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>

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

@@ -7,6 +7,7 @@ package main
 import (
 	"fmt"
 	"log"
+	"path/filepath"
 	"plugin"
 
 	"common"
@@ -36,15 +37,51 @@ func main() {
 		log.Fatalf(`Lookup("Seven") failed: %v`, err)
 	}
 	if got, want := *seven.(*int), 7; got != want {
-		log.Fatalf("via lookup plugin1.Seven=%d, want %d", got, want)
+		log.Fatalf("plugin1.Seven=%d, want %d", got, want)
 	}
 
 	readFunc, err := p.Lookup("ReadCommonX")
 	if err != nil {
-		log.Fatalf(`Lookup("ReadCommonX") failed: %v`, err)
+		log.Fatalf(`plugin1.Lookup("ReadCommonX") failed: %v`, err)
 	}
 	if got := readFunc.(func() int)(); got != wantX {
-		log.Fatalf("via lookup plugin1.ReadCommonX()=%d, want %d", got, wantX)
+		log.Fatalf("plugin1.ReadCommonX()=%d, want %d", got, wantX)
+	}
+
+	// sub/plugin1.so is a different plugin with the same name as
+	// the already loaded plugin. It also depends on common. Test
+	// that we can load the different plugin, it is actually
+	// different, and that it sees the same common package.
+	subpPath, err := filepath.Abs("sub/plugin1.so")
+	if err != nil {
+		log.Fatalf("filepath.Abs(%q) failed: %v", subpPath, err)
+	}
+	subp, err := plugin.Open(subpPath)
+	if err != nil {
+		log.Fatalf("plugin.Open(%q) failed: %v", subpPath, err)
+	}
+
+	readFunc, err = subp.Lookup("ReadCommonX")
+	if err != nil {
+		log.Fatalf(`sub/plugin1.Lookup("ReadCommonX") failed: %v`, err)
+	}
+	if got := readFunc.(func() int)(); got != wantX {
+		log.Fatalf("sub/plugin1.ReadCommonX()=%d, want %d", got, wantX)
+	}
+
+	subf, err := subp.Lookup("F")
+	if err != nil {
+		log.Fatalf(`sub/plugin1.Lookup("F") failed: %v`, err)
+	}
+	if gotf := subf.(func() int)(); gotf != 17 {
+		log.Fatalf(`sub/plugin1.F()=%d, want 17`, gotf)
+	}
+	f, err := p.Lookup("F")
+	if err != nil {
+		log.Fatalf(`plugin1.Lookup("F") failed: %v`, err)
+	}
+	if gotf := f.(func() int)(); gotf != 3 {
+		log.Fatalf(`plugin1.F()=%d, want 17`, gotf)
 	}
 
 	fmt.Println("PASS")

misc/cgo/testplugin/src/plugin1/plugin1.go

@@ -9,6 +9,8 @@ import "C"
 
 import "common"
 
+func F() int { return 3 }
+
 func ReadCommonX() int {
 	return common.X
 }

misc/cgo/testplugin/src/sub/plugin1/plugin1.go

@@ -0,0 +1,20 @@
+// 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 main
+
+// // No C code required.
+import "C"
+
+import "common"
+
+func F() int { return 17 }
+
+func ReadCommonX() int {
+	return common.X
+}
+
+func main() {
+	panic("plugin1.main called")
+}

misc/cgo/testplugin/test.bash

@@ -15,13 +15,15 @@ goos=$(go env GOOS)
 goarch=$(go env GOARCH)
 
 function cleanup() {
-	rm -f plugin1.so host pkg
+	rm -rf plugin1.so host pkg sub
 }
 trap cleanup EXIT
 
-rm -rf pkg
+rm -rf pkg sub
+mkdir sub
 
 GOPATH=$(pwd) go build -buildmode=plugin plugin1
+GOPATH=$(pwd) go build -buildmode=plugin -o=sub/plugin1.so sub/plugin1
 GOPATH=$(pwd) go build host
 
 LD_LIBRARY_PATH=$(pwd) ./host

src/cmd/go/build.go

@@ -2546,6 +2546,9 @@ func (gcToolchain) ld(b *builder, root *action, out string, allactions []*action
 	if root.p.omitDWARF {
 		ldflags = append(ldflags, "-w")
 	}
+	if buildBuildmode == "plugin" {
+		ldflags = append(ldflags, "-pluginpath", root.p.ImportPath)
+	}
 
 	// If the user has not specified the -extld option, then specify the
 	// appropriate linker. In case of C++ code, use the compiler named

src/cmd/link/doc.go

@@ -85,6 +85,8 @@ Flags:
 		Link with C/C++ memory sanitizer support.
 	-o file
 		Write output to file (default a.out, or a.out.exe on Windows).
+	-pluginpath path
+		The path name used to prefix exported plugin symbols.
 	-r dir1:dir2:...
 		Set the ELF dynamic linker search path.
 	-race

src/cmd/link/internal/ld/main.go

@@ -37,7 +37,6 @@ import (
 	"flag"
 	"log"
 	"os"
-	"path/filepath"
 	"runtime"
 	"runtime/pprof"
 	"strings"
@@ -59,6 +58,7 @@ var (
 	flagBuildid = flag.String("buildid", "", "record `id` as Go toolchain build id")
 
 	flagOutfile    = flag.String("o", "", "write output to `file`")
+	flagPluginPath = flag.String("pluginpath", "", "full path name for plugin")
 	FlagLinkshared = flag.Bool("linkshared", false, "link against installed Go shared libraries")
 
