Help with inline assembly using Xcode ide

[ispete]

Being a beginner, I wasn't aware that you could even inline ASM into a c++ program until I checked out this keygen challenge and saw the keygen code written by Reaction: http://forum.tuts4yo...-1/page__st__20

I copied the asm portion of Reaction's code into Visual C++ and it compiled and ran fine. However, I'm trying to use the same code in Xcode on a Macbook Pro running OS X 10.6.8, and I'm getting some errors. I don't know if it's differences in syntax or maybe I need to define some things.

I'm attaching a screenshot of the errors with the code. Any help is appreciated!

[ghandi]

I would seriously use Google to search for information first...

You are trying to paste MASM syntax assembler into X-Code, which from what i'm reading is GCC syntax, like trying to put Delphi code into Visual Basic.

http://www.ibiblio.o...mbly-HOWTO.html

Also, apparently there is a compiler switch to tell GCC to use intel syntax assembler, how effective though will be an exercise for you to find out:

.intel_syntax

http://www.reversing.be/article.php?story=20051203194931893

HR,

Ghandi

Edited July 16, 2012 by ghandi

[ispete]

Thank you, I will read through that last link. Also, I only post questions when I'm "googled" out. In fact, I visited the HOW-To link you provided before I even posted my question. I'm still trying to understand as much of it as I can. It seemed to me, the more I read, that the syntax I was using would work on macs utilizing an intel chipset.

Also, the code would compile fine when I tried writing some simple assembly code like "xor eax,eax" and "mov al,bl". I only get the errors when trying to use things like "Dword ptr ds:[]".

I'll continue reading. Thanks again.

[ghandi]

This is taken from the HOWTO website, it explains exactly what you are talking about:

3. GCC Assembler Syntax.

GCC, the GNU C Compiler for Linux, uses AT&T/UNIX assembly syntax. Here we’ll be using AT&T syntax for assembly coding. Don’t worry if you are not familiar with AT&T syntax, I will teach you. This is quite different from Intel syntax. I shall give the major differences.

1. Source-Destination Ordering.
   The direction of the operands in AT&T syntax is opposite to that of Intel. In Intel syntax the first operand is the destination, and the second operand is the source whereas in AT&T syntax the first operand is the source and the second operand is the destination. ie, "Op-code dst src" in Intel syntax changes to "Op-code src dst" in AT&T syntax.
2. Register Naming.
   Register names are prefixed by % ie, if eax is to be used, write %eax.
3. Immediate Operand.
   AT&T immediate operands are preceded by ’$’. For static "C" variables also prefix a ’$’. In Intel syntax, for hexadecimal constants an ’h’ is suffixed, instead of that, here we prefix ’0x’ to the constant. So, for hexadecimals, we first see a ’$’, then ’0x’ and finally the constants.
4. Operand Size.
   In AT&T syntax the size of memory operands is determined from the last character of the op-code name. Op-code suffixes of ’b’, ’w’, and ’l’ specify byte(8-bit), word(16-bit), and long(32-bit) memory references. Intel syntax accomplishes this by prefixing memory operands (not the op-codes) with ’byte ptr’, ’word ptr’, and ’dword ptr’. Thus, Intel "mov al, byte ptr foo" is "movb foo, %al" in AT&T syntax.
5. Memory Operands.
   In Intel syntax the base register is enclosed in ’[’ and ’]’ where as in AT&T they change to ’(’ and ’)’. Additionally, in Intel syntax an indirect memory reference is like section:[base + index*scale + disp], which changes to section:disp(base, index, scale) in AT&T. One point to bear in mind is that, when a constant is used for disp/scale, ’$’ shouldn’t be prefixed.

Now we saw some of the major differences between Intel syntax and AT&T syntax. I’ve wrote only a few of them. For a complete information, refer to GNU Assembler documentations. Now we’ll look at some examples for better understanding.

+------------------------------+------------------------------------+

| Intel Code | AT&T Code |

+------------------------------+------------------------------------+

| mov eax,1 | movl $1,%eax |

| mov ebx,0ffh | movl $0xff,%ebx |

| int 80h | int $0x80 |

| mov ebx, eax | movl %eax, %ebx |

| mov eax,[ecx] | movl (%ecx),%eax |

| mov eax,[ebx+3] | movl 3(%ebx),%eax |

| mov eax,[ebx+20h] | movl 0x20(%ebx),%eax |

| add eax,[ebx+ecx*2h] | addl (%ebx,%ecx,0x2),%eax |

| lea eax,[ebx+ecx] | leal (%ebx,%ecx),%eax |

| sub eax,[ebx+ecx*4h-20h] | subl -0x20(%ebx,%ecx,0x4),%eax |

+------------------------------+------------------------------------+

HR,

Ghandi