harmony-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Ivan Popov" <ivan.g.po...@gmail.com>
Subject Re: [drlvm][verifier] verifier behavior is not compatible with RI
Date Mon, 22 Jan 2007 12:47:58 GMT
[1] http://java.sun.com/javase/6/docs/technotes/tools/windows/java.html

On 1/22/07, Ivan Popov <ivan.g.popov@gmail.com> wrote:
> I've tested instrumented class against Sun JDK 1.5 and 1.6 with
> -Xfuture option, which "turns on stricter class-file format checks
> that enforce closer conformance to the class-file format
> specification" [1].
>
> The instrumented class rejected by DRLVM is still accepted by Sun JVM
> launched with -Xfuture. I've noticed also that DRLVM does not support
> option -Xfuture.
>
> I think that DRLVM verifier should be compatible with RI in default
> mode and can provide additional option for stricter verification
> (-Xfuture or something DRLVM-specific).
>
> Thanks.
> Ivan
>
> On 1/19/07, Gregory Shimansky <gshimansky@gmail.com> wrote:
> > Ivan Popov wrote:
> > > I'd like to discuss the problem with Eclipse TPTP profiler working
> > > with DRLVM, which is described in HARMONY-2905 [1].  The problem is
> > > that verifier in DRLVM rejects class instrumented by TPTP profiler.
> > >
> > > TPTP profiler instruments class bytecodes by enclosing each method
> > > call into try-finally block, in order to report correctly entry/return
> > > of this method. It instruments calls of all methods including
> > > invocation of super() in constructors of class instance. Here is
> > > fragment of instrumented bytecodes:
> > >
> > >         <…>
> > >    try {
> > >    19: aload_0 #0=this
> > >    20: invokespecial #8=<Method java.lang.Object.<init> ()void>
> > >    23: goto_w 28
> > >    28: nop
> > >    29: ldc_w #62=<Integer 70056>
> > >    } finally {
> > >         <…>
> > >
> > > This leads to the value of 'this' variable, which is considered
> > > uninitialized before call to super(), is used inside try-finally
> > > block. This contradicts to the JVMS spec 2nd edition [2], which states
> > > in the last paragraph of section 4.9.4:
> > >
> > >    A valid instruction sequence must not have an uninitialized object
> > >    on the operand stack or in a local variable during a backwards branch,
> > >    or in a local variable in code protected by an exception handler
> > >    or a finally clause. Otherwise, a devious piece of code might fool
> > >    the verifier into thinking it had initialized a class instance when
> > > it had,
> > >    in fact, initialized a class instance created in a previous pass
> > > through a loop.
> > >
> > > And another statement in proposed changes for JDK 1.5 in "Class file
> > > format" [3] in section 4.11.1 (which is new item in this proposal):
> > >
> > >    -- There is never an uninitialized class instance in a local
> > > variable in code protected
> > >    by an exception handler. However, an uninitialized class instance may
> > >    be on the operand stack in code protected by an exception handler.
> > > When an
> > >    exception is thrown, the contents of the operand stack are discarded.
> > >
> > > Verifier in DRLVM follows these statements and rejects class bytecodes
> > > instrumented in such a way. However, both Sun JDK version 1.5 and 1.6
> > > and  JRockit JDK 1.5 accept such instrumented class. Either they just
> > > ignore these statements or interpret 'uninitialized' status of 'this'
> > > variable in a different way.
> > >
> > > I've submitted bug against TPTP profiler [4], which produces incorrect
> > > instrumentation, and this bug was accepted by TPTP developers to be
> > > fixed in the next release. However, this is a general approach for
> > > instrumenting method calls and any other Java profiler may use it and
> > > work fine with RI, but and face this problem with DRLVM. I think it
> > > makes sense to adjust DRLVM verifier to follow RI behavior. I'd like
> > > to see comment from DRLVM gurus.
> >
> > There is always a workaround to verifier exceptions. You can run the
> > program with -Xverify:none to disable verifier completely. Turning this
> > particular check is simple too. The question is whether this should be a
> > default mode in VM or whether it should be enabled by some special
> > option which doesn't disable all other verifications.
> >
> > > [1] https://issues.apache.org/jira/browse/HARMONY-2905
> > > [2]
> > > http://java.sun.com/docs/books/vmspec/2nd-edition/html/ClassFile.doc.html#9839
> > >
> > > [3]
> > > http://java.sun.com/docs/books/vmspec/2nd-edition/ClassFileFormat-Java5.pdf
> > > [4] https://bugs.eclipse.org/bugs/show_bug.cgi?id=170075
> > >
> >
> >
> > --
> > Gregory
> >
> >
>

Mime
View raw message