golang debug 代码
文件路径：/src/cmd/compile/internal/ssa/debug.go
/ Copyright 2017 The Go Authors. All rights reserved.
/ Use of this source code is governed by a BSD-style
/ license that can be found in the LICENSE file.
package ssa
import (
"cmd/compile/internal/abi"
"cmd/compile/internal/abt"
"cmd/compile/internal/ir"
"cmd/compile/internal/types"
"cmd/internal/dwarf"
"cmd/internal/obj"
"cmd/internal/src"
"encoding/hex"
"fmt"
"internal/buildcfg"
"math/bits"
"sort"
"strings"
)
type SlotID int32
type VarID int32
/ A FuncDebug contains all the debug information for the variables in a
/ function. Variables are identified by their LocalSlot, which may be
/ the result of decomposing a larger variable.
type FuncDebug struct {
/ Slots is all the slots used in the debug info, indexed by their SlotID.
Slots []LocalSlot
/ The user variables, indexed by VarID.
Vars []*ir.Name
/ The slots that make up each variable, indexed by VarID.
VarSlots [][]SlotID
/ The location list data, indexed by VarID. Must be processed by PutLocationList.
LocationLists [][]byte
/ Register-resident output parameters for the function. This is filled in at
/ SSA generation time.
RegOutputParams []*ir.Name
/ Filled in by the user. Translates Block and Value ID to PC.
GetPC func(ID, ID) int64
}
type BlockDebug struct {
/ State at the start and end of the block. These are initialized,
/ and updated from new information that flows on back edges.
startState, endState abt.T
/ Use these to avoid excess work in the merge. If none of the
/ predecessors has changed since the last check, the old answer is
/ still good.
lastCheckedTime, lastChangedTime int32
/ Whether the block had any changes to user variables at all.
relevant bool
/ false until the block has been processed at least once. This
/ affects how the merge is done; the goal is to maximize sharing
/ and avoid allocation.
everProcessed bool
}
/ A liveSlot is a slot that's live in loc at entry/exit of a block.
type liveSlot struct {
VarLoc
}
func (ls *liveSlot) String() string {
return fmt.Sprintf("0x%x.%d.%d", ls.Registers, ls.stackOffsetValue(), int32(ls.StackOffset)&1)
}
func (loc liveSlot) absent() bool {
return loc.Registers == 0 && !loc.onStack()
}
/ StackOffset encodes whether a value is on the stack and if so, where.
/ It is a 31-bit integer followed by a presence flag at the low-order
/ bit.
type StackOffset int32
func (s StackOffset) onStack() bool {
return s != 0
}
func (s StackOffset) stackOffsetValue() int32 {
return int32(s) >> 1
}
/ stateAtPC is the current state of all variables at some point.
type stateAtPC struct {
/ The location of each known slot, indexed by SlotID.
slots []VarLoc
/ The slots present in each register, indexed by register number.
registers [][]SlotID
}
/ reset fills state with the live variables from live.
func (state *stateAtPC) reset(live abt.T) {
slots, registers := state.slots, state.registers
for i := range slots {
slots[i] = VarLoc{}
}
for i := range registers {
registers[i] = registers[i][:0]
}
for it := live.Iterator(); !it.Done(); {
k, d := it.Next()
live := d.(*liveSlot)
slots[k] = live.VarLoc
if live.VarLoc.Registers == 0 {
continue
}
mask := uint64(live.VarLoc.Registers)
for {
if mask == 0 {
break
}
reg := uint8(bits.TrailingZeros64(mask))
mask &^= 1 << reg
registers[reg] = append(registers[reg], SlotID(k))
}
}
state.slots, state.registers = slots, registers
}
func (s *debugState) LocString(loc VarLoc) string {
if loc.absent() {
return "<nil>"
}
var storage []string
if loc.onStack() {
storage = append(storage, fmt.Sprintf("@%+d", loc.stackOffsetValue()))
}
mask := uint64(loc.Registers)
for {
if mask == 0 {
break
}
reg := uint8(bits.TrailingZeros64(mask))
mask &^= 1 << reg
storage = append(storage, s.registers[reg].String())
}
return strings.Join(storage, ",")
}
/ A VarLoc describes the storage for part of a user variable.
type VarLoc struct {
/ The registers this variable is available in. There can be more than
/ one in various situations, e.g. it's being moved between registers.
Registers RegisterSet
StackOffset
}
func (loc VarLoc) absent() bool {
return loc.Registers == 0 && !loc.onStack()
}
func (loc VarLoc) intersect(other VarLoc) VarLoc {
if !loc.onStack() || !other.onStack() || loc.StackOffset != other.StackOffset {
loc.StackOffset = 0
}
loc.Registers &= other.Registers
return loc
}
var BlockStart = &Value{
ID: -10000,
Op: OpInvalid,
Aux: StringToAux("BlockStart"),
}
var BlockEnd = &Value{
ID: -20000,
Op: OpInvalid,
Aux: StringToAux("BlockEnd"),
}
var FuncEnd = &Value{
ID: -30000,
Op: OpInvalid,
Aux: StringToAux("FuncEnd"),
}
/ RegisterSet is a bitmap of registers, indexed by Register.num.
type RegisterSet uint64
/ logf prints debug-specific logging to stdout (always stdout) if the
/ current function is tagged by GOSSAFUNC (for ssa output directed
/ either to stdout or html).
func (s *debugState) logf(msg string, args ...interface{}) {
if s.f.PrintOrHtmlSSA {
fmt.Printf(msg, args...)
}
}
type debugState struct {
/ See FuncDebug.
slots []LocalSlot
vars []*ir.Name
varSlots [][]SlotID
lists [][]byte
/ The user variable that each slot rolls up to, indexed by SlotID.
slotVars []VarID
f *Func
loggingLevel int
convergeCount int / testing; iterate over block debug state this many times
registers []Register
stackOffset func(LocalSlot) int32
ctxt *obj.Link
/ The names (slots) associated with each value, indexed by Value ID.
valueNames [][]SlotID
/ The current state of whatever analysis is running.
currentState stateAtPC
changedVars *sparseSet
changedSlots *sparseSet
/ The pending location list entry for each user variable, indexed by VarID.
pendingEntries []pendingEntry
varParts map[*ir.Name][]SlotID
blockDebug []BlockDebug
pendingSlotLocs []VarLoc
partsByVarOffset sort.Interface
}
func (state *debugState) initializeCache(f *Func, numVars, numSlots int) {
/ One blockDebug per block. Initialized in allocBlock.
if cap(state.blockDebug) < f.NumBlocks() {
state.blockDebug = make([]BlockDebug, f.NumBlocks())
} else {
/ This local variable, and the ones like it below, enable compiler
/ optimizations. Don't inline them.
b := state.blockDebug[:f.NumBlocks()]
for i := range b {
b[i] = BlockDebug{}
}
}
/ A list of slots per Value. Reuse the previous child slices.
if cap(state.valueNames) < f.NumValues() {
old := state.valueNames
state.valueNames = make([][]SlotID, f.NumValues())
copy(state.valueNames, old)
}
vn := state.valueNames[:f.NumValues()]
for i := range vn {
vn[i] = vn[i][:0]
}
/ Slot and register contents for currentState. Cleared by reset().
if cap(state.currentState.slots) < numSlots {
state.currentState.slots = make([]VarLoc, numSlots)
} else {
state.currentState.slots = state.currentState.slots[:numSlots]
}
if cap(state.currentState.registers) < len(state.registers) {
state.currentState.registers = make([][]SlotID, len(state.registers))
} else {
state.currentState.registers = state.currentState.registers[:len(state.registers)]
}
/ A relatively small slice, but used many times as the return from processValue.
