RFR(M): 8081674: EmptyStackException at startup if running with extended or unsupported charset
Volker Simonis
volker.simonis at gmail.com
Mon Jun 8 14:23:12 UTC 2015
Hi,
can I please get a review at least for the part of this fix which is
common for jdk8 and jdk9. It's only a few lines in
src/share/vm/prims/jni.cpp for the hotspot repository and one line
src/java.base/share/classes/java/lang/ClassLoader.java for the jdk
repository.
Thanks,
Volker
On Tue, Jun 2, 2015 at 6:12 PM, Volker Simonis <volker.simonis at gmail.com> wrote:
> Hi,
>
> can I please have review (and a sponsor) for these changes:
>
> https://bugs.openjdk.java.net/browse/JDK-8081674
> http://cr.openjdk.java.net/~simonis/webrevs/2015/8081674.jdk
> http://cr.openjdk.java.net/~simonis/webrevs/2015/8081674.hs
>
> Please notice that the fix requires synchronous changes in the jdk and the
> hotspot forest.
>
> The changes themselves are by far not that big as this explanation but I
> found the problem to be quite intricate so I tried to explain it as good as
> I could. I'd suggest to read the HTML-formatted explanation in the webrev
> although the content is equal to the one in this mail:
>
> Using an unsupported character encoding (e.g. vi_VN.TCVN on Linux) results
> in an immediate VM failure with jdk 8 and 9:
>
> export LANG=vi_VN.TCVN
> java -version
> Error occurred during initialization of VM
> java.util.EmptyStackException
> at java.util.Stack.peek(Stack.java:102)
> at java.lang.ClassLoader$NativeLibrary.getFromClass(ClassLoader.java:1751)
> at java.lang.ClassLoader$NativeLibrary.findBuiltinLib(Native Method)
> at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1862)
> at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1835)
> at java.lang.Runtime.loadLibrary0(Runtime.java:870)
> at java.lang.System.loadLibrary(System.java:1119)
> at java.lang.System.initializeSystemClass(System.java:1194)
>
> This is a consequence of "8005716: Enhance JNI specification to allow
> support of static JNI libraries in Embedded JREs".
>
> With jdk 9 we get this error even if we're running with a supported charset
> which is in the ExtendedCharsets (as opposed to being in the
> StandardCharsets) class which is a consequence of delegating the loading of
> the ExtendedCharsets class to the ServiceLoader in jdk 9.
>
> export LANG=eo.iso-8859-3
> output-jdk9/images/jdk/bin/java -version
> Error occurred during initialization of VM
> java.util.EmptyStackException
> at java.util.Stack.peek(Stack.java:102)
> at java.lang.ClassLoader$NativeLibrary.getFromClass(ClassLoader.java:1737)
> at java.lang.ClassLoader$NativeLibrary.findBuiltinLib(Native Method)
> at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1866)
> at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1840)
> at java.lang.Runtime.loadLibrary0(Runtime.java:874)
> at java.lang.System.loadLibrary(System.java:1111)
> at java.lang.System.initializeSystemClass(System.java:1186)
>
> Here's why the exception happens for an unsupported charset (see the mixed
> stack trace below for the full details):
>
> java.lang.System.loadLibrary() wants to load libzip.so. It calls
> java.lang.Runtime.loadLibrary0() which at the very beginning calls the
> native method ClassLoader$NativeLibrary.findBuiltinLib() which checks if the
> corresponding library is already statically linked into the VM (introduced
> by 8005716). Java_java_lang_ClassLoader_00024NativeLibrary_findBuiltinLib(),
> the native implementation of findBuiltinLib() in Classloader.c calls
> GetStringPlatformChars() to convert the library name into the native
> platform encoding. GetStringPlatformChars() calls the helper function
> jnuEncodingSupported() to check if the platform encoding which is stored in
> the property "sun.jnu.encoding" is supported by Java. jnuEncodingSupported()
> is implemented as follows:
>
> static jboolean isJNUEncodingSupported = JNI_FALSE;
> static jboolean jnuEncodingSupported(JNIEnv *env) {
> jboolean exe;
> if (isJNUEncodingSupported == JNI_TRUE) {
> return JNI_TRUE;
> }
> isJNUEncodingSupported = (jboolean) JNU_CallStaticMethodByName (
> env, &exe,
> "java/nio/charset/Charset",
> "isSupported",
> "(Ljava/lang/String;)Z",
> jnuEncoding).z;
> return isJNUEncodingSupported;
> }
>
> Once the function finds that the platform encoding is supported (by calling
> java.nio.charset.Charset.isSupported()) it caches this value and always
> returns it on following calls. However if the platform encoding is not
> supported, it ALWAYS calls java.nio.charset.Charset.isSupported() an every
> subsequent invocation.
>
> In order to call the Java method Charset.isSupported() (in
> JNU_CallStaticMethodByName() in file jni_util.c), we have to call
> jni_FindClass() to convert the symbolic class name
> "java.nio.charset.Charset" into a class reference.
