xref: /src/lib/libkvm/kvm_proc.c

/*-
 * Copyright (c) 1994 Charles Hannum.
 * Copyright (c) 1989, 1992, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software developed by the Computer Systems
 * Engineering group at Lawrence Berkeley Laboratory under DARPA contract
 * BG 91-66 and contributed to Berkeley.
 *
 * 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University 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 REGENTS 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 REGENTS 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.
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)kvm_proc.c	8.3 (Berkeley) 9/23/93";
#endif /* LIBC_SCCS and not lint */

/*
 * Proc traversal interface for kvm.  ps and w are (probably) the exclusive
 * users of this code, so we've factored it out into a separate module.
 * Thus, we keep this grunge out of the other kvm applications (i.e.,
 * most other applications are interested only in open/close/read/nlist).
 */

#include <sys/param.h>
#include <sys/user.h>
#include <sys/proc.h>
#include <sys/exec.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/tty.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <nlist.h>
#include <kvm.h>

#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/swap_pager.h>

#include <sys/sysctl.h>

#include <limits.h>
#include <db.h>
#include <paths.h>

#include "kvm_private.h"

#define KREAD(kd, addr, obj) \
	(kvm_read(kd, addr, (char *)(obj), sizeof(*obj)) != sizeof(*obj))

int _kvm_readfromcore __P((kvm_t *, u_long, u_long));
int _kvm_readfrompager __P((kvm_t *, struct vm_object *, u_long));
ssize_t kvm_uread __P((kvm_t *, const struct proc *, u_long, char *, size_t));

char *
_kvm_uread(kd, p, va, cnt)
	kvm_t *kd;
	const struct proc *p;
	u_long va;
	u_long *cnt;
{
	register u_long addr, head;
	register u_long offset;
	struct vm_map_entry vme;
	struct vm_object vmo;
	int rv;

	if (kd->swapspc == 0) {
		kd->swapspc = (char *)_kvm_malloc(kd, kd->nbpg);
		if (kd->swapspc == 0)
			return (0);
	}

	/*
	 * Look through the address map for the memory object
	 * that corresponds to the given virtual address.
	 * The header just has the entire valid range.
	 */
	head = (u_long)&p->p_vmspace->vm_map.header;
	addr = head;
	while (1) {
		if (KREAD(kd, addr, &vme))
			return (0);

		if (va >= vme.start && va < vme.end &&
		    vme.object.vm_object != 0)
			break;

		addr = (u_long)vme.next;
		if (addr == head)
			return (0);
	}

	/*
	 * We found the right object -- follow shadow links.
	 */
	offset = va - vme.start + vme.offset;
	addr = (u_long)vme.object.vm_object;

	while (1) {
		/* Try reading the page from core first. */
		if ((rv = _kvm_readfromcore(kd, addr, offset)))
			break;

		if (KREAD(kd, addr, &vmo))
			return (0);

		/* If there is a pager here, see if it has the page. */
		if (vmo.pager != 0 &&
		    (rv = _kvm_readfrompager(kd, &vmo, offset)))
			break;

		/* Move down the shadow chain. */
		addr = (u_long)vmo.shadow;
		if (addr == 0)
			return (0);
		offset += vmo.shadow_offset;
	}

	if (rv == -1)
		return (0);

	/* Found the page. */
	offset %= kd->nbpg;
	*cnt = kd->nbpg - offset;
	return (&kd->swapspc[offset]);
}

