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maps: maps.Clone reference semantics when cloning a map with large value types #64474

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santegoeds opened this issue Nov 30, 2023 · 7 comments
Closed

maps: maps.Clone reference semantics when cloning a map with large value types #64474

santegoeds opened this issue Nov 30, 2023 · 7 comments
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@randall77
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compiler/runtime Issues related to the Go compiler and/or runtime. NeedsFix The path to resolution is known, but the work has not been done. release-blocker
Milestone
Go1.22

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@santegoeds
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santegoeds commented Nov 30, 2023 •
edited by findleyr

Go version

go version go1.21.4 linux/amd64

What operating system and processor architecture are you using (go env)?

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/tdog/.cache/go-build'
GOENV='/home/tdog/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/tdog/.asdf/installs/golang/1.21.4/packages/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/tdog/.asdf/installs/golang/1.21.4/packages'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/tdog/.asdf/installs/golang/1.21.4/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/home/tdog/.asdf/installs/golang/1.21.4/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.21.4'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/home/tdog/dev/maps-clone/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build1194712858=/tmp/go-build -gno-record-gcc-switches'

What did you do?

https://go.dev/play/p/vkz2JOzn6zV

package main

import (
	"fmt"
	"maps"
)

type Value struct {
	Val     int
	padding [100]int
}

func main() {
	const key = "key"

	m := make(map[string]Value)

	m[key] = Value{Val: 1}

	c := maps.Clone(m)

	v := m[key]
	v.Val = 2
	m[key] = v

	fmt.Println(m[key].Val, c[key].Val)
}

Possibly related to https://go-review.googlesource.com/c/go/+/471400

What did you expect to see?

2 1

What did you see instead?

2 2
@bcmills bcmills added compiler/runtime Issues related to the Go compiler and/or runtime. NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels Nov 30, 2023
@bcmills
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bcmills commented Nov 30, 2023

@gopherbot, please backport to Go 1.21. This appears to cause subtle aliasing bugs in cloned maps.

@gopherbot gopherbot mentioned this issue Nov 30, 2023
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@gopherbot
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Backport issue(s) opened: #64475 (for 1.21).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://go.dev/wiki/MinorReleases.

@findleyr
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(I made a minor correction to the original report, changing the expectation to 2 1 (from 1 2)).

@mauri870
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I can confirm this behavior changed after CL 471400 moved the Clone implementation to the runtime.

@randall77
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@cuiweixie

@mauri870
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mauri870 commented Nov 30, 2023 •
edited

The bug triggers this branch of mapclone2 https://go.googlesource.com/go/+/refs/heads/master/src/runtime/map.go#1512

	if src.B == 0 {
		dst.buckets = newobject(t.Bucket)
		dst.count = src.count
		typedmemmove(t.Bucket, dst.buckets, src.buckets)
		return dst
	}

@dmitshur dmitshur added this to the Go1.22 milestone Nov 30, 2023
@gopherbot
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Change https://go.dev/cl/546515 mentions this issue: maps: fix aliasing problems with Clone

@dmitshur dmitshur added NeedsFix The path to resolution is known, but the work has not been done. and removed NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels Dec 1, 2023
ezz-no pushed a commit to ezz-no/go-ezzno that referenced this issue Feb 18, 2024
@randall77 @ezz-no
maps: fix aliasing problems with Clone
f766a95 
Make sure to alloc+copy large keys and values instead of aliasing them,
when they might be updated by a future assignment.

Fixes golang#64474

Change-Id: Ie2226a81cf3897e4e2ee24472f2966d397ace53f
Reviewed-on: https://go-review.googlesource.com/c/go/+/546515
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>
Reviewed-by: Mauri de Souza Meneguzzo <mauri870@gmail.com>
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@randall77 randall77

Labels
compiler/runtime Issues related to the Go compiler and/or runtime. NeedsFix The path to resolution is known, but the work has not been done. release-blocker
Projects
Release Status & Release Blockers
Status: Done
Milestone
Go1.22
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8 participants
@santegoeds @dmitshur @bcmills @randall77 @gopherbot @mauri870 @heschi @findleyr