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halt_breakpoints.go
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halt_breakpoints.go
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// This file is part of Gopher2600.
//
// Gopher2600 is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Gopher2600 is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Gopher2600. If not, see <https://www.gnu.org/licenses/>.
// breakpoints are used to halt execution when a target is *changed to* a
// specific value. compare to traps which are used to halt execution when the
// target *changes from* its current value *to* any other value.
package debugger
import (
"fmt"
"strconv"
"strings"
"github.com/jetsetilly/gopher2600/debugger/terminal"
"github.com/jetsetilly/gopher2600/debugger/terminal/commandline"
"github.com/jetsetilly/gopher2600/disassembly"
"github.com/jetsetilly/gopher2600/hardware/memory/memorymap"
"github.com/jetsetilly/gopher2600/hardware/television/specification"
)
// breakpoints keeps track of all the currently defined breakers.
type breakpoints struct {
dbg *Debugger
// array of breakers are ORed together
breaks []breaker
// prepared targets which we use in hasBreak(). we don't want to setup
// these targets every time hasBreak() is called.
checkPcBreak *target
checkBankBreak *target
}
// breaker defines a specific break condition.
type breaker struct {
target *target
// the requested value to break on
value targetValue
// skipNext indicates that a break success should be skipped or ignored
// because the target value isn't new. in other words, we only break when
// the target has changed *to* the value not when it already *is* the value
//
// without this we risk the user becoming trapped in a perpetual break
// condition, which probably isn't what the user wants or expects
skipNext bool
// single linked list ANDs breakers together
next *breaker
}
func (bk breaker) String() string {
s := strings.Builder{}
s.WriteString(fmt.Sprintf("%s->%s", bk.target.label, bk.target.stringValue(bk.value)))
n := bk.next
for n != nil {
s.WriteString(fmt.Sprintf(" & %s->%s", n.target.label, n.target.stringValue(n.value)))
n = n.next
}
return s.String()
}
// compares two breakers for equality. returns true if the two breakers are
// logically the same.
func (bk breaker) cmp(ck breaker) bool {
// count number of nodes
bn := 0
b := &bk
for b != nil {
bn++
b = b.next
}
cn := 0
c := &ck
for c != nil {
cn++
c = c.next
}
// if counts are different then the comparison has failed
if cn != bn {
return false
}
// compare all nodes with one another
b = &bk
for b != nil {
c = &ck
match := false
for c != nil {
match = (b.target.label == c.target.label && b.value == c.value)
if match {
break // for loop
}
c = c.next
}
if !match {
return false
}
b = b.next
}
return true
}
type checkResult int
const (
checkMatch checkResult = iota
checkNoMatch
checkIgnoredValue
)
// check checks the specific break condition with the current value of
// the break target.
func (bk *breaker) check() checkResult {
if bk.target.value() != bk.value {
bk.skipNext = false
return checkNoMatch
}
// target value matches break value but it hasn't changed since the
// previous check. we don't want to break if this is true
if bk.skipNext {
return checkIgnoredValue
}
if bk.next != nil {
if bk.next.check() == checkNoMatch {
return checkNoMatch
}
}
// this is a match. we should skip the next match.
bk.skipNext = true
return checkMatch
}
// add a new breaker by linking it to the end of an existing breaker.
func (bk *breaker) add(nbk *breaker) {
n := bk
for n.next != nil {
n = n.next
}
n.next = nbk
}
// newBreakpoints is the preferred method of initialisation for breakpoints.
func newBreakpoints(dbg *Debugger) (*breakpoints, error) {
bp := &breakpoints{dbg: dbg}
bp.clear()
var err error
bp.checkPcBreak, err = parseTarget(bp.dbg, commandline.TokeniseInput("PC"))
if err != nil {
return nil, fmt.Errorf("breakpoint: this should not have failed: %w", err)
}
bp.checkBankBreak, err = parseTarget(bp.dbg, commandline.TokeniseInput("BANK"))
if err != nil {
return nil, fmt.Errorf("breakpoint: this should not have failed: %w", err)
}
return bp, err
}
// clear all breakpoints.
func (bp *breakpoints) clear() {
bp.breaks = make([]breaker, 0, 10)
}
// isEmpty returns true if there are no currently defined breakpoints.
func (bp *breakpoints) isEmpty() bool {
return len(bp.breaks) == 0
}
// drop a specific breakpoint by position in list.
func (bp *breakpoints) drop(num int) error {
if len(bp.breaks)-1 < num {
return fmt.Errorf("breakpoint #%d is not defined", num)
}
h := bp.breaks[:num]
t := bp.breaks[num+1:]
bp.breaks = make([]breaker, len(h)+len(t), cap(bp.breaks))
copy(bp.breaks, h)
copy(bp.breaks[len(h):], t)
return nil
}
// check compares the current state of the emulation with every breakpoint
// condition. returns a string listing every condition that matches (separated
// by \n).
