User: MannyMax

My take on how to learn x86 ASM

On: Is Assembly Programming Still Relevant, Today?

I spent some time last summer doing exactly this, learning x86 assembly language. Granted, I tried to emphasize a specific area that may or may not be important to you (fast, high-accuracy scientific floating-point), and I already had a passable familiarity with assembly from C dumps, but that just meant I could skip large chunks of many of these references -- they're still good stuff. Some of my opinions on how to go about it:

• Don't use Windows. Seriously. Don't. I'm a Windows geek at heart; I know Linux OK and can use it happily on a daily basis, but I'm really at home in Windows. I have been for 15 years. And it's the absolute worst way to learn ASM you can possibly come up with. The problem is that Windows is built on DOS, and in assembly that really shows. Not in the sense that it behaves like DOS -- it doesn't -- but all the interfaces were clearly designed in the DOS era, and few have been updated. Linux, in contrast, has the perfect environment for learning assembly: the system calls are easy to make, reasonably well documented (the documentation is actually pretty bad, but it's better than Windows' -- it exists.), and it's got all the things you'd expect of a modern OS, not all of which Windows always has (like a flat 32-bit address space for everything!). Even 64-bit Linux has no trouble running even pure 32-bit assembly programs once you get the linker flags right.
• Don't use as (or gas, GNU as). If you must, stay the hell away from AT&T syntax, as's default, since no one but as ever uses it. Make sure you learn the standard Intel syntax (like MASM uses) or a very close approximation (NASM or FASM). as used to only accept AT&T syntax, but now it's got a command-line option to accept Intel syntax; honestly, I prefer NASM's slightly simplified, streamlined Intel syntax. They're very close to each other, close enough that once you know NASM syntax you can read Intel syntax no problem. FASM is similar to NASM, and another decent place to start.
• Use NASM. It's free and open-source. It works. Its no-frills approach is perfect for assembly, and a real breath of fresh air compared to convoluted messes like AT&T syntax. The only downside to NASM is that it's 32-bit-only at the moment; this isn't too big a problem, because almost all existing tutorials teach 32-bit anyway (and all the migration guides for 64-bit ASM assume you know 32-bit). If you want to graduate to 32-bit later, there's FASM, which is free and close enough to NASM that you'll have no trouble.
• Stay the HELL away from old 16-bit code in any form. It's ugly. It's obsolete. It's just not worth your time. Of course, using the 16-bit registers is fine when they're the appropriate tools for the job, but seriously, any tutorial that mentions segmentation? Just say no. You'll thank me for this later.
• Don't put too much faith in the Art of Assembly books. In my opinion, they just aren't that good. They were first written in the 16-bit era, and it shows in far too many places. They're also very DOS/Windows-centric, even the Linux version (also not that good), and learning on Linux is much easier with a native Linux tutorial, like this one:
• Get Paul Carter's NASM tutorial. It's nice and low-level, explaining all the basics from the ground up. It does assume you know C, and it does use libc for a lot of the dirty work, but you can always do it the way I prefer and build everything from the ground up with pure ASM and system calls. I figure that if you're going to use C, just write a C-program and call an assembly function or two. If you're going to write it all in ASM, write it all in ASM. There are lots of nice tutorials out there for doing either (calling ASM from C or pure Linux ASM); google "linux assembly tutorials".
• Get the official manuals from Intel and AMD. They are the single best references out there. Yes, get both co