plugin: plugin loading fails if the plugin itself imports the plugin package (even indirectly)

[brunoga]

Please answer these questions before submitting your issue. Thanks!

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

go version go1.9 linux/amd64

Does this issue reproduce with the latest release?

Yes.

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

GOARCH="amd64"
GOBIN="/home/bga/Development/go/bin"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/bga/Development/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-build198786462=/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"

What did you do?

I wrote down and ran the plugin example here:

https://golang.org/pkg/plugin/#Symbol

I compiled the plugin code with "go build -buildmode=plugin" then I ran the loader program with "go run".

It worked as expected:

$ go run main.go
Hello, number 7

Then I changed the plugin code from:

package main

import "fmt"

var V int

func F() { fmt.Printf("Hello, number %d\n", V) }

To:

package main

import (
  "fmt"
  _ "plugin"
)

var V int

func F() { fmt.Printf("Hello, number %d\n", V) }

Recompiled the plugin and ran the loader program again.

What did you expect to see?

$ go run main.go
Hello, number 7

What did you see instead?

$ go run main.go
panic: plugin.Open: plugin was built with a different version of package plugin

goroutine 1 [running]:
main.main()
/home/bga/Development/go/src/bga-local/plugin2/main.go:10 +0x3bb
exit status 2

[ianlancetaylor]

CC @crawshaw

[crawshaw]

I believe this is a duplicate of #21373.

The fix, https://golang.org/cl/63693, is currently marked for 1.9.1 because the underlying issue is also responsible for a -trimpath failure.