freebsd-src/sys/kern/sys_process.c

/*-
 * SPDX-License-Identifier: BSD-4-Clause
 *
 * Copyright (c) 1994, Sean Eric Fagan
 * 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by Sean Eric Fagan.
 * 4. The name of the author may not 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/systm.h>
#include <sys/ktr.h>
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/reg.h>
#include <sys/syscallsubr.h>
#include <sys/sysent.h>
#include <sys/sysproto.h>
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/vnode.h>
#include <sys/ptrace.h>
#include <sys/rwlock.h>
#include <sys/sx.h>
#include <sys/malloc.h>
#include <sys/signalvar.h>
#include <sys/caprights.h>
#include <sys/filedesc.h>

#include <security/audit/audit.h>

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

#ifdef COMPAT_FREEBSD32
#include <sys/procfs.h>
#endif

/* Assert it's safe to unlock a process, e.g. to allocate working memory */
#define	PROC_ASSERT_TRACEREQ(p)	MPASS(((p)->p_flag2 & P2_PTRACEREQ) != 0)

/*
 * Functions implemented using PROC_ACTION():
 *
 * proc_read_regs(proc, regs)
 *	Get the current user-visible register set from the process
 *	and copy it into the regs structure (<machine/reg.h>).
 *	The process is stopped at the time read_regs is called.
 *
 * proc_write_regs(proc, regs)
 *	Update the current register set from the passed in regs
 *	structure.  Take care to avoid clobbering special CPU
 *	registers or privileged bits in the PSL.
 *	Depending on the architecture this may have fix-up work to do,
 *	especially if the IAR or PCW are modified.
 *	The process is stopped at the time write_regs is called.
 *
 * proc_read_fpregs, proc_write_fpregs
 *	deal with the floating point register set, otherwise as above.
 *
 * proc_read_dbregs, proc_write_dbregs
 *	deal with the processor debug register set, otherwise as above.
 *
 * proc_sstep(proc)
 *	Arrange for the process to trap after executing a single instruction.
 */

#define	PROC_ACTION(action) do {					\
	int error;							\
									\
	PROC_LOCK_ASSERT(td->td_proc, MA_OWNED);			\
	if ((td->td_proc->p_flag & P_INMEM) == 0)			\
		error = EIO;						\
	else								\
		error = (action);					\
	return (error);							\
} while (0)

int
proc_read_regs(struct thread *td, struct reg *regs)
{

	PROC_ACTION(fill_regs(td, regs));
}

int
proc_write_regs(struct thread *td, struct reg *regs)
{

	PROC_ACTION(set_regs(td, regs));
}

int
proc_read_dbregs(struct thread *td, struct dbreg *dbregs)
{

	PROC_ACTION(fill_dbregs(td, dbregs));
}

int
proc_write_dbregs(struct thread *td, struct dbreg *dbregs)
{

	PROC_ACTION(set_dbregs(td, dbregs));
}

/*
 * Ptrace doesn't support fpregs at all, and there are no security holes
 * or translations for fpregs, so we can just copy them.
 */
int
proc_read_fpregs(struct thread *td, struct fpreg *fpregs)
{

	PROC_ACTION(fill_fpregs(td, fpregs));
}

int
proc_write_fpregs(struct thread *td, struct fpreg *fpregs)
{

	PROC_ACTION(set_fpregs(td, fpregs));
}

static struct regset *
proc_find_regset(struct thread *td, int note)
{
	struct regset **regsetp, **regset_end, *regset;
	struct sysentvec *sv;

	sv = td->td_proc->p_sysent;
	regsetp = sv->sv_regset_begin;
	if (regsetp == NULL)
		return (NULL);
	regset_end = sv->sv_regset_end;
	MPASS(regset_end != NULL);
	for (; regsetp < regset_end; regsetp++) {
		regset = *regsetp;
		if (regset->note != note)
			continue;

		return (regset);
	}

	return (NULL);
}

static int
proc_read_regset(struct thread *td, int note, struct iovec *iov)
{
	struct regset *regset;
	struct proc *p;
	void *buf;
	size_t size;
	int error;

	regset = proc_find_regset(td, note);
	if (regset == NULL)
		return (EINVAL);

	if (regset->get == NULL)
		return (EINVAL);

	size = regset->size;
	/*
	 * The regset is dynamically sized, e.g. the size could change
	 * depending on the hardware, or may have a per-thread size.
	 */
	if (size == 0) {
		if (!regset->get(regset, td, NULL, &size))
			return (EINVAL);
	}

	if (iov->iov_base == NULL) {
		iov->iov_len = size;
		if (iov->iov_len == 0)
			return (EINVAL);

		return (0);
	}

	/* The length is wrong, return an error */
	if (iov->iov_len != size)
		return (EINVAL);

	error = 0;
	p = td->td_proc;

	/* Drop the proc lock while allocating the temp buffer */
	PROC_ASSERT_TRACEREQ(p);
	PROC_UNLOCK(p);
	buf = malloc(size, M_TEMP, M_WAITOK);
	PROC_LOCK(p);

	if (!regset->get(regset, td, buf, &size)) {
		error = EINVAL;
	} else {
		KASSERT(size == regset->size || regset->size == 0,
		    ("%s: Getter function changed the size", __func__));

		iov->iov_len = size;
		PROC_UNLOCK(p);
		error = copyout(buf, iov->iov_base, size);
		PROC_LOCK(p);
	}

	free(buf, M_TEMP);

	return (error);
}

static int
proc_write_regset(struct thread *td, int note, struct iovec *iov)
{
	struct regset *regset;
	struct proc *p;
	void *buf;
	size_t size;
	int error;

	regset = proc_find_regset(td, note);
	if (regset == NULL)
		return (EINVAL);

	size = regset->size;
	/*
	 * The regset is dynamically sized, e.g. the size could change
	 * depending on the hardware, or may have a per-thread size.
	 */
	if (size == 0) {
		if (!regset->get(regset, td, NULL, &size))
			return (EINVAL);
	}

	/* The length is wrong, return an error */
	if (iov->iov_len != size)
		return (EINVAL);

	if (regset->set == NULL)
		return (EINVAL);

	p = td->td_proc;

	/* Drop the proc lock while allocating the temp buffer */
	PROC_ASSERT_TRACEREQ(p);
	PROC_UNLOCK(p);
	buf = malloc(size, M_TEMP, M_WAITOK);
	error = copyin(iov->iov_base, buf, size);
	PROC_LOCK(p);

	if (error == 0) {
		if (!regset->set(regset, td, buf, size)) {
			error = EINVAL;
		}
	}

	free(buf, M_TEMP);

	return (error);
}

#ifdef COMPAT_FREEBSD32
/* For 32 bit binaries, we need to expose the 32 bit regs layouts. */
int
proc_read_regs32(struct thread *td, struct reg32 *regs32)
{

