blob: 1caccb7c18d3c43ca24ff9814ef7b10d0660826d [file] [log] [blame] [edit]
// Copyright 2016 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/reflectdata"
"cmd/compile/internal/types"
"cmd/internal/obj"
"cmd/internal/objabi"
"cmd/internal/src"
"fmt"
"internal/buildcfg"
)
// A ZeroRegion records parts of an object which are known to be zero.
// A ZeroRegion only applies to a single memory state.
// Each bit in mask is set if the corresponding pointer-sized word of
// the base object is known to be zero.
// In other words, if mask & (1<<i) != 0, then [base+i*ptrSize, base+(i+1)*ptrSize)
// is known to be zero.
type ZeroRegion struct {
base *Value
mask uint64
}
// mightBeHeapPointer reports whether v might point to the heap.
// v must have pointer type.
func mightBeHeapPointer(v *Value) bool {
if IsGlobalAddr(v) {
return false
}
return true
}
// mightContainHeapPointer reports whether the data currently at addresses
// [ptr,ptr+size) might contain heap pointers. "currently" means at memory state mem.
// zeroes contains ZeroRegion data to help make that decision (see computeZeroMap).
func mightContainHeapPointer(ptr *Value, size int64, mem *Value, zeroes map[ID]ZeroRegion) bool {
if IsReadOnlyGlobalAddr(ptr) {
// The read-only globals section cannot contain any heap pointers.
return false
}
// See if we can prove that the queried memory is all zero.
// Find base pointer and offset. Hopefully, the base is the result of a new(T).
var off int64
for ptr.Op == OpOffPtr {
off += ptr.AuxInt
ptr = ptr.Args[0]
}
ptrSize := ptr.Block.Func.Config.PtrSize
if off%ptrSize != 0 {
return true // see issue 61187
}
if size%ptrSize != 0 {
ptr.Fatalf("unaligned pointer write")
}
if off < 0 || off+size > 64*ptrSize {
// memory range goes off end of tracked offsets
return true
}
z := zeroes[mem.ID]
if ptr != z.base {
// This isn't the object we know about at this memory state.
return true
}
// Mask of bits we're asking about
m := (uint64(1)<<(size/ptrSize) - 1) << (off / ptrSize)
if z.mask&m == m {
// All locations are known to be zero, so no heap pointers.
return false
}
return true
}
// needwb reports whether we need write barrier for store op v.
// v must be Store/Move/Zero.
// zeroes provides known zero information (keyed by ID of memory-type values).
func needwb(v *Value, zeroes map[ID]ZeroRegion) bool {
t, ok := v.Aux.(*types.Type)
if !ok {
v.Fatalf("store aux is not a type: %s", v.LongString())
}
if !t.HasPointers() {
return false
}
dst := v.Args[0]
if IsStackAddr(dst) {
return false // writes into the stack don't need write barrier
}
// If we're writing to a place that might have heap pointers, we need
// the write barrier.
if mightContainHeapPointer(dst, t.Size(), v.MemoryArg(), zeroes) {
return true
}
// Lastly, check if the values we're writing might be heap pointers.
// If they aren't, we don't need a write barrier.
switch v.Op {
case OpStore:
if !mightBeHeapPointer(v.Args[1]) {
return false
}
case OpZero:
return false // nil is not a heap pointer
case OpMove:
if !mightContainHeapPointer(v.Args[1], t.Size(), v.Args[2], zeroes) {
return false
}
default:
v.Fatalf("store op unknown: %s", v.LongString())
}
return true
}
// needWBsrc reports whether GC needs to see v when it is the source of a store.
func needWBsrc(v *Value) bool {
return !IsGlobalAddr(v)
}
// needWBdst reports whether GC needs to see what used to be in *ptr when ptr is
// the target of a pointer store.
func needWBdst(ptr, mem *Value, zeroes map[ID]ZeroRegion) bool {
// Detect storing to zeroed memory.
var off int64
for ptr.Op == OpOffPtr {
off += ptr.AuxInt
ptr = ptr.Args[0]
}
ptrSize := ptr.Block.Func.Config.PtrSize
if off%ptrSize != 0 {
return true // see issue 61187
}
if off < 0 || off >= 64*ptrSize {
// write goes off end of tracked offsets
return true
}
z := zeroes[mem.ID]
if ptr != z.base {
return true
}
// If destination is known to be zeroed, we don't need the write barrier
// to record the old value in *ptr.
return z.mask>>uint(off/ptrSize)&1 == 0
}
// writebarrier pass inserts write barriers for store ops (Store, Move, Zero)
// when necessary (the condition above). It rewrites store ops to branches
// and runtime calls, like
//
// if writeBarrier.enabled {
// buf := gcWriteBarrier2() // Not a regular Go call
// buf[0] = val
// buf[1] = *ptr
// }
// *ptr = val
//
// A sequence of WB stores for many pointer fields of a single type will
// be emitted together, with a single branch.
func writebarrier(f *Func) {
if !f.fe.UseWriteBarrier() {
return
}
// Number of write buffer entries we can request at once.
