breakpoints.go

package proc

import (
	"errors"
	"fmt"
	"go/ast"
	"go/constant"
	"reflect"
)

// Breakpoint represents a breakpoint. Stores information on the break
// point including the byte of data that originally was stored at that
// address.
type Breakpoint struct {
	// File & line information for printing.
	FunctionName string
	File         string
	Line         int

	Addr         uint64 // Address breakpoint is set for.
	OriginalData []byte // If software breakpoint, the data we replace with breakpoint instruction.
	Name         string // User defined name of the breakpoint
	ID           int    // Monotonically increasing ID.

	// Kind describes whether this is an internal breakpoint (for next'ing or
	// stepping).
	// A single breakpoint can be both a UserBreakpoint and some kind of
	// internal breakpoint, but it can not be two different kinds of internal
	// breakpoint.
	Kind BreakpointKind

	// Breakpoint information
	Tracepoint    bool     // Tracepoint flag
	Goroutine     bool     // Retrieve goroutine information
	Stacktrace    int      // Number of stack frames to retrieve
	Variables     []string // Variables to evaluate
	LoadArgs      *LoadConfig
	LoadLocals    *LoadConfig
	HitCount      map[int]uint64 // Number of times a breakpoint has been reached in a certain goroutine
	TotalHitCount uint64         // Number of times a breakpoint has been reached

	// DeferReturns: when kind == NextDeferBreakpoint this breakpoint
	// will also check if the caller is runtime.gopanic or if the return
	// address is in the DeferReturns array.
	// Next uses NextDeferBreakpoints for the breakpoint it sets on the
	// deferred function, DeferReturns is populated with the
	// addresses of calls to runtime.deferreturn in the current
	// function. This insures that the breakpoint on the deferred
	// function only triggers on panic or on the defer call to
	// the function, not when the function is called directly
	DeferReturns []uint64
	// Cond: if not nil the breakpoint will be triggered only if evaluating Cond returns true
	Cond ast.Expr
	// internalCond is the same as Cond but used for the condition of internal breakpoints
	internalCond ast.Expr
}

// Breakpoint Kind determines the behavior of delve when the
// breakpoint is reached.
type BreakpointKind uint16

const (
	// UserBreakpoint is a user set breakpoint
	UserBreakpoint BreakpointKind = (1 << iota)
	// NextBreakpoint is a breakpoint set by Next, Continue
	// will stop on it and delete it
	NextBreakpoint
	// NextDeferBreakpoint is a breakpoint set by Next on the
	// first deferred function. In addition to checking their condition
	// breakpoints of this kind will also check that the function has been
	// called by runtime.gopanic or through runtime.deferreturn.
	NextDeferBreakpoint
	// StepBreakpoint is a breakpoint set by Step on a CALL instruction,
	// Continue will set a new breakpoint (of NextBreakpoint kind) on the
	// destination of CALL, delete this breakpoint and then continue again
	StepBreakpoint
)

func (bp *Breakpoint) String() string {
	return fmt.Sprintf("Breakpoint %d at %#v %s:%d (%d)", bp.ID, bp.Addr, bp.File, bp.Line, bp.TotalHitCount)
}

// BreakpointExistsError is returned when trying to set a breakpoint at
// an address that already has a breakpoint set for it.
type BreakpointExistsError struct {
	File string
	Line int
	Addr uint64
}

func (bpe BreakpointExistsError) Error() string {
	return fmt.Sprintf("Breakpoint exists at %s:%d at %x", bpe.File, bpe.Line, bpe.Addr)
}

// InvalidAddressError represents the result of
// attempting to set a breakpoint at an invalid address.
type InvalidAddressError struct {
	Address uint64
}

func (iae InvalidAddressError) Error() string {
	return fmt.Sprintf("Invalid address %#v\n", iae.Address)
}