	PROC_ACTION(fill_regs32(td, regs32));
}

int
proc_write_regs32(struct thread *td, struct reg32 *regs32)
{

	PROC_ACTION(set_regs32(td, regs32));
}

int
proc_read_dbregs32(struct thread *td, struct dbreg32 *dbregs32)
{

	PROC_ACTION(fill_dbregs32(td, dbregs32));
}

int
proc_write_dbregs32(struct thread *td, struct dbreg32 *dbregs32)
{

	PROC_ACTION(set_dbregs32(td, dbregs32));
}

int
proc_read_fpregs32(struct thread *td, struct fpreg32 *fpregs32)
{

	PROC_ACTION(fill_fpregs32(td, fpregs32));
}

int
proc_write_fpregs32(struct thread *td, struct fpreg32 *fpregs32)
{

	PROC_ACTION(set_fpregs32(td, fpregs32));
}
#endif

int
proc_sstep(struct thread *td)
{

	PROC_ACTION(ptrace_single_step(td));
}

int
proc_rwmem(struct proc *p, struct uio *uio)
{
	vm_map_t map;
	vm_offset_t pageno;		/* page number */
	vm_prot_t reqprot;
	int error, fault_flags, page_offset, writing;

	/*
	 * Make sure that the process' vmspace remains live.
	 */
	if (p != curproc)
		PROC_ASSERT_HELD(p);
	PROC_LOCK_ASSERT(p, MA_NOTOWNED);

	/*
	 * The map we want...
	 */
	map = &p->p_vmspace->vm_map;

	/*
	 * If we are writing, then we request vm_fault() to create a private
	 * copy of each page.  Since these copies will not be writeable by the
	 * process, we must explicity request that they be dirtied.
	 */
	writing = uio->uio_rw == UIO_WRITE;
	reqprot = writing ? VM_PROT_COPY | VM_PROT_READ : VM_PROT_READ;
	fault_flags = writing ? VM_FAULT_DIRTY : VM_FAULT_NORMAL;

	/*
	 * Only map in one page at a time.  We don't have to, but it
	 * makes things easier.  This way is trivial - right?
	 */
	do {
		vm_offset_t uva;
		u_int len;
		vm_page_t m;

		uva = (vm_offset_t)uio->uio_offset;

		/*
		 * Get the page number of this segment.
		 */
		pageno = trunc_page(uva);
		page_offset = uva - pageno;

		/*
		 * How many bytes to copy
		 */
		len = min(PAGE_SIZE - page_offset, uio->uio_resid);

		/*
		 * Fault and hold the page on behalf of the process.
		 */
		error = vm_fault(map, pageno, reqprot, fault_flags, &m);
		if (error != KERN_SUCCESS) {
			if (error == KERN_RESOURCE_SHORTAGE)
				error = ENOMEM;
			else
				error = EFAULT;
			break;
		}

		/*
		 * Now do the i/o move.
		 */
		error = uiomove_fromphys(&m, page_offset, len, uio);

		/* Make the I-cache coherent for breakpoints. */
		if (writing && error == 0) {
			vm_map_lock_read(map);
			if (vm_map_check_protection(map, pageno, pageno +
			    PAGE_SIZE, VM_PROT_EXECUTE))
				vm_sync_icache(map, uva, len);
			vm_map_unlock_read(map);
		}

		/*
		 * Release the page.
		 */
		vm_page_unwire(m, PQ_ACTIVE);

	} while (error == 0 && uio->uio_resid > 0);

	return (error);
}

static ssize_t
proc_iop(struct thread *td, struct proc *p, vm_offset_t va, void *buf,
    size_t len, enum uio_rw rw)
{
	struct iovec iov;
	struct uio uio;
	ssize_t slen;

	MPASS(len < SSIZE_MAX);
	slen = (ssize_t)len;

	iov.iov_base = (caddr_t)buf;
	iov.iov_len = len;
	uio.uio_iov = &iov;
	uio.uio_iovcnt = 1;
	uio.uio_offset = va;
	uio.uio_resid = slen;
	uio.uio_segflg = UIO_SYSSPACE;
	uio.uio_rw = rw;
	uio.uio_td = td;
	proc_rwmem(p, &uio);
	if (uio.uio_resid == slen)
		return (-1);
	return (slen - uio.uio_resid);
}

ssize_t
proc_readmem(struct thread *td, struct proc *p, vm_offset_t va, void *buf,
    size_t len)
{

	return (proc_iop(td, p, va, buf, len, UIO_READ));
}

ssize_t
proc_writemem(struct thread *td, struct proc *p, vm_offset_t va, void *buf,
    size_t len)
{

	return (proc_iop(td, p, va, buf, len, UIO_WRITE));
}

static int
ptrace_vm_entry(struct thread *td, struct proc *p, struct ptrace_vm_entry *pve)
{
	struct vattr vattr;
	vm_map_t map;
	vm_map_entry_t entry;
	vm_object_t obj, tobj, lobj;
	struct vmspace *vm;
	struct vnode *vp;
	char *freepath, *fullpath;
	u_int pathlen;
	int error, index;

	error = 0;
	obj = NULL;

	vm = vmspace_acquire_ref(p);
	map = &vm->vm_map;
	vm_map_lock_read(map);

	do {
		KASSERT((map->header.eflags & MAP_ENTRY_IS_SUB_MAP) == 0,
		    ("Submap in map header"));
		index = 0;
		VM_MAP_ENTRY_FOREACH(entry, map) {
			if (index >= pve->pve_entry &&
			    (entry->eflags & MAP_ENTRY_IS_SUB_MAP) == 0)
				break;
			index++;
		}
		if (index < pve->pve_entry) {
			error = EINVAL;
			break;
		}
		if (entry == &map->header) {
			error = ENOENT;
			break;
		}

		/* We got an entry. */
		pve->pve_entry = index + 1;
		pve->pve_timestamp = map->timestamp;
		pve->pve_start = entry->start;
		pve->pve_end = entry->end - 1;
		pve->pve_offset = entry->offset;
		pve->pve_prot = entry->protection;

