diff --git a/usr/austin/process.go b/usr/austin/process.go
new file mode 100644
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--- /dev/null
+++ b/usr/austin/process.go
@@ -0,0 +1,215 @@
+// Copyright 2009 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package ptrace provides a platform-independent interface for
+// tracing and controlling running processes.  It supports
+// multi-threaded processes and provides typical low-level debugging
+// controls such as breakpoints, single stepping, and manipulating
+// memory and registers.
+package ptrace
+
+import (
+	"os";
+	"strconv";
+)
+
+type Word uint64
+
+// A Cause explains why a thread is stopped.
+type Cause interface {
+	String() string;
+}
+
+// Regs is a set of named machine registers, including a program
+// counter, link register, and stack pointer.
+type Regs interface {
+	// PC returns the value of the program counter.
+	PC() Word;
+
+	// Link returns the link register, if any.
+	Link() Word;
+
+	// SP returns the value of the stack pointer.
+	SP() Word;
+
+	// Names returns the names of all of the registers.
+	Names() []string;
+
+	// Get returns the value of a register, where i corresponds to
+	// the index of the register's name in the array returned by
+	// Names.
+	Get(i int) Word;
+
+	// Set sets the value of a register.
+	Set(i int, val Word);
+}
+
+// Thread is a thread in the process being traced.
+type Thread interface {
+	// Step steps this thread by a single instruction.  The thread
+	// must be stopped.  If the thread is currently stopped on a
+	// breakpoint, this will step over the breakpoint.
+	//
+	// XXX What if it's stopped because of a signal?
+	Step() os.Error;
+
+	// Stopped returns the reason that this thread is stopped.  It
+	// is an error is the thread not stopped.
+	Stopped() (Cause, os.Error);
+
+	// Regs retrieves the current register values from this
+	// thread.  The thread must be stopped.
+	Regs() (Regs, os.Error);
+
+	// Peek reads len(out) bytes from the address addr in this
+	// thread into out.  The thread must be stopped.  It returns
+	// the number of bytes successfully read.  If an error occurs,
+	// such as attempting to read unmapped memory, this count
+	// could be short and an error will be returned.  If this does
+	// encounter unmapped memory, it will read up to the byte
+	// preceding the unmapped area.
+	Peek(addr Word, out []byte) (int, os.Error);
+
+	// Poke writes b to the address addr in this thread.  The
+	// thread must be stopped.  It returns the number of bytes
+	// successfully written.  If an error occurs, such as
+	// attempting to write to unmapped memory, this count could be
+	// short and an error will be returned.  If this does
+	// encounter unmapped memory, it will write up to the byte
+	// preceding the unmapped area.
+	Poke(addr Word, b []byte) (int, os.Error);
+}
+
+// Process is a process being traced.  It consists of a set of
+// threads.  A process can be running, stopped, or terminated.  The
+// process's state extends to all of its threads.
+type Process interface {
+	// Threads returns an array of all threads in this process.
+	Threads() []*Thread;
+
+	// AddBreakpoint creates a new breakpoint at program counter
+	// pc.  Breakpoints can only be created when the process is
+	// stopped.  It is an error if a breakpoint already exists at
+	// pc.
+	AddBreakpoint(pc Word) os.Error;
+
+	// RemoveBreakpoint removes the breakpoint at the program
+	// counter pc.  It is an error if no breakpoint exists at pc.
+	RemoveBreakpoint(pc Word) os.Error;
+
+	// Stop stops all running threads in this process before
+	// returning.
+	Stop() os.Error;
+
+	// Continue resumes execution of all threads in this process.
+	// Any thread that is stopped on a breakpoint will be stepped
+	// over that breakpoint.  Any thread that is stopped because
+	// of a signal will receive the pending signal.
+	Continue() os.Error;
+
+	// WaitStop waits until all threads in process p are stopped
+	// as a result of some thread hitting a breakpoint, receiving
+	// a signal, creating a new thread, or exiting.
+	WaitStop() os.Error;
+
+	// Detach detaches from this process.  All stopped threads
+	// will be resumed.
+	Detach() os.Error;
+}
+
+// Paused is a stop cause used for threads that are stopped either by
+// user request (e.g., from the Stop method or after single stepping),
+// or that are stopped because some other thread caused the program to
+// stop.
+type Paused struct {}
+
+func (c Paused) String() string {
+	return "paused";
+}
+
+// Breakpoint is a stop cause resulting from a thread reaching a set
+// breakpoint.
+type Breakpoint	Word
+
+// PC returns the program counter that the program is stopped at.
+func (c Breakpoint) PC() Word {
+	return Word(c);
+}
+
+func (c Breakpoint) String() string {
+	return "breakpoint at 0x" + strconv.Uitob64(uint64(c.PC()), 16);
+}
+
+// Signal is a stop cause resulting from a thread receiving a signal.
+// When the process is continued, the signal will be delivered.
+type Signal string
+
+// Signal returns the signal being delivered to the thread.
+func (c Signal) Name() string {
+	return string(c);
+}
+
+func (c Signal) String() string {
+	return c.Name();
+}
+
+// ThreadCreate is a stop cause returned from an existing thread when
+// it creates a new thread.  The new thread exists in a primordial
+// form at this point and will begin executing in earnest when the
+// process is continued.
+type ThreadCreate struct {
+	thread Thread;
+}
+
+func (c ThreadCreate) NewThread() Thread {
+	return c.thread;
+}
+
+func (c ThreadCreate) String() string {
+	return "thread create";
+}
+
+// ThreadExit is a stop cause resulting from a thread exiting.  When
+// this cause first arises, the thread will still be in the list of
+// process threads and its registers and memory will still be
+// accessible.
+type ThreadExit struct {
+	exitStatus int;
+	signal int;
+}
+
+// Exited returns true if the thread exited normally.
+func (c ThreadExit) Exited() bool {
+	return c.exitStatus != -1;
+}
+
+// ExitStatus returns the exit status of the thread if it exited
+// normally or -1 otherwise.
+func (c ThreadExit) ExitStatus() int {
+	return c.exitStatus;
+}
+
+// Signaled returns true if the thread was terminated by a signal.
+func (c ThreadExit) Signaled() bool {
+	return c.signal != -1;
+}
+
+// StopSignal returns the signal that terminated the thread, or -1 if
+// it was not terminated by a signal.
+func (c ThreadExit) StopSignal() int {
+	return c.signal;
+}
+
+func (c ThreadExit) String() string {
+	res := "thread exited ";
+	switch {
+	case c.Exited():
+		res += "with status " + strconv.Itoa(c.ExitStatus());
+	case c.Signaled():
+		res += "from signal " + strconv.Itoa(c.StopSignal());
+	default:
+		res += "from unknown cause";
+	}
+	return res;
+}