv - imgp->args->begin_argv;
	if (ps_arg_cache_limit >= i + sizeof(struct pargs)) {
		MALLOC(p->p_args, struct pargs *, sizeof(struct pargs) + i, 
		    M_PARGS, M_WAITOK);
		p->p_args->ar_ref = 1;
		p->p_args->ar_length = i;
		bcopy(imgp->args->begin_argv, p->p_args->ar_args, i);
	}

exec_fail_dealloc:

	/*
	 * free various allocated resources
	 */
	if (imgp->firstpage)
		exec_unmap_first_page(imgp);

	if (imgp->image_header != NULL)
		kmem_free_wakeup(exec_map, (vm_offset_t)imgp->image_header,
		    PAGE_SIZE);

	if (imgp->vp) {
		NDFREE(ndp, NDF_ONLY_PNBUF);
		vrele(imgp->vp);
	}

	if (error == 0)
		return (0);

exec_fail:
	/* we're done here, clear P_INEXEC */
	p->p_flag &= ~P_INEXEC;
	if (imgp->vmspace_destroyed) {
		/* sorry, no more process anymore. exit gracefully */
		exit1(W_EXITCODE(0, SIGABRT));
		/* NOT REACHED */
		return(0);
	} else {
		return(error);
	}
}

/*
 * execve() system call.
 */
int
execve(struct execve_args *uap)
{
	struct thread *td = curthread;
	struct nameidata nd;
	struct image_args args;
	int error;

	NDINIT(&nd, NAMEI_LOOKUP, CNP_LOCKLEAF | CNP_FOLLOW | CNP_SAVENAME,
	    UIO_USERSPACE, uap->fname, td);

	error = exec_copyin_args(&args, uap->fname, PATH_USERSPACE,
				uap->argv, uap->envv);
	if (error == 0)
		error = kern_execve(&nd, &args);

	exec_free_args(&args);

	/*
	 * The syscall result is returned in registers to the new program.
	 * Linux will register %edx as an atexit function and we must be
	 * sure to set it to 0.  XXX
	 */
	if (error == 0)
		uap->sysmsg_result64 = 0;

	return (error);
}

int
exec_map_first_page(struct image_params *imgp)
{
	int s, rv, i;
	int initial_pagein;
	vm_page_t ma[VM_INITIAL_PAGEIN];
	vm_object_t object;


	if (imgp->firstpage) {
		exec_unmap_first_page(imgp);
	}

	VOP_GETVOBJECT(imgp->vp, &object);
	s = splvm();

	ma[0] = vm_page_grab(object, 0, VM_ALLOC_NORMAL | VM_ALLOC_RETRY);

	if ((ma[0]->valid & VM_PAGE_BITS_ALL) != VM_PAGE_BITS_ALL) {
		initial_pagein = VM_INITIAL_PAGEIN;
		if (initial_pagein > object->size)
			initial_pagein = object->size;
		for (i = 1; i < initial_pagein; i++) {
			if ((ma[i] = vm_page_lookup(object, i)) != NULL) {
				if ((ma[i]->flags & PG_BUSY) || ma[i]->busy)
					break;
				if (ma[i]->valid)
					break;
				vm_page_busy(ma[i]);
			} else {
				ma[i] = vm_page_alloc(object, i, VM_ALLOC_NORMAL);
				if (ma[i] == NULL)
					break;
			}
		}
		initial_pagein = i;

		rv = vm_pager_get_pages(object, ma, initial_pagein, 0);
		ma[0] = vm_page_lookup(object, 0);

		if ((rv != VM_PAGER_OK) || (ma[0] == NULL) || (ma[0]->valid == 0)) {
			if (ma[0]) {
				vm_page_protect(ma[0], VM_PROT_NONE);
				vm_page_free(ma[0]);
			}
			splx(s);
			return EIO;
		}
	}

	vm_page_wire(ma[0]);
	vm_page_wakeup(ma[0]);
	splx(s);

	pmap_kenter((vm_offset_t) imgp->image_header, VM_PAGE_TO_PHYS(ma[0]));
	imgp->firstpage = ma[0];

	return 0;
}

void
exec_unmap_first_page(imgp)
	struct image_params *imgp;
{
	if (imgp->firstpage) {
		pmap_kremove((vm_offset_t) imgp->image_header);
		vm_page_unwire(imgp->firstpage, 1);
		imgp->firstpage = NULL;
	}
}