state.changedVars = newSparseSet(numVars)
state.changedSlots = newSparseSet(numSlots)
/ A pending entry per user variable, with space to track each of its pieces.
numPieces := 0
for i := range state.varSlots {
numPieces += len(state.varSlots[i])
}
if cap(state.pendingSlotLocs) < numPieces {
state.pendingSlotLocs = make([]VarLoc, numPieces)
} else {
psl := state.pendingSlotLocs[:numPieces]
for i := range psl {
psl[i] = VarLoc{}
}
}
if cap(state.pendingEntries) < numVars {
state.pendingEntries = make([]pendingEntry, numVars)
}
pe := state.pendingEntries[:numVars]
freePieceIdx := 0
for varID, slots := range state.varSlots {
pe[varID] = pendingEntry{
pieces: state.pendingSlotLocs[freePieceIdx : freePieceIdx+len(slots)],
}
freePieceIdx += len(slots)
}
state.pendingEntries = pe
if cap(state.lists) < numVars {
state.lists = make([][]byte, numVars)
} else {
state.lists = state.lists[:numVars]
for i := range state.lists {
state.lists[i] = nil
}
}
}
func (state *debugState) allocBlock(b *Block) *BlockDebug {
return &state.blockDebug[b.ID]
}
func (s *debugState) blockEndStateString(b *BlockDebug) string {
endState := stateAtPC{slots: make([]VarLoc, len(s.slots)), registers: make([][]SlotID, len(s.registers))}
endState.reset(b.endState)
return s.stateString(endState)
}
func (s *debugState) stateString(state stateAtPC) string {
var strs []string
for slotID, loc := range state.slots {
if !loc.absent() {
strs = append(strs, fmt.Sprintf("\t%v = %v\n", s.slots[slotID], s.LocString(loc)))
}
}
strs = append(strs, "\n")
for reg, slots := range state.registers {
if len(slots) != 0 {
var slotStrs []string
for _, slot := range slots {
slotStrs = append(slotStrs, s.slots[slot].String())
}
strs = append(strs, fmt.Sprintf("\t%v = %v\n", &s.registers[reg], slotStrs))
}
}
if len(strs) == 1 {
return "(no vars)\n"
}
return strings.Join(strs, "")
}
/ slotCanonicalizer is a table used to lookup and canonicalize
/ LocalSlot's in a type insensitive way (e.g. taking into account the
/ base name, offset, and width of the slot, but ignoring the slot
/ type).
type slotCanonicalizer struct {
slmap map[slotKey]SlKeyIdx
slkeys []LocalSlot
}
func newSlotCanonicalizer() *slotCanonicalizer {
return &slotCanonicalizer{
slmap: make(map[slotKey]SlKeyIdx),
slkeys: []LocalSlot{LocalSlot{N: nil}},
}
}
type SlKeyIdx uint32
const noSlot = SlKeyIdx(0)
/ slotKey is a type-insensitive encapsulation of a LocalSlot; it
/ is used to key a map within slotCanonicalizer.
type slotKey struct {
name *ir.Name
offset int64
width int64
splitOf SlKeyIdx / idx in slkeys slice in slotCanonicalizer
splitOffset int64
}
/ lookup looks up a LocalSlot in the slot canonicalizer "sc", returning
/ a canonical index for the slot, and adding it to the table if need
/ be. Return value is the canonical slot index, and a boolean indicating
/ whether the slot was found in the table already (TRUE => found).
func (sc *slotCanonicalizer) lookup(ls LocalSlot) (SlKeyIdx, bool) {
split := noSlot
if ls.SplitOf != nil {
split, _ = sc.lookup(*ls.SplitOf)
}
k := slotKey{
name: ls.N, offset: ls.Off, width: ls.Type.Size(),
splitOf: split, splitOffset: ls.SplitOffset,
}
if idx, ok := sc.slmap[k]; ok {
return idx, true
}
rv := SlKeyIdx(len(sc.slkeys))
sc.slkeys = append(sc.slkeys, ls)
sc.slmap[k] = rv
return rv, false
}
func (sc *slotCanonicalizer) canonSlot(idx SlKeyIdx) LocalSlot {
return sc.slkeys[idx]
}
/ PopulateABIInRegArgOps examines the entry block of the function
/ and looks for incoming parameters that have missing or partial
/ OpArg{Int,Float}Reg values, inserting additional values in
/ cases where they are missing. Example:
/
/ func foo(s string, used int, notused int) int {
/ return len(s) + used
/ }
/
/ In the function above, the incoming parameter "used" is fully live,
/ "notused" is not live, and "s" is partially live (only the length
/ field of the string is used). At the point where debug value
/ analysis runs, we might expect to see an entry block with:
/
/ b1:
/ v4 = ArgIntReg <uintptr> {s+8} [0] : BX
/ v5 = ArgIntReg <int> {used} [0] : CX
/
/ While this is an accurate picture of the live incoming params,
/ we also want to have debug locations for non-live params (or
/ their non-live pieces), e.g. something like
/
/ b1:
/ v9 = ArgIntReg <*uint8> {s+0} [0] : AX
/ v4 = ArgIntReg <uintptr> {s+8} [0] : BX
/ v5 = ArgIntReg <int> {used} [0] : CX
/ v10 = ArgIntReg <int> {unused} [0] : DI
/
/ This function examines the live OpArg{Int,Float}Reg values and
/ synthesizes new (dead) values for the non-live params or the
/ non-live pieces of partially live params.
func PopulateABIInRegArgOps(f *Func) {
pri := f.ABISelf.ABIAnalyzeFuncType(f.Type.FuncType())
/ When manufacturing new slots that correspond to splits of
/ composite parameters, we want to avoid creating a new sub-slot
/ that differs from some existing sub-slot only by type, since
/ the debug location analysis will treat that slot as a separate
/ entity. To achieve this, create a lookup table of existing
/ slots that is type-insenstitive.
sc := newSlotCanonicalizer()
for _, sl := range f.Names {
sc.lookup(*sl)
}
/ Add slot -> value entry to f.NamedValues if not already present.
addToNV := func(v *Value, sl LocalSlot) {
values, ok := f.NamedValues[sl]
if !ok {
/ Haven't seen this slot yet.
sla := f.localSlotAddr(sl)
f.Names = append(f.Names, sla)
} else {
for _, ev := range values {
if v == ev {
return
}
}
}
values = append(values, v)
f.NamedValues[sl] = values
}
newValues := []*Value{}
abiRegIndexToRegister := func(reg abi.RegIndex) int8 {
i := f.ABISelf.FloatIndexFor(reg)
if i >= 0 { / float PR
return f.Config.floatParamRegs[i]
} else {
return f.Config.intParamRegs[reg]
}
}
/ Helper to construct a new OpArg{Float,Int}Reg op value.
var pos src.XPos
if len(f.Entry.Values) != 0 {
pos = f.Entry.Values[0].Pos
}
synthesizeOpIntFloatArg := func(n *ir.Name, t *types.Type, reg abi.RegIndex, sl LocalSlot) *Value {
aux := &AuxNameOffset{n, sl.Off}
op, auxInt := ArgOpAndRegisterFor(reg, f.ABISelf)
v := f.newValueNoBlock(op, t, pos)
v.AuxInt = auxInt
v.Aux = aux
v.Args = nil
v.Block = f.Entry
newValues = append(newValues, v)
addToNV(v, sl)
f.setHome(v, &f.Config.registers[abiRegIndexToRegister(reg)])
return v
}
/ Make a pass through the entry block looking for
/ OpArg{Int,Float}Reg ops. Record the slots they use in a table
/ ("sc"). We use a type-insensitive lookup for the slot table,
/ since the type we get from the ABI analyzer won't always match
/ what the compiler uses when creating OpArg{Int,Float}Reg ops.
