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I wonder if there exists some kind of universal and easy-to-code opcode (or assembly) language which provides basic set of instructions available in most of today's CPUs (not some fancy CISC, register-only computer, just common one). With possibility to "compile", micro-optimize and "interpret" on any mentioned CPUs?
I'm thinking about something like MARS MIPS simulator (rather simple and easy to read code), with possibility to make real programs. No libraries necessary (but nice thing if that possible), just to make things (libraries or UNIX-like tools) faster in uniform way.
Sorry if that's silly question, I'm new to assembler. I just don't find NASM or UNIX assembly language neither extremely cross-platform nor easy to read and code.
The JVM bytecode is sort of like assembly language, but without pointer arithmetic. However, it's quite object-oriented. On the positive side, it's totally cross-platform.
You might want to look at LLVM bytecode - but bear in mind this warning: http://llvm.org/docs/FAQ.html#can-i-compile-c-or-c-code-to-platform-independent-llvm-bitcode
First thing: writing in Assembly does not guarantee a speed increase. Using the correct algorithm for the job at hand has the greatest impact on speed. By the time you need to go down to Assembly to squeeze the last few drops out you can only really do that by adapting the algorithm to the specific architecture of the hardware in question. A generic HLA (High Level Assembler) pretty much defeats the purpose of writing your code in Assembly. Note that I am not knocking Randall Hyde’s HLA, which is a great product, I’m just saying that you don’t gain anything from writing Assembly the way a compiler generates machine code. Most C and C++ compilers have very good optimizers, and can produce machine code superior to almost any naïve implementation in ASM.
See if you can find these books (2nd hand, they are out of print) by Michael Abrash: "Zen of Assembly Language", and "Zen of Code Optimization". Or look if you can find his articles on DDJ. They will give you an insight into optimization second to none,
Related stuff, so I hope might be useful :
There is
flat assembler
with an approach of a kind of portable assembler.
Interesting project of operating system with graphical user interface written in assembler, and great assembly API :
Menuet OS
LLVM IR provides quite portable assembly, backed with powerful compiler, backing many projects including Clang
I'm trying to learn this basic thing about processors that should be taught in every CS department of every university. Yet i can't find it on the net (Google doesn't help) and i can't find it in my class materials either.
Do you know any good resource on how addressing modes work on a physical level? I'm particularly interested in Intel processors.
You might want to take a look into the book "Modern Operating Systems" from Tanenbaum.
If you are interested in the x86 architecture the Intel Manuals might help (but they go really deep)
http://www.intel.com/products/processor/manuals/
Start on the Wikipedia Virtual Memory page for a bit of background, then follow up with specific pages such as the MMU etc. as to satisfy your curiosity.
You will normally go in detail over all of the above concepts (and some more, such as pipelined and superscalar architectures, caches, etc.) in any decent Computer Architecture course, typically taught by the Faculty of (Electrical or Computer) Engineering.
This page might help. I did a search for HC12 addressing modes since that's what we learnt with, and it is MUCH better to learn on a simple processor rather than jumping into the deep end with something like an Intel processor. The basic concepts should be similar for any processor though.
http://spx.arizona.edu/ECE372/Supporting%20Documents/lecture/HCS12%20Addressing%20Modes%20and%20Subroutines.pdf
I wouldn't imagine you'd need to know any of the more complicated ones in an introductory course. We only really used the basic ones, then had to explain a few of the others in our exam.
You should be able to see what's going on on a physical level from that provided you understand the assembly code examples. The inherent addressing command inca for example is going to use a set of logic gates within the processor (http://en.wikipedia.org/wiki/Adder_%28electronics%29) in order to increment register A by one. That's all well and good but trying to understand the physical layer of anything more complicated than that is just going to give you headaches. You really don't need to know it, which is the whole point of using a microprocessor in the first place.
So I just found out GCC could do inline assembly and I was wondering two things:
What's the benefit of being able to inline assembly?
Is it possible to use GCC as an assembly compiler/assembler to learn assembly?