#define	vm_page_hash(kd, object, offset) \
	(((u_long)object + (u_long)(offset / kd->nbpg)) & kd->vm_page_hash_mask)

int
_kvm_coreinit(kd)
	kvm_t *kd;
{
	struct nlist nlist[3];

	nlist[0].n_name = "_vm_page_buckets";
	nlist[1].n_name = "_vm_page_hash_mask";
	nlist[2].n_name = 0;
	if (kvm_nlist(kd, nlist) != 0)
		return (-1);

	if (KREAD(kd, nlist[0].n_value, &kd->vm_page_buckets) ||
	    KREAD(kd, nlist[1].n_value, &kd->vm_page_hash_mask))
		return (-1);

	return (0);
}

int
_kvm_readfromcore(kd, object, offset)
	kvm_t *kd;
	u_long object, offset;
{
	u_long addr;
	struct pglist bucket;
	struct vm_page mem;
	off_t seekpoint;

	if (kd->vm_page_buckets == 0 &&
	    _kvm_coreinit(kd))
		return (-1);

	addr = (u_long)&kd->vm_page_buckets[vm_page_hash(kd, object, offset)];
	if (KREAD(kd, addr, &bucket))
		return (-1);

	addr = (u_long)bucket.tqh_first;
	offset &= ~(kd->nbpg -1);
	while (1) {
		if (addr == 0)
			return (0);

		if (KREAD(kd, addr, &mem))
			return (-1);

		if ((u_long)mem.object == object &&
		    (u_long)mem.offset == offset)
			break;

		addr = (u_long)mem.hashq.tqe_next;
	}

	seekpoint = mem.phys_addr;

	if (lseek(kd->pmfd, seekpoint, 0) == -1)
		return (-1);
	if (read(kd->pmfd, kd->swapspc, kd->nbpg) != kd->nbpg)
		return (-1);

	return (1);
}

int
_kvm_readfrompager(kd, vmop, offset)
	kvm_t *kd;
	struct vm_object *vmop;
	u_long offset;
{
	u_long addr;
	struct pager_struct pager;
	struct swpager swap;
	int ix;
	struct swblock swb;
	off_t seekpoint;

	/* Read in the pager info and make sure it's a swap device. */
	addr = (u_long)vmop->pager;
	if (KREAD(kd, addr, &pager) || pager.pg_type != PG_SWAP)
		return (-1);

	/* Read in the swap_pager private data. */
	addr = (u_long)pager.pg_data;
	if (KREAD(kd, addr, &swap))
		return (-1);

	/*
	 * Calculate the paging offset, and make sure it's within the
	 * bounds of the pager.
	 */
	offset += vmop->paging_offset;
	ix = offset / dbtob(swap.sw_bsize);
#if 0
	if (swap.sw_blocks == 0 || ix >= swap.sw_nblocks)
		return (-1);
#else
	if (swap.sw_blocks == 0 || ix >= swap.sw_nblocks) {
		int i;
		printf("BUG BUG BUG BUG:\n");
		printf("object %x offset %x pgoffset %x pager %x swpager %x\n",
		    vmop, offset - vmop->paging_offset, vmop->paging_offset,
		    vmop->pager, pager.pg_data);
		printf("osize %x bsize %x blocks %x nblocks %x\n",
		    swap.sw_osize, swap.sw_bsize, swap.sw_blocks,
		    swap.sw_nblocks);
		for (ix = 0; ix < swap.sw_nblocks; ix++) {
			addr = (u_long)&swap.sw_blocks[ix];
			if (KREAD(kd, addr, &swb))
				return (0);
			printf("sw_blocks[%d]: block %x mask %x\n", ix,
			    swb.swb_block, swb.swb_mask);
		}
		return (-1);
	}
#endif

	/* Read in the swap records. */
	addr = (u_long)&swap.sw_blocks[ix];
	if (KREAD(kd, addr, &swb))
		return (-1);

	/* Calculate offset within pager. */
	offset %= dbtob(swap.sw_bsize);

	/* Check that the page is actually present. */
	if ((swb.swb_mask & (1 << (offset / kd->nbpg))) == 0)
		return (0);

	if (!ISALIVE(kd))
		return (-1);