for _, v := range f.Entry.Values {
if v.Op == OpArgIntReg || v.Op == OpArgFloatReg {
aux := v.Aux.(*AuxNameOffset)
sl := LocalSlot{N: aux.Name, Type: v.Type, Off: aux.Offset}
/ install slot in lookup table
idx, _ := sc.lookup(sl)
/ add to f.NamedValues if not already present
addToNV(v, sc.canonSlot(idx))
} else if v.Op.IsCall() {
/ if we hit a call, we've gone too far.
break
}
}
/ Now make a pass through the ABI in-params, looking for params
/ or pieces of params that we didn't encounter in the loop above.
for _, inp := range pri.InParams() {
if !isNamedRegParam(inp) {
continue
}
n := inp.Name.(*ir.Name)
/ Param is spread across one or more registers. Walk through
/ each piece to see whether we've seen an arg reg op for it.
types, offsets := inp.RegisterTypesAndOffsets()
for k, t := range types {
/ Note: this recipe for creating a LocalSlot is designed
/ to be compatible with the one used in expand_calls.go
/ as opposed to decompose.go. The expand calls code just
/ takes the base name and creates an offset into it,
/ without using the SplitOf/SplitOffset fields. The code
/ in decompose.go does the opposite -- it creates a
/ LocalSlot object with "Off" set to zero, but with
/ SplitOf pointing to a parent slot, and SplitOffset
/ holding the offset into the parent object.
pieceSlot := LocalSlot{N: n, Type: t, Off: offsets[k]}
/ Look up this piece to see if we've seen a reg op
/ for it. If not, create one.
_, found := sc.lookup(pieceSlot)
if !found {
/ This slot doesn't appear in the map, meaning it
/ corresponds to an in-param that is not live, or
/ a portion of an in-param that is not live/used.
/ Add a new dummy OpArg{Int,Float}Reg for it.
synthesizeOpIntFloatArg(n, t, inp.Registers[k],
pieceSlot)
}
}
}
/ Insert the new values into the head of the block.
f.Entry.Values = append(newValues, f.Entry.Values...)
}
/ BuildFuncDebug debug information for f, placing the results
/ in "rval". f must be fully processed, so that each Value is where it
/ will be when machine code is emitted.
func BuildFuncDebug(ctxt *obj.Link, f *Func, loggingLevel int, stackOffset func(LocalSlot) int32, rval *FuncDebug) {
if f.RegAlloc == nil {
f.Fatalf("BuildFuncDebug on func %v that has not been fully processed", f)
}
state := &f.Cache.debugState
state.loggingLevel = loggingLevel % 1000
/ A specific number demands exactly that many iterations. Under
/ particular circumstances it make require more than the total of
/ 2 passes implied by a single run through liveness and a single
/ run through location list generation.
state.convergeCount = loggingLevel / 1000
state.f = f
state.registers = f.Config.registers
state.stackOffset = stackOffset
state.ctxt = ctxt
if buildcfg.Experiment.RegabiArgs {
PopulateABIInRegArgOps(f)
}
if state.loggingLevel > 0 {
state.logf("Generating location lists for function %q\n", f.Name)
}
if state.varParts == nil {
state.varParts = make(map[*ir.Name][]SlotID)
} else {
for n := range state.varParts {
delete(state.varParts, n)
}
}
/ Recompose any decomposed variables, and establish the canonical
/ IDs for each var and slot by filling out state.vars and state.slots.
state.slots = state.slots[:0]
state.vars = state.vars[:0]
for i, slot := range f.Names {
state.slots = append(state.slots, *slot)
if ir.IsSynthetic(slot.N) {
continue
}
topSlot := slot
for topSlot.SplitOf != nil {
topSlot = topSlot.SplitOf
}
if _, ok := state.varParts[topSlot.N]; !ok {
state.vars = append(state.vars, topSlot.N)
}
state.varParts[topSlot.N] = append(state.varParts[topSlot.N], SlotID(i))
}
/ Recreate the LocalSlot for each stack-only variable.
/ This would probably be better as an output from stackframe.
for _, b := range f.Blocks {
for _, v := range b.Values {
if v.Op == OpVarDef || v.Op == OpVarKill {
n := v.Aux.(*ir.Name)
if ir.IsSynthetic(n) {
continue
}
if _, ok := state.varParts[n]; !ok {
slot := LocalSlot{N: n, Type: v.Type, Off: 0}
state.slots = append(state.slots, slot)
state.varParts[n] = []SlotID{SlotID(len(state.slots) - 1)}
state.vars = append(state.vars, n)
}
}
}
}
/ Fill in the var<->slot mappings.
if cap(state.varSlots) < len(state.vars) {
state.varSlots = make([][]SlotID, len(state.vars))
} else {
state.varSlots = state.varSlots[:len(state.vars)]
for i := range state.varSlots {
state.varSlots[i] = state.varSlots[i][:0]
}
}
if cap(state.slotVars) < len(state.slots) {
state.slotVars = make([]VarID, len(state.slots))
} else {
state.slotVars = state.slotVars[:len(state.slots)]
}
if state.partsByVarOffset == nil {
state.partsByVarOffset = &partsByVarOffset{}
}
for varID, n := range state.vars {
parts := state.varParts[n]
state.varSlots[varID] = parts
for _, slotID := range parts {
state.slotVars[slotID] = VarID(varID)
}
*state.partsByVarOffset.(*partsByVarOffset) = partsByVarOffset{parts, state.slots}
sort.Sort(state.partsByVarOffset)
}
state.initializeCache(f, len(state.varParts), len(state.slots))
for i, slot := range f.Names {
if ir.IsSynthetic(slot.N) {
continue
}
for _, value := range f.NamedValues[*slot] {
state.valueNames[value.ID] = append(state.valueNames[value.ID], SlotID(i))
}
}
blockLocs := state.liveness()
state.buildLocationLists(blockLocs)
/ Populate "rval" with what we've computed.
rval.Slots = state.slots
rval.VarSlots = state.varSlots
rval.Vars = state.vars
rval.LocationLists = state.lists
}
/ liveness walks the function in control flow order, calculating the start
/ and end state of each block.
func (state *debugState) liveness() []*BlockDebug {
blockLocs := make([]*BlockDebug, state.f.NumBlocks())
counterTime := int32(1)
/ Reverse postorder: visit a block after as many as possible of its
/ predecessors have been visited.
po := state.f.Postorder()
converged := false
/ The iteration rule is that by default, run until converged, but
/ if a particular iteration count is specified, run that many
/ iterations, no more, no less. A count is specified as the
/ thousands digit of the location lists debug flag,
/ e.g. -d=locationlists=4000
keepGoing := func(k int) bool {
if state.convergeCount == 0 {
return !converged
}
return k < state.convergeCount
}
for k := 0; keepGoing(k); k++ {
if state.loggingLevel > 0 {
state.logf("Liveness pass %d\n", k)
}
converged = true
for i := len(po) - 1; i >= 0; i-- {
b := po[i]
locs := blockLocs[b.ID]
if locs == nil {
locs = state.allocBlock(b)
blockLocs[b.ID] = locs
}
/ Build the starting state for the block from the final
/ state of its predecessors.
startState, blockChanged := state.mergePredecessors(b, blockLocs, nil, false)
locs.lastCheckedTime = counterTime
counterTime++
if state.loggingLevel > 1 {
state.logf("Processing %v, block changed %v, initial state:\n%v", b, blockChanged, state.stateString(state.currentState))
}
if blockChanged {
/ If the start did not change, then the old endState is good
converged = false
changed := false
state.changedSlots.clear()
/ Update locs/registers with the effects of each Value.
