Document that nata(4) is now our default ATA driver:

[dragonfly/vkernel-mp.git] / sys / kern / kern_exec.c

/*
 * 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 1.57 2007/06/07 23:14:25 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/ktrace.h>
#include <sys/signalvar.h>
#include <sys/pioctl.h>
#include <sys/nlookup.h>
#include <sys/sfbuf.h>
#include <sys/sysent.h>
#include <sys/shm.h>
#include <sys/sysctl.h>
#include <sys/vnode.h>
#include <sys/vmmeter.h>
#include <sys/aio.h>
#include <sys/libkern.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 <sys/reg.h>

#include <sys/thread2.h>

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

/*
 * Exec arguments object cache
 */
static struct objcache *exec_objcache;

static
void
exec_objcache_init(void *arg __unused)
{
        exec_objcache = objcache_create_mbacked(
                                        M_EXECARGS, PATH_MAX + ARG_MAX,
                                        16,     /* up to this many objects */
                                        2,      /* minimal magazine capacity */
                                        NULL, NULL, NULL);
}
SYSINIT(exec_objcache, SI_BOOT2_MACHDEP, SI_ORDER_ANY, exec_objcache_init, 0);

/*
 * stackgap_random specifies if the stackgap should have a random size added
 * to it.  It must be a power of 2.  If non-zero, the stack gap will be 
 * calculated as: ALIGN(karc4random() & (stackgap_random - 1)).
 */
static int stackgap_random = 1024;
static int
sysctl_kern_stackgap(SYSCTL_HANDLER_ARGS)
{
        int error, new_val;
        new_val = stackgap_random;
        error = sysctl_handle_int(oidp, &new_val, 0, req);
        if (error != 0 || req->newptr == NULL)
                return (error);
        if ((new_val < 0) || (new_val > 16 * PAGE_SIZE) || ! powerof2(new_val))
                return (EINVAL);
        stackgap_random = new_val;

        return(0);
}

SYSCTL_PROC(_kern, OID_AUTO, stackgap_random, CTLFLAG_RW|CTLTYPE_UINT, 
        0, 0, sysctl_kern_stackgap, "IU", "Max random stack gap (power of 2)");
        
void
print_execve_args(struct image_args *args)
{
        char *cp;
        int ndx;

        cp = args->begin_argv;
        for (ndx = 0; ndx < args->argc; ndx++) {
                kprintf("\targv[%d]: %s\n", ndx, cp);
                while (*cp++ != '\0');
        }
        for (ndx = 0; ndx < args->envc; ndx++) {
                kprintf("\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 nlookupdata *nd, struct image_args *args)
{
        struct thread *td = curthread;
        struct lwp *lp = td->td_lwp;
        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) {
                kprintf("%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;
        imgp->image_header = NULL;

interpret:

        /*
         * Translate the file name to a vnode.  Unlock the cache entry to
         * improve parallelism for programs exec'd in parallel.
         */
        if ((error = nlookup(nd)) != 0)
                goto exec_fail;
        error = cache_vget(&nd->nl_nch, nd->nl_cred, LK_EXCLUSIVE, &imgp->vp);
        KKASSERT(nd->nl_flags & NLC_NCPISLOCKED);
        nd->nl_flags &= ~NLC_NCPISLOCKED;
        cache_unlock(&nd->nl_nch);
        if (error)
                goto exec_fail;

        /*
         * Check file permissions (also 'opens' file)
         */
        error = exec_check_permissions(imgp);
        if (error) {
                vn_unlock(imgp->vp);
                goto exec_fail_dealloc;
        }

        error = exec_map_first_page(imgp);
        vn_unlock(imgp->vp);
        if (error)
                goto exec_fail_dealloc;

        if (debug_execve_args && imgp->interpreted) {
                kprintf("    target is interpreted -- recursive pass\n");
                kprintf("    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);
                nlookup_done(nd);
                vrele(imgp->vp);
                imgp->vp = NULL;
                error = nlookup_init(nd, imgp->interpreter_name, UIO_SYSSPACE,
                                        NLC_FOLLOW);
                if (error)
                        goto exec_fail;
                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_sigacts->ps_refcnt > 1) {
                struct sigacts *newsigacts;

                newsigacts = (struct sigacts *)kmalloc(sizeof(*newsigacts),
                       M_SUBPROC, M_WAITOK);
                bcopy(p->p_sigacts, newsigacts, sizeof(*newsigacts));
                p->p_sigacts->ps_refcnt--;
                p->p_sigacts = newsigacts;
                p->p_sigacts->ps_refcnt = 1;
        }

        /*
         * For security and other reasons virtual kernels cannot be
         * inherited by an exec.  This also allows a virtual kernel
         * to fork/exec unrelated applications.
         */
        if (p->p_vkernel)
                vkernel_exit(p);

        /* Stop profiling */
        stopprofclock(p);

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

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

        /* name this process - nameiexec(p, ndp) */
        len = min(nd->nl_nch.ncp->nc_nlen, MAXCOMLEN);
        bcopy(nd->nl_nch.ncp->nc_name, p->p_comm, len);
        p->p_comm[len] = 0;
        bcopy(p->p_comm, lp->lwp_thread->td_comm, MAXCOMLEN+1);

        /*
         * 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_tracenode && suser(td) != 0) {
                        ktrdestroy(&p->p_tracenode);
                        p->p_traceflag = 0;
                }
                /* 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);
        p->p_textvp = imgp->vp;
        vref(p->p_textvp);

        /*
         * 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)
                ksignal(p, SIGTRAP);