		/* Backing object's path needed? */
		if (pve->pve_pathlen == 0)
			break;

		pathlen = pve->pve_pathlen;
		pve->pve_pathlen = 0;

		obj = entry->object.vm_object;
		if (obj != NULL)
			VM_OBJECT_RLOCK(obj);
	} while (0);

	vm_map_unlock_read(map);

	pve->pve_fsid = VNOVAL;
	pve->pve_fileid = VNOVAL;

	if (error == 0 && obj != NULL) {
		lobj = obj;
		for (tobj = obj; tobj != NULL; tobj = tobj->backing_object) {
			if (tobj != obj)
				VM_OBJECT_RLOCK(tobj);
			if (lobj != obj)
				VM_OBJECT_RUNLOCK(lobj);
			lobj = tobj;
			pve->pve_offset += tobj->backing_object_offset;
		}
		vp = vm_object_vnode(lobj);
		if (vp != NULL)
			vref(vp);
		if (lobj != obj)
			VM_OBJECT_RUNLOCK(lobj);
		VM_OBJECT_RUNLOCK(obj);

		if (vp != NULL) {
			freepath = NULL;
			fullpath = NULL;
			vn_fullpath(vp, &fullpath, &freepath);
			vn_lock(vp, LK_SHARED | LK_RETRY);
			if (VOP_GETATTR(vp, &vattr, td->td_ucred) == 0) {
				pve->pve_fileid = vattr.va_fileid;
				pve->pve_fsid = vattr.va_fsid;
			}
			vput(vp);

			if (fullpath != NULL) {
				pve->pve_pathlen = strlen(fullpath) + 1;
				if (pve->pve_pathlen <= pathlen) {
					error = copyout(fullpath, pve->pve_path,
					    pve->pve_pathlen);
				} else
					error = ENAMETOOLONG;
			}
			if (freepath != NULL)
				free(freepath, M_TEMP);
		}
	}
	vmspace_free(vm);
	if (error == 0)
		CTR3(KTR_PTRACE, "PT_VM_ENTRY: pid %d, entry %d, start %p",
		    p->p_pid, pve->pve_entry, pve->pve_start);

	return (error);
}

/*
 * Process debugging system call.
 */
#ifndef _SYS_SYSPROTO_H_
struct ptrace_args {
	int	req;
	pid_t	pid;
	caddr_t	addr;
	int	data;
};
#endif

int
sys_ptrace(struct thread *td, struct ptrace_args *uap)
{
	/*
	 * XXX this obfuscation is to reduce stack usage, but the register
	 * structs may be too large to put on the stack anyway.
	 */
	union {
		struct ptrace_io_desc piod;
		struct ptrace_lwpinfo pl;
		struct ptrace_vm_entry pve;
		struct ptrace_coredump pc;
		struct ptrace_sc_remote sr;
		struct dbreg dbreg;
		struct fpreg fpreg;
		struct reg reg;
		struct iovec vec;
		syscallarg_t args[nitems(td->td_sa.args)];
		struct ptrace_sc_ret psr;
		int ptevents;
	} r;
	syscallarg_t pscr_args[nitems(td->td_sa.args)];
	void *addr;
	int error;

	if (!allow_ptrace)
		return (ENOSYS);
	error = 0;

	AUDIT_ARG_PID(uap->pid);
	AUDIT_ARG_CMD(uap->req);
	AUDIT_ARG_VALUE(uap->data);
	addr = &r;
	switch (uap->req) {
	case PT_GET_EVENT_MASK:
	case PT_LWPINFO:
	case PT_GET_SC_ARGS:
	case PT_GET_SC_RET:
		break;
	case PT_GETREGS:
		bzero(&r.reg, sizeof(r.reg));
		break;
	case PT_GETFPREGS:
		bzero(&r.fpreg, sizeof(r.fpreg));
		break;
	case PT_GETDBREGS:
		bzero(&r.dbreg, sizeof(r.dbreg));
		break;
	case PT_GETREGSET:
	case PT_SETREGSET:
		error = copyin(uap->addr, &r.vec, sizeof(r.vec));
		break;
	case PT_SETREGS:
		error = copyin(uap->addr, &r.reg, sizeof(r.reg));
		break;
	case PT_SETFPREGS:
		error = copyin(uap->addr, &r.fpreg, sizeof(r.fpreg));
		break;
	case PT_SETDBREGS:
		error = copyin(uap->addr, &r.dbreg, sizeof(r.dbreg));
		break;
	case PT_SET_EVENT_MASK:
		if (uap->data != sizeof(r.ptevents))
			error = EINVAL;
		else
			error = copyin(uap->addr, &r.ptevents, uap->data);
		break;
	case PT_IO:
		error = copyin(uap->addr, &r.piod, sizeof(r.piod));
		break;
	case PT_VM_ENTRY:
		error = copyin(uap->addr, &r.pve, sizeof(r.pve));
		break;
	case PT_COREDUMP:
		if (uap->data != sizeof(r.pc))
			error = EINVAL;
		else
			error = copyin(uap->addr, &r.pc, uap->data);
		break;
	case PT_SC_REMOTE:
		if (uap->data != sizeof(r.sr)) {
			error = EINVAL;
			break;
		}
		error = copyin(uap->addr, &r.sr, uap->data);
		if (error != 0)
			break;
		if (r.sr.pscr_nargs > nitems(td->td_sa.args)) {
			error = EINVAL;
			break;
		}
		error = copyin(r.sr.pscr_args, pscr_args,
		    sizeof(u_long) * r.sr.pscr_nargs);
		if (error != 0)
			break;
		r.sr.pscr_args = pscr_args;
		break;
	default:
		addr = uap->addr;
		break;
	}
	if (error)
		return (error);

	error = kern_ptrace(td, uap->req, uap->pid, addr, uap->data);
	if (error)
		return (error);

	switch (uap->req) {
	case PT_VM_ENTRY:
		error = copyout(&r.pve, uap->addr, sizeof(r.pve));
		break;
	case PT_IO:
		error = copyout(&r.piod, uap->addr, sizeof(r.piod));
		break;
	case PT_GETREGS:
		error = copyout(&r.reg, uap->addr, sizeof(r.reg));
		break;
	case PT_GETFPREGS:
		error = copyout(&r.fpreg, uap->addr, sizeof(r.fpreg));
		break;
	case PT_GETDBREGS:
		error = copyout(&r.dbreg, uap->addr, sizeof(r.dbreg));
		break;
	case PT_GETREGSET:
		error = copyout(&r.vec, uap->addr, sizeof(r.vec));
		break;
	case PT_GET_EVENT_MASK:
		/* NB: The size in uap->data is validated in kern_ptrace(). */
		error = copyout(&r.ptevents, uap->addr, uap->data);
		break;
	case PT_LWPINFO:
		/* NB: The size in uap->data is validated in kern_ptrace(). */
		error = copyout(&r.pl, uap->addr, uap->data);
		break;
	case PT_GET_SC_ARGS:
		error = copyout(r.args, uap->addr, MIN(uap->data,
		    sizeof(r.args)));
		break;
	case PT_GET_SC_RET:
		error = copyout(&r.psr, uap->addr, MIN(uap->data,
		    sizeof(r.psr)));
		break;
	case PT_SC_REMOTE:
		error = copyout(&r.sr.pscr_ret, uap->addr +
		    offsetof(struct ptrace_sc_remote, pscr_ret),
		    sizeof(r.sr.pscr_ret));
		break;
	}

