Questions tagged [assembly]
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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What is beyond ordinary c++, when trying to optimize a function?
Backstory:
Writing a QImage to Sixel renderer.
Feel like I have optimized it the best I can using basic c++.
I have heard suggestions here or there that you can utilize things like GPU, SIMD, insert ...
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Are shorter variants of machine instructions worth it?
I'm writing a JIT runtime, and I've started thinking about shorter variants of some instructions.
In x64 we can do at least two kinds of jumps: rel8 and rel32. The first one takes say 2 bytes (opcode +...
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How To Share Code Between Assembly Files In A Modular Way
Recently, I started learning Arm64 assembly. The assembler I'm using is the GNU Assembler (GAS). The version of GAS I'm using is GNU assembler (GNU Binutils for Ubuntu) 2.42.
I want to make my code ...
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Why does jl test for the second operand of cmp to be less than the first, instead of the other way around?
Something like this
cmp $0, %eax
jl exit
jumps to the exit: label if the content of register eax is less than 0.
So it's kind of jl applies the < operator to the operands of cmp, but in reverse ...
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Debugging miscompile [closed]
Recently I encountered an issue at work where a unit test written in C++ would crash only when being compiled with MSVC 2017 (MSVC 2019 and up are fine). I tried to debug this issue and it seems like ...
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How does a JIT compiler actually emit and then call the emitted native code?
Assuming that a VM runs a JIT compiler on otherwise "interpreted" code, such as a line by line interpreter or some form of bytecode/IL code and determines that it can create optimised native ...
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When making a compiler, what's the best way for compiling to machine code in the backend? [closed]
I know that a lot of compilers use an assembler to compile to machine code, to make an executable (compiled program).
Some people even made their own assemblers, or they just use an existing assembler,...
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Archival-quality future-proof pseudo-CPU architecture
Suppose we maintain a massive electronic library of texts/photos/videos etc., and want to ensure that these files are readable indefinitely long in the future. [Update] one of the major problems with ...
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Where to put files (interfaces) that link two independent assemblies: Authentication and Main Program
I'm having an issue with dependencies in a C# app that I'm creating.
I have an assembly for my authentication process, and a separate assembly for starting up the main program once authentication is ...
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How do these two ways of enforcing alignment work together?
In Computer Systems: a Programmer's Perspective,
Alignment is enforced by making sure that every data type is
organized and allocated in such a way that every object within the
type satisfies its ...
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Is an assembly program a procedure itself and does it occupy a stack frame?
If I am correct, an assembly language uses the program stack to store data.
Is it correct that the program stack is partitioned to frames, each of which is for a call to a procedure? So there is no ...
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What specifies the agreement (i.e. the convention) of which registers are used to pass which arguments and to return which values?
In Computer Systems: a Programmer's Perspective:
procedure calls may involve
passing data as arguments, and returning from a procedure may also
involve returning a value. With x86-64, most of these ...
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Do differences between ATT and Intel formats of assembly languages come from differences between their underlying machine languages?
From Computer Systems: a Programmer's Perspective, about assembly languages:
We see that the Intel and ATT formats differ in the following ways:
The Intel code omits the size designation suffixes. We ...
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Does the assembler perform the same tasks as the translator from C to assembly?
When compiling C programs to assembly programs and then to machine programs, does the assembler (e.g. the one used in GCC or other popular C compilers) perform the same tasks as the translator from C ...
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Why will it take approximately 2 years for Apple to transition Mac to ARM? [closed]
Why will it take that long to transition all Mac software to ARM according to Apple? I thought all they would need to do is to recompile the source code of their apps and rewrite SIMD code from intel ...
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If you're building an algorithm from the C stdlib in pure Assembly (with no help), what is the best workflow for debugging/iterating?
I am a JavaScript developer mainly, so I am familiar with object-oriented code and dealing with things you can see easily and interact with, like the GUI, even HTTP requests, etc. Plus you can put ...
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Why is Assembly Language called "Assembly"?
Why is assembly language called "assembly"?
I was just watching the 1st video in the "Crockford on JavaScript" series.
In it, Douglas says,
". . . the first program to make programming easier was ...
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Difference between direct and indirect function() calls
I am curious about the Difference between direct and indirect function() calls
Could anyone help in the diff analysis ?
The c source code could be found at subroutine_direct.c and ...
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How are primitives stored in memory
In my searching although this question seems to get answered a lot, the answers don't really cover what I want to ask.
I'm learning assembly and my question is, in higher level languages e.g C data ...
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How is x86 assembly different from Windows assembly, and does that let me circumvent Windows?
As I can understand, assembly language is just a symbolic representation of hardware instruction opcodes that a hardware manufacturer has offered/documented, based on the way they have designed their ...
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What is meant by /0 in AMD64 specification?
The AMD64 specification talks about /0 with regards to instruction encoding but I don't have a clue what is meant by that. For example, in Volume 3 the ADD instruction has three forms:
ADD reg/mem16,...
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How is a first assembler assembled? (without cross-compiling)
I know there are a lot of threads regarding this topic, but I can't find the answer for this precise topic:
First of all, with the "first assembler" I mean the program that translates, let's say, the ...
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Why do we still grow the stack backwards?
When compiling C code and looking at assembly, it all has the stack grow backwards like this:
_main:
pushq %rbp
movl $5, -4(%rbp)
popq %rbp
ret
-4(%rbp) - does this mean the ...
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How many bytes is a long in a 64 bit machine [closed]
I have compiled the following simple c++ code:
#include <iostream>
int main(){
int a = 5;
int b = 6;
long c = 7;
int d = 8;
return 0;
}
and here is the assembly:
pushq %rbp
....