for _, v := range b.Values {
slots := state.valueNames[v.ID]
/ Loads and stores inherit the names of their sources.
var source *Value
switch v.Op {
case OpStoreReg:
source = v.Args[0]
case OpLoadReg:
switch a := v.Args[0]; a.Op {
case OpArg, OpPhi:
source = a
case OpStoreReg:
source = a.Args[0]
default:
if state.loggingLevel > 1 {
state.logf("at %v: load with unexpected source op: %v (%v)\n", v, a.Op, a)
}
}
}
/ Update valueNames with the source so that later steps
/ don't need special handling.
if source != nil && k == 0 {
/ limit to k == 0 otherwise there are duplicates.
slots = append(slots, state.valueNames[source.ID]...)
state.valueNames[v.ID] = slots
}
reg, _ := state.f.getHome(v.ID).(*Register)
c := state.processValue(v, slots, reg)
changed = changed || c
}
if state.loggingLevel > 1 {
state.logf("Block %v done, locs:\n%v", b, state.stateString(state.currentState))
}
locs.relevant = locs.relevant || changed
if !changed {
locs.endState = startState
} else {
for _, id := range state.changedSlots.contents() {
slotID := SlotID(id)
slotLoc := state.currentState.slots[slotID]
if slotLoc.absent() {
startState.Delete(int32(slotID))
continue
}
old := startState.Find(int32(slotID)) / do NOT replace existing values
if oldLS, ok := old.(*liveSlot); !ok || oldLS.VarLoc != slotLoc {
startState.Insert(int32(slotID),
&liveSlot{VarLoc: slotLoc})
}
}
locs.endState = startState
}
locs.lastChangedTime = counterTime
}
counterTime++
}
}
return blockLocs
}
/ mergePredecessors takes the end state of each of b's predecessors and
/ intersects them to form the starting state for b. It puts that state
/ in blockLocs[b.ID].startState, and fills state.currentState with it.
/ It returns the start state and whether this is changed from the
/ previously approximated value of startState for this block. After
/ the first call, subsequent calls can only shrink startState.
/
/ Passing forLocationLists=true enables additional side-effects that
/ are necessary for building location lists but superflous while still
/ iterating to an answer.
/
/ If previousBlock is non-nil, it registers changes vs. that block's
/ end state in state.changedVars. Note that previousBlock will often
/ not be a predecessor.
/
/ Note that mergePredecessors behaves slightly differently between
/ first and subsequent calls for a block. For the first call, the
/ starting state is approximated by taking the state from the
/ predecessor whose state is smallest, and removing any elements not
/ in all the other predecessors; this makes the smallest number of
/ changes and shares the most state. On subsequent calls the old
/ value of startState is adjusted with new information; this is judged
/ to do the least amount of extra work.
/
/ To improve performance, each block's state information is marked with
/ lastChanged and lastChecked "times" so unchanged predecessors can be
/ skipped on after-the-first iterations. Doing this allows extra
/ iterations by the caller to be almost free.
/
/ It is important to know that the set representation used for
/ startState, endState, and merges can share data for two sets where
/ one is a small delta from the other. Doing this does require a
/ little care in how sets are updated, both in mergePredecessors, and
/ using its result.
func (state *debugState) mergePredecessors(b *Block, blockLocs []*BlockDebug, previousBlock *Block, forLocationLists bool) (abt.T, bool) {
/ Filter out back branches.
var predsBuf [10]*Block
preds := predsBuf[:0]
locs := blockLocs[b.ID]
blockChanged := !locs.everProcessed / the first time it always changes.
updating := locs.everProcessed
/ For the first merge, exclude predecessors that have not been seen yet.
/ I.e., backedges.
for _, pred := range b.Preds {
if bl := blockLocs[pred.b.ID]; bl != nil && bl.everProcessed {
/ crucially, a self-edge has bl != nil, but bl.everProcessed is false the first time.
preds = append(preds, pred.b)
}
}
locs.everProcessed = true
if state.loggingLevel > 1 {
/ The logf below would cause preds to be heap-allocated if
/ it were passed directly.
preds2 := make([]*Block, len(preds))
copy(preds2, preds)
state.logf("Merging %v into %v (changed=%d, checked=%d)\n", preds2, b, locs.lastChangedTime, locs.lastCheckedTime)
}
state.changedVars.clear()
markChangedVars := func(slots, merged abt.T) {
if !forLocationLists {
return
}
/ Fill changedVars with those that differ between the previous
/ block (in the emit order, not necessarily a flow predecessor)
/ and the start state for this block.
for it := slots.Iterator(); !it.Done(); {
k, v := it.Next()
m := merged.Find(k)
if m == nil || v.(*liveSlot).VarLoc != m.(*liveSlot).VarLoc {
state.changedVars.add(ID(state.slotVars[k]))
}
}
}
reset := func(ourStartState abt.T) {
if !(forLocationLists || blockChanged) {
/ there is no change and this is not for location lists, do
/ not bother to reset currentState because it will not be
/ examined.
return
}
state.currentState.reset(ourStartState)
}
/ Zero predecessors
if len(preds) == 0 {
if previousBlock != nil {
state.f.Fatalf("Function %v, block %s with no predecessors is not first block, has previous %s", state.f, b.String(), previousBlock.String())
}
/ startState is empty
reset(abt.T{})
return abt.T{}, blockChanged
}
/ One predecessor
l0 := blockLocs[preds[0].ID]
p0 := l0.endState
if len(preds) == 1 {
if previousBlock != nil && preds[0].ID != previousBlock.ID {
/ Change from previous block is its endState minus the predecessor's endState
markChangedVars(blockLocs[previousBlock.ID].endState, p0)
}
locs.startState = p0
blockChanged = blockChanged || l0.lastChangedTime > locs.lastCheckedTime
reset(p0)
return p0, blockChanged
}
/ More than one predecessor
if updating {
/ After the first approximation, i.e., when updating, results
/ can only get smaller, because initially backedge
/ predecessors do not participate in the intersection. This
/ means that for the update, given the prior approximation of
/ startState, there is no need to re-intersect with unchanged
/ blocks. Therefore remove unchanged blocks from the
/ predecessor list.
for i := len(preds) - 1; i >= 0; i-- {
pred := preds[i]
if blockLocs[pred.ID].lastChangedTime > locs.lastCheckedTime {
continue / keep this predecessor
}
preds[i] = preds[len(preds)-1]
preds = preds[:len(preds)-1]
if state.loggingLevel > 2 {
state.logf("Pruned b%d, lastChanged was %d but b%d lastChecked is %d\n", pred.ID, blockLocs[pred.ID].lastChangedTime, b.ID, locs.lastCheckedTime)
}
}
/ Check for an early out; this should always hit for the update
/ if there are no cycles.
if len(preds) == 0 {
blockChanged = false
reset(locs.startState)
if state.loggingLevel > 2 {
state.logf("Early out, no predecessors changed since last check\n")
}
if previousBlock != nil {
markChangedVars(blockLocs[previousBlock.ID].endState, locs.startState)
}
return locs.startState, blockChanged
}
}
baseID := preds[0].ID
baseState := p0
/ Choose the predecessor with the smallest endState for intersection work
for _, pred := range preds[1:] {
if blockLocs[pred.ID].endState.Size() < baseState.Size() {
baseState = blockLocs[pred.ID].endState
baseID = pred.ID
}
}
if state.loggingLevel > 2 {
state.logf("Starting %v with state from b%v:\n%v", b, baseID, state.blockEndStateString(blockLocs[baseID]))
for _, pred := range preds {
if pred.ID == baseID {
continue
}
state.logf("Merging in state from %v:\n%v", pred, state.blockEndStateString(blockLocs[pred.ID]))
}
}
state.currentState.reset(abt.T{})
/ The normal logic of "reset" is incuded in the intersection loop below.