// CheckCondition evaluates bp's condition on thread.
func (bp *Breakpoint) CheckCondition(thread Thread) BreakpointState {
	bpstate := BreakpointState{Breakpoint: bp, Active: false, Internal: false, CondError: nil}
	if bp.Cond == nil && bp.internalCond == nil {
		bpstate.Active = true
		bpstate.Internal = bp.Kind != UserBreakpoint
		return bpstate
	}
	nextDeferOk := true
	if bp.Kind&NextDeferBreakpoint != 0 {
		frames, err := ThreadStacktrace(thread, 2)
		if err == nil {
			ispanic := len(frames) >= 3 && frames[2].Current.Fn != nil && frames[2].Current.Fn.Name == "runtime.gopanic"
			isdeferreturn := false
			if len(frames) >= 1 {
				for _, pc := range bp.DeferReturns {
					if frames[0].Ret == pc {
						isdeferreturn = true
						break
					}
				}
			}
			nextDeferOk = ispanic || isdeferreturn
		}
	}
	if bp.Kind != UserBreakpoint {
		// Check internalCondition if this is also an internal breakpoint
		bpstate.Active, bpstate.CondError = evalBreakpointCondition(thread, bp.internalCond)
		bpstate.Active = bpstate.Active && nextDeferOk
		if bpstate.Active || bpstate.CondError != nil {
			bpstate.Internal = true
			return bpstate
		}
	}
	if bp.Kind&UserBreakpoint != 0 {
		// Check normal condition if this is also a user breakpoint
		bpstate.Active, bpstate.CondError = evalBreakpointCondition(thread, bp.Cond)
	}
	return bpstate
}

// IsInternal returns true if bp is an internal breakpoint.
// User-set breakpoints can overlap with internal breakpoints, in that case
// both IsUser and IsInternal will be true.
func (bp *Breakpoint) IsInternal() bool {
	return bp.Kind != UserBreakpoint
}

// IsUser returns true if bp is a user-set breakpoint.
// User-set breakpoints can overlap with internal breakpoints, in that case
// both IsUser and IsInternal will be true.
func (bp *Breakpoint) IsUser() bool {
	return bp.Kind&UserBreakpoint != 0
}

func evalBreakpointCondition(thread Thread, cond ast.Expr) (bool, error) {
	if cond == nil {
		return true, nil
	}
	scope, err := GoroutineScope(thread)
	if err != nil {
		return true, err
	}
	v, err := scope.evalAST(cond)
	if err != nil {
		return true, fmt.Errorf("error evaluating expression: %v", err)
	}
	if v.Unreadable != nil {
		return true, fmt.Errorf("condition expression unreadable: %v", v.Unreadable)
	}
	if v.Kind != reflect.Bool {
		return true, errors.New("condition expression not boolean")
	}
	return constant.BoolVal(v.Value), nil
}

// NoBreakpointError is returned when trying to
// clear a breakpoint that does not exist.
type NoBreakpointError struct {
	Addr uint64
}

func (nbp NoBreakpointError) Error() string {
	return fmt.Sprintf("no breakpoint at %#v", nbp.Addr)
}

// BreakpointMap represents an (address, breakpoint) map.
type BreakpointMap struct {
	M map[uint64]*Breakpoint

	breakpointIDCounter         int
	internalBreakpointIDCounter int
}

// NewBreakpointMap creates a new BreakpointMap.
func NewBreakpointMap() BreakpointMap {
	return BreakpointMap{
		M: make(map[uint64]*Breakpoint),
	}
}

// ResetBreakpointIDCounter resets the breakpoint ID counter of bpmap.
func (bpmap *BreakpointMap) ResetBreakpointIDCounter() {
	bpmap.breakpointIDCounter = 0
}

type writeBreakpointFn func(addr uint64) (file string, line int, fn *Function, originalData []byte, err error)
type clearBreakpointFn func(*Breakpoint) error

