--- /dev/null
+// 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.
+
+ptrace and NTPL, the missing manpage
+
+== Signals ==
+
+A signal sent to a ptrace'd process or thread causes only the thread
+that receives it to stop and report to the attached process.
+
+Use tgkill to target a signal (for example, SIGSTOP) at a particular
+thread. If you use kill, the signal could be delivered to another
+thread in the same process.
+
+Note that SIGSTOP differs from its usual behavior when a process is
+being traced. Usually, a SIGSTOP sent to any thread in a thread group
+will stop all threads in the thread group. When a thread is traced,
+however, a SIGSTOP affects only the receiving thread (and any other
+threads in the thread group that are not traced).
+
+SIGKILL behaves like it does for non-traced processes. It affects all
+threads in the process and terminates them without the WSTOPSIG event
+generated by other signals. However, if PTRACE_O_TRACEEXIT is set,
+the attached process will still receive PTRACE_EVENT_EXIT events
+before receiving WIFSIGNALED events.
+
+See "Following thread death" for a caveat regarding signal delivery to
+zombie threads.
+
+== Waiting on threads ==
+
+Cloned threads in ptrace'd processes are treated similarly to cloned
+threads in your own process. Thus, you must use the __WALL option in
+order to receive notifications from threads created by the child
+process. Similarly, the __WCLONE option will wait only on
+notifications from threads created by the child process and *not* on
+notifications from the initial child thread.
+
+Even when waiting on a specific thread's PID using waitpid or similar,
+__WALL or __WCLONE is necessary or waitpid will return ECHILD.
+
+== Attaching to existing threads ==
+
+libthread_db (which gdb uses), attaches to existing threads by pulling
+the pthread data structures out of the traced process. The much
+easier way is to traverse the /proc/PID/task directory, though it's
+unclear how the semantics of these two approaches differ.
+
+Unfortunately, if the main thread has exited (but the overall process
+has not), it sticks around as a zombie process. This zombie will
+appear in the /proc/PID/task directory, but trying to attach to it
+will yield EPERM. In this case, the third field of the
+/proc/PID/task/PID/stat file will be "Z". Attempting to open the stat
+file is also a convenient way to detect races between listing the task
+directory and the thread exiting. Coincidentally, gdb will simply
+fail to attach to a process whose main thread is a zombie.
+
+Because new threads may be created while the debugger is in the
+process of attaching to existing threads, the debugger must repeatedly
+re-list the task directory until it has attached to (and thus stopped)
+every thread listed.
+
+In order to follow new threads created by existing threads,
+PTRACE_O_TRACECLONE must be set on each thread attached to.
+
+== Following new threads ==
+
+With the child process stopped, use PTRACE_SETOPTIONS to set the
+PTRACE_O_TRACECLONE option. This option is per-thread, and thus must
+be set on each existing thread individually. When an existing thread
+with PTRACE_O_TRACECLONE set spawns a new thread, the existing thread
+will stop with (SIGTRAP | PTRACE_EVENT_CLONE << 8) and the PID of the
+new thread can be retrieved with PTRACE_GETEVENTMSG on the creating
+thread. At this time, the new thread will exist, but will initially
+be stopped with a SIGSTOP. The new thread will automatically be
+traced and will inherit the PTRACE_O_TRACECLONE option from its
+parent. The attached process should wait on the new thread to receive
+the SIGSTOP notification.
+
+When using waitpid(-1, ...), don't rely on the parent thread reporting
+a SIGTRAP before receiving the SIGSTOP from the new child thread.
+
+Without PTRACE_O_TRACECLONE, newly cloned threads will not be
+ptrace'd. As a result, signals received by new threads will be
+handled in the usual way, which may affect the parent and in turn
+appear to the attached process, but attributed to the parent (possibly
+in unexpected ways).
+
+== Following thread death ==
+
+If any thread with the PTRACE_O_TRACEEXIT option set exits (either by
+returning or pthread_exit'ing), the tracing process will receive an
+immediate PTRACE_EVENT_EXIT. At this point, the thread will still
+exist. The exit status, encoded as for wait, can be queried using
+PTRACE_GETEVENTMSG on the exiting thread's PID. The thread should be
+continued so it can actually exit, after which its wait behavior is
+the same as for a thread without the PTRACE_O_TRACEEXIT option.
+
+If a non-main thread exits (either by returning or pthread_exit'ing),
+its corresponding process will also exit, producing a WIFEXITED event
+(after the process is continued from a possible PTRACE_EVENT_EXIT
+event). It is *not* necessary for another thread to ptrace_join for
+this to happen.
+
+If the main thread exits by returning, then all threads will exit,
+first generating a PTRACE_EVENT_EXIT event for each thread if
+appropriate, then producing a WIFEXITED event for each thread.
+
+If the main thread exits using pthread_exit, then it enters a
+non-waitable zombie state. It will still produce an immediate
+PTRACE_O_TRACEEXIT event, but the WIFEXITED event will be delayed
+until the entire process exits. This state exists so that shells
+don't think the process is done until all of the threads have exited.
+Unfortunately, signals cannot be delivered to non-waitable zombies.
+Most notably, SIGSTOP cannot be delivered; as a result, when you
+broadcast SIGSTOP to all of the threads, you must not wait for
+non-waitable zombies to stop.
