mirror of
https://github.com/golang/go
synced 2024-11-18 16:14:46 -07:00
go.tools/go/pointer: fix solver nontermination bug due to reflective type construction cycles.
Programs such as this cause the PtrTo solver to attempt to
enumerate an infinite set of types {T, *T, ..., *******T, etc}.
t := reflect.TypeOf(T{})
for {
t = reflect.PtrTo(t)
}
The fix is to bound the depth of reflectively created types at
about 4 map/chan/slice/pointer constructors.
+ test.
LGTM=gri
R=gri
CC=crawshaw, golang-codereviews
https://golang.org/cl/102030044
This commit is contained in:
Alan Donovan
parent
fd72015344
commit
43c97eab79
@ -11,8 +11,6 @@ package pointer
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// memoize as much as possible, like TypeOf and Zero do for their
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// tagged objects.
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//
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// TODO(adonovan): all {} functions are TODO.
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//
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// TODO(adonovan): this file is rather subtle. Explain how we derive
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// the implementation of each reflect operator from its spec,
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// including the subtleties of reflect.flag{Addr,RO,Indir}.
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@ -151,7 +149,7 @@ func init() {
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// -------------------- (reflect.Value) --------------------
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func ext۰reflect۰Value۰Addr(a *analysis, cgn *cgnode) {}
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func ext۰reflect۰Value۰Addr(a *analysis, cgn *cgnode) {} // TODO(adonovan)
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// ---------- func (Value).Bytes() Value ----------
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@ -352,7 +350,7 @@ func ext۰reflect۰Value۰CallSlice(a *analysis, cgn *cgnode) {
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}
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}
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func ext۰reflect۰Value۰Convert(a *analysis, cgn *cgnode) {}
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func ext۰reflect۰Value۰Convert(a *analysis, cgn *cgnode) {} // TODO(adonovan)
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// ---------- func (Value).Elem() Value ----------
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@ -411,10 +409,10 @@ func ext۰reflect۰Value۰Elem(a *analysis, cgn *cgnode) {
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})
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}
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func ext۰reflect۰Value۰Field(a *analysis, cgn *cgnode) {}
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func ext۰reflect۰Value۰FieldByIndex(a *analysis, cgn *cgnode) {}
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func ext۰reflect۰Value۰FieldByName(a *analysis, cgn *cgnode) {}
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func ext۰reflect۰Value۰FieldByNameFunc(a *analysis, cgn *cgnode) {}
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func ext۰reflect۰Value۰Field(a *analysis, cgn *cgnode) {} // TODO(adonovan)
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func ext۰reflect۰Value۰FieldByIndex(a *analysis, cgn *cgnode) {} // TODO(adonovan)
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func ext۰reflect۰Value۰FieldByName(a *analysis, cgn *cgnode) {} // TODO(adonovan)
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func ext۰reflect۰Value۰FieldByNameFunc(a *analysis, cgn *cgnode) {} // TODO(adonovan)
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// ---------- func (Value).Index() Value ----------
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@ -642,8 +640,8 @@ func ext۰reflect۰Value۰MapKeys(a *analysis, cgn *cgnode) {
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})
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}
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func ext۰reflect۰Value۰Method(a *analysis, cgn *cgnode) {}
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func ext۰reflect۰Value۰MethodByName(a *analysis, cgn *cgnode) {}
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func ext۰reflect۰Value۰Method(a *analysis, cgn *cgnode) {} // TODO(adonovan)
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func ext۰reflect۰Value۰MethodByName(a *analysis, cgn *cgnode) {} // TODO(adonovan)
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// ---------- func (Value).Recv(Value) ----------
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@ -749,7 +747,7 @@ func ext۰reflect۰Value۰Send(a *analysis, cgn *cgnode) {
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})
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}
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func ext۰reflect۰Value۰Set(a *analysis, cgn *cgnode) {}
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func ext۰reflect۰Value۰Set(a *analysis, cgn *cgnode) {} // TODO(adonovan)
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// ---------- func (Value).SetBytes(x []byte) ----------
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@ -857,7 +855,7 @@ func ext۰reflect۰Value۰SetMapIndex(a *analysis, cgn *cgnode) {
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})
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}
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func ext۰reflect۰Value۰SetPointer(a *analysis, cgn *cgnode) {}
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func ext۰reflect۰Value۰SetPointer(a *analysis, cgn *cgnode) {} // TODO(adonovan)
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// ---------- func (Value).Slice(v Value, i, j int) ----------
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@ -932,9 +930,9 @@ func ext۰reflect۰Value۰Slice(a *analysis, cgn *cgnode) {
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// -------------------- Standalone reflect functions --------------------
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func ext۰reflect۰Append(a *analysis, cgn *cgnode) {}
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func ext۰reflect۰AppendSlice(a *analysis, cgn *cgnode) {}
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func ext۰reflect۰Copy(a *analysis, cgn *cgnode) {}
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func ext۰reflect۰Append(a *analysis, cgn *cgnode) {} // TODO(adonovan)
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func ext۰reflect۰AppendSlice(a *analysis, cgn *cgnode) {} // TODO(adonovan)
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func ext۰reflect۰Copy(a *analysis, cgn *cgnode) {} // TODO(adonovan)
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// ---------- func ChanOf(ChanDir, Type) Type ----------
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@ -962,6 +960,10 @@ func (c *reflectChanOfConstraint) solve(a *analysis, _ *node, delta nodeset) {
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for tObj := range delta {
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T := a.rtypeTaggedValue(tObj)
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if typeTooHigh(T) {
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continue
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}
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for _, dir := range c.dirs {
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if a.addLabel(c.result, a.makeRtype(types.NewChan(dir, T))) {
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changed = true
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@ -1110,7 +1112,7 @@ func ext۰reflect۰MakeChan(a *analysis, cgn *cgnode) {
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})
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}
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func ext۰reflect۰MakeFunc(a *analysis, cgn *cgnode) {}
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func ext۰reflect۰MakeFunc(a *analysis, cgn *cgnode) {} // TODO(adonovan)
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// ---------- func MakeMap(Type) Value ----------
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@ -1222,7 +1224,7 @@ func ext۰reflect۰MakeSlice(a *analysis, cgn *cgnode) {
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})
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}
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func ext۰reflect۰MapOf(a *analysis, cgn *cgnode) {}
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func ext۰reflect۰MapOf(a *analysis, cgn *cgnode) {} // TODO(adonovan)
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// ---------- func New(Type) Value ----------
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@ -1310,6 +1312,10 @@ func (c *reflectPtrToConstraint) solve(a *analysis, _ *node, delta nodeset) {
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for tObj := range delta {
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T := a.rtypeTaggedValue(tObj)