I've found a couple articles but they are all oldish, 2000 and 2001, not really sure of their relevance.
Thanks
The benefit of inline assembly is to have the assembly code, inlined (wait wait, don't kill me). By doing this, you don't have to worry about calling conventions, and you have much more control of the final object file (meaning you can decide where each variable goes- to which register or if it's memory stored), because that code won't be optimized (assuming you use the volatile keyword).
Regarding your second question, yes, it's possible. What you can do is write simple C programs, and then translate them to assembly, using
gcc -S source.c
With this, and the architecture manuals (MIPS, Intel, etc) as well as the GCC manual, you can go a long way.
There's some material online.
http://www.ibiblio.org/gferg/ldp/GCC-Inline-Assembly-HOWTO.html
http://gcc.gnu.org/onlinedocs/gcc-4.4.2/gcc/
The downside of inline assembly, is that usually your code will not be portable between different compilers.
Hope it helps.
Inline Assembly is useful for in-place optimizations, and access to CPU features not exposed by any libraries or the operating system.
For example, some applications need strict tracking of timing. On x86 systems, the RDTSC assembly command can be used to read the internal CPU timer.
Time Stamp Counter - Wikipedia
Using GCC or any C/C++ compiler with inline assembly is useful for small snippets of code, but many environments do not have good debugging support- which will be more important when developing projects where inline assembly provides specific functionality. Also, portability will become a recurring issue if you use inline assembly. It is preferable to create specific items in a suitable environment (GNU assembler, MASM) and import them projects as needed.
Inline assembly is generally used to access hardware features not otherwise exposed by the compiler (e.g. vector SIMD instructions where no intrinsics are provided), and/or for hand-optimizing performance critical sections of code where the compiler generates suboptimal code.
Certainly there is nothing to stop you using the inline assembler to test routines you have written in assembly language; however, if you intend to write large sections of code you are better off using a real assembler to avoid getting bogged down with irrelevancies. You will likely find the GNU assembler got installed along with the rest of the toolchain ;)
The benefit of embedding custom assembly code is that sometimes (dare I say, often times) a developer can write more efficient assembly code than a compiler can. So for extremely performance intensive items, custom written assembly might be beneficial. Games tend to come to mind....
As far as using it to learn assembly, I have no doubt that you could. But, I imagine that using an actual assembly SDK might be a better choice. Aside from the standard experimentation of learning how to use the language, you'd probably want the knowledge around setting up a development environment.
You should not learn assembly language by using the inline asm feature.
Regarding what it's good for, I agree with jldupont, mostly obfuscation. In theory, it allows you to easily integrate with the compiler, because the complex syntax of extended asm allows you to cooperate with the compiler on register usage, and it allows you to tell the compiler that you want this and that to be loaded from memory and placed in registers for you, and finally, it allows the compiler to be warned that you have clobbered this register or that one.
However, all of that could have been done by simply writing standard-conforming C code and then writing an assembler module, and calling the extension as a normal function. Perhaps ages ago the procedure call machine op was too slow to tolerate, but you won't notice today.
I believe the real answer is that it is easier, once you know the contraint DSL. People just throw in an asm and obfuscate the C program rather than go to the trouble of modifying the Makefile and adding a new module to the build and deploy workflow.
This isn't really an answer, but kind of an extended comment on other peoples' answers.
Inline assembly is still used to access CPU features. For instance, in the ARM chips used in cell phones, different manufacturers distinguish their offerings via special features that require unusual machine language instructions that would have no equivalent in C/C++.
Back in the 80s and early 90s, I used inline assembly a lot for optimizing loops. For instance, C compilers targeting 680x0 processors back then would do really stupid things, like:
calculate a value and put it in data register D1
PUSH D1, A7 # Put the value from D1 onto the stack in RAM
POP D1, A7 # Pop it back off again
do something else with the value in D1
But I haven't needed to do that in, oh, probably fifteen years, because modern compilers are much smarter. In fact, current compilers will sometimes generate more efficient code than most humans would. Especially given CPUs with long pipelines, branch prediction, and so on, the fastest-executing sequence of instructions is not always the one that would make most sense to a human. So you can say, "Do A B C D in that order", and the compiler will scramble the order all around for greater efficiency.
