Questions tagged [assembly]
Assembly language questions. Please tag the processor and/or the instruction set you are using, as well as the assembler, a valid set should be like this: ([assembly] [x86] [gnu-assembler] or [att]). Use the [.net-assembly] tag instead for .NET assemblies, [cil] for .NET assembly language, [wasm] for web assembly, and for Java bytecode, use the tag java-bytecode-asm instead.
assembly
44,617
questions
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When an embedded c program is created, why is there extra machine code around my compiled c program?
This C program blinks an LED attached to an AVR ATmega32u4.
ISR(TIMER1_OVF_vect) // attach Interrupt Sub Routine to TIMER1
{
// toggle LED
PIND = (1 << PIND5); // #define PIND (*(...
-1
votes
0
answers
22
views
Difference between comiss and comisd in x64 asm
I wrote some code to compare the value of xmm10 and xmm6 using:
comiss xmm10, xmm6 and then comisd xmm10, xmm6
The first one works, and the second one doesn't.
I tried using subss xmm10, xmm6 followed ...
0
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0
answers
39
views
Why is my array value not equal to a literal?
I am new to assembly and was trying to work with an array. However, I was geting caught when try to compare the array value to a constant stored in a register.
From the following code I was expecting ...
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2
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0
answers
23
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Printing 2D array in MIPS
I have been using a few other posts on here to try and figure out what I am doing wrong but I am stuck and could use some help. I am making a game that has an 8x8 "board" (2d array) similar ...
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-1
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1
answer
29
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What is wrong with this control for the brightness of a lamp in ATmega328P?
I'm new to assembly and I'm trying to develop a control for the brightness of a lamp for my college. The lamp must have 5 distinct levels of brightness, one off and four levels with gradual increase. ...
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0
votes
0
answers
43
views
signal SIGSEGV: address access protected in __run_exit_handlers
I'm trying to do a packer project for my school, it is made in C and ASM, and for the moment it is supposed to target only ELF files.
I have managed to do my section injection, correctly align my new ...
0
votes
1
answer
38
views
CMake does not compile asm-files (cross-compile)
We set up our build system with CMake and besides C and C++-files we need to compile asm-files (.s).
We use a tiarmclang-compiler (LTS3.2.0) and thus need to crosscompile.
While everything works for C ...
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1
vote
1
answer
88
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multidimensional slice access performance in golang
I am working on a little and simple game-of-life in Golang and stumbled on a performance problem during slice access.
This is the primary data structure for the game:
type Neighbor struct {
X, Y ...
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-1
votes
0
answers
53
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Why does gdb combine byte values when examining memory as words? [closed]
While examining 4 addresses from $rip as bytes in GDB, it shows 4 individual values. However, when I examine the same addresses as words, it combines that 4 byte values into a single word value. Why ...
2
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0
answers
54
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NASM ORG doesn't like SECTION [closed]
Looks like NASM ORG directive doesn't behave correctly in the presence of SECTION directive, in spite that it's compiled to the binary format. I wonder if there's an alternative for ORG in NASM which ...
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1
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0
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35
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I'm trying to build a nand2tetris assembler but the ply.lex library in python keep breaking my assembly instructions to different lines
the first thought I had was that I didn't manage to handle the new line character properly because it keeps throwing the new line character "\n" whenever I try to append the instructions for ...
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1
vote
0
answers
32
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Unable to compile NASM without -no_pie on macOS
I'm trying to follow the tutorial for NASM and I made a few adjustments (like changing the entrypoint function from "start" to "_main") to get the following hello.asm to compile ...
1
vote
1
answer
47
views
data segment of AVR store nonsense after compiling
So i'm trying to change the first element of an array that i'm storing in sram and i checked if the data after compile is equal to the value of pre-initialaztion and it wasn't equal. so this my code:
....
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0
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0
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42
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Why do I keep getting a Segmentation Fault from trying to access /dev/mem in ARM64 on the Raspberry Pi 4?
I've been working at this program for months, and I've fixed many errors, errors with alignment, other segmentation faults, and I've gotten down to this one, where it throws a segmentation fault when ...
1
vote
1
answer
54
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gnu inline assembly constraint `i` for memory address
Recetly, this function rip_rel_ptr has been added to Linux kernel.
https://elixir.bootlin.com/linux/latest/source/arch/x86/include/asm/asm.h#L118.
I can compile the kernel, but when I copy this ...
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0
answers
24
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How to run an LC-3 Assembly program
I am creating an LC-3 Assembly program. I have managed to assemble it into an obj file. I'm not sure what linker to use / what arguments to use from here. Any help would be much appreciated.
