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

$ go version
go version devel +e5ba612637 Thu Mar 7 14:12:01 2019 -0500 linux/amd64
$ gccgo --version
gccgo (GCC) 9.0.1 20190304 (experimental)

Does this issue reproduce with the latest release?

Yes

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

linux/amd64

$ go env
GOARCH="amd64"
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/ssd2/go1"
GOPROXY=""
GORACE=""
GOROOT="/ssd2/go"
GOTMPDIR=""
GCCGO="/ssd/gcc-trunk/cross/bin/gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
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 -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build042808661=/tmp/go-build -gno-record-gcc-switches"

What did you do?

There is a problem with gccgo regarding how it handles exported inlinable methods that are marked with the //go:nointerface flag. Here are a couple of packages that will reproduce the problem:

In $GOPATH/src/noitfimp:

package noitfimp

var pl int

type NoitfStruct struct {
	F int
	G int
}

//go:nointerface
func (t *NoitfStruct) GMethod() int {
	return t.G
}

func (t *NoitfStruct) FMethod() int {
	return t.F
}

//go:nointerface
func (t *NoitfStruct) NoInterfaceMethod() {}

and then in $GOPATH/src/noitfmain:

package noitfmain

import (
	"noitfimp"
)

type EmbedImported struct {
	noitfimp.NoitfStruct
}

func Test() []string {
	bad := []string{}
	x := interface{}(new(noitfimp.NoitfStruct))
	if _, ok := x.(interface {
		NoInterfaceMethod()
	}); ok {
		bad = append(bad, "fail 1")
	}

	x = interface{}(new(EmbedImported))
	if _, ok := x.(interface {
		NoInterfaceMethod()
	}); ok {
		bad = append(bad, "fail 2")
	}
	return bad
}

and then finally a driver program in $GOPATH/src/noitfdriver:

package main

import (
	"fmt"
	"noitfmain"
	"os"
)

func main() {
	bad := noitfmain.Test()
	if len(bad) > 0 {
		for _, s := range bad {
			fmt.Fprintf(os.Stderr, "test failed: %s\n", s)
		}
		os.Exit(1)
	}
}

Then compiler and run the final package (e.g. "go run -compiler gccgo itfdriver").

What did you expect to see?

Empty result from itfmain.Test

What did you see instead?

When executed, prints "test failed: fail 2".

It appears that the 'go:nointerface' property is being lost somehow when the imported type noitfimp.NoitfStruct is embedded into the itfmain type EmbedImported. If I look at the generated assembly, I can see that an additional method NoInterfaceMethod is being incorrectly attached to the type (other than FMethod).

The problem appears to be related to inlining -- in package noitfimp the method in question is empty, meaning that the body gets written out to the export data. If I modify the method body to include more complex statement (for example, a defer) then the problem goes away.