	/* Calculate the physical address and read the page. */
	seekpoint = dbtob(swb.swb_block) + (offset & ~(kd->nbpg -1));

	if (lseek(kd->swfd, seekpoint, 0) == -1)
		return (-1);
	if (read(kd->swfd, kd->swapspc, kd->nbpg) != kd->nbpg)
		return (-1);

	return (1);
}

/*
 * Read proc's from memory file into buffer bp, which has space to hold
 * at most maxcnt procs.
 */
static int
kvm_proclist(kd, what, arg, p, bp, maxcnt)
	kvm_t *kd;
	int what, arg;
	struct proc *p;
	struct kinfo_proc *bp;
	int maxcnt;
{
	register int cnt = 0;
	struct eproc eproc;
	struct pgrp pgrp;
	struct session sess;
	struct tty tty;
	struct proc proc;

	for (; cnt < maxcnt && p != NULL; p = proc.p_list.le_next) {
		if (KREAD(kd, (u_long)p, &proc)) {
			_kvm_err(kd, kd->program, "can't read proc at %x", p);
			return (-1);
		}
		if (KREAD(kd, (u_long)proc.p_cred, &eproc.e_pcred) == 0)
			KREAD(kd, (u_long)eproc.e_pcred.pc_ucred,
			      &eproc.e_ucred);

		switch(what) {

		case KERN_PROC_PID:
			if (proc.p_pid != (pid_t)arg)
				continue;
			break;

		case KERN_PROC_UID:
			if (eproc.e_ucred.cr_uid != (uid_t)arg)
				continue;
			break;

		case KERN_PROC_RUID:
			if (eproc.e_pcred.p_ruid != (uid_t)arg)
				continue;
			break;
		}
		/*
		 * We're going to add another proc to the set.  If this
		 * will overflow the buffer, assume the reason is because
		 * nprocs (or the proc list) is corrupt and declare an error.
		 */
		if (cnt >= maxcnt) {
			_kvm_err(kd, kd->program, "nprocs corrupt");
			return (-1);
		}
		/*
		 * gather eproc
		 */
		eproc.e_paddr = p;
		if (KREAD(kd, (u_long)proc.p_pgrp, &pgrp)) {
			_kvm_err(kd, kd->program, "can't read pgrp at %x",
				 proc.p_pgrp);
			return (-1);
		}
		eproc.e_sess = pgrp.pg_session;
		eproc.e_pgid = pgrp.pg_id;
		eproc.e_jobc = pgrp.pg_jobc;
		if (KREAD(kd, (u_long)pgrp.pg_session, &sess)) {
			_kvm_err(kd, kd->program, "can't read session at %x",
				pgrp.pg_session);
			return (-1);
		}
		if ((proc.p_flag & P_CONTROLT) && sess.s_ttyp != NULL) {
			if (KREAD(kd, (u_long)sess.s_ttyp, &tty)) {
				_kvm_err(kd, kd->program,
					 "can't read tty at %x", sess.s_ttyp);
				return (-1);
			}
			eproc.e_tdev = tty.t_dev;
			eproc.e_tsess = tty.t_session;
			if (tty.t_pgrp != NULL) {
				if (KREAD(kd, (u_long)tty.t_pgrp, &pgrp)) {
					_kvm_err(kd, kd->program,
						 "can't read tpgrp at &x",
						tty.t_pgrp);
					return (-1);
				}
				eproc.e_tpgid = pgrp.pg_id;
			} else
				eproc.e_tpgid = -1;
		} else
			eproc.e_tdev = NODEV;
		eproc.e_flag = sess.s_ttyvp ? EPROC_CTTY : 0;
		if (sess.s_leader == p)
			eproc.e_flag |= EPROC_SLEADER;
		if (proc.p_wmesg)
			(void)kvm_read(kd, (u_long)proc.p_wmesg,
			    eproc.e_wmesg, WMESGLEN);

		(void)kvm_read(kd, (u_long)proc.p_vmspace,
		    (char *)&eproc.e_vm, sizeof(eproc.e_vm));

		eproc.e_xsize = eproc.e_xrssize = 0;
		eproc.e_xccount = eproc.e_xswrss = 0;

		switch (what) {

		case KERN_PROC_PGRP:
			if (eproc.e_pgid != (pid_t)arg)
				continue;
			break;

		case KERN_PROC_TTY:
			if ((proc.p_flag & P_CONTROLT) == 0 ||
			     eproc.e_tdev != (dev_t)arg)
				continue;
			break;
		}
		bcopy(&proc, &bp->kp_proc, sizeof(proc));
		bcopy(&eproc, &bp->kp_eproc, sizeof(eproc));
		++bp;
		++cnt;
	}
	return (cnt);
}

