cmd/go: plugin versions do not match when built within vs. outside a module

[zimnx]

What did you do?

I have simple application that loads Go plugins and allows them to communicate with app via exported interface.

Simplified version can be found here.
Shared interface is stored under ext directory, real implementation is located underplugin directory.
Application passes pointer to real implementation to dynamically loaded plugin which expects interface.

Example plugin code can be found here.

Unfortunately combination of Go Modules and Go Plugins doesn't work unless go.mod of plugins module has replace entry with local relative path for shared interface path.
When I use remote location in plugins module, application crashes because of wrong version of packages.

Build app:

~/tmp/go-plugin-bug/central on  master ⌚ 16:12:19
$ go clean -modcache 

~/tmp/go-plugin-bug/central on  master ⌚ 16:12:21
$ git checkout v1.0.0
Note: checking out 'v1.0.0'.

~/tmp/go-plugin-bug/central on  f1d7e9f ⌚ 16:12:22
$ go install -a

Then build plugin

~/tmp/go-plugin-bug/central on  f1d7e9f ⌚ 16:12:27
$ cd ../plugins 

~/tmp/go-plugin-bug/plugins on  master ⌚ 16:12:28
$ cat go.mod 
module github.com/zimnx/plugins

go 1.12

require github.com/zimnx/central v1.0.0


~/tmp/go-plugin-bug/plugins on  master ⌚ 16:12:30
$ go build -buildmode=plugin -o plugin.so
go: finding github.com/zimnx/central v1.0.0
go: downloading github.com/zimnx/central v1.0.0
go: extracting github.com/zimnx/central v1.0.0

~/tmp/go-plugin-bug/plugins on  master ⌚ 16:12:39
$ central plugin.so 
2019/04/08 16:12:42 cant open plugin: plugin.Open("plugin"): plugin was built with a different version of package github.com/zimnx/central/ext

When I change plugins go mod to use local path instead of remote one everything works.

~/tmp/go-plugin-bug/plugins on  master ⌚ 16:12:42
$ cat go.mod                             
module github.com/zimnx/plugins

go 1.12

require github.com/zimnx/central v1.0.0

replace github.com/zimnx/central => ../central

~/tmp/go-plugin-bug/plugins on  master! ⌚ 16:14:30
$ go build -buildmode=plugin -o plugin.so

~/tmp/go-plugin-bug/plugins on  master! ⌚ 16:14:33
$ central plugin.so 
hello = world

What did you expect to see?

Go Modules and plugins working fine when remote path is used.

What did you see instead?

Error about different package versions.

Does this issue reproduce with the latest release (go1.12.3)?

Yes.

System details

go version go1.12.3 linux/amd64
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/maciej/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/maciej/work"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/maciej/tmp/go-plugin-bug/plugins/go.mod"
GOROOT/bin/go version: go version go1.12.3 linux/amd64
GOROOT/bin/go tool compile -V: compile version go1.12.3
uname -sr: Linux 4.14.13-041413-generic
Distributor ID:	Ubuntu
Description:	Ubuntu 17.10
Release:	17.10
Codename:	artful
/lib/x86_64-linux-gnu/libc.so.6: GNU C Library (Ubuntu GLIBC 2.26-0ubuntu2.1) stable release version 2.26, by Roland McGrath et al.
gdb --version: GNU gdb (Ubuntu 8.0.1-0ubuntu1) 8.0.1

[zimnx]

Bump. Any plans to fix this? Seems that algorithm which verifies package version integrity needs alignment.

[bcmills]

This is the same underlying problem as #29814.

The workaround should be to build both the plugin and the main binary from outside of their respective repositories, or (as you note) to use a replace directive when building locally.

[bcmills]

CC @jayconrod

[bcmills]

See also #31278, of which this may be a duplicate.

[juhwany]

@bcmills

Is this issue related to #16860 ?

Building plugin and main binary with -trimpath flag doesn't solve this issue even using a go toolchain built from head.

[xxxserxxx]

There are several similar tickets; apologies if this is not the right place to comment.