// Must match runtime/mwbbuf.go:wbMaxEntriesPerCall.
// It must also match the number of instances of runtime.gcWriteBarrier{X}.
const maxEntries = 8
var sb, sp, wbaddr, const0 *Value
var cgoCheckPtrWrite, cgoCheckMemmove *obj.LSym
var wbZero, wbMove *obj.LSym
var stores, after []*Value
var sset, sset2 *sparseSet
var storeNumber []int32
// Compute map from a value to the SelectN [1] value that uses it.
select1 := f.Cache.allocValueSlice(f.NumValues())
defer func() { f.Cache.freeValueSlice(select1) }()
for _, b := range f.Blocks {
for _, v := range b.Values {
if v.Op != OpSelectN {
continue
}
if v.AuxInt != 1 {
continue
}
select1[v.Args[0].ID] = v
}
}
zeroes := f.computeZeroMap(select1)
for _, b := range f.Blocks { // range loop is safe since the blocks we added contain no stores to expand
// first, identify all the stores that need to insert a write barrier.
// mark them with WB ops temporarily. record presence of WB ops.
nWBops := 0 // count of temporarily created WB ops remaining to be rewritten in the current block
for _, v := range b.Values {
switch v.Op {
case OpStore, OpMove, OpZero:
if needwb(v, zeroes) {
switch v.Op {
case OpStore:
v.Op = OpStoreWB
case OpMove:
v.Op = OpMoveWB
case OpZero:
v.Op = OpZeroWB
}
nWBops++
}
}
}
if nWBops == 0 {
continue
}
if wbaddr == nil {
// lazily initialize global values for write barrier test and calls
// find SB and SP values in entry block
initpos := f.Entry.Pos
sp, sb = f.spSb()
wbsym := f.fe.Syslook("writeBarrier")
wbaddr = f.Entry.NewValue1A(initpos, OpAddr, f.Config.Types.UInt32Ptr, wbsym, sb)
wbZero = f.fe.Syslook("wbZero")
wbMove = f.fe.Syslook("wbMove")
if buildcfg.Experiment.CgoCheck2 {
cgoCheckPtrWrite = f.fe.Syslook("cgoCheckPtrWrite")
cgoCheckMemmove = f.fe.Syslook("cgoCheckMemmove")
}
const0 = f.ConstInt32(f.Config.Types.UInt32, 0)
// allocate auxiliary data structures for computing store order
sset = f.newSparseSet(f.NumValues())
defer f.retSparseSet(sset)
sset2 = f.newSparseSet(f.NumValues())
defer f.retSparseSet(sset2)
storeNumber = f.Cache.allocInt32Slice(f.NumValues())
defer f.Cache.freeInt32Slice(storeNumber)
}
// order values in store order
b.Values = storeOrder(b.Values, sset, storeNumber)
again:
// find the start and end of the last contiguous WB store sequence.
// a branch will be inserted there. values after it will be moved
// to a new block.
var last *Value
var start, end int
var nonPtrStores int
values := b.Values
FindSeq:
for i := len(values) - 1; i >= 0; i-- {
w := values[i]
switch w.Op {
case OpStoreWB, OpMoveWB, OpZeroWB:
start = i
if last == nil {
last = w
end = i + 1
}
nonPtrStores = 0
case OpVarDef, OpVarLive:
continue
case OpStore:
if last == nil {
continue
}
nonPtrStores++
if nonPtrStores > 2 {
break FindSeq
}
default:
if last == nil {
continue
}
break FindSeq
}
}
stores = append(stores[:0], b.Values[start:end]...) // copy to avoid aliasing
after = append(after[:0], b.Values[end:]...)
b.Values = b.Values[:start]
// find the memory before the WB stores
mem := stores[0].MemoryArg()
pos := stores[0].Pos
// If the source of a MoveWB is volatile (will be clobbered by a
// function call), we need to copy it to a temporary location, as
// marshaling the args of wbMove might clobber the value we're
// trying to move.
