[BC ABI] gcj-abi-2-dev-branch created

[Andrew Haley]

This branch is for work on the new ABI.

For those who haven't seen the discussions, the idea of the new ABI is
to conform fully to the Java Binary Compatibility specification, which
is Chapter 13 of the Java Language Specification.

Now classes are looked up at runtime rather than compile time, so the
runtime of libgcj has to be completely reorganized.

Some of this work is already done: the compiler changes so that we no
longer emit hard references to classes are already done, and some of
the runtime is done but it's very Alpha at the present time.  There's
a ton of debugging code in there, too.

Much remains to be done.  Some of the important missing things are:

* The compiler must output assertions so that at runtime incompatible
  class changes are detected.  At the moment it just emits warnings to
  the console.

* In resolve.cc, we need to look for precompiled classes and if they
  are not found launch gcj to compile them to shared objects.

* The compiler should no longer open class files referred to when
  compiling class files.  Instead, where any type checking is needed,
  it should embed type check assertions in the generated object file.

* The bytecode verifier in the compiler needs to be fixed in order to
  verify some of the weirder bytecode out there.

* We need to control the export of symbols from libraries.

* We need to fix mangling so we can use generics.

* The runtime class resolution is insanely complicated, messy, and
  probably totally wrong.  It doesn't correctly lock tables.

* gdb will not work well with this ABI.

* We need to rip out -fno-assume-compiled support.

To summarize: the completion of this work will greatly lower the bar
for people who want to use gcj.  They'll only have to precompile their
jarfiles, and everything else should Just Work.  This will increase
the takeup of gcj.  I hope...  :-)

Rules for working on the branch:

* Talk about what you're going to do on this list before starting.
  This is to reduce wasted effort.

* By all means commit debugging stuff, and stuff that still has
  FIXMEs.  Don't forget to mark stuff you're not sure about.

* Post patches for approval as usual on java-patches, marked [BC ABI].

Andrew.