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

[Snawoot]

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]

Related Issues

• runtime: Invalid "concurrent map writes" after recovered runtime-panic on previous map assign with non-comparable key #19359 (closed)
• reflect: Type.Comparable returns incorrect values for some types obtained via reflection #21011 (closed)
• hash/maphash, runtime: Fallback versions of the hash function are likely vulnerable to hash-flooding DoS #66841 (closed)
• cmd/go2go: panic in type checker #43526 (closed)
• SIGSEGV when testing, version bdfc3faa253a #387 (closed)
• encoding/json: panic if marshaling pointer and non-pointer of same base type #6458 (closed)
• internal/concurrent: hashtriemap uses abi.NoEscape cause incorrect inlining decision #68511 (closed)
• fmt: printing a map with unsafe.Pointer keys crashes #42622 (closed)
• hash/maphash: Hash always escapes #35636 (closed)

Related Code Changes

• runtime: improve performance of empty map with interface key type

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[qiulaidongfeng]

Thanks for report.
You can send the fix, See https://go.dev/doc/contribute.

[gopherbot]

Change https://go.dev/cl/671655 mentions this issue: hash/maphash: hash channels in purego version of maphash.Comparable

[qiulaidongfeng]

@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]

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]

Change https://go.dev/cl/676817 mentions this issue: [release-branch.go1.24] hash/maphash: hash channels in purego version of maphash.Comparable