// Look for volatile source, copy it to temporary before we check
// the write barrier flag.
// It is unlikely to have more than one of them. Just do a linear
// search instead of using a map.
// See issue 15854.
type volatileCopy struct {
src *Value // address of original volatile value
tmp *Value // address of temporary we've copied the volatile value into
}
var volatiles []volatileCopy
if !(f.ABIDefault == f.ABI1 && len(f.Config.intParamRegs) >= 3) {
// We don't need to do this if the calls we're going to do take
// all their arguments in registers.
// 3 is the magic number because it covers wbZero, wbMove, cgoCheckMemmove.
copyLoop:
for _, w := range stores {
if w.Op == OpMoveWB {
val := w.Args[1]
if isVolatile(val) {
for _, c := range volatiles {
if val == c.src {
continue copyLoop // already copied
}
}
t := val.Type.Elem()
tmp := f.NewLocal(w.Pos, t)
mem = b.NewValue1A(w.Pos, OpVarDef, types.TypeMem, tmp, mem)
tmpaddr := b.NewValue2A(w.Pos, OpLocalAddr, t.PtrTo(), tmp, sp, mem)
siz := t.Size()
mem = b.NewValue3I(w.Pos, OpMove, types.TypeMem, siz, tmpaddr, val, mem)
mem.Aux = t
volatiles = append(volatiles, volatileCopy{val, tmpaddr})
}
}
}
}
// Build branch point.
bThen := f.NewBlock(BlockPlain)
bEnd := f.NewBlock(b.Kind)
bThen.Pos = pos
bEnd.Pos = b.Pos
b.Pos = pos
// Set up control flow for end block.
bEnd.CopyControls(b)
bEnd.Likely = b.Likely
for _, e := range b.Succs {
bEnd.Succs = append(bEnd.Succs, e)
e.b.Preds[e.i].b = bEnd
}
// set up control flow for write barrier test
// load word, test word, avoiding partial register write from load byte.
cfgtypes := &f.Config.Types
flag := b.NewValue2(pos, OpLoad, cfgtypes.UInt32, wbaddr, mem)
flag = b.NewValue2(pos, OpNeq32, cfgtypes.Bool, flag, const0)
b.Kind = BlockIf
b.SetControl(flag)
b.Likely = BranchUnlikely
b.Succs = b.Succs[:0]
b.AddEdgeTo(bThen)
b.AddEdgeTo(bEnd)
bThen.AddEdgeTo(bEnd)
// For each write barrier store, append write barrier code to bThen.
memThen := mem
var curCall *Value
var curPtr *Value
addEntry := func(pos src.XPos, v *Value) {
if curCall == nil || curCall.AuxInt == maxEntries {
t := types.NewTuple(types.Types[types.TUINTPTR].PtrTo(), types.TypeMem)
curCall = bThen.NewValue1(pos, OpWB, t, memThen)
curPtr = bThen.NewValue1(pos, OpSelect0, types.Types[types.TUINTPTR].PtrTo(), curCall)
memThen = bThen.NewValue1(pos, OpSelect1, types.TypeMem, curCall)
}
// Store value in write buffer
num := curCall.AuxInt
curCall.AuxInt = num + 1
wbuf := bThen.NewValue1I(pos, OpOffPtr, types.Types[types.TUINTPTR].PtrTo(), num*f.Config.PtrSize, curPtr)
memThen = bThen.NewValue3A(pos, OpStore, types.TypeMem, types.Types[types.TUINTPTR], wbuf, v, memThen)
}
// Note: we can issue the write barrier code in any order. In particular,
// it doesn't matter if they are in a different order *even if* they end
// up referring to overlapping memory regions. For instance if an OpStore
// stores to a location that is later read by an OpMove. In all cases
// any pointers we must get into the write barrier buffer still make it,
// possibly in a different order and possibly a different (but definitely
// more than 0) number of times.
// In light of that, we process all the OpStoreWBs first. This minimizes
// the amount of spill/restore code we need around the Zero/Move calls.
// srcs contains the value IDs of pointer values we've put in the write barrier buffer.
srcs := sset
srcs.clear()
// dsts contains the value IDs of locations which we've read a pointer out of
// and put the result in the write barrier buffer.
dsts := sset2
dsts.clear()
for _, w := range stores {
if w.Op != OpStoreWB {
continue
}
pos := w.Pos
ptr := w.Args[0]
val := w.Args[1]
if !srcs.contains(val.ID) && needWBsrc(val) {
srcs.add(val.ID)
addEntry(pos, val)
}
if !dsts.contains(ptr.ID) && needWBdst(ptr, w.Args[2], zeroes) {
dsts.add(ptr.ID)
// Load old value from store target.