>
> But unfortunately, jni_FindClass() (from jni.cpp in libjvm.so) has a special
> handling if called from java.lang.ClassLoader$NativeLibrary to ensure that
> JNI_OnLoad/JNI_OnUnload are executed in the correct class context:
>
> instanceKlassHandle k (THREAD, thread->security_get_caller_class(0));
> if (k.not_null()) {
> loader = Handle(THREAD, k->class_loader());
> // Special handling to make sure JNI_OnLoad and JNI_OnUnload are
> executed
> // in the correct class context.
> if (loader.is_null() &&
> k->name() == vmSymbols::java_lang_ClassLoader_NativeLibrary()) {
> JavaValue result(T_OBJECT);
> JavaCalls::call_static(&result, k,
> vmSymbols::getFromClass_name(),
> vmSymbols::void_class_signature(),
> thread);
> if (HAS_PENDING_EXCEPTION) {
> Handle ex(thread, thread->pending_exception());
> CLEAR_PENDING_EXCEPTION;
> THROW_HANDLE_0(ex);
> }
>
> So if that's the case and jni_FindClass() was reallycalled from
> ClassLoader$NativeLibrary, then jni_FindClass() calles
> ClassLoader$NativeLibrary().getFromClass() to find out the corresponding
> context class which is supposed to be saved there in a field of type
> java.util.Stack named "nativeLibraryContext":
>
> // Invoked in the VM to determine the context class in
> // JNI_Load/JNI_Unload
> static Class<?> getFromClass() {
> return ClassLoader.nativeLibraryContext.peek().fromClass;
> }
>
> Unfortunately, "nativeLibraryContext" doesn't contain any entry at this
> point and the invocation of Stack.peek() will throw the exception shown
> before. In general, the "nativeLibraryContext" stack will be filled later on
> in Runtime.loadLibrary0() like this:
>
> NativeLibrary lib = new NativeLibrary(fromClass, name, isBuiltin);
> nativeLibraryContext.push(lib);
> try {
> lib.load(name, isBuiltin);
> } finally {
> nativeLibraryContext.pop();
> }
>
> such that it always contains at least one element later when jni_FindClass()
> will be invoked.
>
> So in summary, the problem is that the implementors of 8005716 didn't took
> into account that calling ClassLoader$NativeLibrary.findBuiltinLib() may
> trigger a call to jni_FindClass() if we are running on a system with an
> unsupported character encoding.
>
> I'd suggest the following fix for this problem:
>
> Change ClassLoader$NativeLibrary().getFromClass() to return null if the
> stack is empty instead of throwing an exception:
>
> static Class<?> getFromClass() {
> return ClassLoader.nativeLibraryContext.empty() ?
> null : ClassLoader.nativeLibraryContext.peek().fromClass;
> }
>
> Unfortunately this also requires a HotSpot change in jni_FindClass() in
> order to properly handle the new 'null' return value:
>
> if (k.not_null()) {
> loader = Handle(THREAD, k->class_loader());
> // Special handling to make sure JNI_OnLoad and JNI_OnUnload are
> executed
> // in the correct class context.
> if (loader.is_null() &&
> k->name() == vmSymbols::java_lang_ClassLoader_NativeLibrary()) {
> JavaValue result(T_OBJECT);
> JavaCalls::call_static(&result, k,
> vmSymbols::getFromClass_name(),
> vmSymbols::void_class_signature(),
> thread);
> if (HAS_PENDING_EXCEPTION) {
> Handle ex(thread, thread->pending_exception());
> CLEAR_PENDING_EXCEPTION;
> THROW_HANDLE_0(ex);
> }
> oop mirror = (oop) result.get_jobject();
> if (oopDesc::is_null(mirror)) {
> loader = Handle(THREAD, SystemDictionary::java_system_loader());
> } else {
> loader = Handle(THREAD,
>
> InstanceKlass::cast(java_lang_Class::as_Klass(mirror))->class_loader());
> protection_domain = Handle(THREAD,
>
> InstanceKlass::cast(java_lang_Class::as_Klass(mirror))->protection_domain());
> }
> }
> } else {
> // We call ClassLoader.getSystemClassLoader to obtain the system class
> loader.
> loader = Handle(THREAD, SystemDictionary::java_system_loader());
> }
>
> These changes are sufficient to solve the problem in Java 8. Unfortunately,
> that's still not enough in Java 9 because there the loading of the extended
> charsets has been delegated to ServiceLoader. But ServiceLoader calls
> ClassLoader.getBootstrapResources() which calls
> sun.misc.Launcher.getBootstrapClassPath(). This leads to another problem
> during class initialization of sun.misc.Launcher if running on an
> unsupported locale.
