//===---------------------------------------------------------------------===//
// General notes
//===---------------------------------------------------------------------===//

VMKit is the composition of three libraries:
1) MVM: mostly a garbage collector
2) JnJVM: a Java Virtual Machine implemented with MVM and LLVM
3) N3: a CLI implementation with MVM and LLVM


You must first patch llvm with vmkit-llvm-svn.patch if you're with SVN, or
vmkit-llvm-2.2.patch if you're with 2.2. 


JnJVM and N3 work on Linux/x86 (note that you may have to disable SSE on some 
architecture), and mostly work on Linux/PPC (there are some errors with
floating points). Portage to Darwin has been done some time ago, so it should
not be too hard.

JnJVM and N3 use GCC's unwinding library (libgcc_s.so).

There are mainly two options in the ./configure script
--with-gnu-classpath-local-prefix: the local build of GNU classpath
--with-llvm: the local build of LLVM

Running make on the root tree will produce three executables:
1) lib/Mvm/main: a command line tool to load virtual machines dynamically
2) lib/JnJVM/main: running the JnJVM like any other JVM
3) lib/N3/main: running N3 like CLR

JnJVM and N3 have their own README notes. N3 requires to patch pnet-0.7.4.


//===---------------------------------------------------------------------===//
// LLVM patch
//===---------------------------------------------------------------------===//

The patched files are:
- include/llvm/Target/TargetOptions.h: new option SizedMemoryCode to know
  before emitting the size of the code
- include/llvm/CodeGen/SizeEmitter.h: new file
- include/llvm/CodeGen/MachineCodeEmitter.h: uses virtual methods to implement
  SizeEmitter
- lib/CodeGen/LLVMTargetMachine.cpp: enables SizeEmitter if SiedMemoryCode is 
  true
- lib/CogeGen/SizeEmitter.cpp: new file
- lib/Target/PowerPC/PPCInstrInfo.td: being able to load extern symbols (probably
  a bug fix in LLVM)
- lib/Target/PowerPC/PPCJITInfo.cpp: adds Dwarf debugging output to callbacks,
  and makes the patching code thread-safe
- lib/Target/PowerPC/PPCISelLowering.cpp: lowers external symbol, and comments
  double word alignment (TODO in TOT)
- lib/ExecutionEngine/JIT/JITEmitter.cpp: helpers for SizedMemoryCode, make the
  JIT more thread-safe wrt Java (which can execute code when looking for a 
  class)
- lib/ExecutionEngine/ExecutionEngine.cpp: Don't check existing mappings (check
  if TOT is correct)
- lib/VMCore/AsmWriter.cpp: enables printing of Ghost functions
  (for debugging purposes)
- lib/Target/X86/X86JITInfo.cpp: enables Dwarf debugging output to callbacks

//===---------------------------------------------------------------------===//
// TODOs
//===---------------------------------------------------------------------===//

- Merge LLVM patch with TOT
- A compiler/system dependency interface
- A better autoconf support
- Remove old, historical references and files
- Currently old object are allocated by MVM'GC. Make some classes 
  hand-allocated.
- Port to Darwin
- Improve exception handling performance: it's currently ugly and inefficient

//===---------------------------------------------------------------------===//
// Disclaimer
//===---------------------------------------------------------------------===//

JnJVM, N3 and MVM were developed with "having functional virtual machines as 
quick as possible" in mind. The usage of mixed  C/C++ and the absence of clean 
interfaces, is due to the initial developers lazyness. But now that the VMs
run, things should go better.