/*
 * Destroy old address space, and allocate a new stack
 *	The new stack is only SGROWSIZ large because it is grown
 *	automatically in trap.c.
 */
int
exec_new_vmspace(struct image_params *imgp, struct vmspace *vmcopy)
{
	int error;
	struct vmspace *vmspace = imgp->proc->p_vmspace;
	vm_offset_t stack_addr = USRSTACK - maxssiz;
	vm_map_t map;

	imgp->vmspace_destroyed = 1;

	/*
	 * Prevent a pending AIO from modifying the new address space.
	 */
	aio_proc_rundown(imgp->proc);

	/*
	 * Blow away entire process VM, if address space not shared,
	 * otherwise, create a new VM space so that other threads are
	 * not disrupted.  If we are execing a resident vmspace we
	 * create a duplicate of it and remap the stack.
	 */
	map = &vmspace->vm_map;
	if (vmcopy) {
		vmspace_exec(imgp->proc, vmcopy);
		vmspace = imgp->proc->p_vmspace;
		pmap_remove_pages(vmspace_pmap(vmspace), stack_addr, USRSTACK);
		map = &vmspace->vm_map;
	} else if (vmspace->vm_refcnt == 1) {
		shmexit(vmspace);
		pmap_remove_pages(vmspace_pmap(vmspace), 0, VM_MAXUSER_ADDRESS);
		vm_map_remove(map, 0, VM_MAXUSER_ADDRESS);
	} else {
		vmspace_exec(imgp->proc, NULL);
		vmspace = imgp->proc->p_vmspace;
		map = &vmspace->vm_map;
	}

	/* Allocate a new stack */
	error = vm_map_stack(&vmspace->vm_map, stack_addr, (vm_size_t)maxssiz,
	    VM_PROT_ALL, VM_PROT_ALL, 0);
	if (error)
		return (error);

	/* vm_ssize and vm_maxsaddr are somewhat antiquated concepts in the
	 * VM_STACK case, but they are still used to monitor the size of the
	 * process stack so we can check the stack rlimit.
	 */
	vmspace->vm_ssize = sgrowsiz >> PAGE_SHIFT;
	vmspace->vm_maxsaddr = (char *)USRSTACK - maxssiz;

	return(0);
}

/*
 * Copy out argument and environment strings from the old process
 *	address space into the temporary string buffer.
 */
int
exec_copyin_args(struct image_args *args, char *fname,
		enum exec_path_segflg segflg, char **argv, char **envv)
{
	char	*argp, *envp;
	int	error = 0;
	size_t	length;

	bzero(args, sizeof(*args));
	args->buf = (char *) kmem_alloc_wait(exec_map, PATH_MAX + ARG_MAX);
	if (args->buf == NULL)
		return (ENOMEM);
	args->begin_argv = args->buf;
	args->endp = args->begin_argv;
	args->space = ARG_MAX;

	args->fname = args->buf + ARG_MAX;

	/*
	 * Copy the file name.
	 */
	if (segflg == PATH_SYSSPACE) {
		error = copystr(fname, args->fname, PATH_MAX, &length);
	} else if (segflg == PATH_USERSPACE) {
		error = copyinstr(fname, args->fname, PATH_MAX, &length);
	}

