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cmd/compile: move checkptr alignment to SSA generation
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This is followup of CL 343972, moving the checkptr alignment
instrumentation during SSA generation instead of walk.

Change-Id: I29b2953e4eb8631277fe2e0f44b9d987dd7a69f9
Reviewed-on: https://go-review.googlesource.com/c/go/+/345430
Trust: Cuong Manh Le <[email protected]>
Run-TryBot: Cuong Manh Le <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Matthew Dempsky <[email protected]>
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@cuonglm
cuonglm committed Sep 9, 2021
1 parent 8fad81c commit d62866e
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Showing 5 changed files with 77 additions and 89 deletions.
9 changes: 4 additions & 5 deletions src/cmd/compile/internal/ir/expr.go
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Original file line number Diff line number Diff line change
Expand Up @@ -570,11 +570,10 @@ func (*SelectorExpr) CanBeNtype() {}
// A SliceExpr is a slice expression X[Low:High] or X[Low:High:Max].
type SliceExpr struct {
miniExpr
X Node
Low Node
High Node
Max Node
CheckPtrCall *CallExpr `mknode:"-"`
X Node
Low Node
High Node
Max Node
}

func NewSliceExpr(pos src.XPos, op Op, x, low, high, max Node) *SliceExpr {
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55 changes: 28 additions & 27 deletions src/cmd/compile/internal/ir/symtab.go
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Original file line number Diff line number Diff line change
Expand Up @@ -11,33 +11,34 @@ import (

// Syms holds known symbols.
var Syms struct {
AssertE2I *obj.LSym
AssertE2I2 *obj.LSym
AssertI2I *obj.LSym
AssertI2I2 *obj.LSym
Deferproc *obj.LSym
DeferprocStack *obj.LSym
Deferreturn *obj.LSym
Duffcopy *obj.LSym
Duffzero *obj.LSym
GCWriteBarrier *obj.LSym
Goschedguarded *obj.LSym
Growslice *obj.LSym
Msanread *obj.LSym
Msanwrite *obj.LSym
Msanmove *obj.LSym
Newobject *obj.LSym
Newproc *obj.LSym
Panicdivide *obj.LSym
Panicshift *obj.LSym
PanicdottypeE *obj.LSym
PanicdottypeI *obj.LSym
Panicnildottype *obj.LSym
Panicoverflow *obj.LSym
Raceread *obj.LSym
Racereadrange *obj.LSym
Racewrite *obj.LSym
Racewriterange *obj.LSym
AssertE2I *obj.LSym
AssertE2I2 *obj.LSym
AssertI2I *obj.LSym
AssertI2I2 *obj.LSym
CheckPtrAlignment *obj.LSym
Deferproc *obj.LSym
DeferprocStack *obj.LSym
Deferreturn *obj.LSym
Duffcopy *obj.LSym
Duffzero *obj.LSym
GCWriteBarrier *obj.LSym
Goschedguarded *obj.LSym
Growslice *obj.LSym
Msanread *obj.LSym
Msanwrite *obj.LSym
Msanmove *obj.LSym
Newobject *obj.LSym
Newproc *obj.LSym
Panicdivide *obj.LSym
Panicshift *obj.LSym
PanicdottypeE *obj.LSym
PanicdottypeI *obj.LSym
Panicnildottype *obj.LSym
Panicoverflow *obj.LSym
Raceread *obj.LSym
Racereadrange *obj.LSym
Racewrite *obj.LSym
Racewriterange *obj.LSym
// Wasm
SigPanic *obj.LSym
Staticuint64s *obj.LSym
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51 changes: 44 additions & 7 deletions src/cmd/compile/internal/ssagen/ssa.go
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Original file line number Diff line number Diff line change
Expand Up @@ -96,6 +96,7 @@ func InitConfig() {
ir.Syms.AssertE2I2 = typecheck.LookupRuntimeFunc("assertE2I2")
ir.Syms.AssertI2I = typecheck.LookupRuntimeFunc("assertI2I")
ir.Syms.AssertI2I2 = typecheck.LookupRuntimeFunc("assertI2I2")
ir.Syms.CheckPtrAlignment = typecheck.LookupRuntimeFunc("checkptrAlignment")
ir.Syms.Deferproc = typecheck.LookupRuntimeFunc("deferproc")
ir.Syms.DeferprocStack = typecheck.LookupRuntimeFunc("deferprocStack")
ir.Syms.Deferreturn = typecheck.LookupRuntimeFunc("deferreturn")
Expand Down Expand Up @@ -366,6 +367,7 @@ func buildssa(fn *ir.Func, worker int) *ssa.Func {
if fn.Pragma&ir.CgoUnsafeArgs != 0 {
s.cgoUnsafeArgs = true
}
s.checkPtrEnabled = ir.ShouldCheckPtr(fn, 1)

