An assembly language is a low-level programming language for a computer, microcontroller, or other programmable device, in which each statement corresponds to a single machine code instruction.

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Finding register parameters for system calls

By consulting various scattered tutorials and books, I've been able to learn that the 64-bit Linux "exit" system call is 60, and the status value is moved to edi. Similarly, "write" has call number 1, ...
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Does unused code affects the assembly after startup (Memory for example)?

Disclaimer: I come from a PHP background. In PHP, I could have thousands files, which are never loaded, if not needed, due to the autoloader feature (If some code is needed, it would be loaded) How ...
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100 views

Unit Testing: Assembler code and different architectures

I am currently unit testing some C code and I am faced with a problem: Within the code there are called functions that contain inline assembler code for the SPARC 8 architecture. Since I am doing ...
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2answers
116 views

Difference in endianness between operating systems [closed]

There is an assembler that I am writing that is located within the file asm.c located in this repository. It uses the instruction set located in the specs file to produce an output binary. (The ...
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718 views

Development process used for the code on Apollo 11 missions?

The Apollo missions had technology no more complicated than a pocket calculator. From link here, there's an information about Apollo Guidance Computer (AGC) The on-board Apollo Guidance Computer ...
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What's the REAL benefit of using CDECL? (more specifically pushing instead of reg-ing)

So, I'm learning assembly, and I've come to know the ABIs and i got some basics tests working using the cdecl calling convention to use the c's stdlib under nasm. But I've seen other Calling ...
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92 views

How to be sure that a certain code does not call interrupts?

Imagine that you have an object code file from an untrusted source. You want to run this code to know the result of its computation, and you want the code to perform fast, so setting up a whole ...
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4answers
518 views

What are the key differences between low-level C development and higher level OOP development? [duplicate]

I have been using high-level OOP language (like C# and/or Java) for quite some time. I know patterns like the gang of four, can read and write code reasonably well and am considered a senior by his ...
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334 views

Best x86 processor(computer) to learn computer architecture and assembly [closed]

I'm planning to build a computer as a hobby from scratch, with the least basic hardware possible in functionality so I can learn the basics of computer architecture and assembly language. I already ...
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48 views

IBM PC XT 5162 even and odd BIOS

I am writing a whole new BIOS, from scratch, for the 5162. The already existing BIOS is on chips U34 and U35. Normally, exactly one byte (the odd byte) should be on U34, followed by exactly one even ...
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72 views

SPARC and Assembly [closed]

I'm currently self teaching myself programming and became familiar with Python, Java and C and I'm confused as to what are the differences between Assembly and SPARC Assembly and whether or not I ...
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356 views

Why was the AT&T assembly syntax designed this way?

The AT&T assembly syntax, often called the GAS syntax, keeps surprising me. For example, its parameter order: mov $100,%eax /* Destination after source */ This just seems so counter-intuitive! ...
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247 views

How to make absolute jumps relative?

Given I have x86 assembly code disassembled into a list of structures that fully describe it (opcode, regs, imm etc.). How can I now programmatically turn absolute jumps to relative jumps? Basically ...
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72 views

How does a .COM file get loaded for execution

For a bit of fun I thought I would start writing my own emulator for the 80286. I have been reading a bunch about the topic. I thought for simplicity I would start with a really simple COM executable ...
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253 views

Writing Z80 table based assembler/disassembler

I have a long-term project: DIY computer with various processors. One of my wishes not only make hardware, but software too. So I started from assembler/disassembler for Linux, though there is a lot ...
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235 views

Longest x86 Instruction

I read the recent article "Longest x86 Instruction" http://blog.onlinedisassembler.com/blog/?p=23 I attempted to reproduce the curious disassembly issue on a Win7x86 development platform using masm ...
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236 views

Can SSE (or AVX) be used to do large bsf?

I'm faced with having to do a bsf (find the first bit set) in a 512bits bitmap. This is in the hot path so I'd like to see how I can speed things up. Right now I'm maintaining a header entry to know ...
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3answers
229 views

8085 assembly question. Why flag stacks named d0-d7?

I'm trying to make my C programming exciting by learning assembly programming. I've encountered an image of flag registers in 8085 assembly programming. In that image blocks are named from ...
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2answers
115 views

How were assemblers created straight from binary? [duplicate]

How did these earlier programmers know what combinations of binary produced certain results? Is there a way I can create an assembler from binary today?
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168 views

Implementing a VM for simulation [closed]

I am aware of this question, and I think I know why it has been closed. I hope that my question manages to be more specific. My skill level: I have a "Computer Science" degree. I have programmed in ...
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343 views

Developing a compiler for a self made CPU Architecture

Recently ive been consumed by creating my own simple CPU architecture that at some point could be easily implemented in hardware (No FPGA, but actual Logic Gate circuits). Naturally to fulfill this ...
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1answer
378 views

Why does GCC use AT&T syntax by default?

I think title says it all :) Is there any particular practical reason (I guess it's mostly historic, but I'm unable to find it on my own) why GCC uses AT&T/GAS syntax? Note: I know this is just ...
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415 views

Assembly vs. algorithmic languages (like C, Algol, etc) [duplicate]

Usually, computer science papers describe algorithms in Algol-like pseudolanguage, similar to Pascal or even C/C++. But Donald Knuth uses his own assembly language (MMIX). Are there any good known ...
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1k views

Polymorphic engines in C and/or C++ [closed]

I stumbled across polymorphic engines and I don't know anything about them. However, I am curious about how they are written. Every example that I've looked up writes them in assembly, my assembly is ...
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1answer
400 views

What are steps in making an operating system in C ? [duplicate]

I am trying to make an my own OS. This is for educational purpose only, so that I get to understand the internals as well as get a good idea of low level programming. I have some prior application ...
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116 views

How do we add software to a machine? [duplicate]

When we build a new machine, how do we add software to that machine? I know we have assemblers and compilers that convert the high-level code into machine code for it to understand. But having ...
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389 views

Reading assembly useful for insights when writing C/C++? [closed]

While in most cases its not necessarily, recently I have taken to reading the generated assembly of my C code every so often, when I'm curious as to the kinds of optimizations my compiler is making. ...
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397 views

How do VMs implement function calling?