	return (error);
}

#ifdef COMPAT_FREEBSD32
/*
 *   PROC_READ(regs, td2, addr);
 * becomes either:
 *   proc_read_regs(td2, addr);
 * or
 *   proc_read_regs32(td2, addr);
 * .. except this is done at runtime.  There is an additional
 * complication in that PROC_WRITE disallows 32 bit consumers
 * from writing to 64 bit address space targets.
 */
#define	PROC_READ(w, t, a)	wrap32 ? \
	proc_read_ ## w ## 32(t, a) : \
	proc_read_ ## w (t, a)
#define	PROC_WRITE(w, t, a)	wrap32 ? \
	(safe ? proc_write_ ## w ## 32(t, a) : EINVAL ) : \
	proc_write_ ## w (t, a)
#else
#define	PROC_READ(w, t, a)	proc_read_ ## w (t, a)
#define	PROC_WRITE(w, t, a)	proc_write_ ## w (t, a)
#endif

void
proc_set_traced(struct proc *p, bool stop)
{

	sx_assert(&proctree_lock, SX_XLOCKED);
	PROC_LOCK_ASSERT(p, MA_OWNED);
	p->p_flag |= P_TRACED;
	if (stop)
		p->p_flag2 |= P2_PTRACE_FSTP;
	p->p_ptevents = PTRACE_DEFAULT;
}

void
ptrace_unsuspend(struct proc *p)
{
	PROC_LOCK_ASSERT(p, MA_OWNED);

	PROC_SLOCK(p);
	p->p_flag &= ~(P_STOPPED_TRACE | P_STOPPED_SIG | P_WAITED);
	thread_unsuspend(p);
	PROC_SUNLOCK(p);
	itimer_proc_continue(p);
	kqtimer_proc_continue(p);
}

static int
proc_can_ptrace(struct thread *td, struct proc *p)
{
	int error;

	PROC_LOCK_ASSERT(p, MA_OWNED);

	if ((p->p_flag & P_WEXIT) != 0)
		return (ESRCH);

	if ((error = p_cansee(td, p)) != 0)
		return (error);
	if ((error = p_candebug(td, p)) != 0)
		return (error);

	/* not being traced... */
	if ((p->p_flag & P_TRACED) == 0)
		return (EPERM);

	/* not being traced by YOU */
	if (p->p_pptr != td->td_proc)
		return (EBUSY);

	/* not currently stopped */
	if ((p->p_flag & P_STOPPED_TRACE) == 0 ||
	    p->p_suspcount != p->p_numthreads  ||
	    (p->p_flag & P_WAITED) == 0)
		return (EBUSY);

	return (0);
}

static struct thread *
ptrace_sel_coredump_thread(struct proc *p)
{
	struct thread *td2;

	PROC_LOCK_ASSERT(p, MA_OWNED);
	MPASS((p->p_flag & P_STOPPED_TRACE) != 0);

	FOREACH_THREAD_IN_PROC(p, td2) {
		if ((td2->td_dbgflags & TDB_SSWITCH) != 0)
			return (td2);
	}
	return (NULL);
}

int
kern_ptrace(struct thread *td, int req, pid_t pid, void *addr, int data)
{
	struct iovec iov;
	struct uio uio;
	struct proc *curp, *p, *pp;
	struct thread *td2 = NULL, *td3;
	struct ptrace_io_desc *piod = NULL;
	struct ptrace_lwpinfo *pl;
	struct ptrace_sc_ret *psr;
	struct ptrace_sc_remote *pscr;
	struct file *fp;
	struct ptrace_coredump *pc;
	struct thr_coredump_req *tcq;
	struct thr_syscall_req *tsr;
	int error, num, tmp;
	lwpid_t tid = 0, *buf;
#ifdef COMPAT_FREEBSD32
	int wrap32 = 0, safe = 0;
#endif
	bool proctree_locked, p2_req_set;

	curp = td->td_proc;
	proctree_locked = false;
	p2_req_set = false;

	/* Lock proctree before locking the process. */
	switch (req) {
	case PT_TRACE_ME:
	case PT_ATTACH:
	case PT_STEP:
	case PT_CONTINUE:
	case PT_TO_SCE:
	case PT_TO_SCX:
	case PT_SYSCALL:
	case PT_FOLLOW_FORK:
	case PT_LWP_EVENTS:
	case PT_GET_EVENT_MASK:
	case PT_SET_EVENT_MASK:
	case PT_DETACH:
	case PT_GET_SC_ARGS:
		sx_xlock(&proctree_lock);
		proctree_locked = true;
		break;
	default:
		break;
	}

	if (req == PT_TRACE_ME) {
		p = td->td_proc;
		PROC_LOCK(p);
	} else {
		if (pid <= PID_MAX) {
			if ((p = pfind(pid)) == NULL) {
				if (proctree_locked)
					sx_xunlock(&proctree_lock);
				return (ESRCH);
			}
		} else {
			td2 = tdfind(pid, -1);
			if (td2 == NULL) {
				if (proctree_locked)
					sx_xunlock(&proctree_lock);
				return (ESRCH);
			}
			p = td2->td_proc;
			tid = pid;
			pid = p->p_pid;
		}
	}
	AUDIT_ARG_PROCESS(p);

	if ((p->p_flag & P_WEXIT) != 0) {
		error = ESRCH;
		goto fail;
	}
	if ((error = p_cansee(td, p)) != 0)
		goto fail;

	if ((error = p_candebug(td, p)) != 0)
		goto fail;

	/*
	 * System processes can't be debugged.
	 */
	if ((p->p_flag & P_SYSTEM) != 0) {
		error = EINVAL;
		goto fail;
	}

	if (tid == 0) {
		if ((p->p_flag & P_STOPPED_TRACE) != 0) {
			KASSERT(p->p_xthread != NULL, ("NULL p_xthread"));
			td2 = p->p_xthread;
		} else {
			td2 = FIRST_THREAD_IN_PROC(p);
		}
		tid = td2->td_tid;
	}

#ifdef COMPAT_FREEBSD32
	/*
	 * Test if we're a 32 bit client and what the target is.
	 * Set the wrap controls accordingly.
	 */
	if (SV_CURPROC_FLAG(SV_ILP32)) {
		if (SV_PROC_FLAG(td2->td_proc, SV_ILP32))
			safe = 1;
		wrap32 = 1;
	}
#endif
	/*
	 * Permissions check
	 */
	switch (req) {
	case PT_TRACE_ME:
		/*
		 * Always legal, when there is a parent process which
		 * could trace us.  Otherwise, reject.
		 */
		if ((p->p_flag & P_TRACED) != 0) {
			error = EBUSY;
			goto fail;
		}
		if (p->p_pptr == initproc) {
			error = EPERM;
			goto fail;
		}
		break;

	case PT_ATTACH:
		/* Self */
		if (p == td->td_proc) {
			error = EINVAL;
			goto fail;
		}

		/* Already traced */
		if (p->p_flag & P_TRACED) {
			error = EBUSY;
			goto fail;
		}

