quote:Original post by Nik02

quote:Original post by Craazer
You say that get disassempler. Well I hapend to have one. But what im suposed to do whit, hack the exe?

Please look at the assembly listing in your disassembler.
The good dasms even show you automatically where your procedures start.

_Or_, compile with some good IDE (i recommend VS.net 2003) and request assembly listings at compiler settings. Usually, you get the symbolic info as well (var&func names) when using this method.

EDIT:
I think all compilers support assembly listings, not just the ones with IDE

EDIT 2: Yohumbus already offered this option, sorry!

[edited by - Nik02 on August 9, 2003 12:21:08 PM]

[edited by - Nik02 on August 9, 2003 12:23:35 PM]

Hi Nik02.

Im using VS studio 6.0 and I have the assembly listin option enabled. And when I look at part printstr(stri); (as showed in my first post) I see lot of symbols and mess behind the call as also showed in the first post.

Wich leads to the problem:

call	??0?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@QAE@ABV01@@Z ; std::basic_string<char,std::char_traits<char>,std::allocator<char> >::basic_string<char,std::char_traits<char>,std::allocator<char> >mov	DWORD PTR -44+[ebp], eaxcall	?printstr@@YAXV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z ; printstr// quite a mess huh?//I can turn last call look like this so it compiles:call	printstr// but I dont know the actual identifier of the first call.

Because of C++'s support for classes, namespaces, and function overloading, every symbol name (functions & variables) has to be 'decorated', to produce a unique name in assembly. Now, since there is no standard way to do this, different compilers do it differently. This is why you can't simply type call printstr in asm.

There is a means to avoid this, however: declare your printstr function as extern "C" void printstr(string str). Then, in asm, it will be called _printstr. Your next problem is with classes. I don't recommend trying to pass class types by value in asm; references are much easier to deal with. So, change your function definition to

extern "C" void printstr(const string& str)

Next, you need to create a string object in your assembly function. To do this, you will need to find the exact size of a std::string. Then, allocate that much space on the stack. Load the address of that space into the ecx register. Then, call the default constructor. From the disassembly you gave, that is called ??0?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@QAE@ABV01@@Z. Unfortunately, there is no way to avoid using mangled names when dealing with class methods. Now, you need to call operator= with the address of a string literal, and the address of your string object still in ecx. This operator is called ??4?$basic_string@DV?$char_traits@D@_STL@@V?$allocator@D@2@@_STL@@QAEAAV01@PBD@Z in VC++ 6 with STLPort, or (I think) ??4?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@QAEAAV01@PBD@Z with the default STL. Remember, you need to clear its argument off the stack afterwards, so add 4 (the size of a pointer) to the esp register. Now, you should have a std::string object on the stack, containing whatever text you gave it. Next, to call your function with it.

This is the (relatively) easy part. Push the address of your string object onto the stack, then call _printstr. Again, remember to add 4 to esp afterwards to clear the argument from the stack.

I haven't dealt with any function prologue/epilogue you may need if you're intending to call your ASM function from C/C++. That bit is fairly simple, though. Of course, the whole business isn't helped by all the template expansions; it would be much easier with a simpler, less flexible string class that isn't templated. I haven't tested this yet, but I hope it is helpful.

[EDIT: I'm assuming you're using MASM or similar for the assembly code, and not VC++'s inline assembler. I'm not sure whether that likes you using decorated names.]

[edited by - sbennett on August 10, 2003 12:50:33 PM]

On trying this out, it appears that the default constructor for std::string needs to be passed an allocator object. I should be able to tell you how to do it in a couple of minutes, unless I am called away...

[EDIT] I'm sorry, but the STL has defeated me. I may be able to get a simpler example working for you, but I have to stop right now.

[edited by - sbennett on August 10, 2003 1:54:20 PM]