I'm reading a compiler textbook that compiles to some form of assembly. Since I don't know this assembly language I decided to invent my own simple "assembly language" and implement a basic "virtual ...
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632 views

If statements in “generic” assembly?

I'm reading a relatively 'friendly' and simple book about compilers named "Let's Build A Compiler" (originally a series of articles). The compiler written in the book generates instructions in some ...
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How are OOP “objects” and “classes” organized in memory in terms of assembly language?

How are objects organized in memory? For instance, I know that a function is a piece of code in memory, that expects parameters via the stack and/or the registers and handles it's own stack frame. ...
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Is there still any value in learning assembly languages today? [closed]

Specifically for a game programmer. If you really needed some assembly routines you could look for help, whereas back in the 80s/90s it was one of the mainstream languages. I read that compilers can ...
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2answers
127 views

gcc -S seems a bit misshapen with shifting and ANDing bits

Example: int c = 4; int p = 5; if (p & (1 << c)) printf("ok\n"); else printf("nop\n"); gcc -S: movl -4(%rbp), %eax /* eax holds the variable c */ movl -8(%rbp), %edx /* ...
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296 views

Why do we need a format for binary executable files

When binary files (i.e. executables) are saved they usually have a format (e.g. ELF or .out) where we have a header containing pointers to where data or code is stored inside the file. But why don't ...
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638 views

How Byte loading/storing is implemented By the CPU?

I know that in 32bit machine, cpu read from memory 32bits at a time. since the registers in this case is 32bit in size too, I can understand how this works. What I don't understand is how the cpu ...
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606 views

Why convert to assembly language instead of machine code?

When I compile a C program, it is compiled first to assembly code, then assembled into machine code. I'm curious why it doesn't just convert straight to machine code in the first place.
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What conclusion to be drawn from no difference in generated assembly from 2 rather different programs?

I might not have had a counterexample when I got the reply "A pointer is just an address, what's the difficulty?" but I didn't really buy such a simple explanation and at assembly code it's not ...
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Creation of an Assembler [closed]

I've always been interested in how programming languages are created, so for the past 8 months I've been researching, practicing and more about the creation of compilers. I've been able to quite ...
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What is the purpose of red zone?

Red zone is a fixed size area in memory beyond the stack pointer that has not been "allocated". Compilers do generate assembly to access that area in simple leaf functions. But I can't see any real ...
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4answers
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How does assembly relate to machine/binary code

How does assembly relate to machine/binary code. For example here is how to print to the screen in mikeOS(a small pure assembly OS), mikeOS it uses NASM to assemble. BITS 16 ORG 32768 ...
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Fetching instructions from memory

So, I am a noob in assembly language and machine instructions. When the discussion came up as to how funtion calls are implemented at the processor level, someone said that the CALL instruction ...
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How do we go from assembly to machine code(code generation) [closed]

I know this is abstract as it's all about signals and switch - (electronics) - underneath, but is there a easy way to visualize the step between assembling code to machine code. For example if you ...
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1answer
215 views

What did machine code for 4-bit architecture look like?

I don't know how a 4-bit instruction could be enough to do something so I read about the Intel 4004 and it says that it used 8-bit instructions and then I can understand how opcode and numbers has ...
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3answers
1k views

Why is the copying instruction usually named MOV?

In quite many assemblers, a value copying instruction is usually named "MOV" and its description in manuals usually also contains "move" (however, other words can be used, like "load", "store", ...
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811 views

Why do some compilers generate direct machine code?

I was taking this course - CMU 18-447, Computer Architecture at Carnegie Mellon to brush my knowledge and concepts. They say that most of the machine level details and implementations is taken care ...
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1answer
1k views

How are I/O port addresses and data sent?

First of all, I'd like to say this is a hardware-level question, which is very closely related to the "in" and "out" command in x86 assembly. I have searched for quite some time, but I still haven't ...
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4answers
505 views

Why do we use to talk about addresses and memory of variable in C?

Why do we use to talk about addresses and memory of variable in C, where in other languages (like in Java, .Net etc) we do not talk about variable address and memory in a program, we will directly use ...
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Is there much difference between X86 Assembly language on Windows and Linux?

I'm a complete beginner at Assembly, and my aim is to learn as much as I can to do with Assembly to one day I can reach expert level (I know I'm way off right now, but you never know). My only problem ...
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393 views

Writing a bootloader with no bootloader

I have a question that I really can't find a straight answer to. Let me start by saying I'm not asking for a step by step tutorial, or even plan on doing anything. I'm just curious. I've been ...
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Any good, easy to learn from books or tutorials for learning assembly? [closed]

I've been a developer since 2009 and I've learnt a lot of languages since, but I've always wanted to understand and be able to code in the lowest level language so I can directly (or at least very ...
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2answers
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How would I make a compiler in C++? [closed]

This probably been asked for but I can't google "How to make a compiler in C++" because I will just get "How to compile C++" as the results. Anyway, for my question, I'd like to make a simple ...