steve smithers wrote:
rvmart...@ntlworld.com wrote on Wed, 8 Feb 2012 14:16:50 +0000 (GMT)
The implementation of calling conventions is up to the code generator as
well. You can invent your own conventions, and map them to any
predefined one. As a starting point it's sufficient to support only one
calling convention, the one for system calls. More conventions for
calling other external libraries may be required, depending on the
target OS conventions.
Where can I find details of the input to the back-end?
I'd like to have a crack at generating assembler code for VM/SP.
Maybe I've misunderstood the logic here, but it's my understanding
that the back-end produces assembler statements to produce executable
code for the processor. So if I want to move something from field a
to field b say, or add two numbers together, the backend generated the
MVC and it's related code or the Add instruction, Handles registers
and addressability and stuff. Anyway, whatever this stuff is called
it lives in the COMPILER/VMSP (apologies to you case-sensitive types)
sub-directory.
The bit that provides code for VM/SP as opposed to say MVS, is the RTL,
so if I want to open a file, there is a routine in the RTL called OpenFile
(or whatever) that issues the VM code for open. This lives in System.pp
or Sysfile.pp or whatever it's called in the RTL/VMSP sub-directory
Now, in order for the compiler to function it needs access to a certain
level of base functionality in the VM/SP RTL. Things like Allocate /
Deallocate memory, Open and Close a file, Read and Write from and to a
file. Create and Delete a file etc. These may, or may not, be written
totally or partially in assembler.
I've added example FPC output at
http://wiki.lazarus.freepascal.org/ZSeries#Digression:_example_FPC_output
which might be useful to the current discussion. I've used David Zhang's
MIPS compiler to do this, since the register etc. model is probably
closer to zSeries than any of the other v2 compilers.
Note that to get this level of detail the compiler has to be built with
-dEXTDEBUG in order to enable the -an option, despite the fact that this
always appears in fpc's -h output. If it were my choice I'd make that
bit of help output conditional.
--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk
[Opinions above are the author's, not those of his employers or colleagues]
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