 	flagInstallSuffix = flag.String("installsuffix", "", "set package directory `suffix`")
@@ -175,8 +175,7 @@ func Main() {
 			addlibpath(ctxt, "command line", "command line", file, pkgpath, "")
 		}
 	case BuildmodePlugin:
-		pluginName := strings.TrimSuffix(filepath.Base(flag.Arg(0)), ".a")
-		addlibpath(ctxt, "command line", "command line", flag.Arg(0), pluginName, "")
+		addlibpath(ctxt, "command line", "command line", flag.Arg(0), *flagPluginPath, "")
 	default:
 		addlibpath(ctxt, "command line", "command line", flag.Arg(0), "main", "")
 	}

src/cmd/link/internal/ld/symtab.go

@@ -603,6 +603,12 @@ func (ctxt *Link) symtab() {
 		adduint(ctxt, moduledata, 0)
 		adduint(ctxt, moduledata, 0)
 	}
+	if Buildmode == BuildmodePlugin {
+		addgostring(ctxt, moduledata, "go.link.thispluginpath", *flagPluginPath)
+	} else {
+		adduint(ctxt, moduledata, 0)
+		adduint(ctxt, moduledata, 0)
+	}
 	if len(ctxt.Shlibs) > 0 {
 		thismodulename := filepath.Base(*flagOutfile)
 		switch Buildmode {

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.

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{})

src/runtime/plugin.go

@@ -7,7 +7,7 @@ package runtime
 import "unsafe"
 
 //go:linkname plugin_lastmoduleinit plugin.lastmoduleinit
-func plugin_lastmoduleinit() map[string]interface{} {
+func plugin_lastmoduleinit() (path string, syms map[string]interface{}) {
 	md := firstmoduledata.next
 	if md == nil {
 		throw("runtime: no plugin module data")
@@ -19,20 +19,27 @@ func plugin_lastmoduleinit() map[string]interface{} {
 		throw("runtime: plugin already initialized")
 	}
 
-	if fmd := &firstmoduledata; inRange(fmd.text, fmd.etext, md.text, md.etext) ||
-		inRange(fmd.bss, fmd.ebss, md.bss, md.ebss) ||
-		inRange(fmd.data, fmd.edata, md.data, md.edata) ||
-		inRange(fmd.types, fmd.etypes, md.types, md.etypes) {
-		println("plugin: new module data overlaps with firstmoduledata")
-		println("\tfirstmoduledata.text-etext=", hex(fmd.text), "-", hex(fmd.etext))
-		println("\tfirstmoduledata.bss-ebss=", hex(fmd.bss), "-", hex(fmd.ebss))
-		println("\tfirstmoduledata.data-edata=", hex(fmd.data), "-", hex(fmd.edata))
-		println("\tfirstmoduledata.types-etypes=", hex(fmd.types), "-", hex(fmd.etypes))
-		println("\tmd.text-etext=", hex(md.text), "-", hex(md.etext))
-		println("\tmd.bss-ebss=", hex(md.bss), "-", hex(md.ebss))
-		println("\tmd.data-edata=", hex(md.data), "-", hex(md.edata))
-		println("\tmd.types-etypes=", hex(md.types), "-", hex(md.etypes))
-		throw("plugin: new module data overlaps with firstmoduledata")
+	for pmd := &firstmoduledata; pmd != md; pmd = pmd.next {
+		if pmd.pluginpath == md.pluginpath {
+			println("plugin: plugin", md.pluginpath, "already loaded")
+			throw("plugin: plugin already loaded")
+		}
+
+		if inRange(pmd.text, pmd.etext, md.text, md.etext) ||
+			inRange(pmd.bss, pmd.ebss, md.bss, md.ebss) ||
+			inRange(pmd.data, pmd.edata, md.data, md.edata) ||
+			inRange(pmd.types, pmd.etypes, md.types, md.etypes) {
+			println("plugin: new module data overlaps with previous moduledata")
+			println("\tpmd.text-etext=", hex(pmd.text), "-", hex(pmd.etext))
+			println("\tpmd.bss-ebss=", hex(pmd.bss), "-", hex(pmd.ebss))
+			println("\tpmd.data-edata=", hex(pmd.data), "-", hex(pmd.edata))
+			println("\tpmd.types-etypes=", hex(pmd.types), "-", hex(pmd.etypes))
+			println("\tmd.text-etext=", hex(md.text), "-", hex(md.etext))
+			println("\tmd.bss-ebss=", hex(md.bss), "-", hex(md.ebss))
+			println("\tmd.data-edata=", hex(md.data), "-", hex(md.edata))
+			println("\tmd.types-etypes=", hex(md.types), "-", hex(md.etypes))
+			throw("plugin: new module data overlaps with previous moduledata")
+		}
 	}
 
 	// Initialize the freshly loaded module.
@@ -54,7 +61,7 @@ func plugin_lastmoduleinit() map[string]interface{} {
 	// Because functions are handled specially in the plugin package,
 	// function symbol names are prefixed here with '.' to avoid
 	// a dependency on the reflect package.
-	syms := make(map[string]interface{}, len(md.ptab))
+	syms = make(map[string]interface{}, len(md.ptab))
 	for _, ptab := range md.ptab {
 		symName := resolveNameOff(unsafe.Pointer(md.types), ptab.name)
 		t := (*_type)(unsafe.Pointer(md.types)).typeOff(ptab.typ)
@@ -68,7 +75,7 @@ func plugin_lastmoduleinit() map[string]interface{} {
 		}
 		syms[name] = val
 	}
-	return syms
+	return md.pluginpath, syms
 }
 
 // inRange reports whether v0 or v1 are in the range [r0, r1].

src/runtime/symtab.go

@@ -201,6 +201,7 @@ type moduledata struct {
 
 	ptab []ptabEntry
 
+	pluginpath   string
 	modulename   string
 	modulehashes []modulehash