fe := ssafn{
curfn: fn,
Expand Down Expand Up @@ -709,6 +711,31 @@ func (s *state) newObject(typ *types.Type) *ssa.Value {
return s.rtcall(ir.Syms.Newobject, true, []*types.Type{types.NewPtr(typ)}, s.reflectType(typ))[0]
}

func (s *state) checkPtrAlignment(n *ir.ConvExpr, v *ssa.Value, count *ssa.Value) {
if !n.Type().IsPtr() {
s.Fatalf("expected pointer type: %v", n.Type())
}
elem := n.Type().Elem()
if count != nil {
if !elem.IsArray() {
s.Fatalf("expected array type: %v", elem)
}
elem = elem.Elem()
}
size := elem.Size()
// Casting from larger type to smaller one is ok, so for smallest type, do nothing.
if elem.Alignment() == 1 && (size == 0 || size == 1 || count == nil) {
return
}
if count == nil {
count = s.constInt(types.Types[types.TUINTPTR], 1)
}
if count.Type.Size() != s.config.PtrSize {
s.Fatalf("expected count fit to an uintptr size, have: %d, want: %d", count.Type.Size(), s.config.PtrSize)
}
s.rtcall(ir.Syms.CheckPtrAlignment, true, nil, v, s.reflectType(elem), count)
}

// reflectType returns an SSA value representing a pointer to typ's
// reflection type descriptor.
func (s *state) reflectType(typ *types.Type) *ssa.Value {
Expand Down Expand Up @@ -861,10 +888,11 @@ type state struct {
// Used to deduplicate panic calls.
panics map[funcLine]*ssa.Block

cgoUnsafeArgs bool
hasdefer bool // whether the function contains a defer statement
softFloat bool
hasOpenDefers bool // whether we are doing open-coded defers
cgoUnsafeArgs bool
hasdefer bool // whether the function contains a defer statement
softFloat bool
hasOpenDefers bool // whether we are doing open-coded defers
checkPtrEnabled bool // whether to insert checkptr instrumentation

// If doing open-coded defers, list of info about the defer calls in
// scanning order. Hence, at exit we should run these defers in reverse
Expand Down Expand Up @@ -2494,6 +2522,10 @@ func (s *state) conv(n ir.Node, v *ssa.Value, ft, tt *types.Type) *ssa.Value {

// expr converts the expression n to ssa, adds it to s and returns the ssa result.
func (s *state) expr(n ir.Node) *ssa.Value {
return s.exprCheckPtr(n, true)
}

func (s *state) exprCheckPtr(n ir.Node, checkPtrOK bool) *ssa.Value {
if ir.HasUniquePos(n) {
// ONAMEs and named OLITERALs have the line number
// of the decl, not the use. See issue 14742.
Expand Down Expand Up @@ -2641,6 +2673,9 @@ func (s *state) expr(n ir.Node) *ssa.Value {

// unsafe.Pointer <--> *T
if to.IsUnsafePtr() && from.IsPtrShaped() || from.IsUnsafePtr() && to.IsPtrShaped() {
if s.checkPtrEnabled && checkPtrOK && to.IsPtr() && from.IsUnsafePtr() {
s.checkPtrAlignment(n, v, nil)
}
return v
}

Expand Down Expand Up @@ -3081,7 +3116,8 @@ func (s *state) expr(n ir.Node) *ssa.Value {

case ir.OSLICE, ir.OSLICEARR, ir.OSLICE3, ir.OSLICE3ARR:
n := n.(*ir.SliceExpr)
v := s.expr(n.X)
check := s.checkPtrEnabled && n.Op() == ir.OSLICE3ARR && n.X.Op() == ir.OCONVNOP && n.X.(*ir.ConvExpr).X.Type().IsUnsafePtr()
v := s.exprCheckPtr(n.X, !check)
var i, j, k *ssa.Value
if n.Low != nil {
i = s.expr(n.Low)
Expand All @@ -3093,8 +3129,9 @@ func (s *state) expr(n ir.Node) *ssa.Value {
k = s.expr(n.Max)
}
p, l, c := s.slice(v, i, j, k, n.Bounded())
if n.CheckPtrCall != nil {
s.stmt(n.CheckPtrCall)
if check {
// Emit checkptr instrumentation after bound check to prevent false positive, see #46938.
s.checkPtrAlignment(n.X.(*ir.ConvExpr), v, s.conv(n.Max, k, k.Type, types.Types[types.TUINTPTR]))
}
return s.newValue3(ssa.OpSliceMake, n.Type(), p, l, c)

