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>

1 files changed, 16 insertions, 8 deletions

diff --git a/src/runtime/plugin.go b/src/runtime/plugin.go
index caecba67f8..5e05be71ec 100644
--- a/src/runtime/plugin.go
+++ b/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
 		}
 	}