/*
 * Build proc info array by reading in proc list from a crash dump.
 * Return number of procs read.  maxcnt is the max we will read.
 */
static int
kvm_deadprocs(kd, what, arg, a_allproc, a_zombproc, maxcnt)
	kvm_t *kd;
	int what, arg;
	u_long a_allproc;
	u_long a_zombproc;
	int maxcnt;
{
	register struct kinfo_proc *bp = kd->procbase;
	register int acnt, zcnt;
	struct proc *p;

	if (KREAD(kd, a_allproc, &p)) {
		_kvm_err(kd, kd->program, "cannot read allproc");
		return (-1);
	}
	acnt = kvm_proclist(kd, what, arg, p, bp, maxcnt);
	if (acnt < 0)
		return (acnt);

	if (KREAD(kd, a_zombproc, &p)) {
		_kvm_err(kd, kd->program, "cannot read zombproc");
		return (-1);
	}
	zcnt = kvm_proclist(kd, what, arg, p, bp + acnt, maxcnt - acnt);
	if (zcnt < 0)
		zcnt = 0;

	return (acnt + zcnt);
}

struct kinfo_proc *
kvm_getprocs(kd, op, arg, cnt)
	kvm_t *kd;
	int op, arg;
	int *cnt;
{
	size_t size;
	int mib[4], st, nprocs;

	if (kd->procbase != 0) {
		free((void *)kd->procbase);
		/*
		 * Clear this pointer in case this call fails.  Otherwise,
		 * kvm_close() will free it again.
		 */
		kd->procbase = 0;
	}
	if (ISALIVE(kd)) {
		size = 0;
		mib[0] = CTL_KERN;
		mib[1] = KERN_PROC;
		mib[2] = op;
		mib[3] = arg;
		st = sysctl(mib, 4, NULL, &size, NULL, 0);
		if (st == -1) {
			_kvm_syserr(kd, kd->program, "kvm_getprocs");
			return (0);
		}
		kd->procbase = (struct kinfo_proc *)_kvm_malloc(kd, size);
		if (kd->procbase == 0)
			return (0);
		st = sysctl(mib, 4, kd->procbase, &size, NULL, 0);
		if (st == -1) {
			_kvm_syserr(kd, kd->program, "kvm_getprocs");
			return (0);
		}
		if (size % sizeof(struct kinfo_proc) != 0) {
			_kvm_err(kd, kd->program,
				"proc size mismatch (%d total, %d chunks)",
				size, sizeof(struct kinfo_proc));
			return (0);
		}
		nprocs = size / sizeof(struct kinfo_proc);
	} else {
		struct nlist nl[4], *p;

		nl[0].n_name = "_nprocs";
		nl[1].n_name = "_allproc";
		nl[2].n_name = "_zombproc";
		nl[3].n_name = 0;

		if (kvm_nlist(kd, nl) != 0) {
			for (p = nl; p->n_type != 0; ++p)
				;
			_kvm_err(kd, kd->program,
				 "%s: no such symbol", p->n_name);
			return (0);
		}
		if (KREAD(kd, nl[0].n_value, &nprocs)) {
			_kvm_err(kd, kd->program, "can't read nprocs");
			return (0);
		}
		size = nprocs * sizeof(struct kinfo_proc);
		kd->procbase = (struct kinfo_proc *)_kvm_malloc(kd, size);
		if (kd->procbase == 0)
			return (0);

		nprocs = kvm_deadprocs(kd, op, arg, nl[1].n_value,
				      nl[2].n_value, nprocs);
#ifdef notdef
		size = nprocs * sizeof(struct kinfo_proc);
		(void)realloc(kd->procbase, size);
#endif
	}
	*cnt = nprocs;
	return (kd->procbase);
}