	/*
	 * extract argument strings
	 */

	if (argv && error == 0) {
		/*
		 * The argv0 argument for execv() is allowed to be NULL,
		 * in which case we use our filename as argv[0].
		 * This guarantees that
		 * the interpreter knows what file to open in the case
		 * that we exec an interpreted file.
		 */
		argp = (caddr_t) (intptr_t) fuword(argv);
		if (argp == NULL) {
			length = strlen(args->fname) + 1;
			KKASSERT(length <= args->space);
			bcopy(args->fname, args->endp, length);
			args->space -= length;
			args->endp += length;
			args->argc++;
			argv++;
		}
		while ((argp = (caddr_t) (intptr_t) fuword(argv++))) {
			if (argp == (caddr_t) -1) {
				error = EFAULT;
				goto cleanup;
			}
			error = copyinstr(argp, args->endp,
					    args->space, &length);
			if (error == ENAMETOOLONG)
				error = E2BIG;
			if (error)
				goto cleanup;
			args->space -= length;
			args->endp += length;
			args->argc++;
		}
	}	

	args->begin_envv = args->endp;

	/*
	 * extract environment strings
	 */
	if (envv && error == 0) {
		while ((envp = (caddr_t) (intptr_t) fuword(envv++))) {
			if (envp == (caddr_t) -1) {
				error = EFAULT;
				goto cleanup;
			}
			error = copyinstr(envp, args->endp, args->space,
			    &length);
			if (error == ENAMETOOLONG)
				error = E2BIG;
			if (error)
				goto cleanup;
			args->space -= length;
			args->endp += length;
			args->envc++;
		}
	}

cleanup:
	return (error);
}

void
exec_free_args(struct image_args *args)
{
	if (args->buf) {
		kmem_free_wakeup(exec_map,
				(vm_offset_t)args->buf, PATH_MAX + ARG_MAX);
		args->buf = NULL;
	}
}

/*
 * Copy strings out to the new process address space, constructing
 *	new arg and env vector tables. Return a pointer to the base
 *	so that it can be used as the initial stack pointer.
 */
register_t *
exec_copyout_strings(struct image_params *imgp)
{
	int argc, envc;
	char **vectp;
	char *stringp, *destp;
	register_t *stack_base;
	struct ps_strings *arginfo;
	int szsigcode;

	/*
	 * Calculate string base and vector table pointers.
	 * Also deal with signal trampoline code for this exec type.
	 */
	arginfo = (struct ps_strings *)PS_STRINGS;
	szsigcode = *(imgp->proc->p_sysent->sv_szsigcode);
	destp =	(caddr_t)arginfo - szsigcode - SPARE_USRSPACE -
	    roundup((ARG_MAX - imgp->args->space), sizeof(char *));

	/*
	 * install sigcode
	 */
	if (szsigcode)
		copyout(imgp->proc->p_sysent->sv_sigcode,
		    ((caddr_t)arginfo - szsigcode), szsigcode);

	/*
	 * If we have a valid auxargs ptr, prepare some room
	 * on the stack.
	 *
	 * The '+ 2' is for the null pointers at the end of each of the
	 * arg and env vector sets, and 'AT_COUNT*2' is room for the
	 * ELF Auxargs data.
	 */
	if (imgp->auxargs) {
		vectp = (char **)(destp - (imgp->args->argc +
			imgp->args->envc + 2 + AT_COUNT * 2) * sizeof(char*));
	} else {
		vectp = (char **)(destp - (imgp->args->argc +
			imgp->args->envc + 2) * sizeof(char*));
	}

	/*
	 * NOTE: don't bother aligning the stack here for GCC 2.x, it will
	 * be done in crt1.o.  Note that GCC 3.x aligns the stack in main.
	 */

	/*
	 * vectp also becomes our initial stack base
	 */
	stack_base = (register_t *)vectp;

	stringp = imgp->args->begin_argv;
	argc = imgp->args->argc;
	envc = imgp->args->envc;

	/*
	 * Copy out strings - arguments and environment.
	 */
	copyout(stringp, destp, ARG_MAX - imgp->args->space);

	/*
	 * Fill in "ps_strings" struct for ps, w, etc.
	 */
	suword(&arginfo->ps_argvstr, (long)(intptr_t)vectp);
	suword(&arginfo->ps_nargvstr, argc);

