Recent questions tagged Assembly

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assembly - How to calculate time for an asm delay loop on x86 linux?

I was going through this link delay in assembly to add delay in assembly. I want to perform some experiment ... . Thank you in advance. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Segmentation fault on printf - NASM 64bit Linux

I trying to input four floats using scanf, store them onto the stack, and then use vmovupd to copy them over to ... 0 call printf pop rax ret See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Weird performance effects from nearby dependent stores in a pointer-chasing loop on IvyBridge. Adding an extra load speeds it up?

First I have the below setup on an IvyBridge, I will insert measuring payload code in the commented location. ... resource_stalls.any (66.64%) See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Distinguishing memory from constant in GNU as .intel_syntax

I have an instruction written in Intel syntax (using gas as my assembler) that looks like this: mov rdx, ... to get the expected behavior? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - How to multiply a register by 37 using only 2 consecutive leal instructions in x86?

Say %edi contains x and I want to end up with 37*x using only 2 consecutive leal instructions, how would I go ... the result (%eax) will be 37x See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - How are dw and dd different from db directives for strings?

Let's say I want to define a initialized variable string before running my assembly program (in section .data). ... 't help me to understand. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Why does the x86-64 GCC function prologue allocate less stack than the local variables?

Consider the following simple program: int main(int argc, char **argv) { char buffer[256]; buffer[0] = ... separation for the two variables? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - What are the segment and offset in real mode memory addressing?

I am reading about memory addressing. I read about segment offset and then about descriptor offset. I know how to ... me link for this please? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Does a memory barrier ensure that the cache coherence has been completed?

Say I have two threads that manipulate the global variable x. Each thread (or each core I suppose) will ... something to be executed later). See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - VA (Virtual Address) & RVA (Relative Virtual Address)

A file that is given as input to the linker is called Object File. The linker produces an Image file, ... 3rd observation. I cannot explain. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - x86 XOR opcode differences

looking at http://ref.x86asm.net/coder32.html I found two opcodes that match for the statement xor eax,eax ... the XORing two 32bit registers ? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - How to tell the length of an x86 instruction?

I was looking at the different instructions in assembly and I am confused on how the lengths of different operands ... its opcode will require? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Spinlock with XCHG unlocking

The example implementation Wikipedia provides for a spinlock with the x86 XCHG command is: ; Intel syntax locked: ; The ... : mov [locked], 0 See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Is vxorps-zeroing on AMD Jaguar/Bulldozer/Zen faster with xmm registers than ymm?

AMD CPUs handle 256b AVX instructions by decoding into two 128b operations. e.g. vaddps ymm0, ymm1,ymm1 on AMD ... on Intel SnB-family uarches). See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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808 views

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assembly - Why is gcc generating an extra return address?

I am currently learning the basics of assembly and came across something odd when looking at the instructions ... returning from the function. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Why can't I mmap(MAP_FIXED) the highest virtual page in a 32-bit Linux process on a 64-bit kernel?

While attempting to test Is it allowed to access memory that spans the zero boundary in x86? in user-space ... just segfaults when mmap fails.) See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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787 views

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assembly - x86 Linux assembler get program parameters from _start

I'm trying to create a program to just write the param on the screen. I created some programs to get the ... 't able to find much information See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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609 views

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assembly - Near call/jump tables don't always work in a bootloader

General Problem I've been developing a simple bootloader and have stumbled on a problem on some environments where ... properly in a bootloader. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - How do I write a bin file (512 bytes) to the first sector (sector 0) of a floppy disk?

How do I write a .bin file to be in the first sector of a floppy disk/virtual floppy disk/floppy image? ... though it has the bootloader sign. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Why not store function parameters in XMM vector registers?

I'm currently reading the book: "Computer Systems - A Programmers Perspective". I've found out that, on the ... and then read it from memory. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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943 views

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assembly - What does the bracket in `movl (%eax), %eax` mean?

I have googled enough but could not figure out what the bracket () means. Also, I see some syntax as movl 8 ... the top 20 results from Google. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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832 views

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assembly - Converting Int to Float or Float to Int using Bitwise operations (software floating point)

I was wondering if you could help explain the process on converting an integer to float, or a float to an ... when converting int to float? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Questions about AT&T x86 Syntax design

Can anyone explain to me why every constant in AT&T syntax has a '$' in front of it? Why do all registers ... know why they did what they did. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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assembly - Why is imul used for multiplying unsigned numbers?

I compiled the following program: #include <stdint.h> uint64_t usquare(uint32_t x) { return (uint64_t)x * (uint64_t)x; ... mov rax,rdi 7: c3 ret See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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936 views

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assembly - What are the sizes of tword, oword and yword operands?

What are the sizes of tword, oword and yword operands, as used in the NASM/YASM manual? And on a related note, is ... (512 bit): zword, DZ, RESZ See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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802 views

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assembly - MOV src, dest (or) MOV dest, src?

MOV is probably the first instruction everyone learns while learning ASM. Just now I encountered a book ... the instruction syntax right? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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787 views

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assembly - Why does the PLT exist in addition to the GOT, instead of just using the GOT?

I understand that in a typical ELF binary, functions get called through the Procedure Linkage Table (PLT). The PLT entry for a ... ------------+ See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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1.0k views

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assembly - CPUID implementations in C++

I would like to know if somebody around here has some good examples of a C++ CPUID implementation that can be ... appeared to be X86 specific. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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