
Instead of trying to be clever and make an 'educated guess' as to where the flow of control may go next, simple do the more naive, yet correct, approach of setting a breakpoint everywhere we can in the function and seeing where we end up. On top of this we were already setting a breakpoint at the return address and deferred functions, so that remains the same. This removes a lot of gnarly, hard to maintain code and takes all the guesswork out of this command. Fixes #281
317 lines
8.3 KiB
Go
317 lines
8.3 KiB
Go
package proc
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import (
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"debug/gosym"
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"encoding/binary"
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"fmt"
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"path/filepath"
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sys "golang.org/x/sys/unix"
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"github.com/derekparker/delve/dwarf/frame"
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)
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// Thread represents a single thread in the traced process
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// Id represents the thread id or port, Process holds a reference to the
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// Process struct that contains info on the process as
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// a whole, and Status represents the last result of a `wait` call
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// on this thread.
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type Thread struct {
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Id int // Thread ID or mach port
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Status *sys.WaitStatus // Status returned from last wait call
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CurrentBreakpoint *Breakpoint // Breakpoint thread is currently stopped at
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dbp *Process
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singleStepping bool
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running bool
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os *OSSpecificDetails
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}
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// Represents the location of a thread.
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// Holds information on the current instruction
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// address, the source file:line, and the function.
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type Location struct {
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PC uint64
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File string
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Line int
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Fn *gosym.Func
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}
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// Continue the execution of this thread.
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//
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// If we are currently at a breakpoint, we'll clear it
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// first and then resume execution. Thread will continue until
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// it hits a breakpoint or is signaled.
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func (thread *Thread) Continue() error {
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pc, err := thread.PC()
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if err != nil {
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return err
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}
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// Check whether we are stopped at a breakpoint, and
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// if so, single step over it before continuing.
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if _, ok := thread.dbp.FindBreakpoint(pc); ok {
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if err := thread.Step(); err != nil {
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return err
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}
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}
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return thread.resume()
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}
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// Step a single instruction.
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//
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// Executes exactly one instruction and then returns.
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// If the thread is at a breakpoint, we first clear it,
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// execute the instruction, and then replace the breakpoint.
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// Otherwise we simply execute the next instruction.
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func (thread *Thread) Step() (err error) {
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thread.running = true
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thread.singleStepping = true
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defer func() {
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thread.singleStepping = false
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thread.running = false
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}()
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pc, err := thread.PC()
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if err != nil {
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return err
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}
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bp, ok := thread.dbp.FindBreakpoint(pc)
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if ok {
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// Clear the breakpoint so that we can continue execution.
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_, err = bp.Clear(thread)
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if err != nil {
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return err
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}
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// Restore breakpoint now that we have passed it.
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defer func() {
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err = thread.dbp.writeSoftwareBreakpoint(thread, bp.Addr)
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}()
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}
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err = thread.singleStep()
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if err != nil {
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return fmt.Errorf("step failed: %s", err.Error())
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}
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return nil
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}
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// Returns the threads location, including the file:line
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// of the corresponding source code, the function we're in
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// and the current instruction address.
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func (thread *Thread) Location() (*Location, error) {
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pc, err := thread.PC()
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if err != nil {
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return nil, err
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}
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f, l, fn := thread.dbp.PCToLine(pc)
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return &Location{PC: pc, File: f, Line: l, Fn: fn}, nil
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}
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type ThreadBlockedError struct{}
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func (tbe ThreadBlockedError) Error() string {
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return ""
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}
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// Set breakpoints for potential next lines.
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func (thread *Thread) setNextBreakpoints() (err error) {
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if thread.blocked() {
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return ThreadBlockedError{}
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}
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curpc, err := thread.PC()
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if err != nil {
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return err
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}
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// Grab info on our current stack frame. Used to determine
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// whether we may be stepping outside of the current function.
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fde, err := thread.dbp.frameEntries.FDEForPC(curpc)
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if err != nil {
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return err
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}
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// Get current file/line.
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loc, err := thread.Location()
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if err != nil {
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return err
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}
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if filepath.Ext(loc.File) == ".go" {
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err = thread.next(curpc, fde, loc.File, loc.Line)
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} else {
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err = thread.cnext(curpc, fde, loc.File)
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}
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return err
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}
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// Go routine is exiting.
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type GoroutineExitingError struct {
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goid int
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}
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func (ge GoroutineExitingError) Error() string {
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return fmt.Sprintf("goroutine %d is exiting", ge.goid)
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}
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// Set breakpoints at every line, and the return address. Also look for
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// a deferred function and set a breakpoint there too.
