runtime, plugin: error not throw on duplicate open

Along the way, track bad modules. Make sure they don't end up on
the active modules list, and aren't accidentally reprocessed as
new plugins.

Fixes #19004

Change-Id: I8a5e7bb11f572f7b657a97d521a7f84822a35c07
Reviewed-on: https://go-review.googlesource.com/61171
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

misc/cgo/testplugin/src/host/host.go

@@ -136,6 +136,14 @@ func main() {
 		log.Fatalf("after loading plugin2, common.X=%d, want %d", got, want)
 	}
 
+	_, err = plugin.Open("plugin2-dup.so")
+	if err == nil {
+		log.Fatal(`plugin.Open("plugin2-dup.so"): duplicate open should have failed`)
+	}
+	if s := err.Error(); !strings.Contains(s, "already loaded") {
+		log.Fatal(`plugin.Open("plugin2.so"): error does not mention "already loaded"`)
+	}
+
 	_, err = plugin.Open("plugin-mismatch.so")
 	if err == nil {
 		log.Fatal(`plugin.Open("plugin-mismatch.so"): should have failed`)
@@ -144,6 +152,15 @@ func main() {
 		log.Fatalf(`plugin.Open("plugin-mismatch.so"): error does not mention "different version": %v`, s)
 	}
 
+	_, err = plugin.Open("plugin2-dup.so")
+	if err == nil {
+		log.Fatal(`plugin.Open("plugin2-dup.so"): duplicate open after bad plugin should have failed`)
+	}
+	_, err = plugin.Open("plugin2.so")
+	if err != nil {
+		log.Fatalf(`plugin.Open("plugin2.so"): second open with same name failed: %v`, err)
+	}
+
 	// Test that unexported types with the same names in
 	// different plugins do not interfere with each other.
 	//

misc/cgo/testplugin/test.bash

@@ -25,6 +25,7 @@ mkdir sub
 
 GOPATH=$(pwd) go build -buildmode=plugin plugin1
 GOPATH=$(pwd) go build -buildmode=plugin plugin2
+cp plugin2.so plugin2-dup.so
 GOPATH=$(pwd)/altpath go build -buildmode=plugin plugin-mismatch
 GOPATH=$(pwd) go build -buildmode=plugin -o=sub/plugin1.so sub/plugin1
 GOPATH=$(pwd) go build -buildmode=plugin -o=unnamed1.so unnamed1/main.go

src/plugin/plugin.go

@@ -20,6 +20,7 @@ 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]interface{}
 }

src/plugin/plugin_dlopen.go

@@ -87,7 +87,7 @@ func open(name string) (*Plugin, error) {
 	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")
+		return nil, errors.New(`plugin.Open("` + name + `"): realpath failed`)
 	}
 
 	filepath := C.GoString((*C.char)(unsafe.Pointer(&cPath[0])))
@@ -95,6 +95,9 @@ func open(name string) (*Plugin, error) {
 	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
 	}
@@ -102,22 +105,25 @@ func open(name string) (*Plugin, error) {
 	h := C.pluginOpen((*C.char)(unsafe.Pointer(&cPath[0])), &cErr)
 	if h == 0 {
 		pluginsMu.Unlock()
-		return nil, errors.New("plugin.Open: " + C.GoString(cErr))
+		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]
 	}
-
-	pluginpath, syms, mismatchpkg := lastmoduleinit()
-	if mismatchpkg != "" {
-		pluginsMu.Unlock()
-		return nil, errors.New("plugin.Open: plugin was built with a different version of package " + mismatchpkg)
-	}
 	if plugins == nil {
 		plugins = make(map[string]*Plugin)
 	}
+	pluginpath, syms, 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{
@@ -153,7 +159,7 @@ func open(name string) (*Plugin, error) {
 
 		p := C.pluginLookup(h, (*C.char)(unsafe.Pointer(&cname[0])), &cErr)
 		if p == nil {
-			return nil, errors.New("plugin.Open: could not find symbol " + symName + ": " + C.GoString(cErr))
+			return nil, errors.New(`plugin.Open("` + name + `"): could not find symbol ` + symName + `: ` + C.GoString(cErr))
 		}
 		valp := (*[2]unsafe.Pointer)(unsafe.Pointer(&sym))
 		if isFunc {
@@ -184,4 +190,4 @@ var (
 )
 
 // lastmoduleinit is defined in package runtime
-func lastmoduleinit() (pluginpath string, syms map[string]interface{}, mismatchpkg string)
+func lastmoduleinit() (pluginpath string, syms map[string]interface{}, errstr string)

src/runtime/plugin.go

@@ -7,22 +7,29 @@ package runtime
 import "unsafe"
 
 //go:linkname plugin_lastmoduleinit plugin.lastmoduleinit
-func plugin_lastmoduleinit() (path string, syms map[string]interface{}, mismatchpkg string) {
-	md := firstmoduledata.next
+func plugin_lastmoduleinit() (path string, syms map[string]interface{}, errstr string) {
+	var md *moduledata
+	for pmd := firstmoduledata.next; pmd != nil; pmd = pmd.next {
+		if pmd.bad {
+			md = nil // we only want the last module
+			continue
+		}
+		md = pmd
+	}
 	if md == nil {
 		throw("runtime: no plugin module data")
 	}
-	for md.next != nil {
-		md = md.next
+	if md.pluginpath == "" {
+		throw("runtime: plugin has empty pluginpath")
 	}
 	if md.typemap != nil {
-		throw("runtime: plugin already initialized")
+		return "", nil, "plugin already loaded"
 	}
 
 	for _, pmd := range activeModules() {
 		if pmd.pluginpath == md.pluginpath {
-			println("plugin: plugin", md.pluginpath, "already loaded")
-			throw("plugin: plugin already loaded")
+			md.bad = true
+			return "", nil, "plugin already loaded"
 		}
 
 		if inRange(pmd.text, pmd.etext, md.text, md.etext) ||
@@ -43,7 +50,8 @@ func plugin_lastmoduleinit() (path string, syms map[string]interface{}, mismatch
 	}
 	for _, pkghash := range md.pkghashes {
 		if pkghash.linktimehash != *pkghash.runtimehash {
-			return "", nil, pkghash.modulename
+			md.bad = true
+			return "", nil, "plugin was built with a different version of package " + pkghash.modulename
 		}
 	}
 

src/runtime/symtab.go

@@ -338,8 +338,8 @@ const (
 // moduledata records information about the layout of the executable
 // image. It is written by the linker. Any changes here must be
 // matched changes to the code in cmd/internal/ld/symtab.go:symtab.
-// moduledata is stored in read-only memory; none of the pointers here
-// are visible to the garbage collector.
+// moduledata is stored in statically allocated non-pointer memory;
+// none of the pointers here are visible to the garbage collector.
 type moduledata struct {
 	pclntable    []byte
 	ftab         []functab
@@ -371,6 +371,8 @@ type moduledata struct {
 
 	typemap map[typeOff]*_type // offset to *_rtype in previous module
 
+	bad bool // module failed to load and should be ignored
+
 	next *moduledata
 }
 
@@ -443,6 +445,9 @@ func activeModules() []*moduledata {
 func modulesinit() {
 	modules := new([]*moduledata)
 	for md := &firstmoduledata; md != nil; md = md.next {
+		if md.bad {
+			continue
+		}
 		*modules = append(*modules, md)
 		if md.gcdatamask == (bitvector{}) {
 			md.gcdatamask = progToPointerMask((*byte)(unsafe.Pointer(md.gcdata)), md.edata-md.data)