+
+== Multi-threaded debuggers ==
+
+If the debugger itself is multi-threaded, ptrace calls must come from
+the same thread that originally attached to the remote thread. The
+kernel simply compares the PID of the caller of ptrace against the
+tracer PID of the process passed to ptrace. Because each debugger
+thread has a different PID, calling ptrace from a different thread
+might as well be calling it from a different process and the kernel
+will return ESRCH.
+
+wait, on the other hand, does not have this restriction. Any debugger
+thread can wait on any thread in the attached process.
--- /dev/null
+// 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
+
+import (
+ "container/vector";
+ "fmt";
+ "io";
+ "os";
+ "ptrace";
+ "runtime";
+ "strconv";
+ "strings";
+ "sync";
+ "syscall";
+)
+
+// This is an implementation of the process tracing interface using
+// Linux's ptrace(2) interface. The implementation is multi-threaded.
+// Each attached process has an associated monitor thread, and each
+// running attached thread has an associated "wait" thread. The wait
+// thread calls wait4 on the thread's TID and reports any wait events
+// or errors via "debug events". The monitor thread consumes these
+// wait events and updates the internally maintained state of each
+// thread. All ptrace calls must run in the monitor thread, so the
+// monitor executes closures received on the debugReq channel.
+//
+// As ptrace's documentation is somewhat light, this is heavily based
+// on information gleaned from the implementation of ptrace found at
+// http://lxr.linux.no/linux+v2.6.30/kernel/ptrace.c
+// http://lxr.linux.no/linux+v2.6.30/arch/x86/kernel/ptrace.c#L854
+// as well as experimentation and examination of gdb's behavior.
+
+const (
+ trace = true;
+ traceIP = false;
+)
+
+/*
+ * Thread state
+ */
+
+// Each thread can be in one of the following set of states.
+// Each state satisfies (isRunning() || isStopped() || isTerminal()).
+type threadState string;
+
+const (
+ running threadState = "Running";
+ singleStepping = "SingleStepping"; // Transient
+ stopping = "Stopping"; // Transient
+ stopped = "Stopped";
+ stoppedBreakpoint = "StoppedBreakpoint";
+ stoppedSignal = "StoppedSignal";
+ stoppedThreadCreate = "StoppedThreadCreate";
+ stoppedExiting = "StoppedExiting";
+ exiting = "Exiting"; // Transient (except main thread)
+ exited = "Exited";
+ detached = "Detached";
+)
+
+func (ts threadState) isRunning() bool {
+ return ts == running || ts == singleStepping || ts == stopping || ts == exiting;
+}
+
+func (ts threadState) isStopped() bool {
+ return ts == stopped || ts == stoppedBreakpoint || ts == stoppedSignal || ts == stoppedThreadCreate || ts == stoppedExiting;
+}
+
+func (ts threadState) isTerminal() bool {
+ return ts == exited || ts == detached;
+}
+
+func (ts threadState) String() string {
+ return string(ts);
+}
+
+/*
+ * Basic types
+ */
+
+type thread struct
+
+// A breakpoint stores information about a single breakpoint,
+// including its program counter, the overwritten text if the
+// breakpoint is installed.
+type breakpoint struct {
+ pc uintptr;
+ olddata []byte;
+}
+
+func (bp *breakpoint) String() string {
+ if bp == nil {
+ return "<nil>";
+ }
+ return fmt.Sprintf("%#x", bp.pc);
+}
+
+// bpinst386 is the breakpoint instruction used on 386 and amd64.
+var bpinst386 = []byte{0xcc};
+
+// A debugEvent represents a reason a thread stopped or a wait error.
+type debugEvent struct {
+ *os.Waitmsg;
+ t *thread;
+ err os.Error;
+}
+
+// A debugReq is a request to execute a closure in the monitor thread.
+type debugReq struct {
+ f func () os.Error;
+ res chan os.Error;
+}
+
+// A transitionHandler specifies a function to be called when a thread
+// changes state and a function to be called when an error occurs in
+// the monitor. Both run in the monitor thread. Before the monitor
+// invokes a handler, it removes the handler from the handler queue.
+// The handler should re-add itself if needed.
+type transitionHandler struct {
+ handle func (*thread, threadState, threadState);
+ onErr func (os.Error);
+}
+
+// A process is a Linux process, which consists of a set of threads.
+// Each running process has one monitor thread, which processes
+// messages from the debugEvents, debugReqs, and stopReq channels and
+// calls transition handlers.
+type process struct {
+ pid int;
+ threads map[int] *thread;
+ breakpoints map[uintptr] *breakpoint;
+ debugEvents chan *debugEvent;
+ debugReqs chan *debugReq;
+ stopReq chan os.Error;
+ transitionHandlers *vector.Vector;
+}
+
+// A thread represents a Linux thread in another process that is being
+// debugged. Each running thread has an associated goroutine that
+// waits for thread updates and sends them to the process monitor.
+type thread struct {
+ tid int;
+ proc *process;
+ // Whether to ignore the next SIGSTOP received by wait.
+ ignoreNextSigstop bool;
+
+ // Thread state. Only modified via setState.