Playing a little with inline assembly is fine for starters, but if you're serious, I echo those who suggest you move to a "real" assembler after a while.
Manual optimization of loops that are executed a lot. This article is old, but can give you an idea about the kinds of optimizations hand-coded assembly is used for.
You can also use the assembler gcc uses directly. It's called as (see man as). However, many books and articles on assembly assume you are using a DOS or Windows environment. So it might be kind of hard to learn on Linux (maybe running FreeDOS on a virtual machine), because you not only need to know the processor (you can usually download the official manuals) you code for but also how hook to into the OS you are running.
A nice beginner book using DOS is the one by Norton and Socha. It's pretty old (the 3rd and latest edition is from 1992), so you can get used copies for like $0.01 (no joke). The only book I know of that is specific to Linux is the free "Programming from the Ground Up"
In my quest for getting some basics down before I start going into programming I am looking for essential knowledge about how the computer works down at the core level.
I have a theory that actually understanding what for instance a stackoverflow let alone a stack is, instead of my sporadic knowledge about computer systems, will help me longer term.
Is there any books or sites that take you through how processors are structured and give a holistic overview and that somehow relates to good to know about digital logic?
Am i making sense?
Yes, you should read some topics of
John L. Hennessy & David A. Patterson, "Computer Architecture: A quantitative Approach"
It has microprocessors' history and theory , (starting with RISC archs - MIPS), pipelining, memory, storage, etc.
David Patterson is a Professor of Computer of Computer Science on EECS Department - U. Berkeley. http://www.eecs.berkeley.edu/~pattrsn/
Hope it helps, here's the link
Tanenbaum's Structured Computer Organization is a good book about how computers work. You might find it hard to get through the book, but that's mostly due to the subject, not the author.
However, I'm not sure I would recommend taking this approach. Understanding how the computer works can certainly be useful, but if you don't really have any programming knowledge, you can't really put your knowledge to good use - and you probably don't need that knowledge yet anyway. You would be better off learning about topics like object-oriented programming and data structures to learn about program design, because unless you're looking at doing embedded programming on very limited systems, you'll find those skills far more useful than knowledge of a computer's inner workings.
In my opinion, 20 years ago it was possible to understand the whole spectrum from BASIC all the way through operating system, hardware, down to the transistor or even quantum level. I don't know that it's possible for one person to understand that whole spectrum with today's technology. (Years ago, everyone serviced their own car. Today it's too hard.)
Some of the "layers" that you might be interested in:
http://en.wikipedia.org/wiki/Boolean_logic (this will be helpful for programming)
http://en.wikipedia.org/wiki/Flip-flop_%28electronics%29
http://en.wikipedia.org/wiki/Finite-state_machine
http://en.wikipedia.org/wiki/Static_random_access_memory
http://en.wikipedia.org/wiki/Bus_%28computing%29
http://en.wikipedia.org/wiki/Microprocessor
http://en.wikipedia.org/wiki/Computer_architecture
It's pretty simple really - the cpu loads instructions and executes them, most of those instructions revolve around loading values into registers or memory locations, and then manipulating those values. Certain memory ranges are set aside for communicating with the peripherals that are attached to the machine, such as the screen or hard drive.
Back in the days of Apple ][ and Commodore 64 you could put a value directly in to a memory location and that would directly change a pixel on the screen - those days are long gone, it is abstracted away from you (the programmer) by several layers of code, such as drivers and the operating system.
You can learn about this sort of stuff, or assembly language (which i am a huge fan of), or AND/NAND gates at the hardware level, but knowing this sort of stuff is not going to help you code up a web application in ASP.NET MVC, or write a quick and dirty Python or Powershell script.
