Loading Go plugin from Go shared library ends up with `fatal error: runtime: no plugin module data`

[Karthik Krishnamurthy]

Hello,

This is probably an unusual situation, but I am working on a product that has the following chain of invocation.

C (native shared library libfoo.so) -> Go (c-shared libbar.so)

So basically, a native C shared library invokes a -buildmode=c-shared type Go shared library. This interaction works just fine.

However, we are augmenting libbar.so (Go shared library) to invoke a Go-style plugin (libplugin.so) using Go's plugin package. The very first attempt of this, failed like this:

fatal error: runtime: no plugin module data


goroutine 17 [running, locked to thread]:
runtime.throw(0xf72b5cc4, 0x1e)
    /usr/local/go/src/runtime/panic.go:774 +0x70 fp=0xc64d1b48 sp=0xc64d1b34 pc=0xf71bfdd0
plugin.lastmoduleinit(0xc648e5e0, 0x1001, 0x1001, 0xc64823e8, 0x95b9588)
    /usr/local/go/src/runtime/plugin.go:20 +0xa50 fp=0xc64d1bd4 sp=0xc64d1b48 pc=0xf71c1420
plugin.open(0xc64a60c0, 0x26, 0x29, 0xc64a6060, 0x2a)
    /usr/local/go/src/plugin/plugin_dlopen.go:77 +0x388 fp=0xc64d1d2c sp=0xc64d1bd4 pc=0xf7275ad8
plugin.Open(...)
    /usr/local/go/src/plugin/plugin.go:32
zero/base/interfaces.glob..func1(0xc64a60c0, 0x29, 0xf72b2610, 0x11, 0x29, 0x0, 0xf719e2e5, 0xf71d958c)
    /app/base/interfaces/plugin.go:12 +0x2e fp=0xc64d1d68 sp=0xc64d1d2c pc=0xf7276cbe
zero/base.glob..func4(0xf7759c60, 0x21, 0xf7357f80, 0xc64823e0, 0xc64a8445, 0x5, 0xf, 0xe, 0xd, 0xd)
    /app/base/zl_helper.go:28 +0xb4 fp=0xc64d1d9c sp=0xc64d1d68 pc=0xf72ac554
main.glob..func10(0xffa1e800, 0x2, 0x2, 0xf7759c60, 0x21, 0xf775ac60, 0x1b, 0x15, 0xc648e5c0, 0x5, ...)
    /app/dec/dec.go:328 +0x7a fp=0xc64d1dd8 sp=0xc64d1d9c pc=0xf72aeb0a
main.glob..func11(0xffa1e800, 0x2, 0x2, 0xf7759c60, 0x21, 0xf775ac60, 0x1b, 0x15, 0xc6496040, 0x5, ...)
    /app/dec/dec.go:368 +0xa3 fp=0xc64d1e34 sp=0xc64d1dd8 pc=0xf72aee13
main.Decorate(0xffa1e800, 0x2, 0x2, 0xf7759c60, 0x21, 0xf775ac60, 0x1b, 0x15, 0xc6436000)
    /app/dec/dec.go:98 +0x1f3 fp=0xc64d1eac sp=0xc64d1e34 pc=0xf72ad0b3
main._cgoexpwrap_079f3b2ec7da_Decorate(0xffa1e800, 0x2, 0x2, 0xf7759c60, 0x21, 0xf775ac60, 0x1b, 0x15, 0x0)
    _cgo_gotypes.go:79 +0x95 fp=0xc64d1ef4 sp=0xc64d1eac pc=0xf72ace15
runtime.call64(0x0, 0xffa1e72c, 0xffa1e79c, 0x24, 0x0)
    /usr/local/go/src/runtime/asm_386.s:571 +0x31 fp=0xc64d1f38 sp=0xc64d1ef4 pc=0xf71e9ad1
runtime.cgocallbackg1(0x0)
    /usr/local/go/src/runtime/cgocall.go:314 +0x162 fp=0xc64d1fb0 sp=0xc64d1f38 pc=0xf71966f2
runtime.cgocallbackg(0x0)
    /usr/local/go/src/runtime/cgocall.go:191 +0x9d fp=0xc64d1fe0 sp=0xc64d1fb0 pc=0xf719650d
runtime.cgocallback_gofunc(0x0, 0x0, 0x0, 0x0)
    /usr/local/go/src/runtime/asm_386.s:810 +0x79 fp=0xc64d1ff0 sp=0xc64d1fe0 pc=0xf71eab79
runtime.goexit()
    /usr/local/go/src/runtime/asm_386.s:1325 +0x1 fp=0xc64d1ff4 sp=0xc64d1ff0 pc=0xf71eb081
Aborted

What is the error indicative of?

Is invoking go plugin from go shared library supported?

I know Go plugins have a few restrictions. I have verified that all the above libraries are built on the same machine with the same gcc/go toolkit.

[Ian Lance Taylor]

I wouldn't be surprised if you are the first person to try this. I'm
not surprised that it doesn't work. I can't think of any fundamental
reason why it wouldn't work, so it may be relatively easy to fix if
you want to dig into the linker. I'm not sure.

Ian

[Karthik Krishnamurthy]

Ian,

I did some more digging on the web and landed on this Go issue where you had a comment: https://github.com/golang/go/issues/18123#issuecomment-264590075. 

The original issue is related c-archive buildmode, but reading further on that thread, I am guessing that even for Go shared libraries built with c-shared buildmode, invoking a plugin doesn't work due to multiple Go runtimes being loaded.

This comment: https://github.com/golang/go/issues/18123#issuecomment-469111906 has a demo that resembles my situation.

Given all this, I am thinking that native C shared library -> Go shared library -> Go plugin is an unsupported situation. Am I missing something? 

Thanks,

Karthik.

[Ian Lance Taylor]

On Tue, Jan 7, 2020 at 7:10 AM Karthik Krishnamurthy
<karth...@gmail.com> wrote:
>
> I did some more digging on the web and landed on this Go issue where you had a comment: https://github.com/golang/go/issues/18123#issuecomment-264590075.
>
> The original issue is related c-archive buildmode, but reading further on that thread, I am guessing that even for Go shared libraries built with c-shared buildmode, invoking a plugin doesn't work due to multiple Go runtimes being loaded.
>
> This comment: https://github.com/golang/go/issues/18123#issuecomment-469111906 has a demo that resembles my situation.
>
> Given all this, I am thinking that native C shared library -> Go shared library -> Go plugin is an unsupported situation. Am I missing something?

I doubt it. Sorry for not being clear in my earlier reply: it's
definitely unsupported. I was speculating as to whether it might be
possible to make it work if you wanted to dig into the linker.

Ian

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