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func (thread *Thread) next(curpc uint64, fde *frame.FrameDescriptionEntry, file string, line int) error {
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pcs := thread.dbp.lineInfo.AllPCsBetween(fde.Begin(), fde.End(), file)
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g, err := thread.GetG()
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if err != nil {
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return err
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}
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if g.DeferPC != 0 {
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f, lineno, _ := thread.dbp.goSymTable.PCToLine(g.DeferPC)
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for {
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lineno++
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dpc, _, err := thread.dbp.goSymTable.LineToPC(f, lineno)
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if err == nil {
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// We want to avoid setting an actual breakpoint on the
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// entry point of the deferred function so instead create
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// a fake breakpoint which will be cleaned up later.
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thread.dbp.Breakpoints[g.DeferPC] = new(Breakpoint)
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defer func() { delete(thread.dbp.Breakpoints, g.DeferPC) }()
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if _, err = thread.dbp.SetTempBreakpoint(dpc); err != nil {
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return err
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}
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break
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}
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}
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}
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ret, err := thread.ReturnAddress()
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if err != nil {
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return err
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}
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var covered bool
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for i := range pcs {
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if fde.Cover(pcs[i]) {
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covered = true
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break
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}
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}
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if !covered {
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fn := thread.dbp.goSymTable.PCToFunc(ret)
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if fn != nil && fn.Name == "runtime.goexit" {
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g, err := thread.GetG()
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if err != nil {
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return err
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}
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return GoroutineExitingError{goid: g.Id}
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}
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}
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pcs = append(pcs, ret)
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return thread.setNextTempBreakpoints(curpc, pcs)
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}
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// Set a breakpoint at every reachable location, as well as the return address. Without
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// the benefit of an AST we can't be sure we're not at a branching statement and thus
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// cannot accurately predict where we may end up.
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func (thread *Thread) cnext(curpc uint64, fde *frame.FrameDescriptionEntry, file string) error {
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pcs := thread.dbp.lineInfo.AllPCsBetween(fde.Begin(), fde.End(), file)
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ret, err := thread.ReturnAddress()
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if err != nil {
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return err
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}
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pcs = append(pcs, ret)
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return thread.setNextTempBreakpoints(curpc, pcs)
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}
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func (thread *Thread) setNextTempBreakpoints(curpc uint64, pcs []uint64) error {
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for i := range pcs {
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if pcs[i] == curpc || pcs[i] == curpc-1 {
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continue
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}
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if _, err := thread.dbp.SetTempBreakpoint(pcs[i]); err != nil {
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if _, ok := err.(BreakpointExistsError); !ok {
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return err
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}
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}
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}
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return nil
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}
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// Sets the PC for this thread.
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func (thread *Thread) SetPC(pc uint64) error {
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regs, err := thread.Registers()
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if err != nil {
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return err
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}
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return regs.SetPC(thread, pc)
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}
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// Returns information on the G (goroutine) that is executing on this thread.
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//
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// The G structure for a thread is stored in thread local memory. Execute instructions
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// that move the *G structure into a CPU register, and then grab
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// the new registers and parse the G structure.
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//
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// We cannot simply use the allg linked list in order to find the M that represents
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// the given OS thread and follow its G pointer because on Darwin mach ports are not
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// universal, so our port for this thread would not map to the `id` attribute of the M
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// structure. Also, when linked against libc, Go prefers the libc version of clone as
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// opposed to the runtime version. This has the consequence of not setting M.id for
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// any thread, regardless of OS.
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//
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// In order to get around all this craziness, we read the address of the G structure for
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// the current thread from the thread local storage area.
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func (thread *Thread) GetG() (g *G, err error) {
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regs, err := thread.Registers()
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if err != nil {
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return nil, err
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}
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if thread.dbp.arch.GStructOffset() == 0 {
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// GetG was called through SwitchThread / updateThreadList during initialization
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// thread.dbp.arch isn't setup yet (it needs a CurrentThread to read global variables from)
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return nil, fmt.Errorf("g struct offset not initialized")
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}
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gaddrbs, err := thread.readMemory(uintptr(regs.TLS()+thread.dbp.arch.GStructOffset()), thread.dbp.arch.PtrSize())
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if err != nil {
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return nil, err
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}
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gaddr := binary.LittleEndian.Uint64(gaddrbs)
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g, err = parseG(thread, gaddr, false)
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if err == nil {
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g.thread = thread
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}
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return
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}
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// Returns whether the thread is stopped at
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// the operating system level. Actual implementation
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// is OS dependant, look in OS thread file.
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func (thread *Thread) Stopped() bool {
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return thread.stopped()
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}
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// Stops this thread from executing. Actual
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// implementation is OS dependant. Look in OS
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// thread file.
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func (thread *Thread) Halt() (err error) {
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defer func() {
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if err == nil {
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thread.running = false
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}
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}()
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if thread.Stopped() {
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return
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}
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err = thread.halt()
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return
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}
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func (thread *Thread) Scope() (*EvalScope, error) {
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locations, err := thread.Stacktrace(0)
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if err != nil {
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return nil, err
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}
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return locations[0].Scope(thread), nil
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}
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