delve/pkg/proc/gdbserver.go

// This file and its companion gdbserver_conn implement a target.Interface
// backed by a connection to a debugger speaking the "Gdb Remote Serial
// Protocol".
//
// The "Gdb Remote Serial Protocol" is a low level debugging protocol
// originally designed so that gdb could be used to debug programs running
// in embedded environments but it was later extended to support programs
// running on any environment and a variety of debuggers support it:
// gdbserver, lldb-server, macOS's debugserver and rr.
//
// The protocol is specified at:
//   https://sourceware.org/gdb/onlinedocs/gdb/Remote-Protocol.html
// with additional documentation for lldb specific extensions described at:
//   https://github.com/llvm-mirror/lldb/blob/master/docs/lldb-gdb-remote.txt
//
// Terminology:
//  * inferior: the program we are trying to debug
//  * stub: the debugger on the other side of the protocol's connection (for
//    example lldb-server)
//  * gdbserver: stub version of gdb
//  * lldb-server: stub version of lldb
//  * debugserver: a different stub version of lldb, installed with lldb on
//    macOS.
//  * mozilla rr: a stub that records the full execution of a program
//    and can then play it back.
//
// Implementations of the protocol vary wildly between stubs, while there is
// a command to query the stub about supported features (qSupported) this
// only covers *some* of the more recent additions to the protocol and most
// of the older packets are optional and *not* implemented by all stubs.
// For example gdbserver implements 'g' (read all registers) but not 'p'
// (read single register) while lldb-server implements 'p' but not 'g'.
//
// The protocol is also underspecified with regards to how the stub should
// handle a multithreaded inferior. Its default mode of operation is
// "all-stop mode", when a thread hits a breakpoint all other threads are
// also stopped. But the protocol doesn't say what happens if a second
// thread hits a breakpoint while the stub is in the process of stopping all
// other threads.
//
// In practice the stub is allowed to swallow the second breakpoint hit or
// to return it at a later time. If the stub chooses the latter behavior
// (like gdbserver does) it is allowed to return delayed events on *any*
// vCont packet. This is incredibly inconvenient since if we get notified
// about a delayed breakpoint while we are trying to singlestep another
// thread it's impossible to know when the singlestep we requested ended.
//
// What this means is that gdbserver can only be supported for multithreaded
// inferiors by selecting non-stop mode, which behaves in a markedly
// different way from all-stop mode and isn't supported by anything except
// gdbserver.
//
// lldb-server/debugserver takes a different approach, only the first stop
// event is reported, if any other event happens "simultaneously" they are
// suppressed by the stub and the debugger can query for them using
// qThreadStopInfo. This is much easier for us to implement and the
// implementation gracefully degrates to the case where qThreadStopInfo is
// unavailable but the inferior is run in single threaded mode.
//
// Therefore the following code will assume lldb-server-like behavior.

package proc

import (
	"debug/gosym"
	"encoding/binary"
	"errors"
	"fmt"
	"go/ast"
	"net"
	"os"
	"os/exec"
	"runtime"
	"strconv"
	"strings"
	"sync"
	"time"

	"golang.org/x/arch/x86/x86asm"
)

const (
	logGdbWire               = false
	logGdbWireFullStopPacket = false
	showLldbServerOutput     = false
	logGdbWireMaxLen         = 120

	maxTransmitAttempts    = 3    // number of retransmission attempts on failed checksum
	initialInputBufferSize = 2048 // size of the input buffer for gdbConn
)

const heartbeatInterval = 10 * time.Second

// GdbserverProcess implements target.Interface using a connection to a
// debugger stub that understands Gdb Remote Serial Protocol.
type GdbserverProcess struct {
	bi   BinaryInfo
	conn gdbConn

	threads           map[int]*GdbserverThread
	currentThread     *GdbserverThread
	selectedGoroutine *G

	exited bool
	ctrlC  bool // ctrl-c was sent to stop inferior

	breakpoints                 map[uint64]*Breakpoint
	breakpointIDCounter         int
	internalBreakpointIDCounter int

	gcmdok         bool // true if the stub supports g and G commands
	threadStopInfo bool // true if the stub supports qThreadStopInfo

	loadGInstrAddr uint64 // address of the g loading instruction, zero if we couldn't allocate it

	process *exec.Cmd

	allGCache []*G
}

// GdbserverThread is a thread of GdbserverProcess.
type GdbserverThread struct {
	ID                       int
	strID                    string
	regs                     gdbRegisters
	CurrentBreakpoint        *Breakpoint
	BreakpointConditionMet   bool
	BreakpointConditionError error
	p                        *GdbserverProcess
	setbp                    bool // thread was stopped because of a breakpoint
}

// gdbRegisters represents the current value of the registers of a thread.
// The storage space for all the registers is allocated as a single memory
// block in buf, the value field inside an individual gdbRegister will be a
// slice of the global buf field.
type gdbRegisters struct {
	regs     map[string]gdbRegister
	regsInfo []gdbRegisterInfo
	tls      uint64
	gaddr    uint64
	hasgaddr bool
	buf      []byte
}

type gdbRegister struct {
	value  []byte
	regnum int
}

// GdbserverConnect creates a GdbserverProcess connected to address addr.
// Path and pid are, respectively, the path to the executable of the target
// program and the PID of the target process, both are optional, however
// some stubs do not provide ways to determine path and pid automatically
// and GdbserverConnect will be unable to function without knowing them.
func GdbserverConnect(addr string, path string, pid int, attempts int) (*GdbserverProcess, error) {
	var conn net.Conn
	var err error
	for i := 0; i < attempts; i++ {
		conn, err = net.Dial("tcp", addr)
		if err == nil {
			break
		}
		time.Sleep(time.Second)
	}
	if err != nil {
		return nil, err
	}

