mirror of
https://github.com/irmen/prog8.git
synced 2024-12-27 05:29:38 +00:00
133 lines
6.4 KiB
ReStructuredText
133 lines
6.4 KiB
ReStructuredText
=================
|
|
Technical details
|
|
=================
|
|
|
|
All variables are static in memory
|
|
----------------------------------
|
|
|
|
All variables are allocated statically, there is no concept of dynamic heap or stack frames.
|
|
Essentially all variables are global (but scoped) and can be accessed and modified anywhere,
|
|
but care should be taken of course to avoid unexpected side effects.
|
|
|
|
Especially when you're dealing with interrupts or re-entrant routines: don't modify variables
|
|
that you not own or else you will break stuff.
|
|
|
|
Variables that are not put into zeropage, will be put into a special 'BSS' section for the assembler.
|
|
This section is usually placed at the end of the resulting program but because it only contains empty space
|
|
it won't actually increase the size of the resulting program binary.
|
|
Prog8 takes care of properly filling this memory area with zeros at program startup and then reinitializes
|
|
the subset of variables that have a nonzero initialization value.
|
|
|
|
Arrays with initialization values are not put into BSS but just occupy a sequence of bytes in
|
|
the program memory: their values are not reinitialized at program start.
|
|
|
|
It is possible to relocate the BSS section using a compiler option
|
|
so that more system ram is available for the program code itself.
|
|
|
|
|
|
.. _symbol-prefixing:
|
|
|
|
Symbol prefixing in generated Assembly code
|
|
-------------------------------------------
|
|
|
|
*All* symbols in the prog8 program will be prefixed with ``p8_`` in the generated assembly code.
|
|
This is to avoid naming conflicts with CPU registers, assembly instructions, etc.
|
|
So if you're referencing symbols from the prog8 program in inlined assembly code, you have to take
|
|
this into account. Stick a ``p8_`` in front of everything that you want to reference that is coming
|
|
from a prog8 source file.
|
|
All elements in scoped names such as ``main.routine.var1`` are prefixed so this becomes ``p8_main.p8_routine.p8_var1``.
|
|
|
|
.. attention::
|
|
Symbols from library modules are *not* prefixed and can be used
|
|
in assembly code as-is. So you can write::
|
|
|
|
%asm {{
|
|
lda #'a'
|
|
jsr cbm.CHROUT
|
|
}}
|
|
|
|
|
|
Subroutine Calling Convention
|
|
-----------------------------
|
|
|
|
Calling a subroutine requires three steps:
|
|
|
|
#. preparing the arguments (if any) and passing them to the routine
|
|
#. calling the routine
|
|
#. preparing the return value (if any) and returning that from the call.
|
|
|
|
|
|
Calling the routine is just a simple JSR instruction, but the other two work like this:
|
|
|
|
|
|
``asmsub`` routines
|
|
^^^^^^^^^^^^^^^^^^^
|
|
|
|
These are usually declarations of Kernal (ROM) routines or low-level assembly only routines,
|
|
that have their arguments solely passed into specific registers.
|
|
Sometimes even via a processor status flag such as the Carry flag.
|
|
Return values also via designated registers.
|
|
The processor status flag is preserved on returning so you can immediately act on that for instance
|
|
via a special branch instruction such as ``if_z`` or ``if_cs`` etc.
|
|
|
|
|
|
regular subroutines
|
|
^^^^^^^^^^^^^^^^^^^
|
|
|
|
- subroutine parameters are just variables scoped to the subroutine.
|
|
- the arguments passed in a call are evaluated and then copied into those variables.
|
|
Using variables for this sometimes can seem inefficient but it's required to allow subroutines to work locally
|
|
with their parameters and allow them to modify them as required, without changing the
|
|
variables used in the call's arguments. If you want to get rid of this overhead you'll
|
|
have to make an ``asmsub`` routine in assembly instead.
|
|
- the order of evaluation of subroutine call arguments *is unspecified* and should not be relied upon.
|
|
- the return value is passed back to the caller via cpu register(s):
|
|
Byte values will be put in ``A`` .
|
|
Word values will be put in ``A`` + ``Y`` register pair.
|
|
Float values will be put in the ``FAC1`` float 'register' (BASIC allocated this somewhere in ram).
|
|
|
|
|
|
Calls to builtin functions are treated in a special way:
|
|
Generally if they have a single argument it's passed in a register or register pair.
|
|
Multiple arguments are passed like a normal subroutine, into variables.
|
|
Some builtin functions have a fully custom implementation.
|
|
|
|
|
|
The compiler will warn about routines that are called and that return a value, if you're not
|
|
doing something with that returnvalue. This can be on purpose if you're simply not interested in it.
|
|
Use the ``void`` keyword in front of the subroutine call to get rid of the warning in that case.
|
|
|
|
|
|
Compiler Internals
|
|
------------------
|
|
|
|
Here is a diagram of how the compiler translates your program source code into a binary program:
|
|
|
|
.. image:: prog8compiler.svg
|
|
|
|
Some notes and references into the compiler's source code modules:
|
|
|
|
#. The ``compileProgram()`` function (in the ``compiler`` module) does all the coordination and basically drives all of the flow shown in the diagram.
|
|
#. ANTLR is a Java parser generator and is used for initial parsing of the source code. (``parser`` module)
|
|
#. Most of the compiler and the optimizer operate on the *Compiler AST*. These are complicated
|
|
syntax nodes closely representing the Prog8 program structure. (``compilerAst`` module)
|
|
#. For code generation, a much simpler AST has been defined that replaces the *Compiler AST*.
|
|
Most notably, node type information is now baked in. (``codeCore`` module, Pt- classes)
|
|
#. An *Intermediate Representation* has been defined that is generated from the intermediate AST. This IR
|
|
is more or less a machine code language for a virtual machine - and indeed this is what the built-in
|
|
prog8 VM will execute if you use the 'virtual' compilation target and use ``-emu`` to launch the VM.
|
|
(``intermediate`` and ``codeGenIntermediate`` modules, and ``virtualmachine`` module for the VM related stuff)
|
|
#. The code generator backends all implement a common interface ``ICodeGeneratorBackend`` defined in the ``codeCore`` module.
|
|
Currently they get handed the program Ast, Symboltable and several other things.
|
|
If the code generator wants it can use the ``IRCodeGen`` class from the ``codeGenIntermediate`` module
|
|
to convert the Ast into IR first. The VM target uses this, but the 6502 codegen doesn't right now.
|
|
|
|
|
|
Upgrading from version 8
|
|
------------------------
|
|
Version 9 introduced several large, incompatible changes. If you still have programs
|
|
written for Prog8 version 8 or earlier, it is likely that you'll have to modify them
|
|
to be able to compile with version 9 or newer.
|
|
|
|
Information about this can be found in `older Prog8 documentation <https://github.com/irmen/prog8/blob/v9.2.1/docs/source/upgrading8.rst>`_ .
|