Expand Down
38 changes: 0 additions & 38 deletions src/cmd/compile/internal/walk/convert.go
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Original file line number Diff line number Diff line change
Expand Up @@ -25,9 +25,6 @@ func walkConv(n *ir.ConvExpr, init *ir.Nodes) ir.Node {
return n.X
}
if n.Op() == ir.OCONVNOP && ir.ShouldCheckPtr(ir.CurFunc, 1) {
if n.Type().IsPtr() && n.X.Type().IsUnsafePtr() { // unsafe.Pointer to *T
return walkCheckPtrAlignment(n, init, nil)
}
if n.Type().IsUnsafePtr() && n.X.Type().IsUintptr() { // uintptr to unsafe.Pointer
return walkCheckPtrArithmetic(n, init)
}
Expand Down Expand Up @@ -414,41 +411,6 @@ func byteindex(n ir.Node) ir.Node {
return n
}

func walkCheckPtrAlignment(n *ir.ConvExpr, init *ir.Nodes, se *ir.SliceExpr) ir.Node {
if !n.Type().IsPtr() {
base.Fatalf("expected pointer type: %v", n.Type())
}
elem := n.Type().Elem()
var count ir.Node
if se != nil {
count = se.Max
}
if count != nil {
if !elem.IsArray() {
base.Fatalf("expected array type: %v", elem)
}
elem = elem.Elem()
}

size := elem.Size()
if elem.Alignment() == 1 && (size == 0 || size == 1 && count == nil) {
return n
}

if count == nil {
count = ir.NewInt(1)
}

n.X = cheapExpr(n.X, init)
checkPtrCall := mkcall("checkptrAlignment", nil, init, typecheck.ConvNop(n.X, types.Types[types.TUNSAFEPTR]), reflectdata.TypePtr(elem), typecheck.Conv(count, types.Types[types.TUINTPTR]))
if se != nil {
se.CheckPtrCall = checkPtrCall
} else {
init.Append(checkPtrCall)
}
return n
}

func walkCheckPtrArithmetic(n *ir.ConvExpr, init *ir.Nodes) ir.Node {
// Calling cheapExpr(n, init) below leads to a recursive call to
// walkExpr, which leads us back here again. Use n.Checkptr to
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13 changes: 1 addition & 12 deletions src/cmd/compile/internal/walk/expr.go
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Original file line number Diff line number Diff line change
Expand Up @@ -807,25 +807,14 @@ func walkSend(n *ir.SendStmt, init *ir.Nodes) ir.Node {

// walkSlice walks an OSLICE, OSLICEARR, OSLICESTR, OSLICE3, or OSLICE3ARR node.
func walkSlice(n *ir.SliceExpr, init *ir.Nodes) ir.Node {

checkSlice := ir.ShouldCheckPtr(ir.CurFunc, 1) && n.Op() == ir.OSLICE3ARR && n.X.Op() == ir.OCONVNOP && n.X.(*ir.ConvExpr).X.Type().IsUnsafePtr()
if checkSlice {
conv := n.X.(*ir.ConvExpr)
conv.X = walkExpr(conv.X, init)
} else {
n.X = walkExpr(n.X, init)
}

n.X = walkExpr(n.X, init)
n.Low = walkExpr(n.Low, init)
if n.Low != nil && ir.IsZero(n.Low) {
// Reduce x[0:j] to x[:j] and x[0:j:k] to x[:j:k].
n.Low = nil
}
n.High = walkExpr(n.High, init)
n.Max = walkExpr(n.Max, init)
if checkSlice {
n.X = walkCheckPtrAlignment(n.X.(*ir.ConvExpr), init, n)
}

if n.Op().IsSlice3() {
if n.Max != nil && n.Max.Op() == ir.OCAP && ir.SameSafeExpr(n.X, n.Max.(*ir.UnaryExpr).X) {
Expand Down

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