	p := &GdbserverProcess{
		conn: gdbConn{
			conn:                conn,
			maxTransmitAttempts: maxTransmitAttempts,
			inbuf:               make([]byte, 0, initialInputBufferSize),
		},

		threads:        make(map[int]*GdbserverThread),
		bi:             NewBinaryInfo(runtime.GOOS, runtime.GOARCH),
		breakpoints:    make(map[uint64]*Breakpoint),
		gcmdok:         true,
		threadStopInfo: true,
	}

	p.conn.pid = pid
	err = p.conn.handshake()
	if err != nil {
		conn.Close()
		return nil, err
	}

	if path == "" {
		// If we are attaching to a running process and the user didn't specify
		// the executable file manually we must ask the stub for it.
		// We support both qXfer:exec-file:read:: (the gdb way) and calling
		// qProcessInfo (the lldb way).
		// Unfortunately debugserver on macOS supports neither.
		path, err = p.conn.readExecFile()
		if err != nil {
			if isProtocolErrorUnsupported(err) {
				_, path, err = p.loadProcessInfo(pid)
				if err != nil {
					conn.Close()
					return nil, err
				}
			} else {
				conn.Close()
				return nil, fmt.Errorf("could not determine executable path: %v", err)
			}
		}
	}

	// None of the stubs we support returns the value of fs_base or gs_base
	// along with the registers, therefore we have to resort to executing a MOV
	// instruction on the inferior to find out where the G struct of a given
	// thread is located.
	// Here we try to allocate some memory on the inferior which we will use to
	// store the MOV instruction.
	// If the stub doesn't support memory allocation reloadRegisters will
	// overwrite some existing memory to store the MOV.
	if addr, err := p.conn.allocMemory(256); err == nil {
		if _, err := p.conn.writeMemory(uintptr(addr), p.loadGInstr()); err == nil {
			p.loadGInstrAddr = addr
		}
	}

	var wg sync.WaitGroup
	err = p.bi.LoadBinaryInfo(path, &wg)
	if err != nil {
		conn.Close()
		return nil, err
	}
	wg.Wait()

	err = p.updateThreadList(&threadUpdater{p: p})
	if err != nil {
		conn.Close()
		p.bi.Close()
		return nil, err
	}

	if p.conn.pid <= 0 {
		p.conn.pid, _, err = p.loadProcessInfo(0)
		if err != nil {
			conn.Close()
			p.bi.Close()
			return nil, err
		}
	}

	scope := &EvalScope{0, 0, p.CurrentThread(), nil, &p.bi}
	ver, isextld, err := scope.getGoInformation()
	if err != nil {
		conn.Close()
		p.bi.Close()
		return nil, err
	}

	p.bi.arch.SetGStructOffset(ver, isextld)
	p.selectedGoroutine, _ = GetG(p.CurrentThread())

	panicpc, err := p.FindFunctionLocation("runtime.startpanic", true, 0)
	if err == nil {
		bp, err := p.SetBreakpoint(panicpc, UserBreakpoint, nil)
		if err == nil {
			bp.Name = "unrecovered-panic"
			bp.ID = -1
			p.breakpointIDCounter--
		}
	}

	return p, nil
}

// unusedPort returns an unused tcp port
// This is a hack and subject to a race condition with other running
// programs, but most (all?) OS will cycle through all ephemeral ports
// before reassigning one port they just assigned, unless there's heavy
// churn in the ephemeral range this should work.
func unusedPort() string {
	addr, err := net.ResolveTCPAddr("tcp", "localhost:0")
	if err != nil {
		return ":8081"
	}
	listener, err := net.ListenTCP("tcp", addr)
	if err != nil {
		return ":8081"
	}
	port := listener.Addr().(*net.TCPAddr).Port
	listener.Close()
	return fmt.Sprintf(":%d", port)
}

const debugserverExecutable = "/Library/Developer/CommandLineTools/Library/PrivateFrameworks/LLDB.framework/Versions/A/Resources/debugserver"

// LLDBLaunch starts an instance of lldb-server and connects to it, asking
// it to launch the specified target program with the specified arguments
// (cmd) on the specified directory wd.
func LLDBLaunch(cmd []string, wd string) (*GdbserverProcess, error) {
	// check that the argument to Launch is an executable file
	if fi, staterr := os.Stat(cmd[0]); staterr == nil && (fi.Mode()&0111) == 0 {
		return nil, NotExecutableErr
	}

	port := unusedPort()
	isDebugserver := false

	var proc *exec.Cmd
	if _, err := os.Stat(debugserverExecutable); err == nil {
		args := make([]string, 0, len(cmd)+1)
		args = append(args, "127.0.0.1"+port)
		args = append(args, cmd...)

		isDebugserver = true

		proc = exec.Command(debugserverExecutable, args...)
	} else {
		args := make([]string, 0, len(cmd)+3)
		args = append(args, "gdbserver")
		args = append(args, port, "--")
		args = append(args, cmd...)

