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Author Topic: asm from delphi to fpc  (Read 618 times)

nanobit

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asm from delphi to fpc
« on: October 23, 2018, 08:26:32 am »
The following delphi asm code (to change the field TFreeObject.VMIndex: Integer)
does not compile with fpc. How could one port this?
Code: Pascal  [Select]
  1. procedure TFreedObject.GetVirtualMethodIndex; assembler;
  2. asm
  3.   Inc(VMIndex); Inc(VMIndex); Inc(VMIndex); Inc(VMIndex); Inc(VMIndex);
  4.   Inc(VMIndex); Inc(VMIndex); Inc(VMIndex); Inc(VMIndex); Inc(VMIndex);
  5.   jmp TFreedObject.VirtualMethodError  
  6. end;


Thaddy

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Re: asm from delphi to fpc
« Reply #1 on: October 23, 2018, 10:13:11 am »
Such code relies on very low level implementation detail and may even change between Delphi versions: it is bad code! in my opinion.
Since it relies on implementation detail it is not FPC compatible.

But you can use e.g. TObject.MethodAddress
Depends what you want?

[edit]
FPC Has a TypeOf() function that returns the VMT, so the index is something like (TYourObject.MethodAddress('methodname') - TypeOf(TYourObject)) div sizeOf(Pointer);
You can get the address and the VMT and subsequently the index.

That also means it is silly to use assembler for it.
« Last Edit: October 23, 2018, 10:25:21 am by Thaddy »
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marcov

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Re: asm from delphi to fpc
« Reply #2 on: October 23, 2018, 10:14:13 am »
Compile a small program that has a pascal version of the method with -Rintel -a and look at the generated code in the .s file.

Thaddy

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Re: asm from delphi to fpc
« Reply #3 on: October 23, 2018, 10:22:44 am »
Marco, I did an edit. Would that work? [edit] No! but something can be done along those lines.
« Last Edit: October 23, 2018, 11:33:44 am by Thaddy »
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nanobit

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Re: asm from delphi to fpc
« Reply #4 on: October 23, 2018, 03:02:33 pm »
Unfortunately, I will give up. I wanted to port fastMM to Lazarus, but it compiles only without the FullDebugMode define. FullDebugMode is required to use detection of memory corruptions, the main reason I wanted to use it.

Thaddy

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Re: asm from delphi to fpc
« Reply #5 on: October 23, 2018, 03:11:08 pm »
heaptrc.pp shows you how to detect memory corruption in much the same way. So examine that.
Also note the memory manager from Freepascal works internally different - not much but significant - from Delphi and is already fast (much faster than the default Delphi one once was before they changed to fastmm light) and it is cross-platform which fastmm isn't...
« Last Edit: October 23, 2018, 03:29:40 pm by Thaddy »
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