// Set creates a breakpoint at addr calling writeBreakpoint. Do not call this
// function, call proc.Process.SetBreakpoint instead, this function exists
// to implement proc.Process.SetBreakpoint.
func (bpmap *BreakpointMap) Set(addr uint64, kind BreakpointKind, cond ast.Expr, writeBreakpoint writeBreakpointFn) (*Breakpoint, error) {
	if bp, ok := bpmap.M[addr]; ok {
		// We can overlap one internal breakpoint with one user breakpoint, we
		// need to support this otherwise a conditional breakpoint can mask a
		// breakpoint set by next or step.
		if (kind != UserBreakpoint && bp.Kind != UserBreakpoint) || (kind == UserBreakpoint && bp.Kind&UserBreakpoint != 0) {
			return bp, BreakpointExistsError{bp.File, bp.Line, bp.Addr}
		}
		bp.Kind |= kind
		if kind != UserBreakpoint {
			bp.internalCond = cond
		} else {
			bp.Cond = cond
		}
		return bp, nil
	}

	f, l, fn, originalData, err := writeBreakpoint(addr)
	if err != nil {
		return nil, err
	}

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

	if kind != UserBreakpoint {
		bpmap.internalBreakpointIDCounter++
		newBreakpoint.ID = bpmap.internalBreakpointIDCounter
		newBreakpoint.internalCond = cond
	} else {
		bpmap.breakpointIDCounter++
		newBreakpoint.ID = bpmap.breakpointIDCounter
		newBreakpoint.Cond = cond
	}

	bpmap.M[addr] = newBreakpoint

	return newBreakpoint, nil
}

// SetWithID creates a breakpoint at addr, with the specified ID.
func (bpmap *BreakpointMap) SetWithID(id int, addr uint64, writeBreakpoint writeBreakpointFn) (*Breakpoint, error) {
	bp, err := bpmap.Set(addr, UserBreakpoint, nil, writeBreakpoint)
	if err == nil {
		bp.ID = id
		bpmap.breakpointIDCounter--
	}
	return bp, err
}

// Clear clears the breakpoint at addr.
// Do not call this function call proc.Process.ClearBreakpoint instead.
func (bpmap *BreakpointMap) Clear(addr uint64, clearBreakpoint clearBreakpointFn) (*Breakpoint, error) {
	bp, ok := bpmap.M[addr]
	if !ok {
		return nil, NoBreakpointError{Addr: addr}
	}

	bp.Kind &= ^UserBreakpoint
	bp.Cond = nil
	if bp.Kind != 0 {
		return bp, nil
	}

	if err := clearBreakpoint(bp); err != nil {
		return nil, err
	}

	delete(bpmap.M, addr)

	return bp, nil
}

// ClearInternalBreakpoints removes all internal breakpoints from the map,
// calling clearBreakpoint on each one.
// Do not call this function, call proc.Process.ClearInternalBreakpoints
// instead, this function is used to implement that.
func (bpmap *BreakpointMap) ClearInternalBreakpoints(clearBreakpoint clearBreakpointFn) error {
	for addr, bp := range bpmap.M {
		bp.Kind = bp.Kind & UserBreakpoint
		bp.internalCond = nil
		if bp.Kind != 0 {
			continue
		}
		if err := clearBreakpoint(bp); err != nil {
			return err
		}
		delete(bpmap.M, addr)
	}
	return nil
}

// HasInternalBreakpoints returns true if bpmap has at least one internal
// breakpoint set.
func (bpmap *BreakpointMap) HasInternalBreakpoints() bool {
	for _, bp := range bpmap.M {
		if bp.Kind != UserBreakpoint {
			return true
		}
	}
	return false
}

// BreakpointState describes the state of a breakpoint in a thread.
type BreakpointState struct {
	*Breakpoint
	// Active is true if the breakpoint condition was met.
	Active bool
	// Internal is true if the breakpoint was matched as an internal
	// breakpoint.
	Internal bool
	// CondError contains any error encountered while evaluating the
	// breakpoint's condition.
	CondError error
}

func (bpstate *BreakpointState) Clear() {
	bpstate.Breakpoint = nil
	bpstate.Active = false
	bpstate.Internal = false
	bpstate.CondError = nil
}

func (bpstate *BreakpointState) String() string {
	s := bpstate.Breakpoint.String()
	if bpstate.Active {
		s += " active"
	}
	if bpstate.Internal {
		s += " internal"
	}
	return s
}