		proc = exec.Command("lldb-server", args...)
	}

	if showLldbServerOutput || logGdbWire {
		proc.Stdout = os.Stdout
		proc.Stderr = os.Stderr
	}
	if wd != "" {
		proc.Dir = wd
	}

	proc.SysProcAttr = backgroundSysProcAttr()

	err := proc.Start()
	if err != nil {
		return nil, err
	}

	p, err := GdbserverConnect(port, cmd[0], 0, 10)
	if err != nil {
		return nil, err
	}

	p.conn.isDebugserver = isDebugserver
	p.process = proc

	return p, nil
}

// LLDBAttach starts an instance of lldb-server and connects to it, asking
// it to attach to the specified pid.
// Path is path to the target's executable, path only needs to be specified
// for some stubs that do not provide an automated way of determining it
// (for example debugserver).
func LLDBAttach(pid int, path string) (*GdbserverProcess, error) {
	port := unusedPort()
	isDebugserver := false
	var proc *exec.Cmd
	if _, err := os.Stat(debugserverExecutable); err == nil {
		isDebugserver = true
		proc = exec.Command(debugserverExecutable, "127.0.0.1"+port, "--attach="+strconv.Itoa(pid))
	} else {
		proc = exec.Command("lldb-server", "gdbserver", "--attach", strconv.Itoa(pid), port)
	}

	proc.Stdout = os.Stdout
	proc.Stderr = os.Stderr

	proc.SysProcAttr = backgroundSysProcAttr()

	err := proc.Start()
	if err != nil {
		return nil, err
	}

	p, err := GdbserverConnect(port, path, pid, 10)
	if err != nil {
		return nil, err
	}

	p.conn.isDebugserver = isDebugserver
	p.process = proc

	return p, nil
}

// loadProcessInfo uses qProcessInfo to load the inferior's PID and
// executable path. This command is not supported by all stubs and not all
// stubs will report both the PID and executable path.
func (p *GdbserverProcess) loadProcessInfo(pid int) (int, string, error) {
	pi, err := p.conn.queryProcessInfo(pid)
	if err != nil {
		return 0, "", err
	}
	if pid == 0 {
		n, _ := strconv.ParseUint(pi["pid"], 16, 64)
		pid = int(n)
	}
	return pid, pi["name"], nil
}

func (p *GdbserverProcess) BinInfo() *BinaryInfo {
	return &p.bi
}

func (p *GdbserverProcess) Pid() int {
	return int(p.conn.pid)
}

func (p *GdbserverProcess) Exited() bool {
	return p.exited
}

func (p *GdbserverProcess) Running() bool {
	return p.conn.running
}

func (p *GdbserverProcess) FindFileLocation(fileName string, lineNumber int) (uint64, error) {
	return FindFileLocation(p.CurrentThread(), p.breakpoints, &p.bi, fileName, lineNumber)
}

func (p *GdbserverProcess) FirstPCAfterPrologue(fn *gosym.Func, sameline bool) (uint64, error) {
	return FirstPCAfterPrologue(p.CurrentThread(), p.breakpoints, &p.bi, fn, sameline)
}

func (p *GdbserverProcess) FindFunctionLocation(funcName string, firstLine bool, lineOffset int) (uint64, error) {
	return FindFunctionLocation(p.CurrentThread(), p.breakpoints, &p.bi, funcName, firstLine, lineOffset)
}

func (p *GdbserverProcess) FindThread(threadID int) (IThread, bool) {
	thread, ok := p.threads[threadID]
	return thread, ok
}

func (p *GdbserverProcess) ThreadList() []IThread {
	r := make([]IThread, 0, len(p.threads))
	for _, thread := range p.threads {
		r = append(r, thread)
	}
	return r
}

func (p *GdbserverProcess) CurrentThread() IThread {
	return p.currentThread
}

func (p *GdbserverProcess) AllGCache() *[]*G {
	return &p.allGCache
}

func (p *GdbserverProcess) SelectedGoroutine() *G {
	return p.selectedGoroutine
}

const (
	interruptSignal  = 0x2
	breakpointSignal = 0x5
	childSignal      = 0x11
	stopSignal       = 0x13
)

func (p *GdbserverProcess) ContinueOnce() (IThread, error) {
	if p.exited {
		return nil, &ProcessExitedError{Pid: p.conn.pid}
	}

	// step threads stopped at any breakpoint over their breakpoint
	for _, thread := range p.threads {
		if thread.CurrentBreakpoint != nil {
			if err := thread.stepInstruction(&threadUpdater{p: p}); err != nil {
				return nil, err
			}
		}
	}

	p.allGCache = nil
	for _, th := range p.threads {
		th.clearBreakpointState()
	}

	p.ctrlC = false

	// resume all threads
	var threadID string
	var sig uint8 = 0
	var tu = threadUpdater{p: p}
	var err error
continueLoop:
	for {
		tu.done = false
		threadID, sig, err = p.conn.resume(sig, &tu)
		if err != nil {
			if _, exited := err.(ProcessExitedError); exited {
				p.exited = true
			}
			return nil, err
		}

		// 0x5 is always a breakpoint, a manual stop either manifests as 0x13
		// (lldb), 0x11 (debugserver) or 0x2 (gdbserver).
		// Since 0x2 could also be produced by the user
		// pressing ^C (in which case it should be passed to the inferior) we need
		// the ctrlC flag to know that we are the originators.
		switch sig {
		case interruptSignal: // interrupt
			if p.ctrlC {
				break continueLoop
			}
		case breakpointSignal: // breakpoint
			break continueLoop
		case childSignal: // stop on debugserver but SIGCHLD on lldb-server/linux
			if p.conn.isDebugserver {
				break continueLoop
			}
		case stopSignal: // stop
			break continueLoop