+ state threadState;
+ // If state == StoppedBreakpoint
+ breakpoint *breakpoint;
+ // If state == StoppedSignal or state == Exited
+ signal int;
+ // If state == StoppedThreadCreate
+ newThread *thread;
+ // If state == Exited
+ exitStatus int;
+}
+
+func (p *process) newThread(tid int) (*thread, os.Error)
+
+/*
+ * Errors
+ */
+
+type badState struct {
+ thread *thread;
+ message string;
+ state threadState;
+}
+
+func (e *badState) String() string {
+ return fmt.Sprintf("Thread %d %s from state %v", e.thread.tid, e.message, e.state);
+}
+
+type breakpointExistsError Word
+
+func (e breakpointExistsError) String() string {
+ return fmt.Sprintf("breakpoint already exists at PC %#x", e);
+}
+
+type noBreakpointError Word
+
+func (e noBreakpointError) String() string {
+ return fmt.Sprintf("no breakpoint at PC %#x", e);
+}
+
+/*
+ * Ptrace wrappers
+ */
+
+func (t *thread) ptracePeekText(addr uintptr, out []byte) (int, os.Error) {
+ c, err := syscall.PtracePeekText(t.tid, addr, out);
+ return c, os.NewSyscallError("ptrace(PEEKTEXT)", err);
+}
+
+func (t *thread) ptracePokeText(addr uintptr, out []byte) (int, os.Error) {
+ c, err := syscall.PtracePokeText(t.tid, addr, out);
+ return c, os.NewSyscallError("ptrace(POKETEXT)", err);
+}
+
+func (t *thread) ptraceGetRegs(regs *syscall.PtraceRegs) os.Error {
+ err := syscall.PtraceGetRegs(t.tid, regs);
+ return os.NewSyscallError("ptrace(GETREGS)", err);
+}
+
+func (t *thread) ptraceSetRegs(regs *syscall.PtraceRegs) os.Error {
+ err := syscall.PtraceSetRegs(t.tid, regs);
+ return os.NewSyscallError("ptrace(SETREGS)", err);
+}
+
+func (t *thread) ptraceSetOptions(options int) os.Error {
+ err := syscall.PtraceSetOptions(t.tid, options);
+ return os.NewSyscallError("ptrace(SETOPTIONS)", err);
+}
+
+func (t *thread) ptraceGetEventMsg() (uint, os.Error) {
+ msg, err := syscall.PtraceGetEventMsg(t.tid);
+ return msg, os.NewSyscallError("ptrace(GETEVENTMSG)", err);
+
+}
+
+func (t *thread) ptraceCont() os.Error {
+ err := syscall.PtraceCont(t.tid, 0);
+ return os.NewSyscallError("ptrace(CONT)", err);
+}
+
+func (t *thread) ptraceContWithSignal(sig int) os.Error {
+ err := syscall.PtraceCont(t.tid, sig);
+ return os.NewSyscallError("ptrace(CONT)", err);
+}
+
+func (t *thread) ptraceStep() os.Error {
+ err := syscall.PtraceSingleStep(t.tid);
+ return os.NewSyscallError("ptrace(SINGLESTEP)", err);
+}
+
+func (t *thread) ptraceDetach() os.Error {
+ err := syscall.PtraceDetach(t.tid);
+ return os.NewSyscallError("ptrace(DETACH)", err);
+}
+
+/*
+ * Logging utilties
+ */
+
+var logLock sync.Mutex
+
+func (t *thread) logTrace(format string, args ...) {
+ if !trace {
+ return;
+ }
+ logLock.Lock();
+ defer logLock.Unlock();
+ fmt.Fprintf(os.Stderr, "Thread %d", t.tid);
+ if traceIP {
+ var regs syscall.PtraceRegs;
+ err := t.ptraceGetRegs(®s);
+ if err == nil {
+ fmt.Fprintf(os.Stderr, "@%x", regs.Rip);
+ }
+ }
+ fmt.Fprint(os.Stderr, ": ");
+ fmt.Fprintf(os.Stderr, format, args);
+ fmt.Fprint(os.Stderr, "\n");
+}
+
+func (t *thread) warn(format string, args ...) {
+ logLock.Lock();
+ defer logLock.Unlock();
+ fmt.Fprintf(os.Stderr, "Thread %d: WARNING ", t.tid);
+ fmt.Fprintf(os.Stderr, format, args);
+ fmt.Fprint(os.Stderr, "\n");
+}
+
+func (p *process) logTrace(format string, args ...) {
+ if !trace {
+ return;
+ }
+ logLock.Lock();
+ defer logLock.Unlock();
+ fmt.Fprintf(os.Stderr, "Process %d: ", p.pid);
+ fmt.Fprintf(os.Stderr, format, args);
+ fmt.Fprint(os.Stderr, "\n");
+}
+
+/*
+ * State utilities
+ */
+
+// someStoppedThread returns a stopped thread from the process.
+// Returns nil if no threads are stopped.
+//
+// Must be called from the monitor thread.
+func (p *process) someStoppedThread() *thread {
+ for _, t := range p.threads {
+ if t.state.isStopped() {
+ return t;
+ }
+ }
+ return nil;
+}
+
+// someRunningThread returns a running thread from the process.
+// Returns nil if no threads are running.
+//
+// Must be called from the monitor thread.
+func (p *process) someRunningThread() *thread {
+ for _, t := range p.threads {
+ if t.state.isRunning() {
+ return t;
+ }
+ }
+ return nil;
+}
+
+/*
+ * Breakpoint utilities
+ */
+
+// installBreakpoints adds breakpoints to the attached process.
+//
+// Must be called from the monitor thread.