There are lots of resources out there sprinkled around the net that will give you insight into how the CPU and the rest of the hardware works, but if you want to get down and dirty i honestly think you should buy one of those older machines off eBay or somewhere, and learn its particular flavour of assembly language (i understand there are also a lot of programmable PIC controllers out there that might also be good to learn on). Picking up an older machine is going to eliminate the software abstractions and make things way easier to learn. You learn way better when you get instant gratification, like making sprites move around a screen or generating sounds by directly toggling the speaker (or using a PIC controller to control a small robot). With those older machines, the schematics for an Apple ][ motherboard fit on to a roughly A2 size sheet of paper that was folded into the back of one of the Apple manuals - i would hate to imagine what they look like these days.
While I agree with the previous answers insofar as it is incredibly difficult to understand the entire process, we can at least break it down into categories, from lowest (closest to electrons) to highest (closest to what you actually see).
Lowest
Solid State Device Physics (How transistors work physically)
Circuit Theory (How transistors are combined to create logic gates)
Digital Logic (How logic gates are put together to create digital functions or digital structures i.e. multiplexers, full adders, etc.)
Hardware Organization (How the data path is laid out in the CPU, the components of a Von Neuman machine -> memory, processor, Arithmetic Logic Unit, fetch/decode/execute)
Microinstructions (Bit level programming)
Assembly (Programming with words, but directly specifying registers and takes forever to program even simple things)
Interpreted/Compiled Languages (Programming languages that get compiled or interpreted to assembly; the operating system may be in one of these)
Operating System (Process scheduling, hardware interfaces, abstracts lower levels)
Higher level languages (these kind of appear twice; it depends on the language. Java is done at a very high level, but C goes straight to assembly, and the C compiler is probably written in C)
User Interfaces/Applications/Gui (Last step, making it look pretty)
You can find out a lot about each of these. I'm only somewhat expert in the digital logic side of things. If you want a thorough tutorial on digital logic from the ground up, go to the electrical engineering menu of my website:
affablyevil.wordpress.com
I'm teaching the class, and adding online lessons as I go.
According to this http://steve-yegge.blogspot.com/2007/06/rich-programmer-food.html article, I defnitely should.
Quote Gentle, yet insistent executive
summary: If you don't know how
compilers work, then you don't know
how computers work. If you're not 100%
sure whether you know how compilers
work, then you don't know how they
work.
I thought that it was a very interesting article, and the field of application is very useful (do yourself a favour and read it)
But then again, I have seen successful senior sw engineers that didn’t know compilers very well, or internal machine architecture for that matter,
but did know a thing or two of each item in the following list :
A programming paradigm (OO, functional,…)
A programming language API (C#, Java..) and at least 2 very different some say! (Java / Haskell)
A programming framework (Java, .NET)
An IDE to make you more productive (Eclipse, VisualStudio, Emacs,….)
Programming best practices (see fxcop rules for example)
Programming Principles (DRY, High Cohesion, Low Coupling, ….)
Programming methodologies (TDD, MDE)
Design patterns (Structural, Behavioural,….)
Architectural Basics (Tiers, Layers, Process Models (Waterfall, Agile,…)
A Testing Tool (Unit Testing, Model Testing, …)
A GUI technique (WPF, Swing)
A documenting tool (Javadoc, Sandcastle..)
A modelling languague (and tool maybe) (UML, VisualParadigm, Rational)
(undoubtedly forgetting very important stuff here)
Not all of these tools are necessary to be a good programmer (like a GUI when you just don’t need it)
but most of them are. Where do compilers come in, and are they really that important, since, as I mentioned,
lots of programmers seems to be doing fine without knowing them and especially, becoming a good programmer is seen the multitude of knowledge domains almost a lifetime achievement :-) , so even if compilers are extremely important, isn't there always stuff still more important?
Or should i order 'The Unleashed Compilers Unlimited Bible (in 24H..))) today?
For those who have read the article, and want to start studying right away :
Learning Resources on Parsers, Interpreters, and Compilers
If you just want to be a run-of-the-mill coder, and write stuff... you don't need to take compilers.
If you want to learn computer science and appreciate and really become a computer scientist, you MUST take compilers.