		// The following are fake BSD-style signals sent by debugserver
		// Unfortunately debugserver can not convert them into signals for the
		// process so we must stop here.
		case 0x91, 0x92, 0x93, 0x94, 0x95, 0x96: /* TARGET_EXC_BAD_ACCESS */
			break continueLoop
		default:
			// any other signal is always propagated to inferior
		}
	}

	if err := p.updateThreadList(&tu); err != nil {
		return nil, err
	}

	if err := p.setCurrentBreakpoints(); err != nil {
		return nil, err
	}

	for _, thread := range p.threads {
		if thread.strID == threadID {
			return thread, nil
		}
	}

	return nil, fmt.Errorf("could not find thread %s", threadID)
}

func (p *GdbserverProcess) StepInstruction() error {
	if p.selectedGoroutine == nil {
		return errors.New("cannot single step: no selected goroutine")
	}
	if p.selectedGoroutine.thread == nil {
		if _, err := p.SetBreakpoint(p.selectedGoroutine.PC, NextBreakpoint, sameGoroutineCondition(p.selectedGoroutine)); err != nil {
			return err
		}
		return Continue(p)
	}
	p.allGCache = nil
	if p.exited {
		return &ProcessExitedError{Pid: p.conn.pid}
	}
	p.selectedGoroutine.thread.(*GdbserverThread).clearBreakpointState()
	err := p.selectedGoroutine.thread.(*GdbserverThread).StepInstruction()
	if err != nil {
		return err
	}
	return p.selectedGoroutine.thread.(*GdbserverThread).SetCurrentBreakpoint()
}

func (p *GdbserverProcess) SwitchThread(tid int) error {
	if th, ok := p.threads[tid]; ok {
		p.currentThread = th
		p.selectedGoroutine, _ = GetG(p.CurrentThread())
		return nil
	}
	return fmt.Errorf("thread %d does not exist", tid)
}

func (p *GdbserverProcess) SwitchGoroutine(gid int) error {
	g, err := FindGoroutine(p, gid)
	if err != nil {
		return err
	}
	if g == nil {
		// user specified -1 and selectedGoroutine is nil
		return nil
	}
	if g.thread != nil {
		return p.SwitchThread(g.thread.ThreadID())
	}
	p.selectedGoroutine = g
	return nil
}

func (p *GdbserverProcess) RequestManualStop() error {
	p.ctrlC = true
	return p.conn.sendCtrlC()
}

func (p *GdbserverProcess) Halt() error {
	p.ctrlC = true
	return p.conn.sendCtrlC()
}

func (p *GdbserverProcess) Kill() error {
	if p.exited {
		return nil
	}
	err := p.conn.kill()
	if _, exited := err.(ProcessExitedError); exited {
		p.exited = true
		return nil
	}
	return err
}

func (p *GdbserverProcess) Detach(kill bool) error {
	if kill {
		if err := p.Kill(); err != nil {
			if _, exited := err.(ProcessExitedError); !exited {
				return err
			}
		}
	}
	if !p.exited {
		if err := p.conn.detach(); err != nil {
			return err
		}
	}
	if p.process != nil {
		p.process.Process.Kill()
		p.process.Wait()
	}
	return p.bi.Close()
}

func (p *GdbserverProcess) Breakpoints() map[uint64]*Breakpoint {
	return p.breakpoints
}

func (p *GdbserverProcess) FindBreakpoint(pc uint64) (*Breakpoint, bool) {
	// Check to see if address is past the breakpoint, (i.e. breakpoint was hit).
	if bp, ok := p.breakpoints[pc-uint64(p.bi.arch.BreakpointSize())]; ok {
		return bp, true
	}
	// Directly use addr to lookup breakpoint.
	if bp, ok := p.breakpoints[pc]; ok {
		return bp, true
	}
	return nil, false
}

func (p *GdbserverProcess) SetBreakpoint(addr uint64, kind BreakpointKind, cond ast.Expr) (*Breakpoint, error) {
	if bp, ok := p.breakpoints[addr]; ok {
		return nil, BreakpointExistsError{bp.File, bp.Line, bp.Addr}
	}
	f, l, fn := p.bi.PCToLine(uint64(addr))
	if fn == nil {
		return nil, InvalidAddressError{address: addr}
	}

	newBreakpoint := &Breakpoint{
		FunctionName: fn.Name,
		File:         f,
		Line:         l,
		Addr:         addr,
		Kind:         kind,
		Cond:         cond,
		HitCount:     map[int]uint64{},
	}

	if kind != UserBreakpoint {
		p.internalBreakpointIDCounter++
		newBreakpoint.ID = p.internalBreakpointIDCounter
	} else {
		p.breakpointIDCounter++
		newBreakpoint.ID = p.breakpointIDCounter
	}

	if err := p.conn.setBreakpoint(addr); err != nil {
		return nil, err
	}
	p.breakpoints[addr] = newBreakpoint
	return newBreakpoint, nil
}

func (p *GdbserverProcess) ClearBreakpoint(addr uint64) (*Breakpoint, error) {
	if p.exited {
		return nil, &ProcessExitedError{Pid: p.conn.pid}
	}
	bp := p.breakpoints[addr]
	if bp == nil {
		return nil, NoBreakpointError{addr: addr}
	}

	if err := p.conn.clearBreakpoint(addr); err != nil {
		return nil, err
	}

	delete(p.breakpoints, addr)

	return bp, nil
}

func (p *GdbserverProcess) ClearInternalBreakpoints() error {
	for _, bp := range p.breakpoints {
		if !bp.Internal() {
			continue
		}
		if _, err := p.ClearBreakpoint(bp.Addr); err != nil {
			return err
		}
	}
	for i := range p.threads {
		if p.threads[i].CurrentBreakpoint != nil && p.threads[i].CurrentBreakpoint.Internal() {
			p.threads[i].CurrentBreakpoint = nil
		}
	}
	return nil
}

type threadUpdater struct {
	p    *GdbserverProcess
	seen map[int]bool
	done bool
}