+func (p *process) installBreakpoints() os.Error {
+ n := 0;
+ main := p.someStoppedThread();
+ for _, b := range p.breakpoints {
+ if b.olddata != nil {
+ continue;
+ }
+
+ b.olddata = make([]byte, len(bpinst386));
+ _, err := main.ptracePeekText(uintptr(b.pc), b.olddata);
+ if err != nil {
+ b.olddata = nil;
+ return err;
+ }
+
+ _, err = main.ptracePokeText(uintptr(b.pc), bpinst386);
+ if err != nil {
+ b.olddata = nil;
+ return err;
+ }
+ n++;
+ }
+ if n > 0 {
+ p.logTrace("installed %d/%d breakpoints", n, len(p.breakpoints));
+ }
+
+ return nil;
+}
+
+// uninstallBreakpoints removes the installed breakpoints from p.
+//
+// Must be called from the monitor thread.
+func (p *process) uninstallBreakpoints() os.Error {
+ n := 0;
+ main := p.someStoppedThread();
+ for _, b := range p.breakpoints {
+ if b.olddata == nil {
+ continue;
+ }
+
+ _, err := main.ptracePokeText(uintptr(b.pc), b.olddata);
+ if err != nil {
+ return err;
+ }
+ b.olddata = nil;
+ n++;
+ }
+ if n > 0 {
+ p.logTrace("uninstalled %d/%d breakpoints", n, len(p.breakpoints));
+ }
+
+ return nil;
+}
+
+/*
+ * Debug event handling
+ */
+
+// wait waits for a wait event from this thread and sends it on the
+// debug events channel for this thread's process. This should be
+// started in its own goroutine when the attached thread enters a
+// running state. The goroutine will exit as soon as it sends a debug
+// event.
+func (t *thread) wait() {
+ for {
+ var err os.Error;
+ var ev debugEvent;
+ ev.t = t;
+ t.logTrace("beginning wait");
+ ev.Waitmsg, ev.err = os.Wait(t.tid, syscall.WALL);
+ if ev.err == nil && ev.Pid != t.tid {
+ panic("Wait returned pid ", ev.Pid, " wanted ", t.tid);
+ }
+ if ev.StopSignal() == syscall.SIGSTOP && t.ignoreNextSigstop {
+ // Spurious SIGSTOP. See Thread.Stop().
+ t.ignoreNextSigstop = false;
+ err := t.ptraceCont();
+ if err == nil {
+ continue;
+ }
+ // If we failed to continue, just let
+ // the stop go through so we can
+ // update the thread's state.
+ }
+ t.proc.debugEvents <- &ev;
+ break;
+ }
+}
+
+// setState sets this thread's state, starts a wait thread if
+// necessary, and invokes state transition handlers.
+//
+// Must be called from the monitor thread.
+func (t *thread) setState(new threadState) {
+ old := t.state;
+ t.state = new;
+ t.logTrace("state %v -> %v", old, new);
+
+ if !old.isRunning() && new.isRunning() {
+ // Start waiting on this thread
+ go t.wait();
+ }
+
+ // Invoke state change handlers
+ handlers := t.proc.transitionHandlers;
+ if handlers.Len() == 0 {
+ return;
+ }
+
+ t.proc.transitionHandlers = vector.New(0);
+ for _, h := range handlers.Data() {
+ h := h.(*transitionHandler);
+ h.handle(t, old, new);
+ }
+}
+
+// sendSigstop sends a SIGSTOP to this thread.
+func (t *thread) sendSigstop() os.Error {
+ t.logTrace("sending SIGSTOP");
+ err := syscall.Tgkill(t.proc.pid, t.tid, syscall.SIGSTOP);
+ return os.NewSyscallError("tgkill", err);
+}
+
+// stopAsync sends SIGSTOP to all threads in state 'running'.
+//
+// Must be called from the monitor thread.
+func (p *process) stopAsync() os.Error {
+ for _, t := range p.threads {
+ if t.state == running {
+ err := t.sendSigstop();
+ if err != nil {
+ return err;
+ }
+ t.setState(stopping);
+ }
+ }
+ return nil;
+}
+
+// doTrap handles SIGTRAP debug events with a cause of 0. These can
+// be caused either by an installed breakpoint, a breakpoint in the
+// program text, or by single stepping.
+func (ev *debugEvent) doTrap() (threadState, os.Error) {
+ t := ev.t;
+
+ if t.state == singleStepping {
+ return stopped, nil;
+ }
+
+ // Hit a breakpoint. Linux leaves the program counter after
+ // the breakpoint. If this is an installed breakpoint, we
+ // need to back the PC up to the breakpoint PC.
+ var regs syscall.PtraceRegs;
+ err := t.ptraceGetRegs(®s);
+ if err != nil {
+ return stopped, err;
+ }
+
+ b, ok := t.proc.breakpoints[uintptr(regs.Rip)-uintptr(len(bpinst386))];
+ if !ok {
+ // We must have hit a breakpoint that was actually in
+ // the program. Leave the IP where it is so we don't
+ // re-execute the breakpoint instruction. Expose the
+ // fact that we stopped with a SIGTRAP.
+ return stoppedSignal, nil;
+ }
+
+ t.breakpoint = b;
+ t.logTrace("at breakpoint %v, backing up PC from %#x", b, regs.Rip);
+
+ regs.Rip = uint64(b.pc);
+ err = t.ptraceSetRegs(®s);
+ if err != nil {
+ return stopped, err;
+ }
+ return stoppedBreakpoint, nil;
+}
+
+// doPtraceClone handles SIGTRAP debug events with a PTRACE_EVENT_CLONE
+// cause. It initializes the new thread, adds it to the process, and
+// returns the appropriate thread state for the existing thread.
