Skybuck Flying schrieb:
I would like to experiment with the pascal programming language at the
binary/assembler/machine level.
For example compile pascal sources to virtual machine instruction sets.
Only one machine (instruction set) is supported by an FPC executable.
This is because some conditional compilation is used to handle machine
or platform specific issues in the parser code.
Look at the various compiler/ppc*.lpi projects, and the related
subdirectories.
I took a look at the free pascal sources and there seem to be some
assemblers inside the folders.
Multiple assemblers may be usable in one FPC executable.
Then my next question is 2:
2. This would mean free pascal is by default a cross compiler, which can
cross-compile to any assembly/intermediate code.
Right.
"make fullcycle" builds all (registered) cross-compilers.
fpc[.exe] is the stub that selects the concrete compiler to use. But
every single compiler can be invoked directly, too.
So then my main/subject question: How to add a new assember to free
pascal compiler makes sense...
Starting with
http://wiki.freepascal.org/Porting_Free_Pascal#Porting_to_a_new_Architecture
you'll find a lack of documentation about this topic :-(
I've been starting once by copying the m68k directory as mycpu, because
I was more familiar with that cpu. You also can use the "vis" directory
for your first steps, it's the smallest (and incomplete) port. Then I
registered the new directory for it (dunno remember how/where). In all
files and identifiers the old cpu name should be replaced by the new one.
Then the instructions (enum) and register sets have to be specified for
the new cpu. The vis cpu turned out to be not very helpful, I had to
look at various cpu's in order to find out what the register data
structures mean.
When you try to compile the rudimentary cpu, you'll get errors about
missing units and more, telling you where more has to be done. Have a
look at the initialization sections of the cpu's, they often call kind
of registration functions or directly initialize global variables, and
let them point to cpu-specific tables.
I searched the documentation about how to do this... but there seems to
be no documentation for this ?
So if somebody could create some (short?) documentation for this or some
tips how/where to start and how to proceed that would be helpfull.
Unfortunately I cannot locate my last-year experiments with a new cpu,
and the docs I wrote then :-(
But if you want to continue with your project, we can work together and
document what we found out.
Perhaps a simple dummy assembler or template might be nice... concerning
this adding for a new assembler my main question would be where to add
this unit, how to make free pascal notice it and use it and such ? Where
to add the compiler directive and perhaps initialization and
finalization of classes/create/destroy that sort of thing.
3. Assuming free pascal is a cross compiler, and looking at the code...
it seems free pascal actually compiles pascal code into an abstract
assembler structure, is this indeed correct ? Can free pascal be
considered a "pascal to abstract assembler compiler ?" (which would be
pretty cool) (which ultimately gets assembled into real assembler...)
The pascal code is translated into nodes (TNode), which represent the
abstract code flow. You must derive your own node classes, and add the
concrete code generation to them. Your cpunode.pas lists (uses) all your
node units, typically named n<cpu>*.pas.
So in short what I am looking for is a pascal compiler which takes care
of all the work like "lexing/tokenizing/parsing/parse tree/syntax
tree/symantec checks/perhaps even optimizing the intermediate code" and
gives me something to work with like a syntax tree or some form of
abstract assembler (structures) like free pascal seems to do...
See above. I'm working more on the front-end side, to add parsers for
other languages.
To me it seems free pascal could be the correct choice... either by
modifieing it or by extending it... So if I have to modify it... I would
for example modify the intel or powerpc or sparc source code and pretend
it's my own thing... but it would probably be better if I can stuff my
own assembler/platform/units into it to start from scratch just to play
nice with free pascal and prevent confusing things later on...
So I think I need to some help with: is this possible and how to do
it/documentation/short tutorial/some tips ?!?
See above. New platforms and processors can be added to Free Pascal
freely, once the related hooks and procedures are known. Modifying
existing assemblers IMO should be done by conditional compilation, so
that eventual updates of the original code are integrated automatically.
DoDi
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