func (bp *breakpoints) check() string {
if len(bp.breaks) == 0 {
return ""
}
checkString := strings.Builder{}
for i := range bp.breaks {
if bp.breaks[i].target.instructionBoundary && !bp.dbg.vcs.CPU.LastResult.Final {
continue // for loop
}
if bp.breaks[i].check() == checkMatch {
checkString.WriteString(fmt.Sprintf("break on %s\n", bp.breaks[i]))
}
}
return checkString.String()
}
// list currently defined breakpoints.
func (bp breakpoints) list() {
if len(bp.breaks) == 0 {
bp.dbg.printLine(terminal.StyleFeedback, "no breakpoints")
} else {
bp.dbg.printLine(terminal.StyleFeedback, "breakpoints:")
for i := range bp.breaks {
bp.dbg.printLine(terminal.StyleFeedback, "% 2d: %s", i, bp.breaks[i])
}
}
}
// parse token and add new breakpoint. for example:
//
// PC 0xf000
// adds a new breakpoint to the PC
//
// in addition to the description in the HELP file, the breakpoint parser has
// some additional features which should probably be removed. if only because
// the commandline template will balk before this function is ever called.
//
// for reference though, and very briefly: the | symbol can be used to add more
// than one condition, instead of calling BREAK more than once.
//
// Also, the & symbol can be placed before the target/value combinations.
// A sort of Polish prefix notation.
//
// & SL 100 CL 0 X 10
//
// !!TODO: simplify breakpoints parser to match help description.
func (bp *breakpoints) parseCommand(tokens *commandline.Tokens) error {
andBreaks := false
// default target of CPU PC. meaning that "BREAK n" will cause a breakpoint
// being set on the PC. breaking on PC is probably the most common type of
// breakpoint. the target will change value when the input string sees
// something appropriate
tgt, err := parseTarget(bp.dbg, commandline.TokeniseInput("PC"))
if err != nil {
return fmt.Errorf("breakpoint: this should not have failed: %w", err)
}
// resolvedTarget keeps track of whether we have specified a target but not
// given any values for that target. we set it to true initially because
// we want to be able to change the default target
resolvedTarget := true
// we don't add new breakpoints to the main list straight away. we append
// them to newBreaks first and then check that we aren't adding duplicates
newBreaks := make([]breaker, 0, 10)
// whether to add a bank condition to a singular PC BREAK target
addBankCondition := true
// loop over tokens:
// - if token is a valid type value then add the breakpoint for the current target
// - if it is not a valid type value, try to change the target
tok, present := tokens.Get()
for present {
var val interface{}
var err error
// try to interpret the token depending on the type of value the target
// expects
switch tgt.value().(type) {
case string:
// if token is string type then make it uppercase for now
val = strings.ToUpper(tok)
case int:
var v int64
v, err = strconv.ParseInt(tok, 0, 32)
if err == nil {
val = int(v)
} else {
// !!TODO: allow symbol lookup for targets with integer values
err = fmt.Errorf("invalid value (%s) for target (%s)", tok, tgt.label)
}
case bool:
switch strings.ToLower(tok) {
case "true":
val = true
case "false":
val = false
default:
err = fmt.Errorf("invalid value (%s) for target (%s)", tok, tgt.label)
}
default:
return fmt.Errorf("unsupported value type (%T) for target (%s)", tgt.value(), tgt.label)
}
if err == nil {
// special handling for some targets
switch tgt.label {
case "PC":
ai := bp.dbg.dbgmem.GetAddressInfo(uint16(val.(int)), true)
val = int(ai.MappedAddress)
// unusual case but if PC break is not in cartridge area we
// don't want to add a bank condition
addBankCondition = addBankCondition && ai.Area == memorymap.Cartridge
case "Scanline":
if val.(int) < 0 {
return fmt.Errorf("scanline value must be greater than or equal to 0")
}
if val.(int) > specification.AbsoluteMaxScanlines {
return fmt.Errorf("scanline value must be less than or equal to %d", specification.AbsoluteMaxScanlines)
}
case "Clock":
if val.(int) < -specification.ClksHBlank {
return fmt.Errorf("clock value must be greater than or equal to %d", -specification.ClksHBlank)
}
if val.(int) > specification.ClksVisible {
return fmt.Errorf("scanline value must be less than or equal to %d", specification.ClksVisible)
}
}
if andBreaks {
newBreaks[len(newBreaks)-1].add(&breaker{target: tgt, value: val})
resolvedTarget = true
} else {
newBreaks = append(newBreaks, breaker{target: tgt, value: val})
resolvedTarget = true
}
} else {
// make sure we've not left a previous target dangling without a value
if !resolvedTarget {
return fmt.Errorf("%w", err)
}
// possibly switch composition mode
if tok == "&" {
andBreaks = true
} else if tok == "|" {
andBreaks = false
} else {
// if PC target has not been explicitly specified then add
// bank condition
addBankCondition = addBankCondition && strings.ToUpper(tok) != "PC"
// token is not a number or a composition symbol so try to
// parse a new target
tokens.Unget()
tgt, err = parseTarget(bp.dbg, tokens)
if err != nil {
return fmt.Errorf("%w", err)
}
resolvedTarget = false
}
}
tok, present = tokens.Get()
}
if !resolvedTarget {
// default values
switch tgt.value().(type) {
case bool:
if andBreaks {
newBreaks[len(newBreaks)-1].add(&breaker{target: tgt, value: true})
} else {
newBreaks = append(newBreaks, breaker{target: tgt, value: true})
}
default:
return fmt.Errorf("need a value (%T) to break on (%s)", tgt.value(), tgt.label)
}
}
for _, nb := range newBreaks {
// if the break is a singular, undecorated PC target then add a BANK
// condition for the current BANK. this is arguably what the user
// intends to happen.