+func (ev *debugEvent) doPtraceClone() (threadState, os.Error) {
+ t := ev.t;
+
+ // Get the TID of the new thread
+ tid, err := t.ptraceGetEventMsg();
+ if err != nil {
+ return stopped, err;
+ }
+
+ nt, err := t.proc.newThread(int(tid));
+ if err != nil {
+ return stopped, err;
+ }
+
+ // Remember the thread
+ t.newThread = nt;
+
+ return stoppedThreadCreate, nil;
+}
+
+// doPtraceExit handles SIGTRAP debug events with a PTRACE_EVENT_EXIT
+// cause. It sets up the thread's state, but does not remove it from
+// the process. A later WIFEXITED debug event will remove it from the
+// process.
+func (ev *debugEvent) doPtraceExit() (threadState, os.Error) {
+ t := ev.t;
+
+ // Get exit status
+ exitStatus, err := t.ptraceGetEventMsg();
+ if err != nil {
+ return stopped, err;
+ }
+ ws := syscall.WaitStatus(exitStatus);
+ t.logTrace("exited with %v", ws);
+ switch {
+ case ws.Exited():
+ t.exitStatus = ws.ExitStatus();
+ case ws.Signaled():
+ t.signal = ws.Signal();
+ }
+
+ // We still need to continue this thread and wait on this
+ // thread's WIFEXITED event. We'll delete it then.
+ return stoppedExiting, nil;
+}
+
+// process handles a debug event. It modifies any thread or process
+// state as necessary, uninstalls breakpoints if necessary, and stops
+// any running threads.
+func (ev *debugEvent) process() os.Error {
+ if ev.err != nil {
+ return ev.err;
+ }
+
+ t := ev.t;
+ t.exitStatus = -1;
+ t.signal = -1;
+
+ // Decode wait status.
+ var state threadState;
+ switch {
+ case ev.Stopped():
+ state = stoppedSignal;
+ t.signal = ev.StopSignal();
+ t.logTrace("stopped with %v", ev);
+ if ev.StopSignal() == syscall.SIGTRAP {
+ // What caused the debug trap?
+ var err os.Error;
+ switch cause := ev.TrapCause(); cause {
+ case 0:
+ // Breakpoint or single stepping
+ state, err = ev.doTrap();
+
+ case syscall.PTRACE_EVENT_CLONE:
+ state, err = ev.doPtraceClone();
+
+ case syscall.PTRACE_EVENT_EXIT:
+ state, err = ev.doPtraceExit();
+
+ default:
+ t.warn("Unknown trap cause %d", cause);
+ }
+
+ if err != nil {
+ t.setState(stopped);
+ t.warn("failed to handle trap %v: %v", ev, err);
+ }
+ }
+
+ case ev.Exited():
+ state = exited;
+ t.proc.threads[t.tid] = nil, false;
+ t.logTrace("exited %v", ev);
+ // We should have gotten the exit status in
+ // PTRACE_EVENT_EXIT, but just in case.
+ t.exitStatus = ev.ExitStatus();
+
+ case ev.Signaled():
+ state = exited;
+ t.proc.threads[t.tid] = nil, false;
+ t.logTrace("signaled %v", ev);
+ // Again, this should be redundant.
+ t.signal = ev.Signal();
+
+ default:
+ panic(fmt.Sprintf("Unexpected wait status %v", ev.Waitmsg));
+ }
+
+ // If we sent a SIGSTOP to the thread (indicated by state
+ // Stopping), we might have raced with a different type of
+ // stop. If we didn't get the stop we expected, then the
+ // SIGSTOP we sent is now queued up, so we should ignore the
+ // next one we get.
+ if t.state == stopping && ev.StopSignal() != syscall.SIGSTOP {
+ t.ignoreNextSigstop = true;
+ }
+
+ t.setState(state);
+
+ if t.proc.someRunningThread() == nil {
+ // Nothing is running, uninstall breakpoints
+ return t.proc.uninstallBreakpoints();
+ }
+ // Stop any other running threads
+ return t.proc.stopAsync();
+}
+
+// onStop adds a handler for state transitions from running to
+// non-running states. The handler will be called from the monitor
+// thread.
+//
+// Must be called from the monitor thread.
+func (t *thread) onStop(handle func (), onErr func (os.Error)) {
+ // TODO(austin) This is rather inefficient for things like
+ // stepping all threads during a continue. Maybe move
+ // transitionHandlers to the thread, or have both per-thread
+ // and per-process transition handlers.
+ h := &transitionHandler{nil, onErr};
+ h.handle = func (st *thread, old, new threadState) {
+ if t == st && old.isRunning() && !new.isRunning() {
+ handle();
+ } else {
+ t.proc.transitionHandlers.Push(h);
+ }
+ };
+ t.proc.transitionHandlers.Push(h);
+}
+
+/*
+ * Event monitor
+ */
+
+// monitor handles debug events and debug requests for p, exiting when
+// there are no threads left in p.
+//
+// TODO(austin) When an unrecoverable error occurs, abort the monitor
+// and record this error so all future calls to do will return it
+// immediately.
+func (p *process) monitor() {
+ var err os.Error;
+
+ // Linux requires that all ptrace calls come from the thread
+ // that originally attached. Prevent the Go scheduler from
+ // migrating us to other OS threads.