If the path is different but the version of the libraries are identical, we get version mismatch errors. A way of replicating this is to build the calling program in a container, and build the plugin outside of the container. The paths may look like this:

# Calling
/go/pkg/mod/github.com/shirou/gopsutil@v2.18.11+incompatible/internal/common/common.go
# Called
/home/ser/go/pkg/mod/github.com/shirou/gopsutil@v2.18.11+incompatible/internal/common/common.go

Building locally, and where:

• the plugin is built using a go.mod with a specific date+revision version for the calling main program, and
• the calling application is built from a checkout at that version, verified that the version in the plugin go.mod matches the checked-out version with:

echo $(TZ=UTC git show -s --format=%cd --date=format-local:%Y%m%d%H%M%S HEAD | cut -b -19 |  tr -cd '[:digit:]')-$(git rev-parse HEAD | cut -b -12)

• and both programs being compiled with the same go executable, and
• using --trimpath on both, and
• both go.mod list the same go version dependency
  I get the same version incompatibility error with a different package:

# Error:
2:31:33 main.go:485: plugin.Open("dummy"): plugin was built with a different version of package github.com/xxxserxxx/gotop/v3/devices
$ #######################################################
$ strings ./gotop | grep 'v3/devices$'
go.link.pkghashbytes.github.com/xxxserxxx/gotop/v3/devices
go.link.pkghash.github.com/xxxserxxx/gotop/v3/devices
%github.com/xxxserxxx/gotop/v3/devices
go.link.pkghashbytes.github.com/xxxserxxx/gotop/v3/devices
go.link.pkghash.github.com/xxxserxxx/gotop/v3/devices
$ #######################################################
$ strings dummy.so | grep 'v3/devices$'
go.link.pkghashbytes.github.com/xxxserxxx/gotop/v3/devices
go.link.pkghash.github.com/xxxserxxx/gotop/v3/devices
github.com/xxxserxxx/gotop-dummygithub.com/xxxserxxx/gotop-dummygithub.com/xxxserxxx/gotop/v3/devices
%github.com/xxxserxxx/gotop/v3/devices
go.link.pkghashbytes.github.com/xxxserxxx/gotop/v3/devices
go.link.pkghash.github.com/xxxserxxx/gotop/v3/devices

I've played with copying the go.sum into the plugin directory so that it's identical to the other project, and have made sure that the entries in both go.mods are the same (except for the plugin's dependency on the main program).

If I add the following to the plugin's go.mod:

replace github.com/xxxserxxx/gotop/v3 => ../gotop

then it works.

Edit

Rewrote some of the text to be more readable, I hope.

Edit 2

I made an error: I need to remove the -trimpath argument in addition to adding the replace directive in the go.mod, or else I still get a version incompatibility error. -trimpath appears to make things worse.

[xplodwild]

Same thing happens for me for a go.mod-based project regarding the -trimpath option. When building both the main app and the plugin with -trimpath enabled, I get a plugin was built with a different version of package github.com/me/myapp/mypackage. Removing -trimpath makes it load fine, however I'm afraid people with other setups might have trouble getting their plugins loaded due to paths inconsistencies.

[xxxserxxx]

Another data point which I can't even begin to interpret:

$ git clone https://github.com/xxxserxxx/gotop
$ git clone https://github.com/xxxserxxx/gotop-dummy
$ cd gotop && git checkout v3.5.0
$ go build -o gotop ./cmd/gotop
$ cd ../gotop-dummy && grep gotop go.mod
require github.com/xxxserxxx/gotop/v3 v3.5.0
$ go mod download
$ go mod vendor
$ go build --buildmode=plugin -o ../gotop/dummy.so .
$ cd ../gotop
$ ./gotop -X dummy    # this hangs for some reason; ^C to break
$ cat ~/.local/state/gotop/errors.log
13:03:16 main.go:485: plugin.Open("dummy"): plugin was built with a different version of package github.com/shirou/gopsutil/internal/common
$ go mod graph | grep gopsutil
github.com/xxxserxxx/gotop/v3 github.com/shirou/gopsutil@v2.18.11+incompatible
➜  gotop git:(be42ba5) ✗ git log -1
commit be42ba538cefc892d1dc3d18c783483f4875baff (HEAD, tag: v3.5.0)
$ cd ../gotop-dummy
$ go mod graph | grep gopsutil
github.com/xxxserxxx/gotop/v3@v3.5.0 github.com/shirou/gopsutil@v2.18.11+incompatible

These are the identical dependencies. Why is the system claiming that they are not?

[hoijui]

This is the same underlying problem as #29814.

