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runtime: don't re-initialize itab while looking for missing function
The itab we're initializing again, just to figure out which method is missing, might be stored in read-only memory. This can only happen in certain weird generics situations, so it is pretty rare, but it causes a runtime crash when it does happen. Fixes #65962 Change-Id: Ia86e216fe33950a794ad8e475e76317f799e9136 Reviewed-on: https://go-review.googlesource.com/c/go/+/567615 Reviewed-by: Cherry Mui <cherryyz@google.com> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Keith Randall <khr@google.com>
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@ -74,7 +74,7 @@ func getitab(inter *interfacetype, typ *_type, canfail bool) *itab {
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// and thus the hash is irrelevant.
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// and thus the hash is irrelevant.
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// Note: m.Hash is _not_ the hash used for the runtime itabTable hash table.
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// Note: m.Hash is _not_ the hash used for the runtime itabTable hash table.
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m.Hash = 0
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m.Hash = 0
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itabInit(m)
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itabInit(m, true)
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itabAdd(m)
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itabAdd(m)
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unlock(&itabLock)
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unlock(&itabLock)
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finish:
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finish:
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@ -90,7 +90,7 @@ finish:
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// The cached result doesn't record which
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// The cached result doesn't record which
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// interface function was missing, so initialize
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// interface function was missing, so initialize
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// the itab again to get the missing function name.
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// the itab again to get the missing function name.
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panic(&TypeAssertionError{concrete: typ, asserted: &inter.Type, missingMethod: itabInit(m)})
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panic(&TypeAssertionError{concrete: typ, asserted: &inter.Type, missingMethod: itabInit(m, false)})
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}
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}
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// find finds the given interface/type pair in t.
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// find finds the given interface/type pair in t.
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@ -186,11 +186,13 @@ func (t *itabTableType) add(m *itab) {
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}
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}
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}
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}
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// init fills in the m.Fun array with all the code pointers for
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// itabInit fills in the m.Fun array with all the code pointers for
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// the m.Inter/m.Type pair. If the type does not implement the interface,
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// the m.Inter/m.Type pair. If the type does not implement the interface,
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// it sets m.Fun[0] to 0 and returns the name of an interface function that is missing.
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// it sets m.Fun[0] to 0 and returns the name of an interface function that is missing.
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// It is ok to call this multiple times on the same m, even concurrently.
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// If !firstTime, itabInit will not write anything to m.Fun (see issue 65962).
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func itabInit(m *itab) string {
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// It is ok to call this multiple times on the same m, even concurrently
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// (although it will only be called once with firstTime==true).
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func itabInit(m *itab, firstTime bool) string {
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inter := m.Inter
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inter := m.Inter
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typ := m.Type
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typ := m.Type
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x := typ.Uncommon()
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x := typ.Uncommon()
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@ -228,7 +230,7 @@ imethods:
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ifn := rtyp.textOff(t.Ifn)
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ifn := rtyp.textOff(t.Ifn)
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if k == 0 {
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if k == 0 {
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fun0 = ifn // we'll set m.Fun[0] at the end
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fun0 = ifn // we'll set m.Fun[0] at the end
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} else {
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} else if firstTime {
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methods[k] = ifn
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methods[k] = ifn
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}
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}
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continue imethods
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continue imethods
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@ -236,10 +238,12 @@ imethods:
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}
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}
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}
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}
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// didn't find method
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// didn't find method
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m.Fun[0] = 0
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// Leaves m.Fun[0] set to 0.
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return iname
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return iname
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}
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}
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m.Fun[0] = uintptr(fun0)
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if firstTime {
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m.Fun[0] = uintptr(fun0)
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}
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return ""
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return ""
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}
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}
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48
test/fixedbugs/issue65962.go
Normal file
48
test/fixedbugs/issue65962.go
Normal file
@ -0,0 +1,48 @@
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// run
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// Copyright 2024 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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func main() {
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test1()
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test2()
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}
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type I interface {
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f()
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g()
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h()
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}
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//go:noinline
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func ld[T any]() {
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var x I
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if _, ok := x.(T); ok {
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}
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}
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func isI(x any) {
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_ = x.(I)
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}
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func test1() {
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defer func() { recover() }()
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ld[bool]() // add <bool,I> itab to binary
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_ = any(false).(I)
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}
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type B bool
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func (B) f() {
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}
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func (B) g() {
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}
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func test2() {
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defer func() { recover() }()
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ld[B]() // add <B,I> itab to binary
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_ = any(B(false)).(I)
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}
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