>
> The first thing done in sun.misc.Launcher.<clinit> is the initialisation of
> the bootstrap URLClassPath in the Launcher. However this initialisation will
> eventually call Charset.isSupported() and if we are running on an
> unsupported locale this will inevitably end in another recursive call to
> ServiceLoader. But as explained below, ServiceLoader will query the
> Launcher's bootstrap URLClassPath which will be still uninitialized at that
> point.
>
> So we'll have to additionally guard guard against this situation on JDK 9
> like this:
>
> private static Charset lookupExtendedCharset(String charsetName) {
> if (!sun.misc.VM.isBooted() || // see lookupViaProviders()
> sun.misc.Launcher.getBootstrapClassPath() == null)
> return null;
>
> This fixes the crashes, but still at the price of not having the extended
> charsets available during initialization until
> Launcher.getBootstrapClassPath is set up properly. This may be still a
> problem if the jdk is installed in a directory which contains characters
> specific to an extended encoding or if we have such characters in the
> command line arguments.
>
> Thank you and best regards,
> Volker
>
>
> Mixed stack trace of the initial EmptyStackException for unsupported
> charsets described before:
>
> Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native
> code)
> j java.util.Stack.peek()Ljava/lang/Object;+1
> j java.lang.ClassLoader$NativeLibrary.getFromClass()Ljava/lang/Class;+3
> v ~StubRoutines::call_stub
> V [libjvm.so+0x9d279a] JavaCalls::call_helper(JavaValue*, methodHandle*,
> JavaCallArguments*, Thread*)+0x6b4
> V [libjvm.so+0xcad591] os::os_exception_wrapper(void (*)(JavaValue*,
> methodHandle*, JavaCallArguments*, Thread*), JavaValue*, methodHandle*,
> JavaCallArguments*, Thread*)+0x45
> V [libjvm.so+0x9d20cf] JavaCalls::call(JavaValue*, methodHandle,
> JavaCallArguments*, Thread*)+0x8b
> V [libjvm.so+0x9d1d3b] JavaCalls::call_static(JavaValue*, KlassHandle,
> Symbol*, Symbol*, JavaCallArguments*, Thread*)+0x139
> V [libjvm.so+0x9d1e3f] JavaCalls::call_static(JavaValue*, KlassHandle,
> Symbol*, Symbol*, Thread*)+0x9d
> V [libjvm.so+0x9e6588] jni_FindClass+0x428
> C [libjava.so+0x20208] JNU_CallStaticMethodByName+0xff
> C [libjava.so+0x21cae] jnuEncodingSupported+0x61
> C [libjava.so+0x22125] JNU_GetStringPlatformChars+0x125
> C [libjava.so+0xedcd]
> Java_java_lang_ClassLoader_00024NativeLibrary_findBuiltinLib+0x8b
> j
> java.lang.ClassLoader$NativeLibrary.findBuiltinLib(Ljava/lang/String;)Ljava/lang/String;+0
> j java.lang.ClassLoader.loadLibrary0(Ljava/lang/Class;Ljava/io/File;)Z+4
> j
> java.lang.ClassLoader.loadLibrary(Ljava/lang/Class;Ljava/lang/String;Z)V+228
> j java.lang.Runtime.loadLibrary0(Ljava/lang/Class;Ljava/lang/String;)V+54
> j java.lang.System.loadLibrary(Ljava/lang/String;)V+7
> j java.lang.System.initializeSystemClass()V+113
> v ~StubRoutines::call_stub
> V [libjvm.so+0x9d279a] JavaCalls::call_helper(JavaValue*, methodHandle*,
> JavaCallArguments*, Thread*)+0x6b4
> V [libjvm.so+0xcad591] os::os_exception_wrapper(void (*)(JavaValue*,
> methodHandle*, JavaCallArguments*, Thread*), JavaValue*, methodHandle*,
> JavaCallArguments*, Thread*)+0x45
> V [libjvm.so+0x9d20cf] JavaCalls::call(JavaValue*, methodHandle,
> JavaCallArguments*, Thread*)+0x8b
> V [libjvm.so+0x9d1d3b] JavaCalls::call_static(JavaValue*, KlassHandle,
> Symbol*, Symbol*, JavaCallArguments*, Thread*)+0x139
> V [libjvm.so+0x9d1e3f] JavaCalls::call_static(JavaValue*, KlassHandle,
> Symbol*, Symbol*, Thread*)+0x9d
> V [libjvm.so+0xe3cceb] call_initializeSystemClass(Thread*)+0xb0
> V [libjvm.so+0xe44444] Threads::initialize_java_lang_classes(JavaThread*,
> Thread*)+0x21a
> V [libjvm.so+0xe44b12] Threads::create_vm(JavaVMInitArgs*, bool*)+0x4a6
> V [libjvm.so+0xa19bd7] JNI_CreateJavaVM+0xc7
> C [libjli.so+0xa520] InitializeJVM+0x154
> C [libjli.so+0x8024] JavaMain+0xcc
>
>
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