Using olly.dll in Assembly project

[FlySky]

Hey Guys,

I am working on disassembling instructions into output text  and assembling instructions back to opcodes.

For the disassembling BEAEngine is a wonderfull piece of software.
What I am struggling with is assembling instructions back into opcodes.
I've been searching a lot but it seems BEAEngine does not support assembling, so I thought let's try Olly.
I've got Olly.dll which has an export called: Assemble.

Function explanation from readme file:
int Assemble(char *cmd,ulong ip,t_asmmodel *model,int attempt,int constsize,char *errtext);

Parameters:
    cmd - pointer to zero terminated ASCII command;
    pi - address of the first byte of generated binary command in memory;
    model - pointer to the structure that receives machine code and mask, see detailed description below;
    attempt - index of alternative encoding of the command. Call Assemble with attempt=0,1,2... to obtain all possible versions of the command. Stop this sequence when Assemble reports error;
    constsize - requested size of address constant and immediate data. Call Assemble with constsize=0,1,2,3 to obtain all possible encodings of the version selected by attempt;
    errtext - pointer to text buffer of length at least TEXTLEN bytes that receives description of detected error.

t_asmmodel: structure that receives assembled code.

typedef struct t_asmmodel {    // Model to search for assembler command
    char code[MAXCMDSIZE];     // Binary code
    char mask[MAXCMDSIZE];     // Mask for binary code (0: bit ignored)
    int length;                // Length of code, bytes (0: empty)
    int jmpsize;               // Offset size if relative jump
    int jmpoffset;             // Offset relative to IP
    int jmppos;                // Position of jump offset in command
} t_asmmodel;

Members:
    code - binary code of the command. Only bits that have 1's in corresponding mask bits are significant;
    mask - comparison mask. Search routine ignores all code bits where mask is set to 0;
    length - length of code and mask, bytes. If length is 0, search model is empty or invalid;
    jmpsize - if nonzero, command is a relative jump and jmpsize is a size of offset in bytes;
    jmpoffset - if jmpsize is nonzero, jump offset relative to address of the following command, otherwise undefined;
    jmppos - if jmpsize is nonzero, position of the first byte of the offset in code, otherwise undefined.

In my code I am using:

AssembleStructure STRUCT
   code DB 256 Dup (?)     // Binary code
    mask DB 256 Dup (?)     // Mask for binary code (0: bit ignored)
    length DD 0             // Length of code, bytes (0: empty)
    jmpsize DD 0            // Offset size if relative jump
    jmpoffset DD 0          // Offset relative to IP
    jmppos DD 0             // Position of jump offset in command
ENDS

_AssembleStructure AssembleStructure <>

invoke [AssembleFunction], offset wsprintbuffer, offset BinaryCode, offset _AssembleStructure, 0, 0
wsprintbuffer holds the string: mov esi, [esp+4b0]

The code doesn't seem to work and returns with an error value in eax.

Anyone been using Olly before in an project or anyone knows of a simple Assembler engine which can transfer a string back into it's opcodes?

[ragdog]

Hi

What for Olly.dll i have look on Ollydbg page and cannot found this dll

[FlySky]

Hey there ragdog,

My findings are based on:

http://www.purebasic.fr/english/viewtopic.php?f=5&t=42527

and if you click on the link from that page: http://sandsprite.com/CodeStuff/olly_dll.html

You will land on a page which explains the use of olly.dll.

I noticed the header files are on OllyDBG website, although the file to run it in Visual Studio isn't.
The Olly.dll I am talking about I picked from the package from the above site.
Although it's coded in Visual Basic, I should be able to use the 'DLL' in my own project calling the apropriate function parameters?.

Any other Assembler engine is fine, there just isn't much information.

[qWord]

You haven't looked in the org. code? The last parameter, which returns a string that describes occurring errors, is not optional.