slotLocs := state.currentState.slots
/ If this is the first call, do updates on the "baseState"; if this
/ is a subsequent call, tweak the startState instead. Note that
/ these "set" values are values; there are no side effects to
/ other values as these are modified.
newState := baseState
if updating {
newState = blockLocs[b.ID].startState
}
for it := newState.Iterator(); !it.Done(); {
k, d := it.Next()
thisSlot := d.(*liveSlot)
x := thisSlot.VarLoc
x0 := x / initial value in newState
/ Intersect this slot with the slot in all the predecessors
for _, other := range preds {
if !updating && other.ID == baseID {
continue
}
otherSlot := blockLocs[other.ID].endState.Find(k)
if otherSlot == nil {
x = VarLoc{}
break
}
y := otherSlot.(*liveSlot).VarLoc
x = x.intersect(y)
if x.absent() {
x = VarLoc{}
break
}
}
/ Delete if necessary, but not otherwise (in order to maximize sharing).
if x.absent() {
if !x0.absent() {
blockChanged = true
newState.Delete(k)
}
slotLocs[k] = VarLoc{}
continue
}
if x != x0 {
blockChanged = true
newState.Insert(k, &liveSlot{VarLoc: x})
}
slotLocs[k] = x
mask := uint64(x.Registers)
for {
if mask == 0 {
break
}
reg := uint8(bits.TrailingZeros64(mask))
mask &^= 1 << reg
state.currentState.registers[reg] = append(state.currentState.registers[reg], SlotID(k))
}
}
if previousBlock != nil {
markChangedVars(blockLocs[previousBlock.ID].endState, newState)
}
locs.startState = newState
return newState, blockChanged
}
/ processValue updates locs and state.registerContents to reflect v, a
/ value with the names in vSlots and homed in vReg. "v" becomes
/ visible after execution of the instructions evaluating it. It
/ returns which VarIDs were modified by the Value's execution.
func (state *debugState) processValue(v *Value, vSlots []SlotID, vReg *Register) bool {
locs := state.currentState
changed := false
setSlot := func(slot SlotID, loc VarLoc) {
changed = true
state.changedVars.add(ID(state.slotVars[slot]))
state.changedSlots.add(ID(slot))
state.currentState.slots[slot] = loc
}
/ Handle any register clobbering. Call operations, for example,
/ clobber all registers even though they don't explicitly write to
/ them.
clobbers := uint64(opcodeTable[v.Op].reg.clobbers)
for {
if clobbers == 0 {
break
}
reg := uint8(bits.TrailingZeros64(clobbers))
clobbers &^= 1 << reg
for _, slot := range locs.registers[reg] {
if state.loggingLevel > 1 {
state.logf("at %v: %v clobbered out of %v\n", v, state.slots[slot], &state.registers[reg])
}
last := locs.slots[slot]
if last.absent() {
state.f.Fatalf("at %v: slot %v in register %v with no location entry", v, state.slots[slot], &state.registers[reg])
continue
}
regs := last.Registers &^ (1 << reg)
setSlot(slot, VarLoc{regs, last.StackOffset})
}
locs.registers[reg] = locs.registers[reg][:0]
}
switch {
case v.Op == OpVarDef, v.Op == OpVarKill:
n := v.Aux.(*ir.Name)
if ir.IsSynthetic(n) {
break
}
slotID := state.varParts[n][0]
var stackOffset StackOffset
if v.Op == OpVarDef {
stackOffset = StackOffset(state.stackOffset(state.slots[slotID])<<1 | 1)
}
setSlot(slotID, VarLoc{0, stackOffset})
if state.loggingLevel > 1 {
if v.Op == OpVarDef {
state.logf("at %v: stack-only var %v now live\n", v, state.slots[slotID])
} else {
state.logf("at %v: stack-only var %v now dead\n", v, state.slots[slotID])
}
}
case v.Op == OpArg:
home := state.f.getHome(v.ID).(LocalSlot)
stackOffset := state.stackOffset(home)<<1 | 1
for _, slot := range vSlots {
if state.loggingLevel > 1 {
state.logf("at %v: arg %v now on stack in location %v\n", v, state.slots[slot], home)
if last := locs.slots[slot]; !last.absent() {
state.logf("at %v: unexpected arg op on already-live slot %v\n", v, state.slots[slot])
}
}
setSlot(slot, VarLoc{0, StackOffset(stackOffset)})
}
case v.Op == OpStoreReg:
home := state.f.getHome(v.ID).(LocalSlot)
stackOffset := state.stackOffset(home)<<1 | 1
for _, slot := range vSlots {
last := locs.slots[slot]
if last.absent() {
if state.loggingLevel > 1 {
state.logf("at %v: unexpected spill of unnamed register %s\n", v, vReg)
}
break
}
setSlot(slot, VarLoc{last.Registers, StackOffset(stackOffset)})
if state.loggingLevel > 1 {
state.logf("at %v: %v spilled to stack location %v@%d\n", v, state.slots[slot], home, state.stackOffset(home))
}
}
case vReg != nil:
if state.loggingLevel > 1 {
newSlots := make([]bool, len(state.slots))
for _, slot := range vSlots {
newSlots[slot] = true
}
for _, slot := range locs.registers[vReg.num] {
if !newSlots[slot] {
state.logf("at %v: overwrote %v in register %v\n", v, state.slots[slot], vReg)
}
}
}
for _, slot := range locs.registers[vReg.num] {
last := locs.slots[slot]
setSlot(slot, VarLoc{last.Registers &^ (1 << uint8(vReg.num)), last.StackOffset})
}
locs.registers[vReg.num] = locs.registers[vReg.num][:0]
locs.registers[vReg.num] = append(locs.registers[vReg.num], vSlots...)
for _, slot := range vSlots {
if state.loggingLevel > 1 {
state.logf("at %v: %v now in %s\n", v, state.slots[slot], vReg)
}
last := locs.slots[slot]
setSlot(slot, VarLoc{1<<uint8(vReg.num) | last.Registers, last.StackOffset})
}
}
return changed
}
/ varOffset returns the offset of slot within the user variable it was
/ decomposed from. This has nothing to do with its stack offset.
func varOffset(slot LocalSlot) int64 {
offset := slot.Off
s := &slot
for ; s.SplitOf != nil; s = s.SplitOf {
offset += s.SplitOffset
}
return offset
}
type partsByVarOffset struct {
slotIDs []SlotID
slots []LocalSlot
}
func (a partsByVarOffset) Len() int { return len(a.slotIDs) }
func (a partsByVarOffset) Less(i, j int) bool {
return varOffset(a.slots[a.slotIDs[i]]) < varOffset(a.slots[a.slotIDs[j]])
}
func (a partsByVarOffset) Swap(i, j int) { a.slotIDs[i], a.slotIDs[j] = a.slotIDs[j], a.slotIDs[i] }
/ A pendingEntry represents the beginning of a location list entry, missing
/ only its end coordinate.
type pendingEntry struct {
present bool
startBlock, startValue ID
/ The location of each piece of the variable, in the same order as the
/ SlotIDs in varParts.
pieces []VarLoc
}
func (e *pendingEntry) clear() {
e.present = false
e.startBlock = 0
e.startValue = 0
for i := range e.pieces {
e.pieces[i] = VarLoc{}
}
}
/ canMerge reports whether a new location description is a superset
/ of the (non-empty) pending location description, if so, the two
/ can be merged (i.e., pending is still a valid and useful location
/ description).
func canMerge(pending, new VarLoc) bool {
if pending.absent() && new.absent() {
return true
}
if pending.absent() || new.absent() {
return false
}
/ pending is not absent, therefore it has either a stack mapping,
/ or registers, or both.
if pending.onStack() && pending.StackOffset != new.StackOffset {
/ if pending has a stack offset, then new must also, and it
/ must be the same (StackOffset encodes onStack).
return false
}
if pending.Registers&new.Registers != pending.Registers {
/ There is at least one register in pending not mentioned in new.
return false
}
return true
}
/ firstReg returns the first register in set that is present.
func firstReg(set RegisterSet) uint8 {
if set == 0 {
/ This is wrong, but there seem to be some situations where we
/ produce locations with no storage.
return 0
}
return uint8(bits.TrailingZeros64(uint64(set)))
}
/ buildLocationLists builds location lists for all the user variables
/ in state.f, using the information about block state in blockLocs.