Compilers is a microcosm of computer science! It contains every single problem, including (but not limited to) AI (greedy algorithms & heuristic search), algorithms, theory (formal languages, automata), systems, architecture, etc.
You get to see a lot of computer science come together in an amazing way. Not only will you understand more about why programming languages work the way that they do, but you will become a better coder for having that understanding. You will learn to understand the low level, which helps at the high level.
As programmers, we very often like to talk about things being a "black box"... but things are a lot smoother when you understand a little bit about what's in the box. Even if you don't build a whole compiler, you will surely learn a lot. You will get to see the formalisms behind parsing (and realize it's not just a bunch of special cases hacked together), and a bunch of NP complete problems. You will see why the theory of computer science is so important to understand for practical things. (After all, compilers are extremely practical... and we wouldn't have the compilers we have today without formalisms).
I really hope you consider learning about them... it will help you get to the next level as a computer scientist :-).
You should learn about compilers, for the simple reason that implementing a compiler makes you a better programmer. The compiler will surely suck, but you will have learned a lot during the way. It is a great way of improving (or practising) your programming skill.
You do not need to understand compilers to be a good programmer, but it can help. One of the things I realized when learning about them, is that compiling is simply a translation.
If you have ever translated from one language to another, you have just done compiling.
So when should you learn about compilers?
When you want to, or need it to solve a problem.
Compiler theory is useful, but not essential.
Although there are some techniques which come in handy, like lexical analysis and parsing.
Another one is error handling. Compilers need a lot of these. User input can contain anything, even the unexpected. And you need to deal with all of these.
If you're going to be working at a high-enough level where you're worrying over UML and self-describing code, you could easily go your entire career without wanting or needing intimate details of how the compiler works.
But, if you're an in-the-trenches coder and have no aspirations to manage your friends, it's likely that one day, you'll realize you're waging war with your compiler. It could be a random bug that comes along or a hallway conversation about while-verses-for loops. You'll realize the assembly (or IL, likely, in the coming years) is just a bit to the left of what you were needing and another universe will unfold.
So, I suppose my answer is, just be aware of the compiler for now, that it's doing quite a lot, but don't worry over it too much.
The compilers courses usually focus on how the high-level code is analyzed and translated into machine code. That's very interesting, but not crucial. It's more important to understand what is this machine code that is generated by the compiler so that you understand how a computer works and what is the cost of each language construct.
So I'd rather say that you should know an assembly language (I mean a limited subset of assembly language for one architecture) to understand how a computer works and the latter is definitely required for a competent programmer so that he understands what segmenation fault is, when to optimize and when not and other similar low-level things.
If you intend to write extremely time-critical real-time code, you will benefit from understanding how the compiler optimises your code. However, you will actually benefit more from understanding the underlying architecture of your hardware.
From my experience, if you understand how the hardware works, and how the compiler interprets your code, you will be able to write code that does exactly what you intend it to do. I have been caught on several occasions, writing code that got optimised away by the compiler and made the hardware do something that I did not intend.
All in all, understanding the entire software-hardware stack is not essential to write good algorithms and code, but it will most certainly help!
From a practical perspective, general compiler theory is less of concern than a assembler, linker and loader to a specific platform. For example, I just consider the GCC compiler as a translator from my high-level C language to the low-level assembly language on a x86 platform. And more often than not, I manually refine ;) the code generated by the compiler.
From a scientific perspective, I would strongly suggest you learning the compiler theory, it will help you understand the great idea that computer is built upon. And even more, you will have a different eye upon the world.
Just my opinion, but I believe compilers is not given enough attention in CS courses, not in mine, and not in any others afaik. I think any CS major should do 2 things after a sabbatical or finishing their major: Re-learn if necessary finite automata and maybe a formal methods language. Apply it.
Write a simple compiler with this knowledge. Alex Aiken has a very useful online tutorial on writing a compiler for the COOL (Classroom Object Oriented Language) which is a subset of Scala as of 2013 ver. At least at time of writing.