func (tu *threadUpdater) Add(threads []string) error {
	if tu.done {
		panic("threadUpdater: Add after Finish")
	}
	if tu.seen == nil {
		tu.seen = map[int]bool{}
	}
	for _, threadID := range threads {
		b := threadID
		if period := strings.Index(b, "."); period >= 0 {
			b = b[period+1:]
		}
		n, err := strconv.ParseUint(b, 16, 32)
		if err != nil {
			return &GdbMalformedThreadIDError{threadID}
		}
		tid := int(n)
		tu.seen[tid] = true
		if _, found := tu.p.threads[tid]; !found {
			tu.p.threads[tid] = &GdbserverThread{ID: tid, strID: threadID, p: tu.p}
		}
	}
	return nil
}

func (tu *threadUpdater) Finish() {
	tu.done = true
	for threadID := range tu.p.threads {
		_, threadSeen := tu.seen[threadID]
		if threadSeen {
			continue
		}
		delete(tu.p.threads, threadID)
		if tu.p.currentThread.ID == threadID {
			tu.p.currentThread = nil
		}
	}
	if tu.p.currentThread == nil {
		for _, thread := range tu.p.threads {
			tu.p.currentThread = thread
			break
		}
	}
}

// updateThreadsList retrieves the list of inferior threads from the stub
// and passes it to the threadUpdater.
// Then it reloads the register information for all running threads.
// Some stubs will return the list of running threads in the stop packet, if
// this happens the threadUpdater will know that we have already updated the
// thread list and the first step of updateThreadList will be skipped.
// Registers are always reloaded.
func (p *GdbserverProcess) updateThreadList(tu *threadUpdater) error {
	if !tu.done {
		first := true
		for {
			threads, err := p.conn.queryThreads(first)
			if err != nil {
				return err
			}
			if len(threads) == 0 {
				break
			}
			first = false
			if err := tu.Add(threads); err != nil {
				return err
			}
		}

		tu.Finish()
	}

	if p.threadStopInfo {
		for _, th := range p.threads {
			sig, reason, err := p.conn.threadStopInfo(th.strID)
			if err != nil {
				if isProtocolErrorUnsupported(err) {
					p.threadStopInfo = false
					break
				}
				return err
			}
			th.setbp = (reason == "breakpoint" || (reason == "" && sig == breakpointSignal))
		}
	}

	for _, thread := range p.threads {
		if err := thread.reloadRegisters(); err != nil {
			return err
		}
	}
	return nil
}

func (p *GdbserverProcess) setCurrentBreakpoints() error {
	if p.threadStopInfo {
		for _, th := range p.threads {
			if th.setbp {
				err := th.SetCurrentBreakpoint()
				if err != nil {
					return err
				}
			}
		}
	}
	if !p.threadStopInfo {
		for _, th := range p.threads {
			if th.CurrentBreakpoint == nil {
				err := th.SetCurrentBreakpoint()
				if err != nil {
					return err
				}
			}
		}
	}
	return nil
}

func (t *GdbserverThread) ReadMemory(data []byte, addr uintptr) (n int, err error) {
	err = t.p.conn.readMemory(data, addr)
	if err != nil {
		return 0, err
	}
	return len(data), nil
}

func (t *GdbserverThread) writeMemory(addr uintptr, data []byte) (written int, err error) {
	return t.p.conn.writeMemory(addr, data)
}

func (t *GdbserverThread) Location() (*Location, error) {
	regs, err := t.Registers(false)
	if err != nil {
		return nil, err
	}
	pc := regs.PC()
	f, l, fn := t.p.bi.PCToLine(pc)
	return &Location{PC: pc, File: f, Line: l, Fn: fn}, nil
}

func (t *GdbserverThread) Breakpoint() (breakpoint *Breakpoint, active bool, condErr error) {
	return t.CurrentBreakpoint, (t.CurrentBreakpoint != nil && t.BreakpointConditionMet), t.BreakpointConditionError
}

func (t *GdbserverThread) ThreadID() int {
	return t.ID
}

func (t *GdbserverThread) Registers(floatingPoint bool) (Registers, error) {
	return &t.regs, nil
}

func (t *GdbserverThread) Arch() Arch {
	return t.p.bi.arch
}

func (t *GdbserverThread) BinInfo() *BinaryInfo {
	return &t.p.bi
}

func (t *GdbserverThread) stepInstruction(tu *threadUpdater) error {
	pc := t.regs.PC()
	if _, atbp := t.p.breakpoints[pc]; atbp {
		err := t.p.conn.clearBreakpoint(pc)
		if err != nil {
			return err
		}
		defer t.p.conn.setBreakpoint(pc)
	}
	_, _, err := t.p.conn.step(t.strID, tu)
	return err
}

func (t *GdbserverThread) StepInstruction() error {
	if err := t.stepInstruction(&threadUpdater{p: t.p}); err != nil {
		return err
	}
	return t.reloadRegisters()
}

// loadGInstr returns the correct MOV instruction for the current
// OS/architecture that can be executed to load the address of G from an
// inferior's thread.
func (p *GdbserverProcess) loadGInstr() []byte {
	switch p.bi.goos {
	case "windows":
		//TODO(aarzilli): implement
		panic("not implemented")
	case "linux":
		switch p.bi.arch.GStructOffset() {
		case 0xfffffffffffffff8, 0x0:
			// mov    rcx,QWORD PTR fs:0xfffffffffffffff8
			return []byte{0x64, 0x48, 0x8B, 0x0C, 0x25, 0xF8, 0xFF, 0xFF, 0xFF}
		case 0xfffffffffffffff0:
			// mov    rcx,QWORD PTR fs:0xfffffffffffffff0
			return []byte{0x64, 0x48, 0x8B, 0x0C, 0x25, 0xF0, 0xFF, 0xFF, 0xFF}
		default:
			panic("not implemented")
		}
	case "darwin":
		// mov    rcx,QWORD PTR gs:0x8a0
		return []byte{0x65, 0x48, 0x8B, 0x0C, 0x25, 0xA0, 0x08, 0x00, 0x00}
	default:
		panic("unsupported operating system attempting to find Goroutine on Thread")
	}
}

