proc: implement attach on windows

Updates #363

proc/proc.go

@@ -79,6 +79,11 @@ func New(pid int) *Process {
 		ptraceChan:     make(chan func()),
 		ptraceDoneChan: make(chan interface{}),
 	}
+	// TODO: find better way to determine proc arch (perhaps use executable file info)
+	switch runtime.GOARCH {
+	case "amd64":
+		dbp.arch = AMD64Arch()
+	}
 	go dbp.handlePtraceFuncs()
 	return dbp
 }
@@ -704,11 +709,6 @@ func initializeDebugProcess(dbp *Process, path string, attach bool) (*Process, e
 		return nil, err
 	}
 
-	switch runtime.GOARCH {
-	case "amd64":
-		dbp.arch = AMD64Arch()
-	}
-
 	if err := dbp.updateThreadList(); err != nil {
 		return nil, err
 	}

proc/proc_windows.go

@@ -8,21 +8,15 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
-	"runtime"
 	"sync"
 	"syscall"
 	"unsafe"
 
 	sys "golang.org/x/sys/windows"
 
-	"golang.org/x/debug/dwarf"
 	"github.com/derekparker/delve/dwarf/frame"
 	"github.com/derekparker/delve/dwarf/line"
-)
-
-const (
-	// DEBUGONLYTHISPROCESS tracks https://msdn.microsoft.com/en-us/library/windows/desktop/ms684863(v=vs.85).aspx
-	DEBUGONLYTHISPROCESS = 0x00000002
+	"golang.org/x/debug/dwarf"
 )
 
 // OSProcessDetails holds Windows specific information.
@@ -97,24 +91,25 @@ func Launch(cmd []string) (*Process, error) {
 	si.StdOutput = sys.Handle(fd[1])
 	si.StdErr = sys.Handle(fd[2])
 	pi := new(sys.ProcessInformation)
-	err = sys.CreateProcess(argv0, cmdLine, nil, nil, true, DEBUGONLYTHISPROCESS, nil, nil, si, pi)
+	err = sys.CreateProcess(argv0, cmdLine, nil, nil, true, _DEBUG_ONLY_THIS_PROCESS, nil, nil, si, pi)
 	if err != nil {
 		return nil, err
 	}
 	sys.CloseHandle(sys.Handle(pi.Process))
 	sys.CloseHandle(sys.Handle(pi.Thread))
 
-	dbp := New(int(pi.ProcessId))
-
-	switch runtime.GOARCH {
-	case "amd64":
-		dbp.arch = AMD64Arch()
-	}
+	return newDebugProcess(int(pi.ProcessId), argv0Go)
+}
 
-	// Note - it should not actually be possible for the
+// newDebugProcess prepares process pid for debugging.
+func newDebugProcess(pid int, exepath string) (*Process, error) {
+	dbp := New(pid)
+	// It should not actually be possible for the
 	// call to waitForDebugEvent to fail, since Windows
-	// will always fire a CreateProcess event immediately
-	// after launching under DEBUGONLYTHISPROCESS.
+	// will always fire a CREATE_PROCESS_DEBUG_EVENT event
+	// immediately after launching under DEBUG_ONLY_THIS_PROCESS.
+	// Attaching with DebugActiveProcess has similar effect.
+	var err error
 	var tid, exitCode int
 	dbp.execPtraceFunc(func() {
 		tid, exitCode, err = dbp.waitForDebugEvent()
@@ -126,13 +121,55 @@ func Launch(cmd []string) (*Process, error) {
 		dbp.postExit()
 		return nil, ProcessExitedError{Pid: dbp.Pid, Status: exitCode}
 	}
+	return initializeDebugProcess(dbp, exepath, false)
+}
+
+// findExePath searches for process pid, and returns its executable path.
+func findExePath(pid int) (string, error) {
+	// Original code suggested different approach (see below).
+	// Maybe it could be useful in the future.
+	//
+	// Find executable path from PID/handle on Windows:
+	// https://msdn.microsoft.com/en-us/library/aa366789(VS.85).aspx
+
+	p, err := syscall.OpenProcess(syscall.PROCESS_QUERY_INFORMATION, false, uint32(pid))
+	if err != nil {
+		return "", err
+	}
+	defer syscall.CloseHandle(p)
 
-	return initializeDebugProcess(dbp, argv0Go, false)
+	n := uint32(128)
+	for {
+		buf := make([]uint16, int(n))
+		err = _QueryFullProcessImageName(p, 0, &buf[0], &n)
+		switch err {
+		case syscall.ERROR_INSUFFICIENT_BUFFER:
+			// try bigger buffer
+			n *= 2
+			// but stop if it gets too big
+			if n > 10000 {
+				return "", err
+			}
+		case nil:
+			return syscall.UTF16ToString(buf[:n]), nil
+		default:
+			return "", err
+		}
+	}
 }
 
 // Attach to an existing process with the given PID.
 func Attach(pid int) (*Process, error) {
-	return nil, fmt.Errorf("not implemented: Attach")
+	// TODO: Probably should have SeDebugPrivilege before starting here.
+	err := _DebugActiveProcess(uint32(pid))
+	if err != nil {
+		return nil, err
+	}
+	exepath, err := findExePath(pid)
+	if err != nil {
+		return nil, err
+	}
+	return newDebugProcess(pid, exepath)
 }
 
