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threads.go
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threads.go
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package proc
import (
"debug/gosym"
"encoding/binary"
"fmt"
"path/filepath"
"reflect"
"runtime"
"golang.org/x/debug/dwarf"
"github.com/derekparker/delve/dwarf/frame"
)
// Thread represents a single thread in the traced process
// ID represents the thread id or port, Process holds a reference to the
// Process struct that contains info on the process as
// a whole, and Status represents the last result of a `wait` call
// on this thread.
type Thread struct {
ID int // Thread ID or mach port
Status *WaitStatus // Status returned from last wait call
CurrentBreakpoint *Breakpoint // Breakpoint thread is currently stopped at
BreakpointConditionMet bool // Output of evaluating the breakpoint's condition
BreakpointConditionError error // Error evaluating the breakpoint's condition
dbp *Process
singleStepping bool
running bool
os *OSSpecificDetails
}
// Location represents the location of a thread.
// Holds information on the current instruction
// address, the source file:line, and the function.
type Location struct {
PC uint64
File string
Line int
Fn *gosym.Func
}
// Continue the execution of this thread.
//
// If we are currently at a breakpoint, we'll clear it
// first and then resume execution. Thread will continue until
// it hits a breakpoint or is signaled.
func (thread *Thread) Continue() error {
pc, err := thread.PC()
if err != nil {
return err
}
// Check whether we are stopped at a breakpoint, and
// if so, single step over it before continuing.
if _, ok := thread.dbp.FindBreakpoint(pc); ok {
if err := thread.StepInstruction(); err != nil {
return err
}
}
return thread.resume()
}
// StepInstruction steps a single instruction.
//
// Executes exactly one instruction and then returns.
// If the thread is at a breakpoint, we first clear it,
// execute the instruction, and then replace the breakpoint.
// Otherwise we simply execute the next instruction.
func (thread *Thread) StepInstruction() (err error) {
thread.running = true
thread.singleStepping = true
defer func() {
thread.singleStepping = false
thread.running = false
}()
pc, err := thread.PC()
if err != nil {
return err
}
bp, ok := thread.dbp.FindBreakpoint(pc)
if ok {
// Clear the breakpoint so that we can continue execution.
_, err = bp.Clear(thread)
if err != nil {
return err
}
// Restore breakpoint now that we have passed it.
defer func() {
err = thread.dbp.writeSoftwareBreakpoint(thread, bp.Addr)
}()
}
err = thread.singleStep()
if err != nil {
return fmt.Errorf("step failed: %s", err.Error())
}
return nil
}
// Location returns the threads location, including the file:line
// of the corresponding source code, the function we're in
// and the current instruction address.
func (thread *Thread) Location() (*Location, error) {
pc, err := thread.PC()
if err != nil {
return nil, err
}
f, l, fn := thread.dbp.PCToLine(pc)
return &Location{PC: pc, File: f, Line: l, Fn: fn}, nil
}
// ThreadBlockedError is returned when the thread
// is blocked in the scheduler.
type ThreadBlockedError struct{}
func (tbe ThreadBlockedError) Error() string {
return ""
}
// Set breakpoints for potential next lines.
func (thread *Thread) setNextBreakpoints() (err error) {
if thread.blocked() {
return ThreadBlockedError{}
}
curpc, err := thread.PC()
if err != nil {
return err
}
// Grab info on our current stack frame. Used to determine
// whether we may be stepping outside of the current function.
fde, err := thread.dbp.frameEntries.FDEForPC(curpc)
if err != nil {
return err
}
// Get current file/line.
loc, err := thread.Location()
if err != nil {
return err
}
if filepath.Ext(loc.File) == ".go" {
err = thread.next(curpc, fde, loc.File, loc.Line)
} else {
err = thread.cnext(curpc, fde, loc.File)
}
return err
}
// GoroutineExitingError is returned when the
// goroutine specified by `goid` is in the process
// of exiting.
type GoroutineExitingError struct {
goid int
}
func (ge GoroutineExitingError) Error() string {
return fmt.Sprintf("goroutine %d is exiting", ge.goid)
}
// Set breakpoints at every line, and the return address. Also look for
// a deferred function and set a breakpoint there too.
func (thread *Thread) next(curpc uint64, fde *frame.FrameDescriptionEntry, file string, line int) error {
pcs := thread.dbp.lineInfo.AllPCsBetween(fde.Begin(), fde.End(), file)
g, err := thread.GetG()
if err != nil {
return err
}
if g.DeferPC != 0 {
f, lineno, _ := thread.dbp.goSymTable.PCToLine(g.DeferPC)
for {
lineno++
dpc, _, err := thread.dbp.goSymTable.LineToPC(f, lineno)
if err == nil {
// We want to avoid setting an actual breakpoint on the
// entry point of the deferred function so instead create
// a fake breakpoint which will be cleaned up later.
thread.dbp.Breakpoints[g.DeferPC] = new(Breakpoint)
defer func() { delete(thread.dbp.Breakpoints, g.DeferPC) }()
if _, err = thread.dbp.SetTempBreakpoint(dpc); err != nil {
return err
}
break
}
}
}
ret, err := thread.ReturnAddress()
if err != nil {
return err
}
var covered bool
for i := range pcs {
if fde.Cover(pcs[i]) {
covered = true
break
}
}
if !covered {
fn := thread.dbp.goSymTable.PCToFunc(ret)
if fn != nil && fn.Name == "runtime.goexit" {
g, err := thread.GetG()
if err != nil {
return err
}
return GoroutineExitingError{goid: g.ID}
}
}
pcs = append(pcs, ret)
return thread.setNextTempBreakpoints(curpc, pcs)
}
// Set a breakpoint at every reachable location, as well as the return address. Without
// the benefit of an AST we can't be sure we're not at a branching statement and thus
// cannot accurately predict where we may end up.