		/* Can't trace an ancestor if you're being traced. */
		if (curp->p_flag & P_TRACED) {
			for (pp = curp->p_pptr; pp != NULL; pp = pp->p_pptr) {
				if (pp == p) {
					error = EINVAL;
					goto fail;
				}
			}
		}

		/* OK */
		break;

	case PT_CLEARSTEP:
		/* Allow thread to clear single step for itself */
		if (td->td_tid == tid)
			break;

		/* FALLTHROUGH */
	default:
		/*
		 * Check for ptrace eligibility before waiting for
		 * holds to drain.
		 */
		error = proc_can_ptrace(td, p);
		if (error != 0)
			goto fail;

		/*
		 * Block parallel ptrace requests.  Most important, do
		 * not allow other thread in debugger to continue the
		 * debuggee until coredump finished.
		 */
		while ((p->p_flag2 & P2_PTRACEREQ) != 0) {
			if (proctree_locked)
				sx_xunlock(&proctree_lock);
			error = msleep(&p->p_flag2, &p->p_mtx, PPAUSE | PCATCH |
			    (proctree_locked ? PDROP : 0), "pptrace", 0);
			if (proctree_locked) {
				sx_xlock(&proctree_lock);
				PROC_LOCK(p);
			}
			if (error == 0 && td2->td_proc != p)
				error = ESRCH;
			if (error == 0)
				error = proc_can_ptrace(td, p);
			if (error != 0)
				goto fail;
		}

		/* Ok */
		break;
	}

	/*
	 * Keep this process around and request parallel ptrace()
	 * request to wait until we finish this request.
	 */
	MPASS((p->p_flag2 & P2_PTRACEREQ) == 0);
	p->p_flag2 |= P2_PTRACEREQ;
	p2_req_set = true;
	_PHOLD(p);

	/*
	 * Actually do the requests
	 */

	td->td_retval[0] = 0;

	switch (req) {
	case PT_TRACE_ME:
		/* set my trace flag and "owner" so it can read/write me */
		proc_set_traced(p, false);
		if (p->p_flag & P_PPWAIT)
			p->p_flag |= P_PPTRACE;
		CTR1(KTR_PTRACE, "PT_TRACE_ME: pid %d", p->p_pid);
		break;

	case PT_ATTACH:
		/* security check done above */
		/*
		 * It would be nice if the tracing relationship was separate
		 * from the parent relationship but that would require
		 * another set of links in the proc struct or for "wait"
		 * to scan the entire proc table.  To make life easier,
		 * we just re-parent the process we're trying to trace.
		 * The old parent is remembered so we can put things back
		 * on a "detach".
		 */
		proc_set_traced(p, true);
		proc_reparent(p, td->td_proc, false);
		CTR2(KTR_PTRACE, "PT_ATTACH: pid %d, oppid %d", p->p_pid,
		    p->p_oppid);

		sx_xunlock(&proctree_lock);
		proctree_locked = false;
		MPASS(p->p_xthread == NULL);
		MPASS((p->p_flag & P_STOPPED_TRACE) == 0);

		/*
		 * If already stopped due to a stop signal, clear the
		 * existing stop before triggering a traced SIGSTOP.
		 */
		if ((p->p_flag & P_STOPPED_SIG) != 0) {
			PROC_SLOCK(p);
			p->p_flag &= ~(P_STOPPED_SIG | P_WAITED);
			thread_unsuspend(p);
			PROC_SUNLOCK(p);
		}

		kern_psignal(p, SIGSTOP);
		break;

	case PT_CLEARSTEP:
		CTR2(KTR_PTRACE, "PT_CLEARSTEP: tid %d (pid %d)", td2->td_tid,
		    p->p_pid);
		error = ptrace_clear_single_step(td2);
		break;

	case PT_SETSTEP:
		CTR2(KTR_PTRACE, "PT_SETSTEP: tid %d (pid %d)", td2->td_tid,
		    p->p_pid);
		error = ptrace_single_step(td2);
		break;

	case PT_SUSPEND:
		CTR2(KTR_PTRACE, "PT_SUSPEND: tid %d (pid %d)", td2->td_tid,
		    p->p_pid);
		td2->td_dbgflags |= TDB_SUSPEND;
		ast_sched(td2, TDA_SUSPEND);
		break;

	case PT_RESUME:
		CTR2(KTR_PTRACE, "PT_RESUME: tid %d (pid %d)", td2->td_tid,
		    p->p_pid);
		td2->td_dbgflags &= ~TDB_SUSPEND;
		break;

	case PT_FOLLOW_FORK:
		CTR3(KTR_PTRACE, "PT_FOLLOW_FORK: pid %d %s -> %s", p->p_pid,
		    p->p_ptevents & PTRACE_FORK ? "enabled" : "disabled",
		    data ? "enabled" : "disabled");
		if (data)
			p->p_ptevents |= PTRACE_FORK;
		else
			p->p_ptevents &= ~PTRACE_FORK;
		break;

	case PT_LWP_EVENTS:
		CTR3(KTR_PTRACE, "PT_LWP_EVENTS: pid %d %s -> %s", p->p_pid,
		    p->p_ptevents & PTRACE_LWP ? "enabled" : "disabled",
		    data ? "enabled" : "disabled");
		if (data)
			p->p_ptevents |= PTRACE_LWP;
		else
			p->p_ptevents &= ~PTRACE_LWP;
		break;

	case PT_GET_EVENT_MASK:
		if (data != sizeof(p->p_ptevents)) {
			error = EINVAL;
			break;
		}
		CTR2(KTR_PTRACE, "PT_GET_EVENT_MASK: pid %d mask %#x", p->p_pid,
		    p->p_ptevents);
		*(int *)addr = p->p_ptevents;
		break;

	case PT_SET_EVENT_MASK:
		if (data != sizeof(p->p_ptevents)) {
			error = EINVAL;
			break;
		}
		tmp = *(int *)addr;
		if ((tmp & ~(PTRACE_EXEC | PTRACE_SCE | PTRACE_SCX |
		    PTRACE_FORK | PTRACE_LWP | PTRACE_VFORK)) != 0) {
			error = EINVAL;
			break;
		}
		CTR3(KTR_PTRACE, "PT_SET_EVENT_MASK: pid %d mask %#x -> %#x",
		    p->p_pid, p->p_ptevents, tmp);
		p->p_ptevents = tmp;
		break;

	case PT_GET_SC_ARGS:
		CTR1(KTR_PTRACE, "PT_GET_SC_ARGS: pid %d", p->p_pid);
		if ((td2->td_dbgflags & (TDB_SCE | TDB_SCX)) == 0
#ifdef COMPAT_FREEBSD32
		    || (wrap32 && !safe)
#endif
		    ) {
			error = EINVAL;
			break;
		}
		bzero(addr, sizeof(td2->td_sa.args));
		/* See the explanation in linux_ptrace_get_syscall_info(). */
		bcopy(td2->td_sa.args, addr, SV_PROC_ABI(td->td_proc) ==
		    SV_ABI_LINUX ? sizeof(td2->td_sa.args) :
		    td2->td_sa.callp->sy_narg * sizeof(syscallarg_t));
		break;

