plugin: using same type in map across two plugins causes stackoverflow

[vimalk78]

Please answer these questions before submitting your issue. Thanks!

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

$ go version
go version go1.8 linux/amd64

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

$ go env
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/vimal/gowork"
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-build121316025=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

What did you do?

using the plugins feature. created the following two plugins using the command go build -buildmode=plugin

plugin1

package main

import "C"
import "log"

func init() {
    log.Printf("testplugin.main.init invoked\n")
}

type innerType struct {
    f1 int
    f2 string
}

type MyStruct struct {
    Name string
    Id   int
    mm   map[string]innerType
}

func InitPlugin() {
    m := MyStruct{Name: "x", Id: 0}
    log.Printf("testplugin.InitPlugin %v", m)
}

plugin2

package main

import "C"
import "log"

func init() {
    log.Printf("testplugin1.main.init invoked\n")
}

type innerType struct {
    f1 int
    f2 string
}

type MyStruct struct {
    Name string
    Id   int
    mm   map[string]innerType
}

func InitPlugin() {
    m := MyStruct{Name: "x", Id: 0}
    log.Printf("testplugin1.InitPlugin %v", m)
}

Both plugins have the same code, except the minor difference in print statements.

a main program loads the plugins using the api plugin.Open(pluginpath)

What did you expect to see?

Both plugins loaded succesfully.

What did you see instead?

a stackoverflow error. I have limited the stack using debug.SetMaxStack(100) so that i can see the beginning of the stack.

runtime: goroutine stack exceeds 100-byte limit
fatal error: stack overflow

runtime stack:
runtime.throw(0x537589, 0xe)
        /usr/local/go/src/runtime/panic.go:596 +0x95
runtime.newstack(0x0)
        /usr/local/go/src/runtime/stack.go:1089 +0x3f2
runtime.morestack()
        /usr/local/go/src/runtime/asm_amd64.s:398 +0x86