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

        /* Set values passed into the program in registers. */
        exec_setregs(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->vp) {
                vrele(imgp->vp);
                imgp->vp = NULL;
        }

        if (error == 0) {
                ++mycpu->gd_cnt.v_exec;
                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
sys_execve(struct execve_args *uap)
{
        struct nlookupdata nd;
        struct image_args args;
        int error;

        error = nlookup_init(&nd, uap->fname, UIO_USERSPACE, NLC_FOLLOW);
        if (error == 0) {
                error = exec_copyin_args(&args, uap->fname, PATH_USERSPACE,
                                        uap->argv, uap->envv);
        }
        if (error == 0)
                error = kern_execve(&nd, &args);
        nlookup_done(&nd);
        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 rv, i;
        int initial_pagein;
        vm_page_t ma[VM_INITIAL_PAGEIN];
        vm_page_t m;
        vm_object_t object;

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

        /*
         * The file has to be mappable.
         */
        if ((object = imgp->vp->v_object) == NULL)
                return (EIO);

        /*
         * We shouldn't need protection for vm_page_grab() but we certainly
         * need it for the lookup loop below (lookup/busy race), since
         * an interrupt can unbusy and free the page before our busy check.
         */
        crit_enter();
        m = vm_page_grab(object, 0, VM_ALLOC_NORMAL | VM_ALLOC_RETRY);

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

                /*
                 * get_pages unbusies all the requested pages except the
                 * primary page (at index 0 in this case).
                 */
                rv = vm_pager_get_pages(object, ma, initial_pagein, 0);
                m = vm_page_lookup(object, 0);

                if (rv != VM_PAGER_OK || m == NULL || m->valid == 0) {
                        if (m) {
                                vm_page_protect(m, VM_PROT_NONE);
                                vm_page_free(m);
                        }
                        crit_exit();
                        return EIO;
                }
        }
        vm_page_hold(m);
        vm_page_wakeup(m);      /* unbusy the page */
        crit_exit();

        imgp->firstpage = sf_buf_alloc(m, SFB_CPUPRIVATE);
        imgp->image_header = (void *)sf_buf_kva(imgp->firstpage);

        return 0;
}

void
exec_unmap_first_page(struct image_params *imgp)
{
        vm_page_t m;

        crit_enter();
        if (imgp->firstpage != NULL) {
                m = sf_buf_page(imgp->firstpage);
                sf_buf_free(imgp->firstpage);
                imgp->firstpage = NULL;
                imgp->image_header = NULL;
                vm_page_unhold(m);
        }
        crit_exit();
}

/*
 * 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;

        if (curthread->td_proc->p_nthreads > 1)
                killlwps(curthread->td_lwp);

        /*
         * 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.
         *
         * The exitingcnt test is not strictly necessary but has been
         * included for code sanity (to make the code more deterministic).
         */
        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_sysref.refcnt == 1 &&
                   vmspace->vm_exitingcnt == 0) {
                shmexit(vmspace);
                if (vmspace->vm_upcalls)
                        upc_release(vmspace, ONLY_LWP_IN_PROC(imgp->proc));
                pmap_remove_pages(vmspace_pmap(vmspace),
                        0, VM_MAX_USER_ADDRESS);
                vm_map_remove(map, 0, VM_MAX_USER_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 = objcache_get(exec_objcache, M_WAITOK);
        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.  argv may not be NULL.  The argv
         * array is terminated by a NULL entry.  We special-case the
         * situation where argv[0] is NULL by passing { filename, NULL }
         * to the new program to guarentee that the interpreter knows what
         * file to open in case we exec an interpreted file.   Note that
         * a NULL argv[0] terminates the argv[] array.
         *
         * XXX the special-casing of argv[0] is historical and needs to be
         * revisited.
         */
        if (argv == NULL)
                error = EFAULT;
        if (error == 0) {
                while ((argp = (caddr_t)(intptr_t)fuword(argv++)) != NULL) {
                        if (argp == (caddr_t)-1) {
                                error = EFAULT;
                                break;
                        }
                        error = copyinstr(argp, args->endp,
                                            args->space, &length);
                        if (error) {
                                if (error == ENAMETOOLONG)
                                        error = E2BIG;
                                break;
                        }
                        args->space -= length;
                        args->endp += length;
                        args->argc++;
                }
                if (args->argc == 0 && error == 0) {
                        length = strlen(args->fname) + 1;
                        if (length > args->space) {
                                error = E2BIG;
                        } else {
                                bcopy(args->fname, args->endp, length);
                                args->space -= length;
                                args->endp += length;
                                args->argc++;
                        }
                }
        }       

        args->begin_envv = args->endp;

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

void
exec_free_args(struct image_args *args)
{
        if (args->buf) {
                objcache_put(exec_objcache, args->buf);
                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, sgap;
        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);
        if (stackgap_random != 0)
                sgap = ALIGN(karc4random() & (stackgap_random - 1));
        else
                sgap = 0;
        destp = (caddr_t)arginfo - szsigcode - SPARE_USRSPACE - sgap -
            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(struct image_params *imgp)
{
        struct proc *p = imgp->proc;
        struct vnode *vp = imgp->vp;
        struct vattr *attr = imgp->attr;
        int error;

        /* Get file attributes */
        error = VOP_GETATTR(vp, attr);
        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);
        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 allows us to read,
         * write, and mmap the file.  Without the VOP_OPEN we can only
         * stat the file.
         */
        error = VOP_OPEN(vp, FREAD, p->p_ucred, NULL);
        if (error)
                return (error);

        return (0);
}

/*
 * Exec handler registration
 */
int
exec_register(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 = kmalloc(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)
                kfree(execsw, M_TEMP);
        execsw = newexecsw;
        return 0;
}

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

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

        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 = kmalloc(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)
                kfree(execsw, M_TEMP);
        execsw = newexecsw;
        return 0;
}