	case PT_GET_SC_RET:
		if ((td2->td_dbgflags & (TDB_SCX)) == 0
#ifdef COMPAT_FREEBSD32
		    || (wrap32 && !safe)
#endif
		    ) {
			error = EINVAL;
			break;
		}
		psr = addr;
		bzero(psr, sizeof(*psr));
		psr->sr_error = td2->td_errno;
		if (psr->sr_error == 0) {
			psr->sr_retval[0] = td2->td_retval[0];
			psr->sr_retval[1] = td2->td_retval[1];
		}
		CTR4(KTR_PTRACE,
		    "PT_GET_SC_RET: pid %d error %d retval %#lx,%#lx",
		    p->p_pid, psr->sr_error, psr->sr_retval[0],
		    psr->sr_retval[1]);
		break;

	case PT_STEP:
	case PT_CONTINUE:
	case PT_TO_SCE:
	case PT_TO_SCX:
	case PT_SYSCALL:
	case PT_DETACH:
		/* Zero means do not send any signal */
		if (data < 0 || data > _SIG_MAXSIG) {
			error = EINVAL;
			break;
		}

		switch (req) {
		case PT_STEP:
			CTR3(KTR_PTRACE, "PT_STEP: tid %d (pid %d), sig = %d",
			    td2->td_tid, p->p_pid, data);
			error = ptrace_single_step(td2);
			if (error)
				goto out;
			break;
		case PT_CONTINUE:
		case PT_TO_SCE:
		case PT_TO_SCX:
		case PT_SYSCALL:
			if (addr != (void *)1) {
				error = ptrace_set_pc(td2,
				    (u_long)(uintfptr_t)addr);
				if (error)
					goto out;
			}
			switch (req) {
			case PT_TO_SCE:
				p->p_ptevents |= PTRACE_SCE;
				CTR4(KTR_PTRACE,
		    "PT_TO_SCE: pid %d, events = %#x, PC = %#lx, sig = %d",
				    p->p_pid, p->p_ptevents,
				    (u_long)(uintfptr_t)addr, data);
				break;
			case PT_TO_SCX:
				p->p_ptevents |= PTRACE_SCX;
				CTR4(KTR_PTRACE,
		    "PT_TO_SCX: pid %d, events = %#x, PC = %#lx, sig = %d",
				    p->p_pid, p->p_ptevents,
				    (u_long)(uintfptr_t)addr, data);
				break;
			case PT_SYSCALL:
				p->p_ptevents |= PTRACE_SYSCALL;
				CTR4(KTR_PTRACE,
		    "PT_SYSCALL: pid %d, events = %#x, PC = %#lx, sig = %d",
				    p->p_pid, p->p_ptevents,
				    (u_long)(uintfptr_t)addr, data);
				break;
			case PT_CONTINUE:
				CTR3(KTR_PTRACE,
				    "PT_CONTINUE: pid %d, PC = %#lx, sig = %d",
				    p->p_pid, (u_long)(uintfptr_t)addr, data);
				break;
			}
			break;
		case PT_DETACH:
			/*
			 * Clear P_TRACED before reparenting
			 * a detached process back to its original
			 * parent.  Otherwise the debugee will be set
			 * as an orphan of the debugger.
			 */
			p->p_flag &= ~(P_TRACED | P_WAITED);

			/*
			 * Reset the process parent.
			 */
			if (p->p_oppid != p->p_pptr->p_pid) {
				PROC_LOCK(p->p_pptr);
				sigqueue_take(p->p_ksi);
				PROC_UNLOCK(p->p_pptr);

				pp = proc_realparent(p);
				proc_reparent(p, pp, false);
				if (pp == initproc)
					p->p_sigparent = SIGCHLD;
				CTR3(KTR_PTRACE,
			    "PT_DETACH: pid %d reparented to pid %d, sig %d",
				    p->p_pid, pp->p_pid, data);
			} else {
				CTR2(KTR_PTRACE, "PT_DETACH: pid %d, sig %d",
				    p->p_pid, data);
			}

			p->p_ptevents = 0;
			FOREACH_THREAD_IN_PROC(p, td3) {
				if ((td3->td_dbgflags & TDB_FSTP) != 0) {
					sigqueue_delete(&td3->td_sigqueue,
					    SIGSTOP);
				}
				td3->td_dbgflags &= ~(TDB_XSIG | TDB_FSTP |
				    TDB_SUSPEND | TDB_BORN);
			}

			if ((p->p_flag2 & P2_PTRACE_FSTP) != 0) {
				sigqueue_delete(&p->p_sigqueue, SIGSTOP);
				p->p_flag2 &= ~P2_PTRACE_FSTP;
			}

			/* should we send SIGCHLD? */
			/* childproc_continued(p); */
			break;
		}

		sx_xunlock(&proctree_lock);
		proctree_locked = false;

	sendsig:
		MPASS(!proctree_locked);

		/*
		 * Clear the pending event for the thread that just
		 * reported its event (p_xthread).  This may not be
		 * the thread passed to PT_CONTINUE, PT_STEP, etc. if
		 * the debugger is resuming a different thread.
		 *
		 * Deliver any pending signal via the reporting thread.
		 */
		MPASS(p->p_xthread != NULL);
		p->p_xthread->td_dbgflags &= ~TDB_XSIG;
		p->p_xthread->td_xsig = data;
		p->p_xthread = NULL;
		p->p_xsig = data;

		/*
		 * P_WKILLED is insurance that a PT_KILL/SIGKILL
		 * always works immediately, even if another thread is
		 * unsuspended first and attempts to handle a
		 * different signal or if the POSIX.1b style signal
		 * queue cannot accommodate any new signals.
		 */
		if (data == SIGKILL)
			proc_wkilled(p);

