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hash/maphash: hashing channels with purego impl. of maphash.Comparable panics #73657

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Snawoot opened this issue May 10, 2025 · 5 comments · May be fixed by #73660
Open

hash/maphash: hashing channels with purego impl. of maphash.Comparable panics #73657

Snawoot opened this issue May 10, 2025 · 5 comments · May be fixed by #73660
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BugReport Issues describing a possible bug in the Go implementation.

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@Snawoot
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Snawoot commented May 10, 2025

Go version

go version go1.24.2 linux/amd64

Output of go env in your module/workspace:

AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/home/user/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/user/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build1565376817=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/dev/null'
GOMODCACHE='/home/user/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/user/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/lib64/go/1.24'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/user/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/usr/lib64/go/1.24/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.24.2'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

Minimal example to reproduce:

package main

import (
	"hash/maphash"
)

func main() {
	maphash.Comparable(maphash.MakeSeed(), make(chan struct{}))
}

What did you see happen?

Run with go run -tags purego main.go causes panic:

$ go run -tags purego main.go
panic: maphash: hash of unhashable type chan struct {}

goroutine 1 [running]:
hash/maphash.appendT(0xc0000a0e78, {0x497e40?, 0xc000096070?, 0x4112fe?})
	/usr/lib64/go/1.24/src/hash/maphash/maphash_purego.go:176 +0x6f7
hash/maphash.writeComparable[...](0xc0000a0e78?, 0x1c0000a0f08)
	/usr/lib64/go/1.24/src/hash/maphash/maphash_purego.go:111 +0x31
hash/maphash.comparableHash[...](0x0?, {0x552308?})
	/usr/lib64/go/1.24/src/hash/maphash/maphash_purego.go:105 +0x58
hash/maphash.Comparable[...](...)
	/usr/lib64/go/1.24/src/hash/maphash/maphash.go:289
main.main()
	/home/user/src/1/main.go:8 +0x3d
exit status 2

The problem is that purego implementation of maphash doesn't handle reflect.Chan kind of values: https://cs.opensource.google/go/go/+/refs/tags/go1.24.3:src/hash/maphash/maphash_purego.go;l=115-175

I can submit pull request which will make it handle reflect.Chan as every other pointer types, hashing v.Pointer() value.

What did you expect to see?

No panic like with regular go run main.go command.
@gabyhelp
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(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)

@gabyhelp gabyhelp added the BugReport Issues describing a possible bug in the Go implementation. label May 10, 2025
@qiulaidongfeng
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Thanks for report.
You can send the fix, See https://go.dev/doc/contribute.

Snawoot added a commit to Snawoot/go that referenced this issue May 10, 2025
@Snawoot
hash/maphash: hash channels in purego version too
1ee053e 
Make maphash properly hash channels as represented by pointer.

Fixes golang#73657
@Snawoot Snawoot linked a pull request May 10, 2025 that will close this issue
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@gopherbot
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Change https://go.dev/cl/671655 mentions this issue: hash/maphash: hash channels in purego version of maphash.Comparable

@qiulaidongfeng
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@gopherbot please consider this for backport to 1.24. This issue causes when using pruego build tags, maphash.Comparable cannot handle channal type correctly. There is no solution.

@gopherbot
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Backport issue(s) opened: #73669 (for 1.24).

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

@gopherbot gopherbot mentioned this issue May 11, 2025
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hash/maphash: hash channels in purego version of maphash.Comparable Snawoot/go
4 participants
@Snawoot @gopherbot @qiulaidongfeng @gabyhelp