map with *[]byte as index/key returns nil map value when map value is not nil #76988
Description
Go version
go version go1.25.3 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/zip/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/zip/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build1641070464=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/dev/null'
GOMODCACHE='/home/zip/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/zip/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/zip/xyzbots/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/zip/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/home/zip/xyzbots/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.25.3'
GOWORK=''
PKG_CONFIG='pkg-config'What did you do?
package main
import (
"fmt"
"math/rand"
"sync"
"time"
)
func main() {
var l = make(map[*[]byte]map[string]string)
var ll = make([]byte, 0)
var existing_pointer *[]byte = &ll
l[existing_pointer] = make(map[string]string)
var m sync.Mutex
var c = 0
for {
if c == 20000 {
break
}
go func() {
time.Sleep(time.Second * time.Duration(rand.Intn(10)))
m.Lock()
var another_pointer *[]byte
for e := range l {
// this is the same pointer as existing_pointer
another_pointer = e
}
if l[another_pointer] == nil {
// this can happen multiple times incorrectly
fmt.Println("another_pointer is not in l")
l[another_pointer] = make(map[string]string)
}
m.Unlock()
}()
c += 1
}
}What did you see happen?
fmt.Println("another_pointer is not in l")This is executed multiple times.
What did you expect to see?
fmt.Println("another_pointer is not in l")This executed once.