+ runtime.LockOSThread();
+ defer runtime.UnlockOSThread();
+
+ hadThreads := false;
+ for {
+ select {
+ case event := <-p.debugEvents:
+ err = event.process();
+ if err != nil {
+ break;
+ }
+
+ case req := <-p.debugReqs:
+ req.res <- req.f();
+
+ case err = <-p.stopReq:
+ break;
+ }
+
+ if len(p.threads) == 0 {
+ if hadThreads {
+ p.logTrace("no more threads; monitor exiting");
+ // TODO(austin) Use a real error do
+ // future operations will fail
+ err = nil;
+ break;
+ }
+ } else {
+ hadThreads = true;
+ }
+ }
+
+ // Abort waiting handlers
+ for _, h := range p.transitionHandlers.Data() {
+ h := h.(*transitionHandler);
+ h.onErr(err);
+ }
+
+ // TODO(austin) How do I stop the wait threads?
+ if err != nil {
+ panic(err.String());
+ }
+}
+
+// do executes f in the monitor thread (and, thus, atomically with
+// respect to thread state changes). f must not block.
+//
+// Must NOT be called from the monitor thread.
+func (p *process) do(f func () os.Error) os.Error {
+ // TODO(austin) If monitor is stopped, return error.
+ req := &debugReq{f, make(chan os.Error)};
+ p.debugReqs <- req;
+ return <-req.res;
+}
+
+// stopMonitor stops the monitor with the given error. If the monitor
+// is already stopped, does nothing.
+func (p *process) stopMonitor(err os.Error) {
+ doNotBlock := p.stopReq <- err;
+ // TODO(austin) Wait until monitor has exited?
+}
+
+/*
+ * Public thread interface
+ */
+
+func (t *thread) Regs() (Regs, os.Error) {
+ var regs syscall.PtraceRegs;
+
+ err := t.proc.do(func () os.Error {
+ if !t.state.isStopped() {
+ return &badState{t, "cannot get registers", t.state};
+ }
+ return t.ptraceGetRegs(®s);
+ });
+ if err != nil {
+ return nil, err;
+ }
+
+ setter := func (r *syscall.PtraceRegs) os.Error {
+ return t.proc.do(func () os.Error {
+ if !t.state.isStopped() {
+ return &badState{t, "cannot get registers", t.state};
+ }
+ return t.ptraceSetRegs(r);
+ });
+ };
+ return newRegs(®s, setter), nil;
+}
+
+func (t *thread) Peek(addr Word, out []byte) (int, os.Error) {
+ var c int;
+
+ err := t.proc.do(func () os.Error {
+ if !t.state.isStopped() {
+ return &badState{t, "cannot peek text", t.state};
+ }
+
+ var err os.Error;
+ c, err = t.ptracePeekText(uintptr(addr), out);
+ return err;
+ });
+
+ return c, err;
+}
+
+func (t *thread) Poke(addr Word, out []byte) (int, os.Error) {
+ var c int;
+
+ err := t.proc.do(func () os.Error {
+ if !t.state.isStopped() {
+ return &badState{t, "cannot poke text", t.state};
+ }
+
+ var err os.Error;
+ c, err = t.ptracePokeText(uintptr(addr), out);
+ return err;
+ });
+
+ return c, err;
+}
+
+// stepAsync starts this thread single stepping. When the single step
+// is complete, it will send nil on the given channel. If an error
+// occurs while setting up the single step, it returns that error. If
+// an error occurs while waiting for the single step to complete, it
+// sends that error on the channel.
+func (t *thread) stepAsync(ready chan os.Error) os.Error {
+ if err := t.ptraceStep(); err != nil {
+ return err;
+ }
+ t.setState(singleStepping);
+ t.onStop(func () {
+ ready <- nil;
+ },
+ func (err os.Error) {
+ ready <- err;
+ });
+ return nil;
+}
+
+func (t *thread) Step() os.Error {
+ t.logTrace("Step {");
+ defer t.logTrace("}");
+
+ ready := make(chan os.Error);
+
+ err := t.proc.do(func () os.Error {
+ if !t.state.isStopped() {
+ return &badState{t, "cannot single step", t.state};
+ }
+ return t.stepAsync(ready);
+ });
+ if err != nil {
+ return err;
+ }
+
+ err = <-ready;
+ return err;
+}
+
+// TODO(austin) We should probably get this via C's strsignal.
+var sigNames = [...]string {
+ "SIGEXIT", "SIGHUP", "SIGINT", "SIGQUIT", "SIGILL",
+ "SIGTRAP", "SIGABRT", "SIGBUS", "SIGFPE", "SIGKILL",
+ "SIGUSR1", "SIGSEGV", "SIGUSR2", "SIGPIPE", "SIGALRM",
+ "SIGTERM", "SIGSTKFLT", "SIGCHLD", "SIGCONT", "SIGSTOP",
+ "SIGTSTP", "SIGTTIN", "SIGTTOU", "SIGURG", "SIGXCPU",
+ "SIGXFSZ", "SIGVTALRM", "SIGPROF", "SIGWINCH", "SIGPOLL",
+ "SIGPWR", "SIGSYS"
+}
+
+// sigName returns the symbolic name for the given signal number. If
+// the signal number is invalid, returns "<invalid>".