if nb.next == nil && nb.target.label == "PC" && addBankCondition {
if bp.dbg.vcs.Mem.Cart.NumBanks() > 1 {
nb.next = &breaker{
target: bankTarget(bp.dbg),
value: bp.dbg.vcs.Mem.Cart.GetBank(bp.dbg.vcs.CPU.PC.Address()).Number,
}
nb.next.skipNext = true
}
}
if i := bp.checkBreaker(nb); i != noBreakEqualivalent {
return fmt.Errorf("already exists (%s)", bp.breaks[i])
}
bp.breaks = append(bp.breaks, nb)
}
return nil
}
const noBreakEqualivalent = -1
// checkBreaker returns the index number of the matching breakpoint. returns
// noBreakEquivalent if no match is found.
func (bp *breakpoints) checkBreaker(nb breaker) int {
for n, ob := range bp.breaks {
if nb.cmp(ob) {
return n
}
}
return noBreakEqualivalent
}
// HasPCBreak returns true ifan address/bank has a PC breakpoint associated with it.
func (bp breakpoints) HasPCBreak(addr uint16, bank int) (bool, int) {
ai := bp.dbg.dbgmem.GetAddressInfo(addr, true)
check := breaker{
target: bp.checkPcBreak,
// casting value to type because that's how the target value is stored
// for the program counter (see TargetValue() implementation for the
// ProgramCounter type in the registers package)
value: int(ai.MappedAddress),
}
// we start with the very specific - address and bank
check.next = &breaker{
target: bp.checkBankBreak,
// critical that we cast to int because we'll be comparing against the
// result of cartridge.GetBank()
value: bank,
}
// check for a breaker for the PC value AND bank value. if
// checkBreaker() fails then from our point of view, this is a success
// and we say that the disassembly.Entry has a breakpoint for *this*
// bank
if i := bp.checkBreaker(check); i != noBreakEqualivalent {
return true, i
}
// if checkBreaker doesn't report an existing breakpoint, we remove the
// Bank condition and try again. if checkBreaker fails (success from our
// point of view) this time, we can say that the disassembly entry has
// a breakpoint for the program counter only and will break for *any*
// bank
check.next = nil
if i := bp.checkBreaker(check); i != noBreakEqualivalent {
return true, i
}
// there is no breakpoint at that matches this disassembly entry
return false, noBreakEqualivalent
}
func (bp *breakpoints) togglePCBreak(e *disassembly.Entry) {
has, i := bp.HasPCBreak(e.Result.Address, e.Bank)
if i != noBreakEqualivalent && has {
_ = bp.drop(i) // ignoring errors
return
}
// no equivalent breakpoint existed so add one
ai := bp.dbg.dbgmem.GetAddressInfo(e.Result.Address, true)
nb := breaker{
target: bp.checkPcBreak,
// see above for casting commentary
value: int(ai.MappedAddress),
}
if bp.dbg.vcs.Mem.Cart.NumBanks() > 1 {
nb.next = &breaker{
target: bp.checkBankBreak,
// see above for casting commentary
value: e.Bank,
}
}
bp.breaks = append(bp.breaks, nb)
}
// CheckBreakpoints is a minimal interface to Breakpoints
type CheckBreakpoints interface {
HasPCBreak(addr uint16, bank int) (bool, int)
}
// GetBreakpoints returns an instance of CheckBreakpoints. This is good for
// allowing other goroutines access to a read-only copy of the list of
// breakpoints.
func (dbg *Debugger) GetBreakpoints() CheckBreakpoints {
bp := *dbg.halting.breakpoints
bp.breaks = make([]breaker, len(dbg.halting.breakpoints.breaks))
copy(bp.breaks, dbg.halting.breakpoints.breaks)
return bp
}