		/*
		 * Unsuspend all threads.  To leave a thread
		 * suspended, use PT_SUSPEND to suspend it before
		 * continuing the process.
		 */
		ptrace_unsuspend(p);
		break;

	case PT_WRITE_I:
	case PT_WRITE_D:
		td2->td_dbgflags |= TDB_USERWR;
		PROC_UNLOCK(p);
		error = 0;
		if (proc_writemem(td, p, (off_t)(uintptr_t)addr, &data,
		    sizeof(int)) != sizeof(int))
			error = ENOMEM;
		else
			CTR3(KTR_PTRACE, "PT_WRITE: pid %d: %p <= %#x",
			    p->p_pid, addr, data);
		PROC_LOCK(p);
		break;

	case PT_READ_I:
	case PT_READ_D:
		PROC_UNLOCK(p);
		error = tmp = 0;
		if (proc_readmem(td, p, (off_t)(uintptr_t)addr, &tmp,
		    sizeof(int)) != sizeof(int))
			error = ENOMEM;
		else
			CTR3(KTR_PTRACE, "PT_READ: pid %d: %p >= %#x",
			    p->p_pid, addr, tmp);
		td->td_retval[0] = tmp;
		PROC_LOCK(p);
		break;

	case PT_IO:
		piod = addr;
		iov.iov_base = piod->piod_addr;
		iov.iov_len = piod->piod_len;
		uio.uio_offset = (off_t)(uintptr_t)piod->piod_offs;
		uio.uio_resid = piod->piod_len;
		uio.uio_iov = &iov;
		uio.uio_iovcnt = 1;
		uio.uio_segflg = UIO_USERSPACE;
		uio.uio_td = td;
		switch (piod->piod_op) {
		case PIOD_READ_D:
		case PIOD_READ_I:
			CTR3(KTR_PTRACE, "PT_IO: pid %d: READ (%p, %#x)",
			    p->p_pid, (uintptr_t)uio.uio_offset, uio.uio_resid);
			uio.uio_rw = UIO_READ;
			break;
		case PIOD_WRITE_D:
		case PIOD_WRITE_I:
			CTR3(KTR_PTRACE, "PT_IO: pid %d: WRITE (%p, %#x)",
			    p->p_pid, (uintptr_t)uio.uio_offset, uio.uio_resid);
			td2->td_dbgflags |= TDB_USERWR;
			uio.uio_rw = UIO_WRITE;
			break;
		default:
			error = EINVAL;
			goto out;
		}
		PROC_UNLOCK(p);
		error = proc_rwmem(p, &uio);
		piod->piod_len -= uio.uio_resid;
		PROC_LOCK(p);
		break;

	case PT_KILL:
		CTR1(KTR_PTRACE, "PT_KILL: pid %d", p->p_pid);
		data = SIGKILL;
		goto sendsig;	/* in PT_CONTINUE above */

	case PT_SETREGS:
		CTR2(KTR_PTRACE, "PT_SETREGS: tid %d (pid %d)", td2->td_tid,
		    p->p_pid);
		td2->td_dbgflags |= TDB_USERWR;
		error = PROC_WRITE(regs, td2, addr);
		break;

	case PT_GETREGS:
		CTR2(KTR_PTRACE, "PT_GETREGS: tid %d (pid %d)", td2->td_tid,
		    p->p_pid);
		error = PROC_READ(regs, td2, addr);
		break;

	case PT_SETFPREGS:
		CTR2(KTR_PTRACE, "PT_SETFPREGS: tid %d (pid %d)", td2->td_tid,
		    p->p_pid);
		td2->td_dbgflags |= TDB_USERWR;
		error = PROC_WRITE(fpregs, td2, addr);
		break;

	case PT_GETFPREGS:
		CTR2(KTR_PTRACE, "PT_GETFPREGS: tid %d (pid %d)", td2->td_tid,
		    p->p_pid);
		error = PROC_READ(fpregs, td2, addr);
		break;

	case PT_SETDBREGS:
		CTR2(KTR_PTRACE, "PT_SETDBREGS: tid %d (pid %d)", td2->td_tid,
		    p->p_pid);
		td2->td_dbgflags |= TDB_USERWR;
		error = PROC_WRITE(dbregs, td2, addr);
		break;

	case PT_GETDBREGS:
		CTR2(KTR_PTRACE, "PT_GETDBREGS: tid %d (pid %d)", td2->td_tid,
		    p->p_pid);
		error = PROC_READ(dbregs, td2, addr);
		break;

	case PT_SETREGSET:
		CTR2(KTR_PTRACE, "PT_SETREGSET: tid %d (pid %d)", td2->td_tid,
		    p->p_pid);
		error = proc_write_regset(td2, data, addr);
		break;

	case PT_GETREGSET:
		CTR2(KTR_PTRACE, "PT_GETREGSET: tid %d (pid %d)", td2->td_tid,
		    p->p_pid);
		error = proc_read_regset(td2, data, addr);
		break;

	case PT_LWPINFO:
		if (data <= 0 || data > sizeof(*pl)) {
			error = EINVAL;
			break;
		}
		pl = addr;
		bzero(pl, sizeof(*pl));
		pl->pl_lwpid = td2->td_tid;
		pl->pl_event = PL_EVENT_NONE;
		pl->pl_flags = 0;
		if (td2->td_dbgflags & TDB_XSIG) {
			pl->pl_event = PL_EVENT_SIGNAL;
			if (td2->td_si.si_signo != 0 &&
			    data >= offsetof(struct ptrace_lwpinfo, pl_siginfo)
			    + sizeof(pl->pl_siginfo)){
				pl->pl_flags |= PL_FLAG_SI;
				pl->pl_siginfo = td2->td_si;
			}
		}
		if (td2->td_dbgflags & TDB_SCE)
			pl->pl_flags |= PL_FLAG_SCE;
		else if (td2->td_dbgflags & TDB_SCX)
			pl->pl_flags |= PL_FLAG_SCX;
		if (td2->td_dbgflags & TDB_EXEC)
			pl->pl_flags |= PL_FLAG_EXEC;
		if (td2->td_dbgflags & TDB_FORK) {
			pl->pl_flags |= PL_FLAG_FORKED;
			pl->pl_child_pid = td2->td_dbg_forked;
			if (td2->td_dbgflags & TDB_VFORK)
				pl->pl_flags |= PL_FLAG_VFORKED;
		} else if ((td2->td_dbgflags & (TDB_SCX | TDB_VFORK)) ==
		    TDB_VFORK)
			pl->pl_flags |= PL_FLAG_VFORK_DONE;
		if (td2->td_dbgflags & TDB_CHILD)
			pl->pl_flags |= PL_FLAG_CHILD;
		if (td2->td_dbgflags & TDB_BORN)
			pl->pl_flags |= PL_FLAG_BORN;
		if (td2->td_dbgflags & TDB_EXIT)
			pl->pl_flags |= PL_FLAG_EXITED;
		pl->pl_sigmask = td2->td_sigmask;
		pl->pl_siglist = td2->td_siglist;
		strcpy(pl->pl_tdname, td2->td_name);
		if ((td2->td_dbgflags & (TDB_SCE | TDB_SCX)) != 0) {
			pl->pl_syscall_code = td2->td_sa.code;
			pl->pl_syscall_narg = td2->td_sa.callp->sy_narg;
		} else {
			pl->pl_syscall_code = 0;
			pl->pl_syscall_narg = 0;
		}
		CTR6(KTR_PTRACE,
    "PT_LWPINFO: tid %d (pid %d) event %d flags %#x child pid %d syscall %d",
		    td2->td_tid, p->p_pid, pl->pl_event, pl->pl_flags,
		    pl->pl_child_pid, pl->pl_syscall_code);
		break;