// Note: This turns bad pointer writes into bad
// pointer reads, which could be confusing. We could avoid
// reading from obviously bad pointers, which would
// take care of the vast majority of these. We could
// patch this up in the signal handler, or use XCHG to
// combine the read and the write.
oldVal := bThen.NewValue2(pos, OpLoad, types.Types[types.TUINTPTR], ptr, memThen)
// Save old value to write buffer.
addEntry(pos, oldVal)
}
f.fe.Func().SetWBPos(pos)
nWBops--
}
for _, w := range stores {
pos := w.Pos
switch w.Op {
case OpZeroWB:
dst := w.Args[0]
typ := reflectdata.TypeLinksym(w.Aux.(*types.Type))
// zeroWB(&typ, dst)
taddr := b.NewValue1A(pos, OpAddr, b.Func.Config.Types.Uintptr, typ, sb)
memThen = wbcall(pos, bThen, wbZero, sp, memThen, taddr, dst)
f.fe.Func().SetWBPos(pos)
nWBops--
case OpMoveWB:
dst := w.Args[0]
src := w.Args[1]
if isVolatile(src) {
for _, c := range volatiles {
if src == c.src {
src = c.tmp
break
}
}
}
typ := reflectdata.TypeLinksym(w.Aux.(*types.Type))
// moveWB(&typ, dst, src)
taddr := b.NewValue1A(pos, OpAddr, b.Func.Config.Types.Uintptr, typ, sb)
memThen = wbcall(pos, bThen, wbMove, sp, memThen, taddr, dst, src)
f.fe.Func().SetWBPos(pos)
nWBops--
}
}
// merge memory
mem = bEnd.NewValue2(pos, OpPhi, types.TypeMem, mem, memThen)
// Do raw stores after merge point.
for _, w := range stores {
pos := w.Pos
switch w.Op {
case OpStoreWB:
ptr := w.Args[0]
val := w.Args[1]
if buildcfg.Experiment.CgoCheck2 {
// Issue cgo checking code.
mem = wbcall(pos, bEnd, cgoCheckPtrWrite, sp, mem, ptr, val)
}
mem = bEnd.NewValue3A(pos, OpStore, types.TypeMem, w.Aux, ptr, val, mem)
case OpZeroWB:
dst := w.Args[0]
mem = bEnd.NewValue2I(pos, OpZero, types.TypeMem, w.AuxInt, dst, mem)
mem.Aux = w.Aux
case OpMoveWB:
dst := w.Args[0]
src := w.Args[1]
if isVolatile(src) {
for _, c := range volatiles {
if src == c.src {
src = c.tmp
break
}
}
}
if buildcfg.Experiment.CgoCheck2 {
// Issue cgo checking code.
typ := reflectdata.TypeLinksym(w.Aux.(*types.Type))
taddr := b.NewValue1A(pos, OpAddr, b.Func.Config.Types.Uintptr, typ, sb)
mem = wbcall(pos, bEnd, cgoCheckMemmove, sp, mem, taddr, dst, src)
}
mem = bEnd.NewValue3I(pos, OpMove, types.TypeMem, w.AuxInt, dst, src, mem)
mem.Aux = w.Aux
case OpVarDef, OpVarLive:
mem = bEnd.NewValue1A(pos, w.Op, types.TypeMem, w.Aux, mem)
case OpStore:
ptr := w.Args[0]
val := w.Args[1]
mem = bEnd.NewValue3A(pos, OpStore, types.TypeMem, w.Aux, ptr, val, mem)
}
}
// The last store becomes the WBend marker. This marker is used by the liveness
// pass to determine what parts of the code are preemption-unsafe.
// All subsequent memory operations use this memory, so we have to sacrifice the
// previous last memory op to become this new value.
bEnd.Values = append(bEnd.Values, last)
last.Block = bEnd
last.reset(OpWBend)
last.Pos = last.Pos.WithNotStmt()
last.Type = types.TypeMem
last.AddArg(mem)
// Free all the old stores, except last which became the WBend marker.
for _, w := range stores {
if w != last {
w.resetArgs()
}
}
for _, w := range stores {
if w != last {
f.freeValue(w)
}
}
// put values after the store sequence into the end block
bEnd.Values = append(bEnd.Values, after...)
for _, w := range after {
w.Block = bEnd
}
// if we have more stores in this block, do this block again
if nWBops > 0 {
goto again
}
}
}
// computeZeroMap returns a map from an ID of a memory value to
// a set of locations that are known to be zeroed at that memory value.
func (f *Func) computeZeroMap(select1 []*Value) map[ID]ZeroRegion {
ptrSize := f.Config.PtrSize
// Keep track of which parts of memory are known to be zero.
