4 files changed, 305 insertions, 0 deletions
diff --git a/src/plugin/plugin.go b/src/plugin/plugin.go
new file mode 100644
index 0000000..187d127
--- /dev/null
+++ b/src/plugin/plugin.go
@@ -0,0 +1,120 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package plugin implements loading and symbol resolution of Go plugins.
+//
+// A plugin is a Go main package with exported functions and variables that
+// has been built with:
+//
+//	go build -buildmode=plugin
+//
+// When a plugin is first opened, the init functions of all packages not
+// already part of the program are called. The main function is not run.
+// A plugin is only initialized once, and cannot be closed.
+//
+// # Warnings
+//
+// The ability to dynamically load parts of an application during
+// execution, perhaps based on user-defined configuration, may be a
+// useful building block in some designs. In particular, because
+// applications and dynamically loaded functions can share data
+// structures directly, plugins may enable very high-performance
+// integration of separate parts.
+//
+// However, the plugin mechanism has many significant drawbacks that
+// should be considered carefully during the design. For example:
+//
+//   - Plugins are currently supported only on Linux, FreeBSD, and
+//     macOS, making them unsuitable for applications intended to be
+//     portable.
+//
+//   - Applications that use plugins may require careful configuration
+//     to ensure that the various parts of the program be made available
+//     in the correct location in the file system (or container image).
+//     By contrast, deploying an application consisting of a single static
+//     executable is straightforward.
+//
+//   - Reasoning about program initialization is more difficult when
+//     some packages may not be initialized until long after the
+//     application has started running.
+//
+//   - Bugs in applications that load plugins could be exploited by
+//     an attacker to load dangerous or untrusted libraries.
+//
+//   - Runtime crashes are likely to occur unless all parts of the
+//     program (the application and all its plugins) are compiled
+//     using exactly the same version of the toolchain, the same build
+//     tags, and the same values of certain flags and environment
+//     variables.
+//
+//   - Similar crashing problems are likely to arise unless all common
+//     dependencies of the application and its plugins are built from
+//     exactly the same source code.
+//
+//   - Together, these restrictions mean that, in practice, the
+//     application and its plugins must all be built together by a
+//     single person or component of a system. In that case, it may
+//     be simpler for that person or component to generate Go source
+//     files that blank-import the desired set of plugins and then
+//     compile a static executable in the usual way.
+//
+// For these reasons, many users decide that traditional interprocess
+// communication (IPC) mechanisms such as sockets, pipes, remote
+// procedure call (RPC), shared memory mappings, or file system
+// operations may be more suitable despite the performance overheads.
+package plugin
+
+// Plugin is a loaded Go plugin.
+type Plugin struct {
+	pluginpath string
+	err        string        // set if plugin failed to load
+	loaded     chan struct{} // closed when loaded
+	syms       map[string]any
+}
+
+// Open opens a Go plugin.
+// If a path has already been opened, then the existing *Plugin is returned.
+// It is safe for concurrent use by multiple goroutines.
+func Open(path string) (*Plugin, error) {
+	return open(path)
+}
+
+// Lookup searches for a symbol named symName in plugin p.
+// A symbol is any exported variable or function.
+// It reports an error if the symbol is not found.
+// It is safe for concurrent use by multiple goroutines.
+func (p *Plugin) Lookup(symName string) (Symbol, error) {
+	return lookup(p, symName)
+}
+
+// A Symbol is a pointer to a variable or function.
+//
+// For example, a plugin defined as
+//
+//	package main
+//
+//	import "fmt"
+//
+//	var V int
+//
+//	func F() { fmt.Printf("Hello, number %d\n", V) }
+//
+// may be loaded with the Open function and then the exported package
+// symbols V and F can be accessed
+//
+//	p, err := plugin.Open("plugin_name.so")
+//	if err != nil {
+//		panic(err)
+//	}
+//	v, err := p.Lookup("V")
+//	if err != nil {
+//		panic(err)
+//	}
+//	f, err := p.Lookup("F")
+//	if err != nil {
+//		panic(err)
+//	}
+//	*v.(*int) = 7
+//	f.(func())() // prints "Hello, number 7"
+type Symbol any
diff --git a/src/plugin/plugin_dlopen.go b/src/plugin/plugin_dlopen.go
new file mode 100644
index 0000000..f6ae219
--- /dev/null
+++ b/src/plugin/plugin_dlopen.go
@@ -0,0 +1,153 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build (linux && cgo) || (darwin && cgo) || (freebsd && cgo)
+
+package plugin
+
+/*
+#cgo linux LDFLAGS: -ldl
+#include <dlfcn.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+#include <stdio.h>
+
+static uintptr_t pluginOpen(const char* path, char** err) {
+	void* h = dlopen(path, RTLD_NOW|RTLD_GLOBAL);
+	if (h == NULL) {
+		*err = (char*)dlerror();
+	}
+	return (uintptr_t)h;
+}
+
+static void* pluginLookup(uintptr_t h, const char* name, char** err) {
+	void* r = dlsym((void*)h, name);
+	if (r == NULL) {
+		*err = (char*)dlerror();
+	}
+	return r;
+}
+*/
+import "C"
+
+import (
+	"errors"
+	"sync"
+	"unsafe"
+)
+
+func open(name string) (*Plugin, error) {
+	cPath := make([]byte, C.PATH_MAX+1)
+	cRelName := make([]byte, len(name)+1)
+	copy(cRelName, name)
+	if C.realpath(
+		(*C.char)(unsafe.Pointer(&cRelName[0])),
+		(*C.char)(unsafe.Pointer(&cPath[0]))) == nil {
+		return nil, errors.New(`plugin.Open("` + name + `"): realpath failed`)
+	}
+
+	filepath := C.GoString((*C.char)(unsafe.Pointer(&cPath[0])))
+
+	pluginsMu.Lock()
+	if p := plugins[filepath]; p != nil {
+		pluginsMu.Unlock()
+		if p.err != "" {
+			return nil, errors.New(`plugin.Open("` + name + `"): ` + p.err + ` (previous failure)`)
+		}
+		<-p.loaded
+		return p, nil
+	}
+	var cErr *C.char
+	h := C.pluginOpen((*C.char)(unsafe.Pointer(&cPath[0])), &cErr)
+	if h == 0 {
+		pluginsMu.Unlock()
+		return nil, errors.New(`plugin.Open("` + name + `"): ` + C.GoString(cErr))
+	}
+	// TODO(crawshaw): look for plugin note, confirm it is a Go plugin
+	// and it was built with the correct toolchain.
