I need to teach assembler, and the easiest way would be to create a driver
and simple I/O library in high level language that can be called from
assembler so that students can focus in programming with assembler more than
dealing with system specific features. It's been quite a while since I go
down to this level, so I might miss something.
Here's the IO library (asmio.pas):
unit asmio;
interface
procedure printc(const c: Char); pascal;
procedure printi(const i: LongInt); pascal;
implementation
procedure printc(const c: Char); pascal; [public, alias: 'printc'];
begin
Write(c);
end;
procedure printi(const i: LongInt); pascal; [public, alias: 'printi'];
begin
Write(i);
end;
end.
The driver program (driver.pas):
program driver;
{$L asmio.o}
{$L test.o}
procedure tes; pascal; external name 'tes';
begin
tes;
end.
And example assembler program which suppose to print 'A' (test.asm):
[bits 32]
extern printc,printi
segment .text
global tes
tes:
push ebp
mov ebp,esp
push 65
call printc
leave
ret
build command:
nasm -f coff test.asm
fpc asmio.pas
fpc -o test driver.pas
As you can see, I didn't use any optimizations because AFAIR FPC would
change parameter passing mechanism when a certain optimizations are
performed. Of course if it works I won't ask here, but it doesn't. I got
access violation instead. However changing the driver program to:
procedure printc(const c: Char); pascal; external name 'printc';
begin
printc('A');
end.
generates the same instruction sequence for calling printc:
push 65
call printc
I've tried omitting the stackframe (with the corresponding modifier in
driver program) but no effect. I wonder where my mistake is...
Additional information:
I've made it to work for non IO functions
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