// reloadRegisters loads the current value of the thread's registers.
// It will also load the address of the thread's G.
// Loading the address of G can be done in one of two ways reloadGAlloc, if
// the stub can allocate memory, or reloadGAtPC, if the stub can't.
func (t *GdbserverThread) reloadRegisters() error {
	if t.regs.regs == nil {
		t.regs.regs = make(map[string]gdbRegister)
		t.regs.regsInfo = t.p.conn.regsInfo

		regsz := 0
		for _, reginfo := range t.p.conn.regsInfo {
			if endoff := reginfo.Offset + (reginfo.Bitsize / 8); endoff > regsz {
				regsz = endoff
			}
		}
		t.regs.buf = make([]byte, regsz)
		for _, reginfo := range t.p.conn.regsInfo {
			t.regs.regs[reginfo.Name] = gdbRegister{regnum: reginfo.Regnum, value: t.regs.buf[reginfo.Offset : reginfo.Offset+reginfo.Bitsize/8]}
		}
	}

	if t.p.gcmdok {
		if err := t.p.conn.readRegisters(t.strID, t.regs.buf); err != nil {
			if isProtocolErrorUnsupported(err) {
				t.p.gcmdok = false
			} else {
				return err
			}
		}
	}
	if !t.p.gcmdok {
		for _, reginfo := range t.p.conn.regsInfo {
			if err := t.p.conn.readRegister(t.strID, reginfo.Regnum, t.regs.regs[reginfo.Name].value); err != nil {
				return err
			}
		}
	}

	if t.p.loadGInstrAddr > 0 {
		return t.reloadGAlloc()
	}
	return t.reloadGAtPC()
}

func (t *GdbserverThread) writeSomeRegisters(regNames ...string) error {
	if t.p.gcmdok {
		return t.p.conn.writeRegisters(t.strID, t.regs.buf)
	}
	for _, regName := range regNames {
		if err := t.p.conn.writeRegister(t.strID, t.regs.regs[regName].regnum, t.regs.regs[regName].value); err != nil {
			return err
		}
	}
	return nil
}

func (t *GdbserverThread) readSomeRegisters(regNames ...string) error {
	if t.p.gcmdok {
		return t.p.conn.readRegisters(t.strID, t.regs.buf)
	}
	for _, regName := range regNames {
		err := t.p.conn.readRegister(t.strID, t.regs.regs[regName].regnum, t.regs.regs[regName].value)
		if err != nil {
			return err
		}
	}
	return nil
}

// reloadGAtPC overwrites the instruction that the thread is stopped at with
// the MOV instruction used to load current G, executes this single
// instruction and then puts everything back the way it was.
func (t *GdbserverThread) reloadGAtPC() error {
	movinstr := t.p.loadGInstr()

	if gdbserverThreadBlocked(t) {
		t.regs.tls = 0
		t.regs.gaddr = 0
		t.regs.hasgaddr = true
		return nil
	}

	cx := t.regs.CX()
	pc := t.regs.PC()

	// We are partially replicating the code of GdbserverThread.stepInstruction
	// here.
	// The reason is that lldb-server has a bug with writing to memory and
	// setting/clearing breakpoints to that same memory which we must work
	// around by clearing and re-setting the breakpoint in a specific sequence
	// with the memory writes.
	// Additionally all breakpoints in [pc, pc+len(movinstr)] need to be removed
	for addr, _ := range t.p.breakpoints {
		if addr >= pc && addr <= pc+uint64(len(movinstr)) {
			err := t.p.conn.clearBreakpoint(addr)
			if err != nil {
				return err
			}
			defer t.p.conn.setBreakpoint(addr)
		}
	}

	savedcode := make([]byte, len(movinstr))
	_, err := t.ReadMemory(savedcode, uintptr(pc))
	if err != nil {
		return err
	}

	_, err = t.writeMemory(uintptr(pc), movinstr)
	if err != nil {
		return err
	}

	defer func() {
		_, err0 := t.writeMemory(uintptr(pc), savedcode)
		if err == nil {
			err = err0
		}
		t.regs.setPC(pc)
		t.regs.setCX(cx)
		err1 := t.writeSomeRegisters(regnamePC, regnameCX)
		if err == nil {
			err = err1
		}
	}()

	_, _, err = t.p.conn.step(t.strID, nil)
	if err != nil {
		return err
	}

	if err := t.readSomeRegisters(regnamePC, regnameCX); err != nil {
		return err
	}

	t.regs.gaddr = t.regs.CX()
	t.regs.hasgaddr = true

	return err
}

// reloadGAlloc makes the specified thread execute one instruction stored at
// t.p.loadGInstrAddr then restores the value of the thread's registers.
// t.p.loadGInstrAddr must point to valid memory on the inferior, containing
// a MOV instruction that loads the address of the current G in the RCX
// register.
func (t *GdbserverThread) reloadGAlloc() error {
	if gdbserverThreadBlocked(t) {
		t.regs.tls = 0
		t.regs.gaddr = 0
		t.regs.hasgaddr = true
		return nil
	}

	cx := t.regs.CX()
	pc := t.regs.PC()

	t.regs.setPC(t.p.loadGInstrAddr)
	if err := t.writeSomeRegisters(regnamePC); err != nil {
		return err
	}

	var err error

	defer func() {
		t.regs.setPC(pc)
		t.regs.setCX(cx)
		err1 := t.writeSomeRegisters(regnamePC, regnameCX)
		if err == nil {
			err = err1
		}
	}()

