Use of +offset(%ebp) for parameters invalid here

[PeterX]

Hi,

I am still looking for a solution to this Lazarus Warning:

Code: Pascal  [Select][+][-]

1. Use of +offset(%ebp) for parameters invalid here

Source of this code seems to be Delphi 5, classes.pas line 1846 :

Code: Pascal  [Select][+][-]

1. class procedure TList.Error(const Msg: string; Data: Integer);
2.  
3.   function ReturnAddr: Pointer;
4.   asm
5.           MOV     EAX,[EBP+4]
6.   end;
7.  
8. begin
9.   raise EListError.CreateFmt(Msg, [Data]) at ReturnAddr;
10. end;

Actually the same code can be found in FPC unit RegExpr.pas in line 4148.
Unit is in  C:\lazarus\fpc\3.0.2\source\packages\regexpr\src

Code: Pascal  [Select][+][-]

1. {$IFDEF reRealExceptionAddr}
2. {$OPTIMIZATION ON}
3. // ReturnAddr works correctly only if compiler optimization is ON
4. // I placed this method at very end of unit because there are no
5. // way to restore compiler optimization flag ...
6. {$ENDIF}
7. procedure TRegExpr.Error (AErrorID : integer);
8. {$IFDEF reRealExceptionAddr}
9.  function ReturnAddr : pointer; //###0.938
10.   asm
11.    mov  eax,[ebp+4]
12.   end;
13. {$ENDIF}
14. ...

Does anybody know enough about ASM
to be able to solve this for the FPC / Lazarus compiler ?

[PeterX]

I just also found it here:

https://sourceforge.net/p/lazarus-ccr/svn/HEAD/tree/components/rx/version/2.1/rxctrls.pas

in line 947 ..

[taazz]

replace returnAddr with get_caller_addr(get_frame);
eg.

Code: Pascal  [Select][+][-]

1. type
2.   TEvsCustomControl = class
3.     class procedure Error(Const aMsg:String; const Params:Array of const);
4.   end;
5. implementation
6. procedure TEvsCustomControl.Error(const aMsg :String; aParams :array of const);
7. begin
8.   raise ETBException.CreateFmt(aMsg, aParams) at get_caller_addr(get_frame);
9. end;
10.  
11.  

[PeterX]

replace returnAddr with get_caller_addr(get_frame);
eg.

Code: Pascal  [Select][+][-]

1. type
2.   TEvsCustomControl = class
3.     class procedure Error(Const aMsg:String; const Params:Array of const);
4.   end;
5. implementation
6. procedure TEvsCustomControl.Error(const aMsg :String; aParams :array of const);
7. begin
8.   raise ETBException.CreateFmt(aMsg, aParams) at get_caller_addr(get_frame);
9. end;
10.  
11.  

What's get_frame ?

[marcov]

What's get_frame ?

A documented function

[Thaddy]

A documented function

I can't help, but smile....

[marcov]

The construct as Taazz describes is exactly meant to avoid the need for assembler as PeterX describes.

With the added advantage that the result is more portable, and better understandable/optimizable to the compiler

[PeterX]

What's get_frame ?

A documented function

The documentation is very .. poor, to me.

I wanted to learn how this assembler code has to be written.

So I searched for the function in other INC files and I found:


x86_64.inc :

Code: Pascal  [Select][+][-]

1. {$IFNDEF INTERNAL_BACKTRACE}
2. {$define FPC_SYSTEM_HAS_GET_FRAME}
3. function get_frame:pointer;assembler;nostackframe;{$ifdef SYSTEMINLINE}inline;{$endif}
4. asm
5.         movq    %rbp,%rax
6. end;
7. {$ENDIF not INTERNAL_BACKTRACE}

i386.inc :

Code: Pascal  [Select][+][-]

1. {$IFNDEF INTERNAL_BACKTRACE}
2. {$define FPC_SYSTEM_HAS_GET_FRAME}
3. function get_frame:pointer;assembler;nostackframe;{$ifdef SYSTEMINLINE}inline;{$endif}
4. asm
5.         movl    %ebp,%eax
6. end;
7. {$ENDIF not INTERNAL_BACKTRACE}
8.  

i8086.inc :

Code: Pascal  [Select][+][-]

1. {$IFNDEF INTERNAL_BACKTRACE}
2. {$define FPC_SYSTEM_HAS_GET_FRAME}
3. function get_frame:pointer;assembler;nostackframe;{$ifdef SYSTEMINLINE}inline;{$endif}
4. asm
5.   mov ax, bp
6. {$if defined(FPC_X86_DATA_FAR) or defined(FPC_X86_DATA_HUGE)}
7.   mov dx, ss
8. {$endif}
9. end;
10. {$ENDIF not INTERNAL_BACKTRACE}
11.  

I still do not understand why "Use of +offset(%ebp) for parameters (is) invalid here"
(for Windows / Laz i386 ..)

Code: Pascal  [Select][+][-]

1.   function ReturnAddr: Pointer;
2.   asm
3.           MOV     EAX,[EBP+4]
4.   end;
5.  

Does anybody know enough about ASM ?

[marcov]

I think the assembler thinks you are trying to load a parameter (typically at positive offset to BP), while there is no parameter to the function.

I don't think this can be avoided, the code is simply not a proper function but something internal.

[Thaddy]

Well a lot of us know. There's only the small matter that the syntax you are using in the Delphi code is Intel syntax. And your question suggest you are mixing this up with the "+offset(%ebp)" is not Intel syntax, but gnu syntax, which has a different instruction order(reverse). Furthermore there is the issue of how to refer: ESP or EBP? Makes a big difference...
While experimenting to solve this yourself, make sure you have {$ASMMODE INTEL} on.
Also, "offset" is only recently added. It does not work in older versions of FPC.

[edit]
Marco's post crossed, basically I gave the same pointer. (Apart from mixing up syntax).

Also note that the internal assembler in FPC is more strict than BASM:

Code: Pascal  [Select][+][-]

1. function ReturnAddr: Pointer;
2.   asm
3.           MOV     EAX,[EBP+4]
4.   end;
5.  

Delphi assumes dword size but [] indicates a pointer. You have to specify the size: dword ptr. It will still be delphi compatble. If you rely on an older version, use  lea instead of offset.

[PeterX]

While experimenting to solve this yourself, make sure you have {$ASMMODE INTEL} on.

Well, I already added ASMMODE some years ago here,
otherwise it wouldn't compile at all .. :

Code: Pascal  [Select][+][-]

1.   function ReturnAddr: Pointer; assembler;
2.   // From classes.pas
3. {$ifdef FPC} {$ASMMODE intel} {$endif}
4.   asm
5.     MOV         EAX,[EBP+4] // sysutils.pas says [EBP-4], but this works !
6.   end;
7.  

But I'll try the get_frame function in IFDEF first now.

[taazz]

One off topic question in 64bit apps does  +4 becomes +8?

[Thaddy]

One off topic question in 64bit apps does  +4 becomes +8?

Actually + SizeOf(Pointer) is perfectly legal in FPC's implementation of inline ASM...