I tried ...
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0
answers
49
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How can I get this STDIN to work in GAS Assembler running on Linux?
I am new to Assembler and am currently reading a book about it by Jonathan Bartlett called 'Learn to Program with Assembly'. On pages 160-1 he gives the following sample program to demonstrate the use ...
0
votes
0
answers
32
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Is there a library to reassemble and rebuild Windows PE binary? [closed]
I want to disassemble a x64 PE binary, add my own inline assembly code somewhere inside the .text section (or any other executable section), and then assemble the binary back and expect it to work.
I'...
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0
votes
0
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30
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Why is my assembly code giving extra output? [duplicate]
Before I start, it's important to say I am a complete beginner to Assembly, so I might be missing something very obvious.
I was trying to make an Assembly program where it prints the following output ...
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1
vote
0
answers
48
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Assembly jump instructions don't seem to work
bits 64
default rel
section .data
fmt db "%s", 0xd, 0xa, 0
err db "Correct usage: echo <string>"
section .text
extern printf
extern ExitProcess
global ...
0
votes
2
answers
56
views
RISC V : I don't understand what the GNU assembler does with labels in the .data segment
I am making my own risc V core as a personal project using the RV32I ISA, I am using a Harvard memory architecture meaning I have a program memory that starts at address 0x0 and a separate data memory ...
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1
vote
1
answer
40
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how to use speaker (msdos) in new computers? [closed]
I'm programming in assembly, and want to use the speaker, I can do that with out 43, al and out 61, al, this in Dosbox. But i've a notebook with DOS 6.22 in hd, all the program works well, but the ...
- 105
0
votes
1
answer
56
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Updating an element in array in AVR Assembly
so i'm trying to update an element in array which get used to print the value inside it but after updating the array, what gets printed is still same, the printer used array buffer and i wanna get the ...
- 23
1
vote
1
answer
56
views
What are the binary representations for the flags used in the Linux open() syscall?
I am learning NASM and currently unsure what values should be used for the flags argument for open() as shown in the man page. I'm mainly asking this for clarification so I don't mess something up, ...
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-2
votes
1
answer
38
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Code in assembly printing alphabets twice instead of next line. (emu8086)
My code in assembly emu 8086 displays alphabets in lower case but it displays them twice instead of
displaying them in new line a single time each. Ive tried everything from AI etc but could not find ...
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0
votes
1
answer
30
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Order in which instructions are printed/executed
Why the output is in diffrent order than it is declared?
Shouldnt the output be in this order?
aaaa
bbbb
cccc
Instead it is:
I assume the issue is in assigning "bbb" value to the text ...
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-5
votes
0
answers
82
views
x86 mulss result is diffrent over time [closed]
I am trying to make C++ neural network library and I noticed, that sometimes model with same inputs and same parameter values drastically changes output for no reason. I have no idea why it happens, ...
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1
answer
81
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How can we read program counter through assembly code in 68k microcontroller
Can anybody please explain how program counter can be read using assembly instruction in MC68000 controller.
Following instruction set gave error - undefined addressing mode
MOVE.L %PC, %D0
Also ...
0
votes
0
answers
21
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how to add an additional dll to an exe file and force it to use
I have an exe file in which I want to make some corrections to the binary code, but I want to do this not just by editing bytes but by using an additional dll, which should patch the current ...
0
votes
1
answer
37
views
How to read the Marie Programme table? [closed]
I want to know how i can read the Marie Simulator table. Im still a beginner to this so can someone explains how the output works in this following example code?
Load x
add y
store z
halt
x, hex 008E
...
- 13
1
vote
1
answer
82
views
What is the difference between these two functions in x64 assembly?
I'm playing around with lower level stuff in C on Windows (x64) to try and learn low level concepts. I ran across something I don't understand and just wonder if someone could explain something to me....
0
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0
answers
30
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System.IO.FileNotFoundException for System.Management Assembly in WPF Application but Works Fine in Console Application
I'm a novice C# developer working with .NET 8.0. I have encountered an issue where my code works perfectly in a dedicated console application but throws an exception when included in my existing WPF ...
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3
votes
0
answers
51
views
How to pass arguments to a windows syscall in NASM assembly? [duplicate]
I am learning how to implement direct system calls using nasm assembly and c code, I have created a funcs.asm that contains
section .text
global NtOpenProcess
NtOpenProcess:
mov rax, 26h
...
- 199
4
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0
answers
59
views
Why does Intel x86 manual use +rd instead of +ro or +rq for 64-bit registers?
