cgo : free pointer can still use

[dreamerjackson]

i study and write the cgo code, i free the pointer but i still can use it ,why?

my code

package main


// #include <stdio.h>
// #include <stdlib.h>
// void myFunc(char *msg) {
// printf("Hello %s,%p!\n", msg,msg);
// }
import "C"
import (
	"fmt"
	"unsafe"
)

func main() {
	m := C.CString("world")
	fmt.Printf("msg.msg:%p,%p\n",unsafe.Pointer(m),m)
	C.free(unsafe.Pointer(m))
	C.myFunc(m)
}

What version of Go are you using (go version)?

$ go version
go 1.14.7 mac and go 1.12 centos all have this problem

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

$ go env
GO111MODULE="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/jackson/Library/Caches/go-build"
GOENV="/Users/jackson/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GONOPROXY="github.com/dreamEducation"
GONOSUMDB="github.com/dreamEducation"
GOOS="darwin"
GOPATH="/Users/xxx/go"
GOPRIVATE="github.com/dreamEducation"
GOPROXY="direct"
GOROOT="/Users/xxx/go/go1.14.7"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/Users/xxx/go/go1.14.7/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/dev/null"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/g2/0l4g444904vbn8wxnrw0j_980000gn/T/go-build764948702=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you expect to see?

panic because use the free pointer

What did you see instead?

msg.msg:0x4205a40,0x4205a40
Hello world,0x4205a40!

[davecheney]

Thank you for raising this issue. I do not believe this is a bug in Go, this is just the way C works. However, it should be noted that as you've freed that memory you are into the area of underfined behaviour, after which, there are no guarentees.

Unlike many projects, the Go project does not use GitHub Issues for general discussion or asking questions. GitHub Issues are used for tracking bugs and proposals only.

For asking questions, see:

• Stack Overflow with questions tagged "go"

• The Go Forum, a web-based forum

• Gophers Slack, use the invite app for access. The #general channel is a good starting point.

• Go Community on Hashnode with questions and posts tagged with "go"

• The golang-nuts mailing list

• IRC channel #go-nuts on Freenode

[dreamerjackson]

@davecheney thanks, i just report a more strange cgo example in Stack Overflow ,can you look it ?
https://stackoverflow.com/questions/65642093/cgo-free-pointer-can-still-use