// This helps with removing write barriers for various initialization patterns.
// This analysis is conservative. We only keep track, for each memory state, of
// which of the first 64 words of a single object are known to be zero.
zeroes := map[ID]ZeroRegion{}
// Find new objects.
for _, b := range f.Blocks {
for _, v := range b.Values {
if mem, ok := IsNewObject(v, select1); ok {
// While compiling package runtime itself, we might see user
// calls to newobject, which will have result type
// unsafe.Pointer instead. We can't easily infer how large the
// allocated memory is, so just skip it.
if types.LocalPkg.Path == "runtime" && v.Type.IsUnsafePtr() {
continue
}
nptr := v.Type.Elem().Size() / ptrSize
if nptr > 64 {
nptr = 64
}
zeroes[mem.ID] = ZeroRegion{base: v, mask: 1<<uint(nptr) - 1}
}
}
}
// Find stores to those new objects.
for {
changed := false
for _, b := range f.Blocks {
// Note: iterating forwards helps convergence, as values are
// typically (but not always!) in store order.
for _, v := range b.Values {
if v.Op != OpStore {
continue
}
z, ok := zeroes[v.MemoryArg().ID]
if !ok {
continue
}
ptr := v.Args[0]
var off int64
size := v.Aux.(*types.Type).Size()
for ptr.Op == OpOffPtr {
off += ptr.AuxInt
ptr = ptr.Args[0]
}
if ptr != z.base {
// Different base object - we don't know anything.
// We could even be writing to the base object we know
// about, but through an aliased but offset pointer.
// So we have to throw all the zero information we have away.
continue
}
// Round to cover any partially written pointer slots.
// Pointer writes should never be unaligned like this, but non-pointer
// writes to pointer-containing types will do this.
if d := off % ptrSize; d != 0 {
off -= d
size += d
}
if d := size % ptrSize; d != 0 {
size += ptrSize - d
}
// Clip to the 64 words that we track.
min := off
max := off + size
if min < 0 {
min = 0
}
if max > 64*ptrSize {
max = 64 * ptrSize
}
// Clear bits for parts that we are writing (and hence
// will no longer necessarily be zero).
for i := min; i < max; i += ptrSize {
bit := i / ptrSize
z.mask &^= 1 << uint(bit)
}
if z.mask == 0 {
// No more known zeros - don't bother keeping.
continue
}
// Save updated known zero contents for new store.
if zeroes[v.ID] != z {
zeroes[v.ID] = z
changed = true
}
}
}
if !changed {
break
}
}
if f.pass.debug > 0 {
fmt.Printf("func %s\n", f.Name)
for mem, z := range zeroes {
fmt.Printf(" memory=v%d ptr=%v zeromask=%b\n", mem, z.base, z.mask)
}
}
return zeroes
}
// wbcall emits write barrier runtime call in b, returns memory.
func wbcall(pos src.XPos, b *Block, fn *obj.LSym, sp, mem *Value, args ...*Value) *Value {
config := b.Func.Config
typ := config.Types.Uintptr // type of all argument values
nargs := len(args)
// TODO (register args) this is a bit of a hack.
inRegs := b.Func.ABIDefault == b.Func.ABI1 && len(config.intParamRegs) >= 3
if !inRegs {
// Store arguments to the appropriate stack slot.
off := config.ctxt.Arch.FixedFrameSize
for _, arg := range args {
stkaddr := b.NewValue1I(pos, OpOffPtr, typ.PtrTo(), off, sp)
mem = b.NewValue3A(pos, OpStore, types.TypeMem, typ, stkaddr, arg, mem)
off += typ.Size()
}
args = args[:0]
}
args = append(args, mem)
// issue call
argTypes := make([]*types.Type, nargs, 3) // at most 3 args; allows stack allocation
for i := 0; i < nargs; i++ {
argTypes[i] = typ
}
call := b.NewValue0A(pos, OpStaticCall, types.TypeResultMem, StaticAuxCall(fn, b.Func.ABIDefault.ABIAnalyzeTypes(argTypes, nil)))
call.AddArgs(args...)
