Recent questions tagged X86

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x86 - Understanding ATT Assembly (immediate)

lets say i have the following assembly lines movl $-1, %edi movl $1, %edx What exactly am I storing into %edi ... " but what does that mean? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 - Why is string comparison so fast in python?

I became curious to understand the internals of how string comparison works in python when I was solving the ... is the relationship 200x? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 - Divide and Get Remainder at the same time?

Apparently, x86 (and probably a lot of other instruction sets) put both the quotient and the remainder of a ... does the syntax look like? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 - How to compare __m128 types?

__m128 a; __m128 b; How to code a != b ? what to use: _mm_cmpneq_ps or _mm_cmpneq_ss ? How to process the result ? Can't find adequate docs. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 64 - Why does the iOS simulator require i386 and x86_64 symbols even though I'm on an x86_64 system only?

I'm trying to get an app running on the simulator that has had some problems doing so before. We don't have ... I'm running on an x86_64 mac. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 - How to multiply 5% in assembly language and display it out in 2 decimal place

I initialize the price of the food and request user to input a quantity and I am able to get an accurate ... of your help is much appreciated! See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 64 - How do you access low-byte registers for r8-r15 from gdb in x86-64?

In gdb, I can't seem to access any of the pseudo-registers: r8b, r9b, r10b, r11b, r12b, r13b, r14b, nor ... registers command. I'm using GDB 10. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 - Assembly: What is the purpose of movl data_items(,%edi,4), %eax in this program

This program (from Jonathan Bartlett's Programming From the Ground Up) cycles through all the numbers stored in ... serve in this situation? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 - Creating a proper Task State Segment (TSS) structure with and without an IO Bitmap?

Reading the documentation between Intel and AMD and looking at code makes it difficult at times to understand how to ... 't that be 11111111? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 64 - Why floating point registers are different than general purpose ones

Most architectures have different set of registers for storing regular integers and floating points. From a binary ... to regular registers? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 - Find the first instance of a character using simd

I am trying to find the first instance of a character, in this case '"' using simd (AVX2 or ... using _mm_movemask_epi8? Any other suggestions? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 - how are barriers/fences and acquire, release semantics implemented microarchitecturally?

A lot of questions SO and articles/books such as https://mirrors.edge.kernel.org/pub/linux/kernel/people/ ... to ensure memory ordering ? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 - In assembly, what does `PTR` stand for?

and dword ptr [ebp-4], 0 In assembly code like above, what does the term PTR stand for? I know their usage -- ... of the [] and PTR operators??? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 - Shifting SSE/AVX registers 32 bits left and right while shifting in zeros

I want to shift SSE/AVX registers multiples of 32 bits left or right while shifting in zeros. Let me be ... _mm256_permute2f128_ps(x, x, 41); See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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433 views

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x86 - AVX-512 and Branching

I'm confused as to what masking can do in theory in relation to branches. Let's say I have a Skylake-SP (ha, I wish. ... b(i) ** 3 end if end do See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 - SSE: convert short integer to float

I want to convert an array of unsigned short numbers to float using SSE. Let's say __m128i xVal; // Has 8 ... know which sse intrinsic to use. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 - Using GDB to read MSRs

Is there some way to read the x86-64 model-specific registers, specifically IA32_FS_BASE and IA32_GS_BASE, while ... appreciated all the same. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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882 views

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x86 - assembly to compare two numbers

What is the assembler syntax to determine which of two numbers is greater? What is the lower level (machine code) for it? ... in 0's and 1's? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 - problem in understanding mul & imul instructions of Assembly language

I'm learning 80386 from PC Assembly by paul caurter mul source If the operand is byte sized, it is multiplied ... register of same size itself? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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487 views

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x86 - complex IF statement in assembly

How should I write such an if statement in assembly? if ((a == b AND a > c) OR c == b) { ... ... . Integers would works fine for me, I guess. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 - Use 32bit "Program Files" directory in msbuild

In 64 bit versions of windows, 32 bit software is installed in "c:program files (x86)". This means you cannot ... there is a easier/better way. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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457 views

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x86 - how does push and pop work in assembly

I'm getting confused on what does pop actually do in assembly. Does pop move the value PUSHed onto the stack ... value pointed to by esp? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 - Branch target prediction in conjunction with branch prediction?

EDIT: My confusion arises because surely by predicting which branch is taken, you are effectively doing the target ... /write-back CPU stages? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 - Endianness inside CPU registers

I need help understanding endianness inside CPU registers of x86 processors. I wrote this small assembly program: ... ) instead of 0x78ff5abc? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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691 views

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x86 - Carry Flag, Auxiliary Flag and Overflow Flag in Assembly

I Cannot seem to tell the difference between the Carry Flag, Auxiliary Flag and Overflow Flag in Assembly. I'm ... used for the sign??? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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791 views

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x86 - What is the purpose of CS and IP registers in Intel 8086 assembly?

So, as the question states, what is the purpose of CS and IP registers in intel's 8086 I found this explanation ... , that would be great :) See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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x86 - assembly system call non-effective

I want to print AAAA with the following: BITS 32; ;write; push 0x41414141; pop ecx ; mov eax, 4 ; write is ... exits, no errors, what is wrong ? See Question&Answers more detail:os...

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

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x86 16 - Is it possible to manipulate the instruction pointer in 8086 assembly?

I want to know if I can manipulate (read and change the value of) the instruction pointer (IP) in 8086 assembly. ... 4020h. How could I do that? See Question&Answers more detail:os...

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

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