goroutine 1 [running]:
runtime.(*_type).string(0x7f29a2dca140, 0x0, 0x0)
        /usr/local/go/src/runtime/type.go:45 +0xad fp=0xc42004c320 sp=0xc42004c318
runtime.typesEqual(0x7f29a2dca140, 0x7f29a31de140, 0x0)
        /usr/local/go/src/runtime/type.go:543 +0x73 fp=0xc42004c448 sp=0xc42004c320
runtime.typesEqual(0x7f29a2dd4a60, 0x7f29a31e8a60, 0x7f29a31d2850)
        /usr/local/go/src/runtime/type.go:647 +0xc0a fp=0xc42004c570 sp=0xc42004c448
runtime.typesEqual(0x7f29a2dc0a60, 0x7f29a31d4a60, 0x0)
        /usr/local/go/src/runtime/type.go:627 +0x9c5 fp=0xc42004c698 sp=0xc42004c570
runtime.typesEqual(0x7f29a2dd4a60, 0x7f29a31e8a60, 0x7f29a31d2850)
        /usr/local/go/src/runtime/type.go:647 +0xc0a fp=0xc42004c7c0 sp=0xc42004c698
runtime.typesEqual(0x7f29a2dc0a60, 0x7f29a31d4a60, 0x0)
        /usr/local/go/src/runtime/type.go:627 +0x9c5 fp=0xc42004c8e8 sp=0xc42004c7c0
runtime.typesEqual(0x7f29a2dd4a60, 0x7f29a31e8a60, 0x7f29a31d2850)
        /usr/local/go/src/runtime/type.go:647 +0xc0a fp=0xc42004ca10 sp=0xc42004c8e8
runtime.typesEqual(0x7f29a2dc0a60, 0x7f29a31d4a60, 0x0)
        /usr/local/go/src/runtime/type.go:627 +0x9c5 fp=0xc42004cb38 sp=0xc42004ca10
runtime.typesEqual(0x7f29a2dd4a60, 0x7f29a31e8a60, 0x7f29a31d2850)
        /usr/local/go/src/runtime/type.go:647 +0xc0a fp=0xc42004cc60 sp=0xc42004cb38
runtime.typesEqual(0x7f29a2dc0a60, 0x7f29a31d4a60, 0x0)
        /usr/local/go/src/runtime/type.go:627 +0x9c5 fp=0xc42004cd88 sp=0xc42004cc60
runtime.typesEqual(0x7f29a2dd4a60, 0x7f29a31e8a60, 0x7f29a31d2850)
        /usr/local/go/src/runtime/type.go:647 +0xc0a fp=0xc42004ceb0 sp=0xc42004cd88
runtime.typesEqual(0x7f29a2dc0a60, 0x7f29a31d4a60, 0x0)
        /usr/local/go/src/runtime/type.go:627 +0x9c5 fp=0xc42004cfd8 sp=0xc42004ceb0
runtime.typesEqual(0x7f29a2dd4a60, 0x7f29a31e8a60, 0x7f29a31d2850)
        /usr/local/go/src/runtime/type.go:647 +0xc0a fp=0xc42004d100 sp=0xc42004cfd8
runtime.typesEqual(0x7f29a2dc0a60, 0x7f29a31d4a60, 0x0)
        /usr/local/go/src/runtime/type.go:627 +0x9c5 fp=0xc42004d228 sp=0xc42004d100
runtime.typesEqual(0x7f29a2dd4a60, 0x7f29a31e8a60, 0x7f29a31d2850)
        /usr/local/go/src/runtime/type.go:647 +0xc0a fp=0xc42004d350 sp=0xc42004d228
runtime.typesEqual(0x7f29a2dc0a60, 0x7f29a31d4a60, 0x0)
        /usr/local/go/src/runtime/type.go:627 +0x9c5 fp=0xc42004d478 sp=0xc42004d350
runtime.typesEqual(0x7f29a2dd4a60, 0x7f29a31e8a60, 0x7f29a31d2850)
        /usr/local/go/src/runtime/type.go:647 +0xc0a fp=0xc42004d5a0 sp=0xc42004d478
runtime.typesEqual(0x7f29a2dc0a60, 0x7f29a31d4a60, 0x0)
        /usr/local/go/src/runtime/type.go:627 +0x9c5 fp=0xc42004d6c8 sp=0xc42004d5a0
runtime.typesEqual(0x7f29a2dd4a60, 0x7f29a31e8a60, 0x7f29a31d2850)
        /usr/local/go/src/runtime/type.go:647 +0xc0a fp=0xc42004d7f0 sp=0xc42004d6c8
runtime.typesEqual(0x7f29a2dc0a60, 0x7f29a31d4a60, 0xc4800c6242)
        /usr/local/go/src/runtime/type.go:627 +0x9c5 fp=0xc42004d918 sp=0xc42004d7f0
runtime.typelinksinit()
        /usr/local/go/src/runtime/type.go:510 +0x432 fp=0xc42004db20 sp=0xc42004d918
plugin.lastmoduleinit(0xc39400, 0xc42000fb48, 0xc3ab60, 0x43, 0x7bbf60)
        /usr/local/go/src/runtime/plugin.go:52 +0x2f9 fp=0xc42004dc50 sp=0xc42004db20
plugin.open(0x7fffaaddfd48, 0x1d, 0x0, 0x0, 0x0)
        /usr/local/go/src/plugin/plugin_dlopen.go:72 +0x25d fp=0xc42004de90 sp=0xc42004dc50
plugin.Open(0x7fffaaddfd48, 0x1d, 0xc42004df28, 0x1, 0x1)
        /usr/local/go/src/plugin/plugin.go:30 +0x35 fp=0xc42004dec8 sp=0xc42004de90
main.loadPlugin(0x7fffaaddfd48, 0x1d, 0xc42000c200)
        /home/vimal/gowork/src/github.com/v70420/pluginfw/main.go:31 +0xd7 fp=0xc42004df48 sp=0xc42004dec8
main.main()
        /home/vimal/gowork/src/github.com/v70420/pluginfw/main.go:19 +0x75 fp=0xc42004df88 sp=0xc42004df48
runtime.main()
        /usr/local/go/src/runtime/proc.go:185 +0x20a fp=0xc42004dfe0 sp=0xc42004df88
runtime.goexit()
        /usr/local/go/src/runtime/asm_amd64.s:2197 +0x1 fp=0xc42004dfe8 sp=0xc42004dfe0

without limiting the stack size, the error is same, except

runtime: goroutine stack exceeds 1000000000-byte limit
fatal error: stack overflow

i narrowed down the issue to this

type MyStruct struct {
    Name string
    Id   int
    mm   map[string]innerType << using the type in map causes the error
}

If the type is not used in the map, the error is gone, and both plugins can be loaded successfully.

type MyStruct struct {
    Name string
    Id   int
    // mm   map[string]innerType << commenting this line does not cause the error
}

also, renaming the type innerType to some other name, say, innerType_xyz in one of the plugins also avoids the stackoverflow.

[tzneal]

It's walking an infinite list of types caused by the overflow buckets in the map. Each bucket has a has a values field of type innerType, and a pointer to a bucket. Since everything else is identical, it recurses through the bucket pointer back to a bucket, and keeps going.

Any identical recursive type definition in two plugins causes it.

[gopherbot]

CL https://golang.org/cl/40292 mentions this issue.

[vimalk78]

not sure, but does it make sense to check reverse way also?

	tp := _typePair{t, v}
	if _, ok := seen[tp]; ok {
		return true
	}
        reversetp := _typePair{v, t}
	if _, ok := seen[reversetp]; ok {
		return true
	}

        ...
        ...
        seen[tp] = struct{}{}
        seen[reversetp] = struct{}{}