	_, _, err = t.p.conn.step(t.strID, nil)
	if err != nil {
		return err
	}

	if err := t.readSomeRegisters(regnameCX); err != nil {
		return err
	}

	t.regs.gaddr = t.regs.CX()
	t.regs.hasgaddr = true

	return err
}

func gdbserverThreadBlocked(t *GdbserverThread) bool {
	regs, err := t.Registers(false)
	if err != nil {
		return false
	}
	pc := regs.PC()
	fn := t.BinInfo().goSymTable.PCToFunc(pc)
	if fn == nil {
		return false
	}
	switch fn.Name {
	case "runtime.futex", "runtime.usleep", "runtime.clone":
		return true
	case "runtime.kevent":
		return true
	case "runtime.mach_semaphore_wait", "runtime.mach_semaphore_timedwait":
		return true
	}
	return false
}

func (t *GdbserverThread) clearBreakpointState() {
	t.setbp = false
	t.CurrentBreakpoint = nil
	t.BreakpointConditionMet = false
	t.BreakpointConditionError = nil
}

func (thread *GdbserverThread) SetCurrentBreakpoint() error {
	thread.CurrentBreakpoint = nil
	regs, err := thread.Registers(false)
	if err != nil {
		return err
	}
	pc := regs.PC()
	if bp, ok := thread.p.FindBreakpoint(pc); ok {
		if thread.regs.PC() != bp.Addr {
			if err := thread.regs.SetPC(thread, bp.Addr); err != nil {
				return err
			}
		}
		thread.CurrentBreakpoint = bp
		thread.BreakpointConditionMet, thread.BreakpointConditionError = bp.checkCondition(thread)
		if thread.CurrentBreakpoint != nil && thread.BreakpointConditionMet {
			if g, err := GetG(thread); err == nil {
				thread.CurrentBreakpoint.HitCount[g.ID]++
			}
			thread.CurrentBreakpoint.TotalHitCount++
		}
	}
	return nil
}

func (regs *gdbRegisters) PC() uint64 {
	return binary.LittleEndian.Uint64(regs.regs[regnamePC].value)
}

func (regs *gdbRegisters) setPC(value uint64) {
	binary.LittleEndian.PutUint64(regs.regs[regnamePC].value, value)
}

func (regs *gdbRegisters) SP() uint64 {
	return binary.LittleEndian.Uint64(regs.regs[regnameSP].value)
}

func (regs *gdbRegisters) BP() uint64 {
	return binary.LittleEndian.Uint64(regs.regs[regnameBP].value)
}

func (regs *gdbRegisters) CX() uint64 {
	return binary.LittleEndian.Uint64(regs.regs[regnameCX].value)
}

func (regs *gdbRegisters) setCX(value uint64) {
	binary.LittleEndian.PutUint64(regs.regs[regnameCX].value, value)
}

func (regs *gdbRegisters) TLS() uint64 {
	return regs.tls
}

func (regs *gdbRegisters) GAddr() (uint64, bool) {
	return regs.gaddr, regs.hasgaddr
}

func (regs *gdbRegisters) byName(name string) uint64 {
	reg, ok := regs.regs[name]
	if !ok {
		return 0
	}
	return binary.LittleEndian.Uint64(reg.value)
}

func (regs *gdbRegisters) Get(n int) (uint64, error) {
	reg := x86asm.Reg(n)
	const (
		mask8  = 0x000f
		mask16 = 0x00ff
		mask32 = 0xffff
	)

	switch reg {
	// 8-bit
	case x86asm.AL:
		return regs.byName("rax") & mask8, nil
	case x86asm.CL:
		return regs.byName("rcx") & mask8, nil
	case x86asm.DL:
		return regs.byName("rdx") & mask8, nil
	case x86asm.BL:
		return regs.byName("rbx") & mask8, nil
	case x86asm.AH:
		return (regs.byName("rax") >> 8) & mask8, nil
	case x86asm.CH:
		return (regs.byName("rcx") >> 8) & mask8, nil
	case x86asm.DH:
		return (regs.byName("rdx") >> 8) & mask8, nil
	case x86asm.BH:
		return (regs.byName("rbx") >> 8) & mask8, nil
	case x86asm.SPB:
		return regs.byName("rsp") & mask8, nil
	case x86asm.BPB:
		return regs.byName("rbp") & mask8, nil
	case x86asm.SIB:
		return regs.byName("rsi") & mask8, nil
	case x86asm.DIB:
		return regs.byName("rdi") & mask8, nil
	case x86asm.R8B:
		return regs.byName("r8") & mask8, nil
	case x86asm.R9B:
		return regs.byName("r9") & mask8, nil
	case x86asm.R10B:
		return regs.byName("r10") & mask8, nil
	case x86asm.R11B:
		return regs.byName("r11") & mask8, nil
	case x86asm.R12B:
		return regs.byName("r12") & mask8, nil
	case x86asm.R13B:
		return regs.byName("r13") & mask8, nil
	case x86asm.R14B:
		return regs.byName("r14") & mask8, nil
	case x86asm.R15B:
		return regs.byName("r15") & mask8, nil

	// 16-bit
	case x86asm.AX:
		return regs.byName("rax") & mask16, nil
	case x86asm.CX:
		return regs.byName("rcx") & mask16, nil
	case x86asm.DX:
		return regs.byName("rdx") & mask16, nil
	case x86asm.BX:
		return regs.byName("rbx") & mask16, nil
	case x86asm.SP:
		return regs.byName("rsp") & mask16, nil
	case x86asm.BP:
		return regs.byName("rbp") & mask16, nil
	case x86asm.SI:
		return regs.byName("rsi") & mask16, nil
	case x86asm.DI:
		return regs.byName("rdi") & mask16, nil
	case x86asm.R8W:
		return regs.byName("r8") & mask16, nil
	case x86asm.R9W:
		return regs.byName("r9") & mask16, nil
	case x86asm.R10W:
		return regs.byName("r10") & mask16, nil
	case x86asm.R11W:
		return regs.byName("r11") & mask16, nil
	case x86asm.R12W:
		return regs.byName("r12") & mask16, nil
	case x86asm.R13W:
		return regs.byName("r13") & mask16, nil
	case x86asm.R14W:
		return regs.byName("r14") & mask16, nil
	case x86asm.R15W:
		return regs.byName("r15") & mask16, nil

