GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/go"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build756041191=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"

package main

import (
	"fmt"
)

type aPlugin struct {
	str *string
}

func (r aPlugin) Init() {
	str := "a"
	r.str = &str
	fmt.Printf("String pointer is %v\n", r.str)
}

func (r aPlugin) String() string {
	fmt.Printf("String pointer is %v\n", r.str)
	return fmt.Sprintf("String: %v", *r.str)
}

var Plugin aPlugin

package main

import "plugin"
import "fmt"

type P interface {
	Init()
	String() string
}

func main() {
	aPlug, _ := plugin.Open("a.so")
	aSymPlug, _ := aPlug.Lookup("Plugin")
	plug, ok := aSymPlug.(P)
	if !ok {
		fmt.Print("Bad plugin\n")
	}
	plug.Init()
	plug.String()
}

go build -buildmode=plugin -o a.so a.go
go build

# ./go-plugin-bug
String pointer is 0xc420010220
String pointer is 0xc420010220

# ./go-plugin-bug
String pointer is 0xc420010220
String pointer is <nil>
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x7f4fe19fc3f7]

goroutine 1 [running]:
plugin/unnamed-43d067c47d00006d749146ae708f2304df4b538b.aPlugin.String(0x0, 0x7f4fe19fc53e, 0x0)
	/go/src/github.com/patrobinson/go-plugin-bug/a.go:19 +0x97
plugin/unnamed-43d067c47d00006d749146ae708f2304df4b538b.(*aPlugin).String(0x7f4fe1cd29b8, 0x7f4fe1c43500, 0x7f4fe1cd29b8)
	<autogenerated>:1 +0x3e
main.main()
	/go/src/github.com/patrobinson/go-plugin-bug/main.go:19 +0xf2