assembler copy char[]

[Daniel Keep]

nobody wrote:
> Wow, that's exactly what i want.
> In dmd it's all ok, but the gdc  didn't like it: 
> 
> mov EDX, dword ptr [mystring+4];
> mov [st+4],EDX;
> 
> 
> gdmd  string.d
> /tmp/cc4h5AKo.s: Assembler messages:
> /tmp/cc4h5AKo.s:30: Error: junk `(%ebp)+4' after expression
> /tmp/cc4h5AKo.s:31: Error: junk `(%ebp)+4' after expression

IIRC, that's because local variables are actually EBP plus some offset.
 I think DMD is inlining the two offsets, but GDC isn't.

If you want to learn assembler, the best way is to just write code in D,
compile it, and then disassemble it.  I assume you're running under
Linux; gdb should have an option to disassemble the current function.
That way, you can read the original line of source code, and what the
compiler actually produces.  Here's what ddbg gives me for the program

void main()
{
    auto mystring = "Hello, World!";
    auto st = mystring;
}

Disassembly:

copy_string.d:2 void main()
00402010: c8200000                enter 0x20, 0x0
00402014: 53                      push ebx

copy_string.d:4     auto mystring = "Hello, World!";
00402015: 8d45e0                  lea eax, [ebp-0x20]
00402018: 50                      push eax
00402019: 6a0d                    push 0xd
0040201b: ff3594f04000            push dword [0x40f094]
00402021: ff3590f04000            push dword [0x40f090]
00402027: 6a01                    push 0x1
00402029: e87e010000              call 0x4021ac __d_arraycopy

copy_string.d:5     auto st = mystring;
0040202e: 8d4df0                  lea ecx, [ebp-0x10]
00402031: 51                      push ecx
00402032: 6a0d                    push 0xd
00402034: 8d55e0                  lea edx, [ebp-0x20]
00402037: bb0d000000              mov ebx, 0xd
0040203c: 52                      push edx
0040203d: 53                      push ebx
0040203e: 6a01                    push 0x1
00402040: e867010000              call 0x4021ac __d_arraycopy
00402045: 31c0                    xor eax, eax
00402047: 83c428                  add esp, 0x28
copy_string.obj
0040204a: 5b                      pop ebx
0040204b: c9                      leave
0040204c: c3                      ret

	-- Daniel