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Opcodes vs Operands
In laymen's terms, what is the difference between opcodes and operands in assembly language programs? I understand that one involves where to get the data and one involves what is to be performed on ...
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How to optimize a mixed stack/register bytecode with control flow and side effects?
I'm trying to figure out a technique to optimize bytecode for the following virtual machine:
Bytecode is a flat list of instructions, with execution starting from the first instruction.
Stack bytecode:...
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Performance question - what are the defects of high level programming languages and compilers that makes assembly still a better choice today [closed]
What I want to know is, how can we still make use of assembly today, in productive manners?
When assembly outperform C, so it would seem practical to write a section of the project in assembly rather ...
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Registers and Stacks in NASM
So, I am more or less voluntarily learning NASM, and I have problems finding sources that really explain it. Unlike with Java or C# I can't just use google as well, since Assembly just isn't used by ...
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Why does the C compiler use memory for simple arithmetic operations
Assume the following C code:
#include <stdio.h>
int main()
{
int a = 5;
int b = 15;
return a + b;
}
Compiling it using gcc creates an assembly code which includes the following:
...
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What is the difference between writing in assembly vs converting high level language into assembly using compiler?
So i heard that in modern operating systems and device drivers, some parts of them are still written in assembly for better memory optimisation and speed
but do developers actually write it in ...
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How can I test generated assembly?
I'm working on a C compiler for Linux for the purpose of personal curiosity/fun. How can I test the generated assembly before the compiler is complete enough to do anything useful?
For example, if I ...
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Simulating Comparison Without Using Comparison Primitives
In the same way that you can simulate the if statement and functions, I am wondering if there is a way to simulate the comparison operators ==, !=, >, >=, <, <=.
For example, in ...
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How to Simulate Control-Flow without using Control-Flow Primitives
Basically, I want to know how to simulate while and if if I'm handling the control flow myself through an array of instructions.
The while loop can be simulated by if, as seen with assembly branching ...
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Why do assembly languages often include symbols as a language feature? [closed]
I wonder why in assembly there are often included symbols as a language feature and what's the purpose of it?
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How to manage dynamically generated variables in Assembly
Along the lines of How v8 JIT compiler manages dynamically changing variables, wondering how you would go about creating dynamically generated variables in assembly. Not necessarily looking for ...
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Assemblers Used During the Development of a Programming Language?
I am currently designing and developing a programming language from scratch. Mostly as a learning experience. Although it's not entirely related to the question, it's important that you know a little ...
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How to make compiler portable?
I am writing a simple compiler. I have written lexer and parser and it now generates assembly code from given code. Now I need to write an assembler which generates machine code. But the problem is ...
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How does x86 deal with register pairs?
I’ve been reading about older processors (8080, 8086 and that) and i’ve seen that those older 8-bit processors had some 16-bit instructions through the use of register pairs. For example, on the 8080, ...
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How does a CPU load multiple bytes at once if memory is byte addressed?
I've been reading about CPUs and how they are implemented, and some big complex architectures (looking at you x86) have instructions that load from memory during one clock cycle. Since one address ...
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Why does GNU AS use different characters for single-line comments depending on the architecture?
The GNU Assembler as uses different characters depending on the architecture to specify single-line comments, such as # on x86, ; on 29k, or @ on ARM. Moreover, regardless of platform, C-style ...
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Help With Memory Mapped I/O and Hardware Interrupts for Virtual Machine
I've been working on a 24-bit virtual machine to help me learn more about computers and programming in general and was hoping to find a bit more information on memory mapped input/output and hardware ...
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How to evaluate efficiency of assembler code?
I was coding some functions in C++ and wondered how different versions of those functions would affect generated assembly code. I put different versions into the Godbolt Compiler Explorer Tool and ...
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Why data alignment is used exactly?
Each data type must be aligned to a multiple of some number of bytes, for example a short int must be aligned to a multiple of 2 bytes, and an int must be aligned to a multiple of 4 bytes.
But why ...
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What is Allison's Algorithm?
What is Allison's Algorithm and how does it aid in converting hex digits into ASCII characters?
;algorithm (found online)
ADD AL, 90h
DAA
ADC AL, 40h
DAA
http://computer-programming-forum.com/...
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Where are the stacks for the other threads located in a process virtual address space?
The following image shows where the sections of a process are laid out in the process's virtual address space:
You can see that there is only one stack section (since this process only has one thread ...
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Does an ISA (Instruction Set Architecture) also specify the registers available in the CPU?
I am new to Assembly, and based on my understanding, an ISA (Instruction Set Architecture) specifies what instructions are available for a particular CPU.
But does an ISA also specify what registers ...
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Intel Memory Addressing Form
I'm am trying to understand machine code memory addressing for x86, and I've encountered two opposing general forms for addressing (using the ModRM and SIB bytes).
Most unofficial resources I consult ...
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When designing an ISA , is it a good design decision to permit a `pop` instruction that does not require an operand to receive the popped value?
A lot of ISAs including x86, x64, ARM, Itanium, have a pop instruction that requires an operand which is usually a register (or, in ARM's case, a register list). In fact, I can't think of an ISA off ...
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Convert program in Java to Assembler? [closed]
I have to do a program to school in Assembler but we did just a few basic things. Is it possible to write code in Java and convert it to Assembler?
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Criteria for a language (Terra as a tricky example) to be usable for operating system development, and how to meet missing criteria
For example, a language that I was looking at recently- Terra. You can address the question in the context of any language, I'm just most comfortable with Lua so I'm starting from there.
The Terra ...