call.AuxInt = int64(nargs) * typ.Size()
return b.NewValue1I(pos, OpSelectN, types.TypeMem, 0, call)
}
// round to a multiple of r, r is a power of 2.
func round(o int64, r int64) int64 {
return (o + r - 1) &^ (r - 1)
}
// IsStackAddr reports whether v is known to be an address of a stack slot.
func IsStackAddr(v *Value) bool {
for v.Op == OpOffPtr || v.Op == OpAddPtr || v.Op == OpPtrIndex || v.Op == OpCopy {
v = v.Args[0]
}
switch v.Op {
case OpSP, OpLocalAddr, OpSelectNAddr, OpGetCallerSP:
return true
}
return false
}
// IsGlobalAddr reports whether v is known to be an address of a global (or nil).
func IsGlobalAddr(v *Value) bool {
for v.Op == OpOffPtr || v.Op == OpAddPtr || v.Op == OpPtrIndex || v.Op == OpCopy {
v = v.Args[0]
}
if v.Op == OpAddr && v.Args[0].Op == OpSB {
return true // address of a global
}
if v.Op == OpConstNil {
return true
}
if v.Op == OpLoad && IsReadOnlyGlobalAddr(v.Args[0]) {
return true // loading from a read-only global - the resulting address can't be a heap address.
}
return false
}
// IsReadOnlyGlobalAddr reports whether v is known to be an address of a read-only global.
func IsReadOnlyGlobalAddr(v *Value) bool {
if v.Op == OpConstNil {
// Nil pointers are read only. See issue 33438.
return true
}
if v.Op == OpAddr && v.Aux != nil && v.Aux.(*obj.LSym).Type == objabi.SRODATA {
return true
}
return false
}
// IsNewObject reports whether v is a pointer to a freshly allocated & zeroed object,
// if so, also returns the memory state mem at which v is zero.
func IsNewObject(v *Value, select1 []*Value) (mem *Value, ok bool) {
f := v.Block.Func
c := f.Config
if f.ABIDefault == f.ABI1 && len(c.intParamRegs) >= 1 {
if v.Op != OpSelectN || v.AuxInt != 0 {
return nil, false
}
mem = select1[v.Args[0].ID]
if mem == nil {
return nil, false
}
} else {
if v.Op != OpLoad {
return nil, false
}
mem = v.MemoryArg()
if mem.Op != OpSelectN {
return nil, false
}
if mem.Type != types.TypeMem {
return nil, false
} // assume it is the right selection if true
}
call := mem.Args[0]
if call.Op != OpStaticCall {
return nil, false
}
if !isSameCall(call.Aux, "runtime.newobject") {
return nil, false
}
if f.ABIDefault == f.ABI1 && len(c.intParamRegs) >= 1 {
if v.Args[0] == call {
return mem, true
}
return nil, false
}
if v.Args[0].Op != OpOffPtr {
return nil, false
}
if v.Args[0].Args[0].Op != OpSP {
return nil, false
}
if v.Args[0].AuxInt != c.ctxt.Arch.FixedFrameSize+c.RegSize { // offset of return value
return nil, false
}
return mem, true
}
// IsSanitizerSafeAddr reports whether v is known to be an address
// that doesn't need instrumentation.
func IsSanitizerSafeAddr(v *Value) bool {
for v.Op == OpOffPtr || v.Op == OpAddPtr || v.Op == OpPtrIndex || v.Op == OpCopy {
v = v.Args[0]
}
switch v.Op {
case OpSP, OpLocalAddr, OpSelectNAddr:
// Stack addresses are always safe.
return true
case OpITab, OpStringPtr, OpGetClosurePtr:
// Itabs, string data, and closure fields are
// read-only once initialized.
return true
case OpAddr:
vt := v.Aux.(*obj.LSym).Type
return vt == objabi.SRODATA || vt == objabi.SLIBFUZZER_8BIT_COUNTER || vt == objabi.SCOVERAGE_COUNTER || vt == objabi.SCOVERAGE_AUXVAR
}
return false
}
// isVolatile reports whether v is a pointer to argument region on stack which
// will be clobbered by a function call.
func isVolatile(v *Value) bool {
for v.Op == OpOffPtr || v.Op == OpAddPtr || v.Op == OpPtrIndex || v.Op == OpCopy || v.Op == OpSelectNAddr {
v = v.Args[0]
}
return v.Op == OpSP
}