	/*
	 * Fill in argument portion of vector table.
	 */
	for (; argc > 0; --argc) {
		suword(vectp++, (long)(intptr_t)destp);
		while (*stringp++ != 0)
			destp++;
		destp++;
	}

	/* a null vector table pointer separates the argp's from the envp's */
	suword(vectp++, 0);

	suword(&arginfo->ps_envstr, (long)(intptr_t)vectp);
	suword(&arginfo->ps_nenvstr, envc);

	/*
	 * Fill in environment portion of vector table.
	 */
	for (; envc > 0; --envc) {
		suword(vectp++, (long)(intptr_t)destp);
		while (*stringp++ != 0)
			destp++;
		destp++;
	}

	/* end of vector table is a null pointer */
	suword(vectp, 0);

	return (stack_base);
}

/*
 * Check permissions of file to execute.
 *	Return 0 for success or error code on failure.
 */
int
exec_check_permissions(imgp)
	struct image_params *imgp;
{
	struct proc *p = imgp->proc;
	struct vnode *vp = imgp->vp;
	struct vattr *attr = imgp->attr;
	struct thread *td = p->p_thread;
	int error;

	/* Get file attributes */
	error = VOP_GETATTR(vp, attr, td);
	if (error)
		return (error);

	/*
	 * 1) Check if file execution is disabled for the filesystem that this
	 *	file resides on.
	 * 2) Insure that at least one execute bit is on - otherwise root
	 *	will always succeed, and we don't want to happen unless the
	 *	file really is executable.
	 * 3) Insure that the file is a regular file.
	 */
	if ((vp->v_mount->mnt_flag & MNT_NOEXEC) ||
	    ((attr->va_mode & 0111) == 0) ||
	    (attr->va_type != VREG)) {
		return (EACCES);
	}

	/*
	 * Zero length files can't be exec'd
	 */
	if (attr->va_size == 0)
		return (ENOEXEC);

	/*
	 *  Check for execute permission to file based on current credentials.
	 */
	error = VOP_ACCESS(vp, VEXEC, p->p_ucred, td);
	if (error)
		return (error);

	/*
	 * Check number of open-for-writes on the file and deny execution
	 * if there are any.
	 */
	if (vp->v_writecount)
		return (ETXTBSY);

	/*
	 * Call filesystem specific open routine (which does nothing in the
	 * general case).
	 */
	error = VOP_OPEN(vp, FREAD, p->p_ucred, td);
	if (error)
		return (error);

	return (0);
}

/*
 * Exec handler registration
 */
int
exec_register(execsw_arg)
	const struct execsw *execsw_arg;
{
	const struct execsw **es, **xs, **newexecsw;
	int count = 2;	/* New slot and trailing NULL */

	if (execsw)
		for (es = execsw; *es; es++)
			count++;
	newexecsw = malloc(count * sizeof(*es), M_TEMP, M_WAITOK);
	if (newexecsw == NULL)
		return ENOMEM;
	xs = newexecsw;
	if (execsw)
		for (es = execsw; *es; es++)
			*xs++ = *es;
	*xs++ = execsw_arg;
	*xs = NULL;
	if (execsw)
		free(execsw, M_TEMP);
	execsw = newexecsw;
	return 0;
}

int
exec_unregister(execsw_arg)
	const struct execsw *execsw_arg;
{
	const struct execsw **es, **xs, **newexecsw;
	int count = 1;

	if (execsw == NULL)
		panic("unregister with no handlers left?\n");

	for (es = execsw; *es; es++) {
		if (*es == execsw_arg)
			break;
	}
	if (*es == NULL)
		return ENOENT;
	for (es = execsw; *es; es++)
		if (*es != execsw_arg)
			count++;
	newexecsw = malloc(count * sizeof(*es), M_TEMP, M_WAITOK);
	if (newexecsw == NULL)
		return ENOMEM;
	xs = newexecsw;
	for (es = execsw; *es; es++)
		if (*es != execsw_arg)
			*xs++ = *es;
	*xs = NULL;
	if (execsw)
		free(execsw, M_TEMP);
	execsw = newexecsw;
	return 0;
}