[fpc-pascal] (no subject)
Hello, guys!
Firstly, thank you for such a great project! It's very nice to use it in a
study process in a school/university.
And now a question :)
I have some trouble working on one of my projects, it's code is here:
https://github.com/Barracuda72/PT
The problem is with function "SentenceSample" in "PT4LibIFace.pas"; there are
two ways - my stupidness or mysterious behavior of FPC compiler.
Code:
-
function SentenceSample(N: integer): string; stdcall;
begin
//writeln('N = ', N);
//SentenceSample := RuGetSentence(N);
inc(N);
end;
-
Of course, inc(N); added just to simplify disassembling. And there is disasm:
-
sentencesample proc near
pushebp
mov ebp, esp
inc [ebp+0Ch]
leave
retn8
-
As you can see, procedure has only one parameter, but FPC generates code as if
there are two
parameters; and the main problem is that it trying to work with wrong variable
(N is in ebp+08,
not 0C; it's obvious and proved by debugging). The result is bad =)
So, can you say, there am I wrong?
Ah, I'm using Lazarus 1.0.14 with FPC 2.6.2, Win32 build
___
fpc-pascal maillist - fpc-pascal@lists.freepascal.org
http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] (no subject)
On 07 Mar 2014, at 20:26, Barracuda wrote:
> -
> function SentenceSample(N: integer): string; stdcall;
> begin
> //writeln('N = ', N);
> //SentenceSample := RuGetSentence(N);
> inc(N);
> end;
> -
[snip]
> -
> As you can see, procedure has only one parameter, but FPC generates code as
> if there are two
> parameters; and the main problem is that it trying to work with wrong
> variable (N is in ebp+08,
> not 0C; it's obvious and proved by debugging). The result is bad =)
> So, can you say, there am I wrong?
Ansistrings results are returned in a hidden call-by-reference parameter, so
the offset should be correct.
Jonas
___
fpc-pascal maillist - fpc-pascal@lists.freepascal.org
http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] (no subject)
On 07.03.2014 20:26, Barracuda wrote:
Code:
-
function SentenceSample(N: integer): string; stdcall;
begin
//writeln('N = ', N);
//SentenceSample := RuGetSentence(N);
inc(N);
end;
-
Of course, inc(N); added just to simplify disassembling. And there is disasm:
You don't need to disassemble. Just pass "-al" and the compiler will
keep the generated assembler files (normally *.s).
-
sentencesample proc near
pushebp
mov ebp, esp
inc [ebp+0Ch]
leave
retn8
-
If you would have used "-al" you would see this:
=== asm begin ===
.section .text.n_p$hiddenarg_$$_sentencesample$longint$$ansistring
.balign 16,0x90
.globl P$HIDDENARG_$$_SENTENCESAMPLE$LONGINT$$ANSISTRING
.type P$HIDDENARG_$$_SENTENCESAMPLE$LONGINT$$ANSISTRING,@function
P$HIDDENARG_$$_SENTENCESAMPLE$LONGINT$$ANSISTRING:
.Lc1:
# [thiddenarg.pas]
# [6] begin
pushl %ebp
.Lc3:
.Lc4:
movl%esp,%ebp
.Lc5:
# Var N located at ebp+12
# Var $result located at ebp+8
# [9] inc(N);
addl$1,12(%ebp)
# [10] end;
leave
ret $8
.Lc2:
.Le0:
.size P$HIDDENARG_$$_SENTENCESAMPLE$LONGINT$$ANSISTRING, .Le0
- P$HIDDENARG_$$_SENTENCESAMPLE$LONGINT$$ANSISTRING
=== asm end ===
Especially note the "N located at ..." and "$result located at ..."
comments ;)
> As you can see, procedure has only one parameter, but FPC generates
code as if there are two
> parameters; and the main problem is that it trying to work with wrong
variable (N is in ebp+08,
> not 0C; it's obvious and proved by debugging). The result is bad =)
Is there a specific reason/problem why you decided to look at the
assembler code?
Regards,
Sven
___
fpc-pascal maillist - fpc-pascal@lists.freepascal.org
http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] (no subject)
OK, thanks. I've really figured that out - function should return PChar, not string. I'm writing an replacement for closed-source component (also written in Pascal), and using disassembler because of that. This component intercommunicate with two others, loadable library (on one side) written in Pascal and application (on other side) written in C#, both are closed-source. Anyway, thanks for help! ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
