How to learn Assembly

[zEr0]

Iczelion's Win32 Assembly Homepage
at http://win32asm.cjb.net/ is very good

but if you prefer to program under WIN32 and sometimes under LINUX then choose NETWIDE ASSEMBLER

this compilator is available under LINUX too
http://sourceforge.net/projects/nasm
http://nasm.sourceforge.net/wakka.php?wakka=HomePage

for writing exploites for LINUX its very useful language

If you aren't opposed to good old-fashioned tomes, I found that "80X86 IBM PC and Compatible Computers: Assembly Language, Design, and Interfacing, Vols. 1 and 2" by Mazidi, et al. to be a pretty solid bottom-up assembly reference. It's getting a little out of date in some respects (lots of old DOS memory management stuff), but it's a good way to get started on assembly from the ground level. Currently about $35 on amazon. The 4th edition is there too, but it's $100 I suppose a clever person could figure out how to read the whole thing on amazon, but you'd need a good monitor, good eyesight, and a good deal more patience than me

I also started to read through AoA, but to be totally honest I was really put-off by the heavy (read: exclusive) use of HLA. Now don't get me wrong, maybe HLA is a good thing to learn for it's own sake, but for the most part it's not going to help you really understand things from a low-level debugging/disassembling standpoint. I laboured through a few chapters, skipping as much of the HLA stuff as I could before I finally decided that it just wasn't what I was looking for at the moment. That said, there's still a lot of good information here, it's just not about assembly, per se. I think a more apt name might be "The Art of System Archtecture and How to Monkey With it Using HLA". I'm still reading through his explanation of memory management, etc., but it's valuable stuff despite the aforementioned flaws.

Perhaps most importantly, there's the Intel specs themselves. Most people wouldn't suggest these as a good starting point, so maybe I'm just a freak. But I like to learn how a piece of technology works generically before getting into specific applications of it. The Intel specs are almost unquestionably the most complete documentation on what each and every opcode does, what it's syntax is, etc. The first volume is a good read for learning how things work from an application program (ring 3) standpoint. It also gives at least a basic explanation of how protected mode in general works, and gives a few slightly vague glimpses into how the OS/executable (ring 0) level works. The third volume gives all the gorey details of system software programming and all the higher privelege levels in protected mode. I haven't read very much of it yet, but there's really no more authoritative source for information on the mechanisms of memory management, task switching, interrupt/exception/trap handling, etc. Then, of course, the second volume is just a massive reference of every opcode, indexed by their mnemonic. Invaluable for finding the specifics of what an opcode does.

The only obvious "catch" with the Intel specs is that it requires a lot more thought to really "get" it. They tell you what everything is and does, but they don't really explain and give examples. You have to figure it out yourself. It also won't cover AMD specific extensions like 3DNow!, of course, but if you dig around you can find the documentation for those instruction sets on AMD's site (fair warning: I like AMD, but prior to the AMD64, their processor documentation can only be described as shitty. Be prepared to concatenate 3 or 4 archived documents and revisions in order to get a complete reference). From a beginner's perspective, I'd say just skim or skip the stuff about MMX, SSE/2/3, and 3DNow for the time being. You can always fill that gap when you actually encounter a need for it. I'm currently working from their P4 version of the IA-32 specs, and I'll just tackle 64-bit assembly when it becomes prevalent enough for me to care about it.
hxxp://developer.intel.com/design/Pentium4/documentation.htm
(check under the manuals section)

If/when you've digested all that, it's time to get into specifics. I'm coming to realize that knowing assembly really isn't enough to understand the disassembly/debuggery of a Windows program. You'll also need to know PE/COFF format so that you can understand how the loader creates the run-time environment for a program. Again, I like to go back to the source:
hxxp://www.microsoft.com/whdc/hwdev/hardware/pecoff.mspx
Yes, it's a PITA to read, but you'll wind up knowing more about PE/COFF than you ever wanted to know. Iczelion's win32asm tutorials have already been mentioned, but his tutorials on PE format are also highly worth reading in this regard.

Apart from that, you need to learn how different calling conventions work. I really can't make a good recommendation on that. Everything I've picked up so far has been from miscellaneous resources that I've hobbled together from googling for "calling conventions"

Oh, and this is kind of a random aside, but I just thought I'd also plug Firefox/Mozilla as valuable research tool. Trying to pop back and forth through 4 or 5 different manuals, specs, and tutorials at once would make you insane without a decent tabbed browser.

[gabri3l]

My 2cents:
I found Randy Hydes Art of Assembley to be a great book I even picked it up now that its been published. If you are anything like me I find having a book you can flip around in is much more condusive than reading it off a computer screen. If you however like to learn off the screen I'll agree with zero on http://win32asm.cjb.net/ an excellent resource of information.

Calling conventions are, well...hopelessly complicated

In a nutshell, when you call a procedure, it's rarely as simple as just executing a CALL statement, executing the procedure code, and then executing a RETN statement. The calling code and the procedure both have to agree on how to do several things:

• Which registers (if any) should be preserved through the procedure?
• How those registers will be preserved. Will the calling code save them before the call and restore them after the return, or will the procedure save them before executing it's own code and restore them before it returns?
• How will parameters be passed? Through registers? Through memory locations? By sticking data on the stack?
• If arguments are passed on the stack, are they pushed from left-to-right or from right-to-left?
• If arguments are passed on the stack, who is responsible for popping them off when the procedure is finished?

I'm sure that's not an all-inclusive list, but basically a calling convention is a set of rules (a protocol, if you will) that answers those questions.

For high-level languages, the calling convention also defines how the function name in the source code will get translated for the export section. This is particularly important for languages like C++ that support function overloading. That is, you have two or more functions declarations in your source code that are represented by the same symbol, but different arguments. Internally, the compiler actually gives each version of the function a unique name according to the name you gave it and the argument list in the function declaration. Then it looks at all the calls in your source code and changes them to the appropriate mangled name. Since the mangled names are what actually go in the export table, the mangling protocol is included in the calling convention.

Probably the most commonly used conventions are:

• STDCALL - the "native" calling mode for Win32 programs. Procedures generated by compilers for most languages in the Windows environment generate their procedures as STDCALL.
• CDECL - used by "C style" procedures. Mainly used for procedures that require a variable number of arguments. In contrast to most other conventions, stack cleanup is performed by the calling code because only the calling code knows how many arguments are actually being passed on the stack.
• FASTCALL - basically the same as STDCALL except that the first two arguments are passed in registers instead of on the stack. Generates slightly faster code because maniuplating registers is faster than PUSH/POP operations. Not really used that much in application programming unless the programmer was a real speed freak.
• THISCALL - Used to call procedures that belong to a C++ object. An offset to the object that the procedure belongs to is passed in ECX.

By the way, I'm just reciting this from my notoriously shakey memory, so it's probable that I've made a mistake somewhere. If I were you, I wouldn't count on it being entirely accurate

http://wasm.ru/ has english mirror site?

Originally Posted by slin777

http://wasm.ru/ has english mirror site?

I don't think it has an english mirror site, but you can use free online translation provided by some websites to help you.

I've tried learning even the most basic ASM, I don't have the attention span for it. I can understand it a little bit, but never write anything massive or complex. I can barely write an ASM program to output text. o_O