void
_kvm_freeprocs(kd)
	kvm_t *kd;
{
	if (kd->procbase) {
		free(kd->procbase);
		kd->procbase = 0;
	}
}

void *
_kvm_realloc(kd, p, n)
	kvm_t *kd;
	void *p;
	size_t n;
{
	void *np = (void *)realloc(p, n);

	if (np == 0)
		_kvm_err(kd, kd->program, "out of memory");
	return (np);
}

#ifndef MAX
#define MAX(a, b) ((a) > (b) ? (a) : (b))
#endif

/*
 * Read in an argument vector from the user address space of process p.
 * addr if the user-space base address of narg null-terminated contiguous
 * strings.  This is used to read in both the command arguments and
 * environment strings.  Read at most maxcnt characters of strings.
 */
static char **
kvm_argv(kd, p, addr, narg, maxcnt)
	kvm_t *kd;
	struct proc *p;
	register u_long addr;
	register int narg;
	register int maxcnt;
{
	register char *np, *cp, *ep, *ap;
	register u_long oaddr = -1;
	register int len, cc;
	register char **argv;

	/*
	 * Check that there aren't an unreasonable number of agruments,
	 * and that the address is in user space.
	 */
	if (narg > ARG_MAX || addr < VM_MIN_ADDRESS || addr >= VM_MAXUSER_ADDRESS)
		return (0);

	if (kd->argv == 0) {
		/*
		 * Try to avoid reallocs.
		 */
		kd->argc = MAX(narg + 1, 32);
		kd->argv = (char **)_kvm_malloc(kd, kd->argc *
						sizeof(*kd->argv));
		if (kd->argv == 0)
			return (0);
	} else if (narg + 1 > kd->argc) {
		kd->argc = MAX(2 * kd->argc, narg + 1);
		kd->argv = (char **)_kvm_realloc(kd, kd->argv, kd->argc *
						sizeof(*kd->argv));
		if (kd->argv == 0)
			return (0);
	}
	if (kd->argspc == 0) {
		kd->argspc = (char *)_kvm_malloc(kd, kd->nbpg);
		if (kd->argspc == 0)
			return (0);
		kd->arglen = kd->nbpg;
	}
	if (kd->argbuf == 0) {
		kd->argbuf = (char *)_kvm_malloc(kd, kd->nbpg);
		if (kd->argbuf == 0)
			return (0);
	}
	cc = sizeof(char *) * narg;
	if (kvm_uread(kd, p, addr, (char *)kd->argv, cc) != cc)
		return (0);
	ap = np = kd->argspc;
	argv = kd->argv;
	len = 0;
	/*
	 * Loop over pages, filling in the argument vector.
	 */
	while (argv < kd->argv + narg && *argv != 0) {
		addr = (u_long)*argv & ~(kd->nbpg - 1);
		if (addr != oaddr) {
			if (kvm_uread(kd, p, addr, kd->argbuf, kd->nbpg) !=
			    kd->nbpg)
				return (0);
			oaddr = addr;
		}
		addr = (u_long)*argv & (kd->nbpg - 1);
		cp = kd->argbuf + addr;
		cc = kd->nbpg - addr;
		if (maxcnt > 0 && cc > maxcnt - len)
			cc = maxcnt - len;;
		ep = memchr(cp, '\0', cc);
		if (ep != 0)
			cc = ep - cp + 1;
		if (len + cc > kd->arglen) {
			register int off;
			register char **pp;
			register char *op = kd->argspc;

