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| layout | title |
|---|---|
| rubyx | RubyX architectural layers |
Main Layers
To implement an object system to execute object oriented languages takes a large system. The parts or abstraction layers are detailed below.
It is important to understand the approach first though, as it differs from the normal interpretation. The idea is to compile ruby. It may be easiest to compare to a static object oriented language like c++. When c++ was created c++ code was translated into c, which then gets translated into assembler, which gets translated to binary code, which is linked and executed. Compiling to binaries is what gives these languages speed, and is the reason to compile ruby.
In a similar way to the c++ example, we need level between ruby and assembler, as it is too big a mental step from ruby to assembler. Off course course one could try to compile to c, but since c is not object oriented that would mean dealing with all off c's non oo heritage, like linking model, memory model, calling convention etc.
Top down the layers are:
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Melon , compiling ruby code into typed layer and includes bootstrapping code
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Typed intermediate layer: Statically typed object oriented with object oriented call semantics.
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Risc register machine abstraction provides a level of machine abstraction, but as the name says, quite a simple one.
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Binary and cpu specific assembler This includes arm assembly and elf support to produce a binary that can then read in ruby programs
Melon
To compile and run ruby, we need to parse and compile ruby code. While parsing ruby is quite a difficult task, it has already been implemented in pure ruby here. The output of the parser is again an ast, which needs to be compiled to the typed layer.
The dynamic aspects of ruby are actually reltively easy to handle, once the whole system is in place, because the whole system is written in ruby without external dependencies. Since (when finished) it can compile ruby, it can do so to produce a binary. This binary can then contain the whole of the system, and so the resulting binary will be able to produce binary code when it runs. With small changes to the linking process (easy in ruby!) it can then extend itself.
The type aspect is more tricky: Ruby is not typed and but the typed layer is after all. And if everything were objects (as we like to pretend in ruby) we could just do a lot of dynamic checking, possibly later introduce some caching. But everything is not an object, minimally integers are not, but maybe also floats and other values. The distinction between what is an integer and what an object has sprouted an elaborate type system, which is (by necessity) present in the typed layer.
Typed intermediate layer
The Typed intermediate layer is more fully described here
In broad strokes it consists off:
- MethodCompiler: compiles the ast into a sequence of Register instructions. and runtime objects (classes, methods etc)
- Parfait: Is the runtime, ie the minimal set of objects needed to create a binary with the required information to be dynamic
- Builtin: A very small set of primitives that are impossible to express in ruby
The idea is to have different methods for different types, but implementing the same ruby logic. In contrast to the usual 1-1 relationship between a ruby method and it's binary definition, there is a 1-n.
The typed layer defines the Type class and BasicTypes and also lets us return to different places from a function. By using this, we can compile a single ruby method into several typed functions. Each such function is typed, ie all arguments and variables are of known type. According to these types we can call functions according to their signatures. Also we can autognerate error methods for unhandled types, and predict that only a fraction of the possible combinations will actually be needed.
Just to summarize a few of typed layer features that are maybe unusual:
- Message based calling: Calling is completely object oriented (not stack based) and uses Message and Frame objects.
- Return addresses: A method call may return to several addresses, according to type, and in case of exception
- Cross method jumps When a type switch is detected, a method may jump into the middle of another method.
Register Machine
The Register machine layer is a relatively close abstraction of risc hardware, but without the quirks.
The register machine has registers, indexed addressing, operators, branches and everything needed for the next layer. It doesn't not try to abstract every possible machine feature (like llvm), but rather "objectifies" the risc view to provide what is needed for the typed layer, the next layer up.
The machine has it's own (abstract) instruction set, and the mapping to arm is quite straightforward. Since the instruction set is implemented as derived classes, additional instructions may be defined and used later, as long as translation is provided for them too. In other words the instruction set is extensible (unlike cpu instruction sets).
Basic object oriented concepts are needed already at this level, to be able to generate a whole self contained system. Ie what an object is, a class, a method etc. This minimal runtime is called parfait, and the same objects will be used at runtime and compile time.
Since working with at this low machine level (essentially assembler) is not easy to follow for everyone, an interpreter was created. Later a graphical interface, a kind of visual debugger was added. Visualizing the control flow and being able to see values updated immediately helped tremendously in creating this layer. And the interpreter helps in testing, ie keeping it working in the face of developer change.
Binary , Arm and Elf
A physical machine will run binaries containing instructions that the cpu understands, in a format the operating system understands (elf). Arm and elf subdirectories hold the code for these layers.
Arm is a risc architecture, but anyone who knows it will attest, with it's own quirks. For example any instruction may be executed conditionally in arm. Or there is no 32bit register load instruction. It is possible to create very dense code using all the arm special features, but this is not implemented yet.
All Arm instructions are (ie derive from) Register instruction and there is an ArmTranslator that translates RegisterInstructions to ArmInstructions.