Application crash after Line: 32

[paule32]

Hello,
the Code above produce me an Application Crash after Line: 32.
How can I fix this ?
The Code, I use it under Windows 10 64-Bit.

Code: Pascal  [Select][+][-]

1. procedure fpc_ansistr_assign(var DestS: Pointer; S2: Pointer); [public, alias: 'FPC_ANSISTR_ASSIGN']; compilerproc;
2. begin
3.     MessageBox(0, LPCSTR( S2 ), '0 0 0 0 0', 0);
4.     DestS := malloc( 200 );
5. {$ASMMODE INTEL}
6.     asm
7.     mov rsi, S2             // src string
8.     mov rdi, DestS          // dst string
9.    
10.     xor rax, rax            // counter for string length
11.     @findLength:
12.     cmp byte ptr [rsi + rax], 0
13.     je @copyInit            // null terminator
14.     inc rax
15.     jmp @findLength
16.        
17.     @copyInit:
18.     mov rcx, rax            // rcx now holds the length of the string
19.    
20.     @copyLoop:
21.     test rcx, rcx           // check if RCX is empty
22.     jz @endCopy             // when yes => done.
23.    
24.     dec rcx
25.     mov al, [rsi + rcx]     // load byte from src in AL
26.     mov [rdi + rcx], al     // store byte into dst
27.     jmp @copyLoop           // to next charcter
28.        
29.     @endCopy:
30.     mov byte ptr [rdi + rax], 0  // null-terminated dst string
31.     end;
32.     MessageBox(0, LPCSTR( S2 ), '1 1 0 1 0', 0);
33.     MessageBox(0, LPCSTR( DestS ), '0 0 0 0 0', 0);
34. end;
35.  

[rvk]

fpc_ansistr_assign is normally an essential part of the RTL.

In that procedure you can messagebox multiple times.
Are you absolutely sure those functions don't call fpc_ansistr_assign themselves because then you get an infinite loop.

Remove the messageboxes.
Does it still crash?
If so... On what line?

[paule32]

the Function will not call it'self.
The first, and second MessageBox will be pop out on screen.
So, there is no Loop.

But the DestS seems be not valide

[KodeZwerg]

I just transaled your asm back to pascal to find out things, here it works okay.

Code: Pascal  [Select][+][-]

1. procedure FPC_ANSISTR_ASSIGN(var DestS: PChar; S2: PChar);
2. var
3.  Len: Integer;
4. begin
5.  MessageBox(0, S2, '0 0 0 0 0', 0);
6.  GetMem(DestS, 200);
7.  try
8.     Len := 0;
9.     while S2[Len] <> #0 do
10.       Inc(Len);
11.     Move(S2^, DestS^, Len);
12.     DestS[Len] := #0;
13.  finally
14. //    FreeMem(DestS); // must be done outside else the pointer is garbage after method runs out of scope
15.  end;
16.  MessageBox(0, S2, '1 1 0 1 0', 0);
17.  MessageBox(0, DestS, '0 0 0 0 0', 0);
18. end;

[jamie]

Lots of holes on that ASM code.... it's like the slit experiment!

[ASerge]

Lots of holes on that ASM code.... it's like the slit experiment!

I agree. Better FPC code:

Code: Pascal  [Select][+][-]

1. procedure FPC_ANSISTR_ASSIGN(out DestS: PAnsiChar; S2: PAnsiChar);
2. var
3.   Len: SizeInt;
4. begin
5.   DestS := nil;
6.   if S2 = nil then
7.     Exit;
8.   Len := IndexByte(S2^, -1, 0);
9.   if Len > 0 then // the only #0 is ignored
10.   begin
11.     Inc(Len); // + #0
12.     GetMem(DestS, Len);
13.     Move(S2^, DestS^, Len);
14.   end;
15. end;