Re: Release [was: Re: [Sablevm-developer] Alpha inlined threading works now, but...]

[Archie C. <ar...@de...>]

Prof. Etienne M. Gagnon wrote:
> Maybe you could get the jikes maintainer to add a jikes1.15 package in
> unstable.  I already tried, but I think he does not like the idea.

FWIW, I think practically speaking you could modify SableVM to accept
classfiles with major version numbers up to 48 without any problems.

I asked on the jikes mailing list about their changes and what spec
they were reading from. Nobody could produce the spec, but I did get
some useful info (see below).

-Archie

__________________________________________________________________________
Archie Cobbs     *     Packet Design     *     http://www.packetdesign.com

> From jik...@ww... Sat Feb 15 10:20:01 2003
> From: Eric Blake <eb...@em...>
> Subject: Re: [Jikes-dev] New class file format
> To: jik...@ww...
> Message-ID: <3E4...@em...>
> MIME-Version: 1.0
> Content-Type: text/plain; format=flowed; charset=us-ascii
> Content-Transfer-Encoding: 7bit
> Sender: jik...@ww...
> List-Archive: <http://www-124.ibm.com/pipermail/jikes-dev/>
> Date: Sat, 15 Feb 2003 11:18:01 -0700
> Status: ORr
> 
> Archie Cobbs wrote:
> >>
> >>So are you saying: the classfiles that jikes generates are exactly
> >>the same - except for the major/minor version number - no matter
> >>what -target flag is given? (If not, can you be specific about what
> >>the differences are?) Is this also true for Sun's javac?
> > 
> > To answer my own question: it appears to me from looking at the source
> > that the only differences in the classfile is synthetic code generated
> > to handle "Foo.class", e.g., using exception chaining.
> > 
> > So the -target flag (so far) only "targets" the version of the base
> > Java classes, rather than the virtual machine.
> > 
> > Let me know if I've gotten myself confused :-)
> 
> Read the source code in src/bytecode.cpp to see the different code 
> sequences that jikes outputs depending on the -target option (search for 
> control.option.target).  For example, this code is different in 1.3 and 1.4:
> 
> class A {
>    void m(final int i) {
>      class B {
>        int j = i;
>      }
>    }
> }
> 
> In 1.3, Sun's VM violated the JVMS, and didn't permit the initialization 
> of instance variables before calling the superconstructor.  Therefore, 
> compiling with -target 1.3 will issue a constructor that looks like this 
> (this.this$0 and this.val$i are synthetic variables necessary to make 
> the local class work correctly):
> 
> A$1B(A this$0, int val$i) {
>    super();
>    this.this$0 = this$0;
>    this.val$i = val$i;
>    j = this.val$i;
> }
> 
> However, this is semantically incorrect, as setting the this$0 variable 
> after the superconstructor can cause spurious NullPointerExceptions.
> 
> In their 1.4 release, Sun corrected their bug and now obey the JLS. 
> Therefore, compiling with -target 1.4 will issue a constructor like this 
> (although this is not valid Java, it is valid in the VM):
> 
> A$1B(A this$0, int val$i) {
>    this.this$0 = this$0;
>    this.val$i = val$i;
>    super();
>    j = this.val$i;
> }
> 
> There are several other changes in emitted code, conditional on the 
> -target flag.
> 
> -- 
> This signature intentionally left boring.
> 
> Eric Blake             eb...@em...
>    BYU student, free software programmer
> 
> ----
> To leave the Jikes-dev mailing list send a message to
> Jik...@ww... with the word
> unsubscribe in the body. For more subscription management:
> http://www-124.ibm.com/developerworks/oss/mailman/listinfo/jikes-dev