The workaround should be to build both the plugin and the main binary from outside of their respective repositories, or (as you note) to use a replace directive when building locally.

do you mean to say, that the ext folder should be its own module, separate from the main app?
would that work?

[mattn]

The current plugin mechanism does not allow you to avoid mixed package hashes. For example, this error occurs when a main application that references package A loads plugins that references A. I often use gophernotes to try to write notebook with Go. gophernotes reference mattn/go-runewidth. So gophernotes can not import mattn/go-runewidth on the notebooks. I have to disable Go code to avoid this.

diff --git a/src/runtime/plugin.go b/src/runtime/plugin.go
index cd7fc5f848..ace1b13ed9 100644
--- a/src/runtime/plugin.go
+++ b/src/runtime/plugin.go
@@ -48,12 +48,14 @@ func plugin_lastmoduleinit() (path string, syms map[string]interface{}, errstr s
                        throw("plugin: new module data overlaps with previous moduledata")
                }
        }
-       for _, pkghash := range md.pkghashes {
-               if pkghash.linktimehash != *pkghash.runtimehash {
-                       md.bad = true
-                       return "", nil, "plugin was built with a different version of package " + pkghash.modulename
+       /*
+               for _, pkghash := range md.pkghashes {
+                       if pkghash.linktimehash != *pkghash.runtimehash {
+                               md.bad = true
+                               return "", nil, "plugin was built with a different version of package " + pkghash.modulename
+                       }
                }
-       }
+       */

        // Initialize the freshly loaded module.
        modulesinit()

[devsergiy]

@rsc Hi Russ,
Is this issue could be fixed in some foreseen future?

[bcmills]

A fix for this issue would require changes to the compiler (to prevent cross-package inlining when building plugins), and probably the linker (to interpret and record a signature for the package ABI). That's possible, but it would be a lot of work to support a fairly esoteric build mode.

@jeremyfaller could perhaps speak to whether the compiler and linker folks are planning to implement that support, but to my knowledge it's not on the roadmap at this time.

[jeremyfaller]

@bcmills's knowledge is correct. We've kicked around improving this for some time, but those things are just thoughts. It's a complicated problem, and it's almost certainly not on the roadmap for 2022.

[marcusholmessumup]

just ran into this problem and cannot get it working even with a replace directive in the plugin's go mod file.

[septatrix]

A fix for this issue would require changes to the compiler (to prevent cross-package inlining when building plugins), and probably the linker (to interpret and record a signature for the package ABI). That's possible, but it would be a lot of work to support a fairly esoteric build mode.

This is mostly a chicken and egg problem where many projects are not utilizing plugins due to their complicated build setup and other limitation (version incompatibility, requiring a main packet, linux only) while the plugin system does not get improved because very few projects are using it. However the demand certainly exists.

[antst]

If look around, there are plenty of incomplete and partially-working attempt to deal with plugins, just because current system is way too restricting. At the end, a lot of efforts lost for nothing and 1) adoption of current plugins system is subpar, and 2) people waste time re-introducing wheel.
I think, for most of it, if we introduce some kind of "unsafe" switch which disables next lines in src/runtime/plugin.go

	for _, pkghash := range md.pkghashes {
		if pkghash.linktimehash != *pkghash.runtimehash {
			md.bad = true
			return "", nil, "plugin was built with a different version of package " + pkghash.modulename
		}
	}

giving user options to make unsafe (and unrecommended) choice and deal with potential fallout on it's own, adoptions of plugin system will jump tremendously, which on it's own will lead to improvement of it. Solving chicken and egg issue from above.

Of course, it is not even close to be real solution. But rather temporary patch. But it give chance to actually use it.

In a current form it is not plugin system, it is merely lazy loading. The only realistic option to ensure than plugin will load, is to build is a part of source tree of the main code as part of the same compilation process.

or just rename to "lazy_load" to stop confusing people :)

[mark4z]

I try to import this and finally give up, maybe try the wasm.

[voodooEntity]

So its 2023 and i did run in the same issue as the rest here. I have a repostiory for my application and a respostiory for the plugin code. The idea was to write an application that can be fed by custom developed plugins for execution. Tho even considering the workarround with the alias it would be quite uncomfortable for people to use Plugins and this way of extending the apllication than.

I think this definatly should be considered to be solved since the net is allover filled with people hitting this issue and this thread now is ongoing for about 4 years with people asking for a solution.