/ The returned location lists are not fully complete. They are in
/ terms of SSA values rather than PCs, and have no base address/end
/ entries. They will be finished by PutLocationList.
func (state *debugState) buildLocationLists(blockLocs []*BlockDebug) {
/ Run through the function in program text order, building up location
/ lists as we go. The heavy lifting has mostly already been done.
var prevBlock *Block
for _, b := range state.f.Blocks {
state.mergePredecessors(b, blockLocs, prevBlock, true)
/ Handle any differences among predecessor blocks and previous block (perhaps not a predecessor)
for _, varID := range state.changedVars.contents() {
state.updateVar(VarID(varID), b, BlockStart)
}
state.changedVars.clear()
if !blockLocs[b.ID].relevant {
continue
}
mustBeFirst := func(v *Value) bool {
return v.Op == OpPhi || v.Op.isLoweredGetClosurePtr() ||
v.Op == OpArgIntReg || v.Op == OpArgFloatReg
}
blockPrologComplete := func(v *Value) bool {
if b.ID != state.f.Entry.ID {
return !opcodeTable[v.Op].zeroWidth
} else {
return v.Op == OpInitMem
}
}
/ Examine the prolog portion of the block to process special
/ zero-width ops such as Arg, Phi, LoweredGetClosurePtr (etc)
/ whose lifetimes begin at the block starting point. In an
/ entry block, allow for the possibility that we may see Arg
/ ops that appear _after_ other non-zero-width operations.
/ Example:
/
/ v33 = ArgIntReg <uintptr> {foo+0} [0] : AX (foo)
/ v34 = ArgIntReg <uintptr> {bar+0} [0] : BX (bar)
/ ...
/ v77 = StoreReg <unsafe.Pointer> v67 : ctx+8[unsafe.Pointer]
/ v78 = StoreReg <unsafe.Pointer> v68 : ctx[unsafe.Pointer]
/ v79 = Arg <*uint8> {args} : args[*uint8] (args[*uint8])
/ v80 = Arg <int> {args} [8] : args+8[int] (args+8[int])
/ ...
/ v1 = InitMem <mem>
/
/ We can stop scanning the initial portion of the block when
/ we either see the InitMem op (for entry blocks) or the
/ first non-zero-width op (for other blocks).
for idx := 0; idx < len(b.Values); idx++ {
v := b.Values[idx]
if blockPrologComplete(v) {
break
}
/ Consider only "lifetime begins at block start" ops.
if !mustBeFirst(v) && v.Op != OpArg {
continue
}
slots := state.valueNames[v.ID]
reg, _ := state.f.getHome(v.ID).(*Register)
changed := state.processValue(v, slots, reg) / changed == added to state.changedVars
if changed {
for _, varID := range state.changedVars.contents() {
state.updateVar(VarID(varID), v.Block, BlockStart)
}
state.changedVars.clear()
}
}
/ Now examine the block again, handling things other than the
/ "begins at block start" lifetimes.
zeroWidthPending := false
prologComplete := false
/ expect to see values in pattern (apc)* (zerowidth|real)*
for _, v := range b.Values {
if blockPrologComplete(v) {
prologComplete = true
}
slots := state.valueNames[v.ID]
reg, _ := state.f.getHome(v.ID).(*Register)
changed := state.processValue(v, slots, reg) / changed == added to state.changedVars
if opcodeTable[v.Op].zeroWidth {
if prologComplete && mustBeFirst(v) {
panic(fmt.Errorf("Unexpected placement of op '%s' appearing after non-pseudo-op at beginning of block %s in %s\n%s", v.LongString(), b, b.Func.Name, b.Func))
}
if changed {
if mustBeFirst(v) || v.Op == OpArg {
/ already taken care of above
continue
}
zeroWidthPending = true
}
continue
}
if !changed && !zeroWidthPending {
continue
}
/ Not zero-width; i.e., a "real" instruction.
zeroWidthPending = false
for _, varID := range state.changedVars.contents() {
state.updateVar(VarID(varID), v.Block, v)
}
state.changedVars.clear()
}
for _, varID := range state.changedVars.contents() {
state.updateVar(VarID(varID), b, BlockEnd)
}
prevBlock = b
}
if state.loggingLevel > 0 {
state.logf("location lists:\n")
}
/ Flush any leftover entries live at the end of the last block.
for varID := range state.lists {
state.writePendingEntry(VarID(varID), state.f.Blocks[len(state.f.Blocks)-1].ID, FuncEnd.ID)
list := state.lists[varID]
if state.loggingLevel > 0 {
if len(list) == 0 {
state.logf("\t%v : empty list\n", state.vars[varID])
} else {
state.logf("\t%v : %q\n", state.vars[varID], hex.EncodeToString(state.lists[varID]))
}
}
}
}
/ updateVar updates the pending location list entry for varID to
/ reflect the new locations in curLoc, beginning at v in block b.
/ v may be one of the special values indicating block start or end.
func (state *debugState) updateVar(varID VarID, b *Block, v *Value) {
curLoc := state.currentState.slots
/ Assemble the location list entry with whatever's live.
empty := true
for _, slotID := range state.varSlots[varID] {
if !curLoc[slotID].absent() {
empty = false
break
}
}
pending := &state.pendingEntries[varID]
if empty {
state.writePendingEntry(varID, b.ID, v.ID)
pending.clear()
return
}
/ Extend the previous entry if possible.
if pending.present {
merge := true
for i, slotID := range state.varSlots[varID] {
if !canMerge(pending.pieces[i], curLoc[slotID]) {
merge = false
break
}
}
if merge {
return
}
}
state.writePendingEntry(varID, b.ID, v.ID)
pending.present = true
pending.startBlock = b.ID
pending.startValue = v.ID
for i, slot := range state.varSlots[varID] {
pending.pieces[i] = curLoc[slot]
}
}
/ writePendingEntry writes out the pending entry for varID, if any,
/ terminated at endBlock/Value.
func (state *debugState) writePendingEntry(varID VarID, endBlock, endValue ID) {
pending := state.pendingEntries[varID]
if !pending.present {
return
}
/ Pack the start/end coordinates into the start/end addresses
/ of the entry, for decoding by PutLocationList.
start, startOK := encodeValue(state.ctxt, pending.startBlock, pending.startValue)
end, endOK := encodeValue(state.ctxt, endBlock, endValue)
if !startOK || !endOK {
/ If someone writes a function that uses >65K values,
/ they get incomplete debug info on 32-bit platforms.
return
}
if start == end {
if state.loggingLevel > 1 {
/ Printf not logf so not gated by GOSSAFUNC; this should fire very rarely.