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if typeTooHigh(T) {
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continue
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}
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if a.addLabel(c.result, a.makeRtype(types.NewPointer(T))) {
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changed = true
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}
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@ -1327,7 +1333,7 @@ func ext۰reflect۰PtrTo(a *analysis, cgn *cgnode) {
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})
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}
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func ext۰reflect۰Select(a *analysis, cgn *cgnode) {}
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func ext۰reflect۰Select(a *analysis, cgn *cgnode) {} // TODO(adonovan)
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// ---------- func SliceOf(Type) Type ----------
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@ -1354,6 +1360,10 @@ func (c *reflectSliceOfConstraint) solve(a *analysis, _ *node, delta nodeset) {
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for tObj := range delta {
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T := a.rtypeTaggedValue(tObj)
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if typeTooHigh(T) {
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continue
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}
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if a.addLabel(c.result, a.makeRtype(types.NewSlice(T))) {
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changed = true
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}
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@ -1613,8 +1623,8 @@ func ext۰reflect۰rtype۰Field(a *analysis, cgn *cgnode) {
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})
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}
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func ext۰reflect۰rtype۰FieldByIndex(a *analysis, cgn *cgnode) {}
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func ext۰reflect۰rtype۰FieldByNameFunc(a *analysis, cgn *cgnode) {}
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func ext۰reflect۰rtype۰FieldByIndex(a *analysis, cgn *cgnode) {} // TODO(adonovan)
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func ext۰reflect۰rtype۰FieldByNameFunc(a *analysis, cgn *cgnode) {} // TODO(adonovan)
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// ---------- func (*rtype) In/Out(i int) Type ----------
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@ -1844,3 +1854,45 @@ func ext۰reflect۰rtype۰Method(a *analysis, cgn *cgnode) {
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result: a.funcResults(cgn.obj),
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})
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}
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// typeHeight returns the "height" of the type, which is roughly
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// speaking the number of chan, map, pointer and slice type constructors
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// at the root of T; these are the four type kinds that can be created
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// via reflection. Chan and map constructors are counted as double the
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// height of slice and pointer constructors since they are less often
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// deeply nested.
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//
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// The solver rules for type constructors must somehow bound the set of
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// types they create to ensure termination of the algorithm in cases
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// where the output of a type constructor flows to its input, e.g.
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//
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// func f(t reflect.Type) {
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// f(reflect.PtrTo(t))
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// }
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//
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// It does this by limiting the type height to k, but this still leaves
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// a potentially exponential (4^k) number of of types that may be
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// enumerated in pathological cases.
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//
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func typeHeight(T types.Type) int {
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switch T := T.(type) {
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case *types.Chan:
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return 2 + typeHeight(T.Elem())
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case *types.Map:
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k := typeHeight(T.Key())
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v := typeHeight(T.Elem())
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if v > k {
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k = v // max(k, v)
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}
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return 2 + k
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case *types.Slice:
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return 1 + typeHeight(T.Elem())
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case *types.Pointer:
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return 1 + typeHeight(T.Elem())
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}
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return 0
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}
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func typeTooHigh(T types.Type) bool {
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return typeHeight(T) > 3
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}
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28
go/pointer/testdata/reflect.go
vendored
28
go/pointer/testdata/reflect.go
vendored
@ -78,10 +78,38 @@ func metareflection() {
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print(x0a.Interface()) // @types int
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}
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type T struct{}
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// When the output of a type constructor flows to its input, we must
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// bound the set of types created to ensure termination of the algorithm.
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func typeCycle() {
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t := reflect.TypeOf(0)
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u := reflect.TypeOf("")
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v := reflect.TypeOf(T{})
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for unknown {
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t = reflect.PtrTo(t)
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t = reflect.SliceOf(t)
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u = reflect.SliceOf(u)
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if unknown {
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v = reflect.ChanOf(reflect.BothDir, v)
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} else {
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v = reflect.PtrTo(v)
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}
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}
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// Type height is bounded to about 4 map/slice/chan/pointer constructors.
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print(reflect.Zero(t).Interface()) // @types int | []*int | []*[]*int
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print(reflect.Zero(u).Interface()) // @types string | []string | [][]string | [][][]string | [][][][]string
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print(reflect.Zero(v).Interface()) // @types T | *T | **T | ***T | ****T | chan T | *chan T | **chan T | chan *T | *chan *T | chan **T | chan ***T | chan chan T | chan *chan T | chan chan *T
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}
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func main() {
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reflectIndirect()
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reflectNewAt()
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reflectTypeOf()
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reflectTypeElem()
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metareflection()
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typeCycle()
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}
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