+func sigName(signal int) string {
+ if signal < 0 || signal >= len(sigNames) {
+ return "<invalid>";
+ }
+ return sigNames[signal];
+}
+
+func (t *thread) Stopped() (Cause, os.Error) {
+ var c Cause;
+ err := t.proc.do(func() os.Error {
+ switch t.state {
+ case stopped:
+ c = Stopped{};
+
+ case stoppedBreakpoint:
+ c = Breakpoint(t.breakpoint.pc);
+
+ case stoppedSignal:
+ c = Signal(sigName(t.signal));
+
+ case stoppedThreadCreate:
+ c = ThreadCreate{t.newThread};
+
+ case stoppedExiting, exiting, exited:
+ if t.signal == -1 {
+ c = ThreadExit{t.exitStatus, ""};
+ } else {
+ c = ThreadExit{t.exitStatus, sigName(t.signal)};
+ }
+
+ default:
+ return &badState{t, "cannot get stop cause", t.state};
+ }
+ return nil;
+ });
+ if err != nil {
+ return nil, err;
+ }
+
+ return c, nil;
+}
+
+func (p *process) Threads() []Thread {
+ var res []Thread;
+
+ p.do(func () os.Error {
+ res = make([]Thread, len(p.threads));
+ i := 0;
+ for _, t := range p.threads {
+ // Exclude zombie threads.
+ st := t.state;
+ if st == exiting || st == exited || st == detached {
+ continue;
+ }
+
+ res[i] = t;
+ i++;
+ }
+ res = res[0:i];
+ return nil;
+ });
+ return res;
+}
+
+func (p *process) AddBreakpoint(pc Word) os.Error {
+ return p.do(func () os.Error {
+ if t := p.someRunningThread(); t != nil {
+ return &badState{t, "cannot add breakpoint", t.state};
+ }
+ if _, ok := p.breakpoints[uintptr(pc)]; ok {
+ return breakpointExistsError(pc);
+ }
+ p.breakpoints[uintptr(pc)] = &breakpoint{pc: uintptr(pc)};
+ return nil;
+ });
+}
+
+func (p *process) RemoveBreakpoint(pc Word) os.Error {
+ return p.do(func () os.Error {
+ if t := p.someRunningThread(); t != nil {
+ return &badState{t, "cannot remove breakpoint", t.state};
+ }
+ if _, ok := p.breakpoints[uintptr(pc)]; !ok {
+ return noBreakpointError(pc);
+ }
+ p.breakpoints[uintptr(pc)] = nil, false;
+ return nil;
+ });
+}
+
+func (p *process) Continue() os.Error {
+ // Single step any threads that are stopped at breakpoints so
+ // we can reinstall breakpoints.
+ var ready chan os.Error;
+ count := 0;
+
+ err := p.do(func () os.Error {
+ // We make the ready channel big enough to hold all
+ // ready message so we don't jam up the monitor if we
+ // stop listening (e.g., if there's an error).
+ ready = make(chan os.Error, len(p.threads));
+
+ for _, t := range p.threads {
+ if !t.state.isStopped() {
+ continue;
+ }
+
+ // We use the breakpoint map directly here
+ // instead of checking the stop cause because
+ // it could have been stopped at a breakpoint
+ // for some other reason, or the breakpoint
+ // could have been added since it was stopped.
+ var regs syscall.PtraceRegs;
+ err := t.ptraceGetRegs(®s);
+ if err != nil {
+ return err;
+ }
+ if b, ok := p.breakpoints[uintptr(regs.Rip)]; ok {
+ t.logTrace("stepping over breakpoint %v", b);
+ if err := t.stepAsync(ready); err != nil {
+ return err;
+ }
+ count++;
+ }
+ }
+ return nil;
+ });
+ if err != nil {
+ p.stopMonitor(err);
+ return err;
+ }
+
+ // Wait for single stepping threads
+ for count > 0 {
+ err = <-ready;
+ if err != nil {
+ p.stopMonitor(err);
+ return err;
+ }
+ count--;
+ }
+
+ // Continue all threads
+ err = p.do(func () os.Error {
+ if err := p.installBreakpoints(); err != nil {
+ return err;
+ }
+
+ for _, t := range p.threads {
+ var err os.Error;
+ switch {
+ case !t.state.isStopped():
+ continue;
+
+ case t.state == stoppedSignal && t.signal != syscall.SIGSTOP && t.signal != syscall.SIGTRAP:
+ t.logTrace("continuing with signal %d", t.signal);
+ err = t.ptraceContWithSignal(t.signal);
+
+ default:
+ t.logTrace("continuing");
+ err = t.ptraceCont();
+ }
+ if err != nil {
+ return err;
+ }
+ t.setState(running);
+ }
+ return nil;
+ });
+ if err != nil {
+ // TODO(austin) Do we need to stop the monitor with
+ // this error atomically with the do-routine above?
+ p.stopMonitor(err);
+ return err;
+ }
+
+ return nil;
+}
+
+func (p *process) WaitStop() os.Error {
+ // We need a non-blocking ready channel for the case where all
+ // threads are already stopped.
+ ready := make(chan os.Error, 1);
+
+ err := p.do(func () os.Error {
+ // Are all of the threads already stopped?