/ TODO this fires a lot, need to figure out why.
state.logf("Skipping empty location list for %v in %s\n", state.vars[varID], state.f.Name)
}
return
}
list := state.lists[varID]
list = appendPtr(state.ctxt, list, start)
list = appendPtr(state.ctxt, list, end)
/ Where to write the length of the location description once
/ we know how big it is.
sizeIdx := len(list)
list = list[:len(list)+2]
if state.loggingLevel > 1 {
var partStrs []string
for i, slot := range state.varSlots[varID] {
partStrs = append(partStrs, fmt.Sprintf("%v@%v", state.slots[slot], state.LocString(pending.pieces[i])))
}
state.logf("Add entry for %v: \tb%vv%v-b%vv%v = \t%v\n", state.vars[varID], pending.startBlock, pending.startValue, endBlock, endValue, strings.Join(partStrs, " "))
}
for i, slotID := range state.varSlots[varID] {
loc := pending.pieces[i]
slot := state.slots[slotID]
if !loc.absent() {
if loc.onStack() {
if loc.stackOffsetValue() == 0 {
list = append(list, dwarf.DW_OP_call_frame_cfa)
} else {
list = append(list, dwarf.DW_OP_fbreg)
list = dwarf.AppendSleb128(list, int64(loc.stackOffsetValue()))
}
} else {
regnum := state.ctxt.Arch.DWARFRegisters[state.registers[firstReg(loc.Registers)].ObjNum()]
if regnum < 32 {
list = append(list, dwarf.DW_OP_reg0+byte(regnum))
} else {
list = append(list, dwarf.DW_OP_regx)
list = dwarf.AppendUleb128(list, uint64(regnum))
}
}
}
if len(state.varSlots[varID]) > 1 {
list = append(list, dwarf.DW_OP_piece)
list = dwarf.AppendUleb128(list, uint64(slot.Type.Size()))
}
}
state.ctxt.Arch.ByteOrder.PutUint16(list[sizeIdx:], uint16(len(list)-sizeIdx-2))
state.lists[varID] = list
}
/ PutLocationList adds list (a location list in its intermediate representation) to listSym.
func (debugInfo *FuncDebug) PutLocationList(list []byte, ctxt *obj.Link, listSym, startPC *obj.LSym) {
getPC := debugInfo.GetPC
if ctxt.UseBASEntries {
listSym.WriteInt(ctxt, listSym.Size, ctxt.Arch.PtrSize, ^0)
listSym.WriteAddr(ctxt, listSym.Size, ctxt.Arch.PtrSize, startPC, 0)
}
/ Re-read list, translating its address from block/value ID to PC.
for i := 0; i < len(list); {
begin := getPC(decodeValue(ctxt, readPtr(ctxt, list[i:])))
end := getPC(decodeValue(ctxt, readPtr(ctxt, list[i+ctxt.Arch.PtrSize:])))
/ Horrible hack. If a range contains only zero-width
/ instructions, e.g. an Arg, and it's at the beginning of the
/ function, this would be indistinguishable from an
/ end entry. Fudge it.
if begin == 0 && end == 0 {
end = 1
}
if ctxt.UseBASEntries {
listSym.WriteInt(ctxt, listSym.Size, ctxt.Arch.PtrSize, int64(begin))
listSym.WriteInt(ctxt, listSym.Size, ctxt.Arch.PtrSize, int64(end))
} else {
listSym.WriteCURelativeAddr(ctxt, listSym.Size, startPC, int64(begin))
listSym.WriteCURelativeAddr(ctxt, listSym.Size, startPC, int64(end))
}
i += 2 * ctxt.Arch.PtrSize
datalen := 2 + int(ctxt.Arch.ByteOrder.Uint16(list[i:]))
listSym.WriteBytes(ctxt, listSym.Size, list[i:i+datalen]) / copy datalen and location encoding
i += datalen
}
/ Location list contents, now with real PCs.
/ End entry.
listSym.WriteInt(ctxt, listSym.Size, ctxt.Arch.PtrSize, 0)
listSym.WriteInt(ctxt, listSym.Size, ctxt.Arch.PtrSize, 0)
}
/ Pack a value and block ID into an address-sized uint, returning
/ encoded value and boolean indicating whether the encoding succeeded.
/ For 32-bit architectures the process may fail for very large
/ procedures(the theory being that it's ok to have degraded debug
/ quality in this case).
func encodeValue(ctxt *obj.Link, b, v ID) (uint64, bool) {
if ctxt.Arch.PtrSize == 8 {
result := uint64(b)<<32 | uint64(uint32(v))
/ctxt.Logf("b %#x (%d) v %#x (%d) -> %#x\n", b, b, v, v, result)
return result, true
}
if ctxt.Arch.PtrSize != 4 {
panic("unexpected pointer size")
}
if ID(int16(b)) != b || ID(int16(v)) != v {
return 0, false
}
return uint64(b)<<16 | uint64(uint16(v)), true
}
/ Unpack a value and block ID encoded by encodeValue.
func decodeValue(ctxt *obj.Link, word uint64) (ID, ID) {
if ctxt.Arch.PtrSize == 8 {
b, v := ID(word>>32), ID(word)
/ctxt.Logf("%#x -> b %#x (%d) v %#x (%d)\n", word, b, b, v, v)
return b, v
}
if ctxt.Arch.PtrSize != 4 {
panic("unexpected pointer size")
}
return ID(word >> 16), ID(int16(word))
}
/ Append a pointer-sized uint to buf.
func appendPtr(ctxt *obj.Link, buf []byte, word uint64) []byte {
if cap(buf) < len(buf)+20 {
b := make([]byte, len(buf), 20+cap(buf)*2)
copy(b, buf)
buf = b
}
writeAt := len(buf)
buf = buf[0 : len(buf)+ctxt.Arch.PtrSize]
writePtr(ctxt, buf[writeAt:], word)
return buf
}
/ Write a pointer-sized uint to the beginning of buf.
func writePtr(ctxt *obj.Link, buf []byte, word uint64) {
switch ctxt.Arch.PtrSize {
case 4:
ctxt.Arch.ByteOrder.PutUint32(buf, uint32(word))
case 8:
ctxt.Arch.ByteOrder.PutUint64(buf, word)
default:
panic("unexpected pointer size")
}
}
/ Read a pointer-sized uint from the beginning of buf.
func readPtr(ctxt *obj.Link, buf []byte) uint64 {
switch ctxt.Arch.PtrSize {
case 4:
return uint64(ctxt.Arch.ByteOrder.Uint32(buf))
case 8:
return ctxt.Arch.ByteOrder.Uint64(buf)
default:
panic("unexpected pointer size")
}
}
/ setupLocList creates the initial portion of a location list for a
/ user variable. It emits the encoded start/end of the range and a
/ placeholder for the size. Return value is the new list plus the
/ slot in the list holding the size (to be updated later).
func setupLocList(ctxt *obj.Link, f *Func, list []byte, st, en ID) ([]byte, int) {
start, startOK := encodeValue(ctxt, f.Entry.ID, st)
end, endOK := encodeValue(ctxt, f.Entry.ID, en)
if !startOK || !endOK {
/ This could happen if someone writes a function that uses
/ >65K values on a 32-bit platform. Hopefully a degraded debugging
/ experience is ok in that case.
return nil, 0
}
list = appendPtr(ctxt, list, start)
list = appendPtr(ctxt, list, end)
/ Where to write the length of the location description once
/ we know how big it is.
sizeIdx := len(list)
list = list[:len(list)+2]
return list, sizeIdx
}
/ locatePrologEnd walks the entry block of a function with incoming
/ register arguments and locates the last instruction in the prolog
/ that spills a register arg. It returns the ID of that instruction
/ Example:
/
/ b1:
/ v3 = ArgIntReg <int> {p1+0} [0] : AX
/ ... more arg regs ..
/ v4 = ArgFloatReg <float32> {f1+0} [0] : X0
/ v52 = MOVQstore <mem> {p1} v2 v3 v1
/ ... more stores ...