The description of the PUSH instruction in the Intel manual (PDF, Volume 2, Chapter 4.3, PUSH) contains the line 50+rd PUSH r64. It seems +rd is used throughout most of the instruction descriptions ...
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1
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0
answers
31
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Link function calls against reverse engineered binary
I created an windows x86 .exe file that I reverse engineer. Imagine I only have the .exe file and I reverse engineered some functions.
The goal is to create a dll that links with this .exe so the dll ...
- 26
0
votes
1
answer
47
views
Debugging assembly to call IUnknown::Release - is shadow space right?
I am getting a bug where sometimes this code works sometimes it does not:
48 8B 41 08 ; MOV RAX, [RCX + 0x08] gets the refcount
48 FF C8 ; DEC RAX ; decrement ...
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1
vote
1
answer
50
views
My bootloader isn't printing after switching to Protected Mode
I'm trying to print the character "C" after switching to the Protected Mode, but it isn't working, and I don't know why. I'm using Assembly AT&T/GAS syntax
Here is the code:
.code16
....
user26135221
0
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0
answers
67
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Game freezes when i call a function in it from a C++ .dll
In IDA Pro, i found a function in the game that writes text to console.
Here is the function:
; void __cdecl write_to_console(char *Format, char ArgList)
write_to_console proc near ; CODE ...
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-1
votes
0
answers
25
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Writing x64 nasm assembly for windows [duplicate]
I would like to learn how to write x64 nasm assembly for windows but I can't find any resources for that.
And also how to compile the assembly into executable program.
So if anyone knows of a ...
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-1
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0
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50
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lmc program division assembly languange
I'm trying to solve this challenge:
create a simple LMC program to determine if a number evenly divides another one:
Input 2 numbers
If they do not evenly divide, then the program outputs 0 and asks ...
1
vote
1
answer
89
views
Why do I get multiple ASM instructions per addition? (Visual Studio 2022 Community)
Here's the C program, I use Visual Studio Community 2022 with MSVC compiler. What are all those mov instructions, I don't use any compiler optimization flags.
#include <stdio.h>
int main(void) {...
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1
vote
0
answers
64
views
How to Fix IMUL and DIV Errors in Assembly Calculator Code?
I'm currently learning assembly language and trying to write a simple calculator program. The program is supposed to read two numbers and an operator (+, -, *, /) from stdin, perform the specified ...
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0
answers
33
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objcopy says one of input files was not recognized as a valid object file
Im trying to objcopy two files together but its just not working...
I tried the following:
objcopy -I bootloader.bin extendedprogram.bin -O bootloader.flp
The result was:
llvm-objcopy: error: '...
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2
votes
1
answer
36
views
Monitor memory modification between instructions in GDB
Is there any way I can check the memory change before and after si, s or something similar commands?
First came out with the idea of dump memory for diff, but haven't dig in how to do it.
Or maybe ...
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3
votes
1
answer
63
views
How to get NASM to encode `push` with a sign-extended 16-bit immediate?
When assembling the following with NASM:
BITS 64
push 32767
I get 68 ff 7f 00 00. This is interesting to me, since this is the 32b encoding (push dword). Any ideas why it doesn't resort to the 16b ...
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1
vote
1
answer
73
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RISC-V assembly: global pointer set to a weird value
I am experimenting with RISC-V assembly language on an emulator (qemu64, ubuntu for RISC-V).
Here is a simple program, its function is to convert the instr string to uppercase, outstr is the resulting ...
- 214
0
votes
1
answer
36
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x86 NASM Crash - Iterate over string
How to iterate over individual characters of a string in x86 assembly and print them?
global _main ; declare _main entry point
extern _printf ; extern method
section ....
0
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0
answers
40
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How can I disassemble a whole obj file in valid asm, amend some sections of such asm code and reassemble to obj?
Is it possible on Linux to use objdump (or any other utility) to fully disassemble an obj file to asm code, modify such code and then pass the asm to as?
The challenge I have with objdump is that it ...
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20
votes
2
answers
1k
views
How to prepare stack pointer for bare metal Rust?
I'm trying to write an x86 bootloader and operating system completely in Rust (no separate assembly files, only inline assembly within Rust).
My bootloader works completely as intended within the QEMU ...
- 305
5
votes
1
answer
116
views
Logical shift right without dedicated shift instruction
I am working with an assembly language that does not contain either multiply, divide, or bit-shift instructions. I am aware that a left bit-shift can be achieved by just adding the same number to ...
- 73