	// 32-bit
	case x86asm.EAX:
		return regs.byName("rax") & mask32, nil
	case x86asm.ECX:
		return regs.byName("rcx") & mask32, nil
	case x86asm.EDX:
		return regs.byName("rdx") & mask32, nil
	case x86asm.EBX:
		return regs.byName("rbx") & mask32, nil
	case x86asm.ESP:
		return regs.byName("rsp") & mask32, nil
	case x86asm.EBP:
		return regs.byName("rbp") & mask32, nil
	case x86asm.ESI:
		return regs.byName("rsi") & mask32, nil
	case x86asm.EDI:
		return regs.byName("rdi") & mask32, nil
	case x86asm.R8L:
		return regs.byName("r8") & mask32, nil
	case x86asm.R9L:
		return regs.byName("r9") & mask32, nil
	case x86asm.R10L:
		return regs.byName("r10") & mask32, nil
	case x86asm.R11L:
		return regs.byName("r11") & mask32, nil
	case x86asm.R12L:
		return regs.byName("r12") & mask32, nil
	case x86asm.R13L:
		return regs.byName("r13") & mask32, nil
	case x86asm.R14L:
		return regs.byName("r14") & mask32, nil
	case x86asm.R15L:
		return regs.byName("r15") & mask32, nil

	// 64-bit
	case x86asm.RAX:
		return regs.byName("rax"), nil
	case x86asm.RCX:
		return regs.byName("rcx"), nil
	case x86asm.RDX:
		return regs.byName("rdx"), nil
	case x86asm.RBX:
		return regs.byName("rbx"), nil
	case x86asm.RSP:
		return regs.byName("rsp"), nil
	case x86asm.RBP:
		return regs.byName("rbp"), nil
	case x86asm.RSI:
		return regs.byName("rsi"), nil
	case x86asm.RDI:
		return regs.byName("rdi"), nil
	case x86asm.R8:
		return regs.byName("r8"), nil
	case x86asm.R9:
		return regs.byName("r9"), nil
	case x86asm.R10:
		return regs.byName("r10"), nil
	case x86asm.R11:
		return regs.byName("r11"), nil
	case x86asm.R12:
		return regs.byName("r12"), nil
	case x86asm.R13:
		return regs.byName("r13"), nil
	case x86asm.R14:
		return regs.byName("r14"), nil
	case x86asm.R15:
		return regs.byName("r15"), nil
	}

	return 0, UnknownRegisterError
}

func (regs *gdbRegisters) SetPC(thread IThread, pc uint64) error {
	regs.setPC(pc)
	t := thread.(*GdbserverThread)
	if t.p.gcmdok {
		return t.p.conn.writeRegisters(t.strID, t.regs.buf)
	}
	reg := regs.regs[regnamePC]
	return t.p.conn.writeRegister(t.strID, reg.regnum, reg.value)
}

func (regs *gdbRegisters) Slice() []Register {
	r := make([]Register, 0, len(regs.regsInfo))
	for _, reginfo := range regs.regsInfo {
		switch {
		case reginfo.Name == "eflags":
			r = appendFlagReg(r, reginfo.Name, uint64(binary.LittleEndian.Uint32(regs.regs[reginfo.Name].value)), eflagsDescription, 32)
		case reginfo.Name == "mxcsr":
			r = appendFlagReg(r, reginfo.Name, uint64(binary.LittleEndian.Uint32(regs.regs[reginfo.Name].value)), mxcsrDescription, 32)
		case reginfo.Bitsize == 16:
			r = appendWordReg(r, reginfo.Name, binary.LittleEndian.Uint16(regs.regs[reginfo.Name].value))
		case reginfo.Bitsize == 32:
			r = appendDwordReg(r, reginfo.Name, binary.LittleEndian.Uint32(regs.regs[reginfo.Name].value))
		case reginfo.Bitsize == 64:
			r = appendQwordReg(r, reginfo.Name, binary.LittleEndian.Uint64(regs.regs[reginfo.Name].value))
		case reginfo.Bitsize == 80:
			idx := 0
			for _, stprefix := range []string{"stmm", "st"} {
				if strings.HasPrefix(reginfo.Name, stprefix) {
					idx, _ = strconv.Atoi(reginfo.Name[len(stprefix):])
					break
				}
			}
			value := regs.regs[reginfo.Name].value
			r = appendX87Reg(r, idx, binary.LittleEndian.Uint16(value[8:]), binary.LittleEndian.Uint64(value[:8]))

		case reginfo.Bitsize == 128:
			r = appendSSEReg(r, strings.ToUpper(reginfo.Name), regs.regs[reginfo.Name].value)

		case reginfo.Bitsize == 256:
			if !strings.HasPrefix(strings.ToLower(reginfo.Name), "ymm") {
				continue
			}

			value := regs.regs[reginfo.Name].value
			xmmName := "x" + reginfo.Name[1:]
			r = appendSSEReg(r, strings.ToUpper(xmmName), value[:16])
			r = appendSSEReg(r, strings.ToUpper(reginfo.Name), value[16:])
		}
	}
	return r
}