func (thread *Thread) cnext(curpc uint64, fde *frame.FrameDescriptionEntry, file string) error {
pcs := thread.dbp.lineInfo.AllPCsBetween(fde.Begin(), fde.End(), file)
ret, err := thread.ReturnAddress()
if err != nil {
return err
}
pcs = append(pcs, ret)
return thread.setNextTempBreakpoints(curpc, pcs)
}
func (thread *Thread) setNextTempBreakpoints(curpc uint64, pcs []uint64) error {
for i := range pcs {
if pcs[i] == curpc || pcs[i] == curpc-1 {
continue
}
if _, err := thread.dbp.SetTempBreakpoint(pcs[i]); err != nil {
if _, ok := err.(BreakpointExistsError); !ok {
return err
}
}
}
return nil
}
// SetPC sets the PC for this thread.
func (thread *Thread) SetPC(pc uint64) error {
regs, err := thread.Registers()
if err != nil {
return err
}
return regs.SetPC(thread, pc)
}
func (thread *Thread) getGVariable() (*Variable, error) {
regs, err := thread.Registers()
if err != nil {
return nil, err
}
if thread.dbp.arch.GStructOffset() == 0 {
// GetG was called through SwitchThread / updateThreadList during initialization
// thread.dbp.arch isn't setup yet (it needs a CurrentThread to read global variables from)
return nil, fmt.Errorf("g struct offset not initialized")
}
gaddrbs, err := thread.readMemory(uintptr(regs.TLS()+thread.dbp.arch.GStructOffset()), thread.dbp.arch.PtrSize())
if err != nil {
return nil, err
}
gaddr := uintptr(binary.LittleEndian.Uint64(gaddrbs))
// On Windows, the value at TLS()+GStructOffset() is a
// pointer to the G struct.
needsDeref := runtime.GOOS == "windows"
return thread.newGVariable(gaddr, needsDeref)
}
func (thread *Thread) newGVariable(gaddr uintptr, deref bool) (*Variable, error) {
typ, err := thread.dbp.findType("runtime.g")
if err != nil {
return nil, err
}
name := ""
if deref {
typ = &dwarf.PtrType{dwarf.CommonType{int64(thread.dbp.arch.PtrSize()), "", reflect.Ptr, 0}, typ}
} else {
name = "runtime.curg"
}
return thread.newVariable(name, gaddr, typ), nil
}
// GetG returns information on the G (goroutine) that is executing on this thread.
//
// The G structure for a thread is stored in thread local storage. Here we simply
// calculate the address and read and parse the G struct.
//
// We cannot simply use the allg linked list in order to find the M that represents
// the given OS thread and follow its G pointer because on Darwin mach ports are not
// universal, so our port for this thread would not map to the `id` attribute of the M
// structure. Also, when linked against libc, Go prefers the libc version of clone as
// opposed to the runtime version. This has the consequence of not setting M.id for
// any thread, regardless of OS.
//
// In order to get around all this craziness, we read the address of the G structure for
// the current thread from the thread local storage area.
func (thread *Thread) GetG() (g *G, err error) {
gaddr, err := thread.getGVariable()
if err != nil {
return nil, err
}
g, err = gaddr.parseG()
if err == nil {
g.thread = thread
}
return
}
// Stopped returns whether the thread is stopped at
// the operating system level. Actual implementation
// is OS dependant, look in OS thread file.
func (thread *Thread) Stopped() bool {
return thread.stopped()
}
// Halt stops this thread from executing. Actual
// implementation is OS dependant. Look in OS
// thread file.
func (thread *Thread) Halt() (err error) {
defer func() {
if err == nil {
thread.running = false
}
}()
if thread.Stopped() {
return
}
err = thread.halt()
return
}
// Scope returns the current EvalScope for this thread.
func (thread *Thread) Scope() (*EvalScope, error) {
locations, err := thread.Stacktrace(0)
if err != nil {
return nil, err
}
return locations[0].Scope(thread), nil
}
// SetCurrentBreakpoint sets the current breakpoint that this
// thread is stopped at as CurrentBreakpoint on the thread struct.
func (thread *Thread) SetCurrentBreakpoint() error {
thread.CurrentBreakpoint = nil
pc, err := thread.PC()
if err != nil {
return err
}
if bp, ok := thread.dbp.FindBreakpoint(pc); ok {
thread.CurrentBreakpoint = bp
if err = thread.SetPC(bp.Addr); err != nil {
return err
}
thread.BreakpointConditionMet, thread.BreakpointConditionError = bp.checkCondition(thread)
if thread.onTriggeredBreakpoint() {
if g, err := thread.GetG(); err == nil {
thread.CurrentBreakpoint.HitCount[g.ID]++
}
thread.CurrentBreakpoint.TotalHitCount++
}
}
return nil
}
func (thread *Thread) onTriggeredBreakpoint() bool {
return (thread.CurrentBreakpoint != nil) && thread.BreakpointConditionMet
}
func (thread *Thread) onTriggeredTempBreakpoint() bool {
return thread.onTriggeredBreakpoint() && thread.CurrentBreakpoint.Temp
}
func (thread *Thread) onRuntimeBreakpoint() bool {
loc, err := thread.Location()
if err != nil {
return false
}
return loc.Fn != nil && loc.Fn.Name == "runtime.breakpoint"
}
// Returns true if this thread is on the goroutine requested by the current 'next' command
func (th *Thread) onNextGoroutine() (bool, error) {
var bp *Breakpoint
for i := range th.dbp.Breakpoints {
if th.dbp.Breakpoints[i].Temp {
bp = th.dbp.Breakpoints[i]
}
}
if bp == nil {
return false, nil
}
return bp.checkCondition(th)
}