/ v68 = MOVSSstore <mem> {f4} v2 v67 v66
/ v38 = MOVQstoreconst <mem> {blob} [val=0,off=0] v2 v32
/
/ Important: locatePrologEnd is expected to work properly only with
/ optimization turned off (e.g. "-N"). If optimization is enabled
/ we can't be assured of finding all input arguments spilled in the
/ entry block prolog.
func locatePrologEnd(f *Func) ID {
/ returns true if this instruction looks like it moves an ABI
/ register to the stack, along with the value being stored.
isRegMoveLike := func(v *Value) (bool, ID) {
n, ok := v.Aux.(*ir.Name)
var r ID
if !ok || n.Class != ir.PPARAM {
return false, r
}
regInputs, memInputs, spInputs := 0, 0, 0
for _, a := range v.Args {
if a.Op == OpArgIntReg || a.Op == OpArgFloatReg {
regInputs++
r = a.ID
} else if a.Type.IsMemory() {
memInputs++
} else if a.Op == OpSP {
spInputs++
} else {
return false, r
}
}
return v.Type.IsMemory() && memInputs == 1 &&
regInputs == 1 && spInputs == 1, r
}
/ OpArg*Reg values we've seen so far on our forward walk,
/ for which we have not yet seen a corresponding spill.
regArgs := make([]ID, 0, 32)
/ removeReg tries to remove a value from regArgs, returning true
/ if found and removed, or false otherwise.
removeReg := func(r ID) bool {
for i := 0; i < len(regArgs); i++ {
if regArgs[i] == r {
regArgs = append(regArgs[:i], regArgs[i+1:]...)
return true
}
}
return false
}
/ Walk forwards through the block. When we see OpArg*Reg, record
/ the value it produces in the regArgs list. When see a store that uses
/ the value, remove the entry. When we hit the last store (use)
/ then we've arrived at the end of the prolog.
for k, v := range f.Entry.Values {
if v.Op == OpArgIntReg || v.Op == OpArgFloatReg {
regArgs = append(regArgs, v.ID)
continue
}
if ok, r := isRegMoveLike(v); ok {
if removed := removeReg(r); removed {
if len(regArgs) == 0 {
/ Found our last spill; return the value after
/ it. Note that it is possible that this spill is
/ the last instruction in the block. If so, then
/ return the "end of block" sentinel.
if k < len(f.Entry.Values)-1 {
return f.Entry.Values[k+1].ID
}
return BlockEnd.ID
}
}
}
if v.Op.IsCall() {
/ if we hit a call, we've gone too far.
return v.ID
}
}
/ nothing found
return ID(-1)
}
/ isNamedRegParam returns true if the param corresponding to "p"
/ is a named, non-blank input parameter assigned to one or more
/ registers.
func isNamedRegParam(p abi.ABIParamAssignment) bool {
if p.Name == nil {
return false
}
n := p.Name.(*ir.Name)
if n.Sym() == nil || n.Sym().IsBlank() {
return false
}
if len(p.Registers) == 0 {
return false
}
return true
}
/ BuildFuncDebugNoOptimized populates a FuncDebug object "rval" with
/ entries corresponding to the register-resident input parameters for
/ the function "f"; it is used when we are compiling without
/ optimization but the register ABI is enabled. For each reg param,
/ it constructs a 2-element location list: the first element holds
/ the input register, and the second element holds the stack location
/ of the param (the assumption being that when optimization is off,
/ each input param reg will be spilled in the prolog.
func BuildFuncDebugNoOptimized(ctxt *obj.Link, f *Func, loggingEnabled bool, stackOffset func(LocalSlot) int32, rval *FuncDebug) {
pri := f.ABISelf.ABIAnalyzeFuncType(f.Type.FuncType())
/ Look to see if we have any named register-promoted parameters.
/ If there are none, bail early and let the caller sort things
/ out for the remainder of the params/locals.
numRegParams := 0
for _, inp := range pri.InParams() {
if isNamedRegParam(inp) {
numRegParams++
}
}
if numRegParams == 0 {
return
}
state := debugState{f: f}
if loggingEnabled {
state.logf("generating -N reg param loc lists for func %q\n", f.Name)
}
/ Allocate location lists.
rval.LocationLists = make([][]byte, numRegParams)
/ Locate the value corresponding to the last spill of
/ an input register.
afterPrologVal := locatePrologEnd(f)
/ Walk the input params again and process the register-resident elements.
pidx := 0
for _, inp := range pri.InParams() {
if !isNamedRegParam(inp) {
/ will be sorted out elsewhere
continue
}
n := inp.Name.(*ir.Name)
sl := LocalSlot{N: n, Type: inp.Type, Off: 0}
rval.Vars = append(rval.Vars, n)
rval.Slots = append(rval.Slots, sl)
slid := len(rval.VarSlots)
rval.VarSlots = append(rval.VarSlots, []SlotID{SlotID(slid)})
if afterPrologVal == ID(-1) {
/ This can happen for degenerate functions with infinite
/ loops such as that in issue 45948. In such cases, leave
/ the var/slot set up for the param, but don't try to
/ emit a location list.
if loggingEnabled {
state.logf("locatePrologEnd failed, skipping %v\n", n)
}
pidx++
continue
}
/ Param is arriving in one or more registers. We need a 2-element
/ location expression for it. First entry in location list
/ will correspond to lifetime in input registers.
list, sizeIdx := setupLocList(ctxt, f, rval.LocationLists[pidx],
BlockStart.ID, afterPrologVal)
if list == nil {
pidx++
continue
}
if loggingEnabled {
state.logf("param %v:\n [<entry>, %d]:\n", n, afterPrologVal)
}
rtypes, _ := inp.RegisterTypesAndOffsets()
padding := make([]uint64, 0, 32)
padding = inp.ComputePadding(padding)
for k, r := range inp.Registers {
reg := ObjRegForAbiReg(r, f.Config)
dwreg := ctxt.Arch.DWARFRegisters[reg]
if dwreg < 32 {
list = append(list, dwarf.DW_OP_reg0+byte(dwreg))
} else {
list = append(list, dwarf.DW_OP_regx)
list = dwarf.AppendUleb128(list, uint64(dwreg))
}
if loggingEnabled {
state.logf(" piece %d -> dwreg %d", k, dwreg)
}
if len(inp.Registers) > 1 {
list = append(list, dwarf.DW_OP_piece)
ts := rtypes[k].Size()
list = dwarf.AppendUleb128(list, uint64(ts))
if padding[k] > 0 {
if loggingEnabled {
state.logf(" [pad %d bytes]", padding[k])
}
list = append(list, dwarf.DW_OP_piece)
list = dwarf.AppendUleb128(list, padding[k])
}
}
if loggingEnabled {
state.logf("\n")
}
}
/ fill in length of location expression element
ctxt.Arch.ByteOrder.PutUint16(list[sizeIdx:], uint16(len(list)-sizeIdx-2))
/ Second entry in the location list will be the stack home
/ of the param, once it has been spilled. Emit that now.
list, sizeIdx = setupLocList(ctxt, f, list,
afterPrologVal, FuncEnd.ID)
if list == nil {
pidx++
continue
}
soff := stackOffset(sl)
if soff == 0 {
list = append(list, dwarf.DW_OP_call_frame_cfa)
} else {
list = append(list, dwarf.DW_OP_fbreg)
list = dwarf.AppendSleb128(list, int64(soff))
}
if loggingEnabled {
state.logf(" [%d, <end>): stackOffset=%d\n", afterPrologVal, soff)
}
/ fill in size
ctxt.Arch.ByteOrder.PutUint16(list[sizeIdx:], uint16(len(list)-sizeIdx-2))
rval.LocationLists[pidx] = list
pidx++
}
}