	case PT_GETNUMLWPS:
		CTR2(KTR_PTRACE, "PT_GETNUMLWPS: pid %d: %d threads", p->p_pid,
		    p->p_numthreads);
		td->td_retval[0] = p->p_numthreads;
		break;

	case PT_GETLWPLIST:
		CTR3(KTR_PTRACE, "PT_GETLWPLIST: pid %d: data %d, actual %d",
		    p->p_pid, data, p->p_numthreads);
		if (data <= 0) {
			error = EINVAL;
			break;
		}
		num = imin(p->p_numthreads, data);
		PROC_UNLOCK(p);
		buf = malloc(num * sizeof(lwpid_t), M_TEMP, M_WAITOK);
		tmp = 0;
		PROC_LOCK(p);
		FOREACH_THREAD_IN_PROC(p, td2) {
			if (tmp >= num)
				break;
			buf[tmp++] = td2->td_tid;
		}
		PROC_UNLOCK(p);
		error = copyout(buf, addr, tmp * sizeof(lwpid_t));
		free(buf, M_TEMP);
		if (!error)
			td->td_retval[0] = tmp;
		PROC_LOCK(p);
		break;

	case PT_VM_TIMESTAMP:
		CTR2(KTR_PTRACE, "PT_VM_TIMESTAMP: pid %d: timestamp %d",
		    p->p_pid, p->p_vmspace->vm_map.timestamp);
		td->td_retval[0] = p->p_vmspace->vm_map.timestamp;
		break;

	case PT_VM_ENTRY:
		PROC_UNLOCK(p);
		error = ptrace_vm_entry(td, p, addr);
		PROC_LOCK(p);
		break;

	case PT_COREDUMP:
		pc = addr;
		CTR2(KTR_PTRACE, "PT_COREDUMP: pid %d, fd %d",
		    p->p_pid, pc->pc_fd);

		if ((pc->pc_flags & ~(PC_COMPRESS | PC_ALL)) != 0) {
			error = EINVAL;
			break;
		}
		PROC_UNLOCK(p);

		tcq = malloc(sizeof(*tcq), M_TEMP, M_WAITOK | M_ZERO);
		fp = NULL;
		error = fget_write(td, pc->pc_fd, &cap_write_rights, &fp);
		if (error != 0)
			goto coredump_cleanup_nofp;
		if (fp->f_type != DTYPE_VNODE || fp->f_vnode->v_type != VREG) {
			error = EPIPE;
			goto coredump_cleanup;
		}

		PROC_LOCK(p);
		error = proc_can_ptrace(td, p);
		if (error != 0)
			goto coredump_cleanup_locked;

		td2 = ptrace_sel_coredump_thread(p);
		if (td2 == NULL) {
			error = EBUSY;
			goto coredump_cleanup_locked;
		}
		KASSERT((td2->td_dbgflags & (TDB_COREDUMPREQ |
		    TDB_SCREMOTEREQ)) == 0,
		    ("proc %d tid %d req coredump", p->p_pid, td2->td_tid));

		tcq->tc_vp = fp->f_vnode;
		tcq->tc_limit = pc->pc_limit == 0 ? OFF_MAX : pc->pc_limit;
		tcq->tc_flags = SVC_PT_COREDUMP;
		if ((pc->pc_flags & PC_COMPRESS) == 0)
			tcq->tc_flags |= SVC_NOCOMPRESS;
		if ((pc->pc_flags & PC_ALL) != 0)
			tcq->tc_flags |= SVC_ALL;
		td2->td_remotereq = tcq;
		td2->td_dbgflags |= TDB_COREDUMPREQ;
		thread_run_flash(td2);
		while ((td2->td_dbgflags & TDB_COREDUMPREQ) != 0)
			msleep(p, &p->p_mtx, PPAUSE, "crdmp", 0);
		error = tcq->tc_error;
coredump_cleanup_locked:
		PROC_UNLOCK(p);
coredump_cleanup:
		fdrop(fp, td);
coredump_cleanup_nofp:
		free(tcq, M_TEMP);
		PROC_LOCK(p);
		break;

	case PT_SC_REMOTE:
		pscr = addr;
		CTR2(KTR_PTRACE, "PT_SC_REMOTE: pid %d, syscall %d",
		    p->p_pid, pscr->pscr_syscall);
		if ((td2->td_dbgflags & TDB_BOUNDARY) == 0) {
			error = EBUSY;
			break;
		}
		PROC_UNLOCK(p);
		MPASS(pscr->pscr_nargs <= nitems(td->td_sa.args));

		tsr = malloc(sizeof(struct thr_syscall_req), M_TEMP,
		    M_WAITOK | M_ZERO);

		tsr->ts_sa.code = pscr->pscr_syscall;
		tsr->ts_nargs = pscr->pscr_nargs;
		memcpy(&tsr->ts_sa.args, pscr->pscr_args,
		    sizeof(syscallarg_t) * tsr->ts_nargs);

		PROC_LOCK(p);
		error = proc_can_ptrace(td, p);
		if (error != 0) {
			free(tsr, M_TEMP);
			break;
		}
		if (td2->td_proc != p) {
			free(tsr, M_TEMP);
			error = ESRCH;
			break;
		}
		KASSERT((td2->td_dbgflags & (TDB_COREDUMPREQ |
		    TDB_SCREMOTEREQ)) == 0,
		    ("proc %d tid %d req coredump", p->p_pid, td2->td_tid));

		td2->td_remotereq = tsr;
		td2->td_dbgflags |= TDB_SCREMOTEREQ;
		thread_run_flash(td2);
		while ((td2->td_dbgflags & TDB_SCREMOTEREQ) != 0)
			msleep(p, &p->p_mtx, PPAUSE, "pscrx", 0);
		error = 0;
		memcpy(&pscr->pscr_ret, &tsr->ts_ret, sizeof(tsr->ts_ret));
		free(tsr, M_TEMP);
		break;

	default:
#ifdef __HAVE_PTRACE_MACHDEP
		if (req >= PT_FIRSTMACH) {
			PROC_UNLOCK(p);
			error = cpu_ptrace(td2, req, addr, data);
			PROC_LOCK(p);
		} else
#endif
			/* Unknown request. */
			error = EINVAL;
		break;
	}
out:
	/* Drop our hold on this process now that the request has completed. */
	_PRELE(p);
fail:
	if (p2_req_set) {
		if ((p->p_flag2 & P2_PTRACEREQ) != 0)
			wakeup(&p->p_flag2);
		p->p_flag2 &= ~P2_PTRACEREQ;
	}
	PROC_UNLOCK(p);
	if (proctree_locked)
		sx_xunlock(&proctree_lock);
	return (error);
}
#undef PROC_READ
#undef PROC_WRITE