+ if p.someRunningThread() == nil {
+ ready <- nil;
+ return nil;
+ }
+
+ // Monitor state transitions
+ h := &transitionHandler{};
+ h.handle = func (st *thread, old, new threadState) {
+ if !new.isRunning() {
+ if p.someRunningThread() == nil {
+ ready <- nil;
+ return;
+ }
+ }
+ p.transitionHandlers.Push(h);
+ };
+ h.onErr = func (err os.Error) {
+ ready <- err;
+ };
+ p.transitionHandlers.Push(h);
+ return nil;
+ });
+ if err != nil {
+ return err;
+ }
+
+ return <-ready;
+}
+
+func (p *process) Stop() os.Error {
+ err := p.do(func () os.Error {
+ return p.stopAsync();
+ });
+ if err != nil {
+ return err;
+ }
+
+ return p.WaitStop();
+}
+
+func (p *process) Detach() os.Error {
+ if err := p.Stop(); err != nil {
+ return err;
+ }
+
+ err := p.do(func () os.Error {
+ if err := p.uninstallBreakpoints(); err != nil {
+ return err;
+ }
+
+ for pid, t := range p.threads {
+ if err := t.ptraceDetach(); err != nil {
+ return err;
+ }
+ t.setState(detached);
+ p.threads[pid] = nil, false;
+ }
+ return nil;
+ });
+ // TODO(austin) Wait for monitor thread to exit?
+ return err;
+}
+
+// newThread creates a new thread object and waits for its initial
+// SIGSTOP.
+//
+// Must be run from the monitor thread.
+func (p *process) newThread(tid int) (*thread, os.Error) {
+ t := &thread{tid: tid, proc: p, state: stopped};
+
+ // Get the SIGSTOP from the thread
+ // TODO(austin) Thread might already be stopped
+ w, err := os.Wait(tid, syscall.WALL);
+ if err != nil {
+ return nil, err;
+ }
+ if w.Pid != tid || w.StopSignal() != syscall.SIGSTOP {
+ return nil, os.EINVAL;
+ }
+
+ p.threads[tid] = t;
+
+ return t, nil;
+}
+
+// attachThread attaches a running thread to the process.
+//
+// Must NOT be run from the monitor thread.
+func (p *process) attachThread(tid int) (*thread, os.Error) {
+ p.logTrace("attaching to thread %d", tid);
+ var thr *thread;
+ err := p.do(func () os.Error {
+ errno := syscall.PtraceAttach(tid);
+ if errno != 0 {
+ return os.NewSyscallError("ptrace(ATTACH)", errno);
+ }
+
+ var err os.Error;
+ thr, err = p.newThread(tid);
+ return err;
+ });
+ return thr, err;
+}
+
+// attachAllThreads attaches to all threads in a process.
+func (p *process) attachAllThreads() os.Error {
+ taskPath := "/proc/" + strconv.Itoa(p.pid) + "/task";
+ taskDir, err := os.Open(taskPath, os.O_RDONLY, 0);
+ if err != nil {
+ return err;
+ }
+ defer taskDir.Close();
+
+ // We stop threads as we attach to them; however, because new
+ // threads can appear while we're looping over all of them, we
+ // have to repeatly scan until we know we're attached to all
+ // of them.
+ for again := true; again; {
+ again = false;
+
+ tids, err := taskDir.Readdirnames(-1);
+ if err != nil {
+ return err;
+ }
+
+ for _, tidStr := range tids {
+ tid, err := strconv.Atoi(tidStr);
+ if err != nil {
+ return err;
+ }
+ if _, ok := p.threads[tid]; ok {
+ continue;
+ }
+
+ t, err := p.attachThread(tid);
+ if err != nil {
+ // There could have been a race, or
+ // this process could be a zobmie.
+ statFile, err2 := io.ReadFile(taskPath + "/" + tidStr + "/stat");
+ if err2 != nil {
+ switch err2 := err2.(type) {
+ case *os.PathError:
+ if err2.Error == os.ENOENT {
+ // Raced with thread exit
+ p.logTrace("raced with thread %d exit", tid);
+ continue;
+ }
+ }
+ // Return the original error
+ return err;
+ }
+
+ statParts := strings.Split(string(statFile), " ", 4);
+ if len(statParts) > 2 && statParts[2] == "Z" {
+ // tid is a zombie
+ p.logTrace("thread %d is a zombie", tid);
+ continue;
+ }
+
+ // Return the original error
+ return err;
+ }
+ again = true;
+ }
+ }
+
+ return nil;
+}
+
+// Attach attaches to process pid and stops all of its threads.
+func Attach(pid int) (Process, os.Error) {
+ p := &process{
+ pid: pid,
+ threads: make(map[int] *thread),
+ breakpoints: make(map[uintptr] *breakpoint),
+ debugEvents: make(chan *debugEvent),
+ debugReqs: make(chan *debugReq),
+ stopReq: make(chan os.Error),
+ transitionHandlers: vector.New(0)
+ };
+
+ // All ptrace calls must be done from the same thread. Start
+ // the monitor thread now so we can attach from within it.
+ go p.monitor();
+
+ // Attach to all threads
+ err := p.attachAllThreads();
+ if err != nil {
+ p.Detach();
+ // TODO(austin) Detach stopped the monitor already
+ //p.stopMonitor(err);
+ return nil, err;
+ }
+
+ // Set ptrace options for all threads
+ err = p.do(func () os.Error {
+ for _, t := range p.threads {
+ err := t.ptraceSetOptions(syscall.PTRACE_O_TRACECLONE | syscall.PTRACE_O_TRACEEXIT);
+ if err != nil {
+ return err;
+ }
+ }
+ return nil;
+ });
+ if err != nil {
+ p.Detach();
+ // TODO(austin)
+ //p.stopMonitor(err);
+ return nil, err;
+ }
+
+ return p, nil;
+}