 // Kill kills the process.
@@ -316,11 +353,6 @@ func (dbp *Process) parseDebugLineInfo(exe *pe.File, wg *sync.WaitGroup) {
 var UnsupportedArchErr = errors.New("unsupported architecture of windows/386 - only windows/amd64 is supported")
 
 func (dbp *Process) findExecutable(path string) (*pe.File, error) {
-	if path == "" {
-		// TODO: Find executable path from PID/handle on Windows:
-		// https://msdn.microsoft.com/en-us/library/aa366789(VS.85).aspx
-		return nil, fmt.Errorf("not yet implemented")
-	}
 	peFile, err := openExecutablePath(path)
 	if err != nil {
 		return nil, err

proc/syscall_windows.go

@@ -69,6 +69,9 @@ const (
 	_UNLOAD_DLL_DEBUG_EVENT     = 7
 	_OUTPUT_DEBUG_STRING_EVENT  = 8
 	_RIP_EVENT                  = 9
+
+	// DEBUG_ONLY_THIS_PROCESS tracks https://msdn.microsoft.com/en-us/library/windows/desktop/ms684863(v=vs.85).aspx
+	_DEBUG_ONLY_THIS_PROCESS = 0x00000002
 )
 
 func _NT_SUCCESS(x _NTSTATUS) bool {
@@ -85,3 +88,5 @@ func _NT_SUCCESS(x _NTSTATUS) bool {
 //sys	_ReadProcessMemory(process syscall.Handle, baseaddr uintptr, buffer *byte, size uintptr, bytesread *uintptr) (err error) = kernel32.ReadProcessMemory
 //sys	_DebugBreakProcess(process syscall.Handle) (err error) = kernel32.DebugBreakProcess
 //sys	_WaitForDebugEvent(debugevent *_DEBUG_EVENT, milliseconds uint32) (err error) = kernel32.WaitForDebugEvent
+//sys	_DebugActiveProcess(processid uint32) (err error) = kernel32.DebugActiveProcess
+//sys	_QueryFullProcessImageName(process syscall.Handle, flags uint32, exename *uint16, size *uint32) (err error) = kernel32.QueryFullProcessImageNameW

proc/zsyscall_windows.go

@@ -2,8 +2,10 @@
 
 package proc
 
-import "unsafe"
-import "syscall"
+import (
+	"syscall"
+	"unsafe"
+)
 
 var _ unsafe.Pointer
 
@@ -11,16 +13,18 @@ var (
 	modntdll    = syscall.NewLazyDLL("ntdll.dll")
 	modkernel32 = syscall.NewLazyDLL("kernel32.dll")
 
-	procNtQueryInformationThread = modntdll.NewProc("NtQueryInformationThread")
-	procGetThreadContext         = modkernel32.NewProc("GetThreadContext")
-	procSetThreadContext         = modkernel32.NewProc("SetThreadContext")
-	procSuspendThread            = modkernel32.NewProc("SuspendThread")
-	procResumeThread             = modkernel32.NewProc("ResumeThread")
-	procContinueDebugEvent       = modkernel32.NewProc("ContinueDebugEvent")
-	procWriteProcessMemory       = modkernel32.NewProc("WriteProcessMemory")
-	procReadProcessMemory        = modkernel32.NewProc("ReadProcessMemory")
-	procDebugBreakProcess        = modkernel32.NewProc("DebugBreakProcess")
-	procWaitForDebugEvent        = modkernel32.NewProc("WaitForDebugEvent")
+	procNtQueryInformationThread   = modntdll.NewProc("NtQueryInformationThread")
+	procGetThreadContext           = modkernel32.NewProc("GetThreadContext")
+	procSetThreadContext           = modkernel32.NewProc("SetThreadContext")
+	procSuspendThread              = modkernel32.NewProc("SuspendThread")
+	procResumeThread               = modkernel32.NewProc("ResumeThread")
+	procContinueDebugEvent         = modkernel32.NewProc("ContinueDebugEvent")
+	procWriteProcessMemory         = modkernel32.NewProc("WriteProcessMemory")
+	procReadProcessMemory          = modkernel32.NewProc("ReadProcessMemory")
+	procDebugBreakProcess          = modkernel32.NewProc("DebugBreakProcess")
+	procWaitForDebugEvent          = modkernel32.NewProc("WaitForDebugEvent")
+	procDebugActiveProcess         = modkernel32.NewProc("DebugActiveProcess")
+	procQueryFullProcessImageNameW = modkernel32.NewProc("QueryFullProcessImageNameW")
 )
 
 func _NtQueryInformationThread(threadHandle syscall.Handle, infoclass int32, info uintptr, infolen uint32, retlen *uint32) (status _NTSTATUS) {
@@ -138,3 +142,27 @@ func _WaitForDebugEvent(debugevent *_DEBUG_EVENT, milliseconds uint32) (err erro
 	}
 	return
 }
+
+func _DebugActiveProcess(processid uint32) (err error) {
+	r1, _, e1 := syscall.Syscall(procDebugActiveProcess.Addr(), 1, uintptr(processid), 0, 0)
+	if r1 == 0 {
+		if e1 != 0 {
+			err = error(e1)
+		} else {
+			err = syscall.EINVAL
+		}
+	}
+	return
+}
+
+func _QueryFullProcessImageName(process syscall.Handle, flags uint32, exename *uint16, size *uint32) (err error) {
+	r1, _, e1 := syscall.Syscall6(procQueryFullProcessImageNameW.Addr(), 4, uintptr(process), uintptr(flags), uintptr(unsafe.Pointer(exename)), uintptr(unsafe.Pointer(size)), 0, 0)
+	if r1 == 0 {
+		if e1 != 0 {
+			err = error(e1)
+		} else {
+			err = syscall.EINVAL
+		}
+	}
+	return
+}