			kd->arglen *= 2;
			kd->argspc = (char *)_kvm_realloc(kd, kd->argspc,
							  kd->arglen);
			if (kd->argspc == 0)
				return (0);
			np = kd->argspc + len;
			/*
			 * Adjust argv pointers in case realloc moved
			 * the string space.
			 */
			off = kd->argspc - op;
			for (pp = kd->argv; pp < argv; ++pp)
				*pp += off;
		}
		memcpy(np, cp, cc);
		np += cc;
		len += cc;
		if (ep != 0) {
			*argv++ = ap;
			ap = np;
		} else
			*argv += cc;
		if (maxcnt > 0 && len >= maxcnt) {
			/*
			 * We're stopping prematurely.  Terminate the
			 * current string.
			 */
			if (ep == 0) {
				*np = '\0';
				++argv;
			}
			break;
		}
	}
	/* Make sure argv is terminated. */
	*argv = 0;
	return (kd->argv);
}

static void
ps_str_a(p, addr, n)
	struct ps_strings *p;
	u_long *addr;
	int *n;
{
	*addr = (u_long)p->ps_argvstr;
	*n = p->ps_nargvstr;
}

static void
ps_str_e(p, addr, n)
	struct ps_strings *p;
	u_long *addr;
	int *n;
{
	*addr = (u_long)p->ps_envstr;
	*n = p->ps_nenvstr;
}

/*
 * Determine if the proc indicated by p is still active.
 * This test is not 100% foolproof in theory, but chances of
 * being wrong are very low.
 */
static int
proc_verify(kd, kernp, p)
	kvm_t *kd;
	u_long kernp;
	const struct proc *p;
{
	struct proc kernproc;

	/*
	 * Just read in the whole proc.  It's not that big relative
	 * to the cost of the read system call.
	 */
	if (kvm_read(kd, kernp, (char *)&kernproc, sizeof(kernproc)) !=
	    sizeof(kernproc))
		return (0);
	return (p->p_pid == kernproc.p_pid &&
		(kernproc.p_stat != SZOMB || p->p_stat == SZOMB));
}

static char **
kvm_doargv(kd, kp, nchr, info)
	kvm_t *kd;
	const struct kinfo_proc *kp;
	int nchr;
	void (*info)(struct ps_strings *, u_long *, int *);
{
	register const struct proc *p = &kp->kp_proc;
	register char **ap;
	u_long addr;
	int cnt;
	struct ps_strings arginfo;

	/*
	 * Pointers are stored at the top of the user stack.
	 */
	if (p->p_stat == SZOMB ||
	    kvm_uread(kd, p, USRSTACK - sizeof(arginfo), (char *)&arginfo,
		      sizeof(arginfo)) != sizeof(arginfo))
		return (0);

	(*info)(&arginfo, &addr, &cnt);
	if (cnt == 0)
		return (0);
	ap = kvm_argv(kd, p, addr, cnt, nchr);
	/*
	 * For live kernels, make sure this process didn't go away.
	 */
	if (ap != 0 && ISALIVE(kd) &&
	    !proc_verify(kd, (u_long)kp->kp_eproc.e_paddr, p))
		ap = 0;
	return (ap);
}

/*
 * Get the command args.  This code is now machine independent.
 */
char **
kvm_getargv(kd, kp, nchr)
	kvm_t *kd;
	const struct kinfo_proc *kp;
	int nchr;
{
	return (kvm_doargv(kd, kp, nchr, ps_str_a));
}

char **
kvm_getenvv(kd, kp, nchr)
	kvm_t *kd;
	const struct kinfo_proc *kp;
	int nchr;
{
	return (kvm_doargv(kd, kp, nchr, ps_str_e));
}

/*
 * Read from user space.  The user context is given by p.
 */
ssize_t
kvm_uread(kd, p, uva, buf, len)
	kvm_t *kd;
	register const struct proc *p;
	register u_long uva;
	register char *buf;
	register size_t len;
{
	register char *cp;

	cp = buf;
	while (len > 0) {
		register int cc;
		register char *dp;
		int cnt;

		dp = _kvm_uread(kd, p, uva, &cnt);
		if (dp == 0) {
			_kvm_err(kd, 0, "invalid address (%x)", uva);
			return (0);
		}
		cc = MIN(cnt, len);
		bcopy(dp, cp, cc);

		cp += cc;
		uva += cc;
		len -= cc;
	}
	return (ssize_t)(cp - buf);
}