3 The Mono runtime implements a JIT engine for the CIL virtual
4 machine (as well as a byte code interpreter, this is to
5 quickly port it to new systems), the class loader, the garbage
6 collector, threading system and metadata access libraries.
8 We currently have two runtimes:
11 * <b>mono:</b> The Just In Time compiler implemented
12 using a BURS instruction selector. We only support
13 x86 machines in the JIT engine at this point.
15 * <b>mint:</b> The Mono interpreter. This is an
16 easy-to-port runtime engine.
19 Currently we are using the Bohem conservative garbage
20 collector, but we working on incorporating the ORP GC engine.
22 ** Executing MSIL/CIL images
24 The code will load an executable and map the references to
25 external assemblies to our own version of the assemblies on
28 Our roadmap looks like this, this has been updated as of
33 * Milestone 1: <b>Done</b> Fully read and parse all CIL byte-codes
34 and metadata tokens (ie, a disassembler).
36 * Milestone 2: <b>Done</b> Complete an interpreter for CIL byte
37 codes. This interpreter can be used temporarly to
38 run CIL byte code on a system where no JIT is
41 * Milestone 3: <b>Done</b>Define an <i>lburg</i>-like
42 instruction selector for the JITer for Intel.
44 * Milestone 4: <b>Done</b> Implement JITer. This is where our
45 current efforts are focused on, the JITer currently runs
46 all of the code we have tested on it. The major limitation
47 is that our class libraries are not complete, and hence not
48 every application can be ran.
50 * Milestone 5: Port of the JITer to non IA32 systems.
53 A setup similar to the Kaffe JIT engine will be used to
54 layout the code to support non-IA32 architectures. Our work
55 will be focused on getting a IA32 version running first.
57 The JIT engine works on Linux and Win32, although you
58 will need to install the CygWin32 development tools to get a
59 Unix-like compilation environment (mostly we use GNU make in
60 a few of the makefiles).
62 ** JIT Engine (<b>updated, April 21, 2002</b>)
64 The JIT engine uses a code-generator generator approach for
65 compilation. Given the properties of CIL byte codes, we can
66 take full advantage of a real instruction selector for our
69 The JIT engine implements a number of optimizations:
72 * Opcode cost estimates (our architecture allows
73 us to generate different code paths depending
74 on the target CPU dynamically).
80 Although compilers typically do
81 constant folding, the combination of inlining with
82 constant folding gives some very good results.
85 There are a couple of books that deal with this technique: "A
86 Retargetable C Compiler" and "Advanced Compiler Design and
87 Implementation" are good references. You can also get a
88 technical description of <a
89 href="http://research.microsoft.com/copyright/accept.asp?path=http://www.research.microsoft.com/~drh/pubs/iburg.pdf&pub=ACM">lbrug</a>.
91 A few papers that describe the instruction selector:
94 * <a href="http://research.microsoft.com/copyright/accept.asp?path=http://www.research.microsoft.com/~drh/pubs/interface.pdf&pub=wiley">A code generation interface for ANSI C</a>
97 * <a href="http://research.microsoft.com/copyright/accept.asp?path=http://www.research.microsoft.com/~drh/pubs/iburg.pdf&pub=ACM">Engineering efficient code generators using tree matching and dynamic programming.</a>
103 We are evaluating the future directions for the JIT engine:
104 both from our needs (optimizations like inlining, better register allocation,
105 instruction scheduling, and porting to other CPUs).
107 We have not yet decided how we will evolve the JIT engine. We
108 might just upgrade our current architecture, and provide optimizations as
111 ** Garbage Collection
113 Currently we are using the Boehm conservative GC. Although our plans
114 are to move to the Intel ORP GC engine, our plans on a next generation
115 dual-JIT engine have to be taken into account.
117 We will be using the Intel ORP GC engine as it provides a precise
118 garbage collector engine, similar to what is available on the
121 Although using a conservative garbage collector like Bohem's
122 would work, all the type information is available at runtime,
123 so we can actually implement a better collector than a
124 conservative collector.
127 * Garbage collection list and FAQ:<br>
128 <a href="http://www.iecc.com/gclist/">http://www.iecc.com/gclist/</a>
130 * "GC points in a Threaded Environment":<br>
131 <a href="http://research.sun.com/techrep/1998/abstract-70.html">
132 http://research.sun.com/techrep/1998/abstract-70.html</a>
134 * "A Generational Mostly-concurrent Garbage Collector":
135 <a href="http://research.sun.com/techrep/2000/abstract-88.html">
136 http://research.sun.com/techrep/2000/abstract-88.html</a>
138 * Details on The Microsoft .NET Garbage Collection Implementation:<br>
139 <a href="http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnmag00/html/GCI.asp">http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnmag00/html/GCI.asp</a>
140 <a href="http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnmag00/html/GCI2.asp">http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnmag00/html/GCI2.asp</a>
145 The ECMA runtime and the .NET runtime assume an IO model and a
146 threading model that is very similar to the Win32 API.
148 Dick Porter has been working on the Mono abstraction layer
149 that allows our runtime to execute code that depend on this
154 Paolo Molaro found a few interesting links:
157 * On compilation of stack-based languages:<br>
158 <a href="http://www.complang.tuwien.ac.at/projects/rafts.html">
159 http://www.complang.tuwien.ac.at/projects/rafts.html</a>
161 * A paper on fast JIT compilation of a stack-based language:<br>
162 <a href="http://www.research.microsoft.com/~cwfraser/pldi99codegen.pdf">
163 http://www.research.microsoft.com/~cwfraser/pldi99codegen.pdf</a>
165 * Vmgen generates much of the code for efficient virtual machine (VM)
166 interpreters from simple descriptions of the VM instructions:<br>
167 <a href="http://www.complang.tuwien.ac.at/anton/vmgen/">
168 http://www.complang.tuwien.ac.at/anton/vmgen</a>
173 PInvoke is the mechanism we are using to wrap Unix API calls
174 as well as talking to system libraries.
176 Initially we used libffi, but it was fairly slow, so we have
177 reused parts of the JIT work to create efficient PInvoke trampolines.
181 Mono has support for remoting and proxy objects, just like
182 .NET does. The runtime provides these facilities.
186 If you are interested in porting the Mono runtime to other
187 platforms, you might find the pre-compiled <a
188 href="archive/mono-tests.tar.gz">Mono regression test
189 suite</a> useful to debug your implementation.
193 We plan on adding support for XPCOM on Unix and COM on Microsoft
194 Windows later in our development process.