cmd/compile: make map.zero symbol content-addressable

The compiler machinery that generates "map.zero" symbols marks them as
RODATA and DUPOK, which is problematic when a given application has
multiple map zero symbols (from different packages) with varying
sizes: the dupok path in the loader assumes that if two symbols have
the same name, it is safe to pick any of the versions. In the case of
map.zero, the link needs to select the largest symbol, not an
arbitrary sym.

To fix this problem, mark map.zero symbols as content-addressable,
since the loader's content addressability processing path already
supports selection of the larger symbol in cases where there are dups.

Fixes #46653.

Change-Id: Iabd2feef01d448670ba795c7eaddc48c191ea276
Reviewed-on: https://go-review.googlesource.com/c/go/+/326211
Trust: Than McIntosh <thanm@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
This commit is contained in:
Than McIntosh 2021-06-08 20:09:49 -04:00
parent 07ca28d529
commit aa5540cd82
4 changed files with 102 additions and 0 deletions

View file

@ -148,6 +148,7 @@ func dumpdata() {
if reflectdata.ZeroSize > 0 {
zero := base.PkgLinksym("go.map", "zero", obj.ABI0)
objw.Global(zero, int32(reflectdata.ZeroSize), obj.DUPOK|obj.RODATA)
zero.Set(obj.AttrContentAddressable, true)
}
staticdata.WriteFuncSyms()

View file

@ -0,0 +1,64 @@
// Copyright 2021 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 a
func Bad() {
m := make(map[int64]A)
a := m[0]
if len(a.B.C1.D2.E2.F1) != 0 ||
len(a.B.C1.D2.E2.F2) != 0 ||
len(a.B.C1.D2.E2.F3) != 0 ||
len(a.B.C1.D2.E2.F4) != 0 ||
len(a.B.C1.D2.E2.F5) != 0 ||
len(a.B.C1.D2.E2.F6) != 0 ||
len(a.B.C1.D2.E2.F7) != 0 ||
len(a.B.C1.D2.E2.F8) != 0 ||
len(a.B.C1.D2.E2.F9) != 0 ||
len(a.B.C1.D2.E2.F10) != 0 ||
len(a.B.C1.D2.E2.F11) != 0 ||
len(a.B.C1.D2.E2.F16) != 0 {
panic("bad")
}
}
type A struct {
B
}
type B struct {
C1 C
C2 C
}
type C struct {
D1 D
D2 D
}
type D struct {
E1 E
E2 E
E3 E
E4 E
}
type E struct {
F1 string
F2 string
F3 string
F4 string
F5 string
F6 string
F7 string
F8 string
F9 string
F10 string
F11 string
F12 string
F13 string
F14 string
F15 string
F16 string
}

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@ -0,0 +1,27 @@
// Copyright 2021 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 main
import (
bad "issue46653.dir/bad"
)
func main() {
bad.Bad()
}
func neverCalled() L {
m := make(map[string]L)
return m[""]
}
type L struct {
A Data
B Data
}
type Data struct {
F1 [22][]string
}

View file

@ -0,0 +1,10 @@
// runindir
// Copyright 2021 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.
// Test to verify compiler and linker handling of multiple
// competing map.zero symbol definitions.
package ignored