+	if len(name) > 3 && name[len(name)-3:] == ".so" {
+		name = name[:len(name)-3]
+	}
+	if plugins == nil {
+		plugins = make(map[string]*Plugin)
+	}
+	pluginpath, syms, initTasks, errstr := lastmoduleinit()
+	if errstr != "" {
+		plugins[filepath] = &Plugin{
+			pluginpath: pluginpath,
+			err:        errstr,
+		}
+		pluginsMu.Unlock()
+		return nil, errors.New(`plugin.Open("` + name + `"): ` + errstr)
+	}
+	// This function can be called from the init function of a plugin.
+	// Drop a placeholder in the map so subsequent opens can wait on it.
+	p := &Plugin{
+		pluginpath: pluginpath,
+		loaded:     make(chan struct{}),
+	}
+	plugins[filepath] = p
+	pluginsMu.Unlock()
+
+	doInit(initTasks)
+
+	// Fill out the value of each plugin symbol.
+	updatedSyms := map[string]any{}
+	for symName, sym := range syms {
+		isFunc := symName[0] == '.'
+		if isFunc {
+			delete(syms, symName)
+			symName = symName[1:]
+		}
+
+		fullName := pluginpath + "." + symName
+		cname := make([]byte, len(fullName)+1)
+		copy(cname, fullName)
+
+		p := C.pluginLookup(h, (*C.char)(unsafe.Pointer(&cname[0])), &cErr)
+		if p == nil {
+			return nil, errors.New(`plugin.Open("` + name + `"): could not find symbol ` + symName + `: ` + C.GoString(cErr))
+		}
+		valp := (*[2]unsafe.Pointer)(unsafe.Pointer(&sym))
+		if isFunc {
+			(*valp)[1] = unsafe.Pointer(&p)
+		} else {
+			(*valp)[1] = p
+		}
+		// we can't add to syms during iteration as we'll end up processing
+		// some symbols twice with the inability to tell if the symbol is a function
+		updatedSyms[symName] = sym
+	}
+	p.syms = updatedSyms
+
+	close(p.loaded)
+	return p, nil
+}
+
+func lookup(p *Plugin, symName string) (Symbol, error) {
+	if s := p.syms[symName]; s != nil {
+		return s, nil
+	}
+	return nil, errors.New("plugin: symbol " + symName + " not found in plugin " + p.pluginpath)
+}
+
+var (
+	pluginsMu sync.Mutex
+	plugins   map[string]*Plugin
+)
+
+// lastmoduleinit is defined in package runtime.
+func lastmoduleinit() (pluginpath string, syms map[string]any, inittasks []*initTask, errstr string)
+
+// doInit is defined in package runtime.
+//
+//go:linkname doInit runtime.doInit
+func doInit(t []*initTask)
+
+type initTask struct {
+	// fields defined in runtime.initTask. We only handle pointers to an initTask
+	// in this package, so the contents are irrelevant.
+}
diff --git a/src/plugin/plugin_stubs.go b/src/plugin/plugin_stubs.go
new file mode 100644
index 0000000..2e9492e
--- /dev/null
+++ b/src/plugin/plugin_stubs.go
@@ -0,0 +1,17 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build (!linux && !freebsd && !darwin) || !cgo
+
+package plugin
+
+import "errors"
+
+func lookup(p *Plugin, symName string) (Symbol, error) {
+	return nil, errors.New("plugin: not implemented")
+}
+
+func open(name string) (*Plugin, error) {
+	return nil, errors.New("plugin: not implemented")
+}
diff --git a/src/plugin/plugin_test.go b/src/plugin/plugin_test.go
new file mode 100644
index 0000000..557987c
--- /dev/null
+++ b/src/plugin/plugin_test.go
@@ -0,0 +1,15 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package plugin_test
+
+import (
+	_ "plugin"
+	"testing"
+)
+
+func TestPlugin(t *testing.T) {
+	// This test makes sure that executable that imports plugin
+	// package can actually run. See issue #28789 for details.
+}