cmd/link, plugin: use full plugin path for symbols

Plumb the import path of a plugin package through to the linker, and
use it as the prefix on the exported symbol names.

Before this we used the basename of the plugin file as the prefix,
which could conflict and result in multiple loaded plugins sharing
symbols that are distinct.

Fixes #17155
Fixes #17579

Change-Id: I7ce966ca82d04e8507c0bcb8ea4ad946809b1ef5
Reviewed-on: https://go-review.googlesource.com/32355
Reviewed-by: Ian Lance Taylor <iant@golang.org>

2 files changed, 15 insertions, 15 deletions

diff --git a/src/plugin/plugin.go b/src/plugin/plugin.go
index 93ae23f3f1..e812a2f677 100644
--- a/src/plugin/plugin.go
+++ b/src/plugin/plugin.go
@@ -18,9 +18,9 @@ package plugin
 
 // Plugin is a loaded Go plugin.
 type Plugin struct {
-	name   string
-	loaded chan struct{} // closed when loaded
-	syms   map[string]interface{}
+	pluginpath string
+	loaded     chan struct{} // closed when loaded
+	syms       map[string]interface{}
 }
 
 // Open opens a Go plugin.
diff --git a/src/plugin/plugin_dlopen.go b/src/plugin/plugin_dlopen.go
index e881b258e0..4a3eb3d861 100644
--- a/src/plugin/plugin_dlopen.go
+++ b/src/plugin/plugin_dlopen.go
@@ -49,10 +49,10 @@ func open(name string) (*Plugin, error) {
 	}
 	C.free(unsafe.Pointer(cRelName))
 
-	path := C.GoString(cPath)
+	filepath := C.GoString(cPath)
 
 	pluginsMu.Lock()
-	if p := plugins[path]; p != nil {
+	if p := plugins[filepath]; p != nil {
 		pluginsMu.Unlock()
 		<-p.loaded
 		return p, nil
@@ -65,26 +65,25 @@ func open(name string) (*Plugin, error) {
 	}
 	// TODO(crawshaw): look for plugin note, confirm it is a Go plugin
 	// and it was built with the correct toolchain.
-	// TODO(crawshaw): get full plugin name from note.
 	if len(name) > 3 && name[len(name)-3:] == ".so" {
 		name = name[:len(name)-3]
 	}
 
-	syms := lastmoduleinit()
+	pluginpath, syms := lastmoduleinit()
 	if plugins == nil {
 		plugins = make(map[string]*Plugin)
 	}
 	// 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{
-		name:   name,
-		loaded: make(chan struct{}),
-		syms:   syms,
+		pluginpath: pluginpath,
+		loaded:     make(chan struct{}),
+		syms:       syms,
 	}
-	plugins[path] = p
+	plugins[filepath] = p
 	pluginsMu.Unlock()
 
-	initStr := C.CString(name + ".init")
+	initStr := C.CString(pluginpath + ".init")
 	initFuncPC := C.pluginLookup(h, initStr, &cErr)
 	C.free(unsafe.Pointer(initStr))
 	if initFuncPC != nil {
@@ -101,7 +100,7 @@ func open(name string) (*Plugin, error) {
 			symName = symName[1:]
 		}
 
-		cname := C.CString(name + "." + symName)
+		cname := C.CString(pluginpath + "." + symName)
 		p := C.pluginLookup(h, cname, &cErr)
 		C.free(unsafe.Pointer(cname))
 		if p == nil {
@@ -123,7 +122,7 @@ 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.name)
+	return nil, errors.New("plugin: symbol " + symName + " not found in plugin " + p.pluginpath)
 }
 
 var (
@@ -131,4 +130,5 @@ var (
 	plugins   map[string]*Plugin
 )
 
-func lastmoduleinit() map[string]interface{} // in package runtime
+// lastmoduleinit is defined in package runtime
+func lastmoduleinit() (pluginpath string, syms map[string]interface{})