x86

问题 I know how a GDT (Global Descriptor Table) is implemented and the use of segment registers and segment descriptors. However how/when is a GDT entry accessed? Is it accessed in basic mov instructions like mov [eax],ebx Does this implicitly invoke ds segment register and then access the GDT segment descriptor or there is some other way via which access to the GDT entry happens? 回答1: TL;DR : The Global Descriptor Table (GDT) or Local Descriptor Table (LDT) is only accessed when a segment

问题 I know how a GDT (Global Descriptor Table) is implemented and the use of segment registers and segment descriptors. However how/when is a GDT entry accessed? Is it accessed in basic mov instructions like mov [eax],ebx Does this implicitly invoke ds segment register and then access the GDT segment descriptor or there is some other way via which access to the GDT entry happens? 回答1: TL;DR : The Global Descriptor Table (GDT) or Local Descriptor Table (LDT) is only accessed when a segment

问题 Given the following code : .section .rodata str: .string "Hello World!\n" input: .long 2 ######## .text .globl main .type main, @function main: pushl %ebp movl %esp, %ebp pushl $str call printf #return from printf: movl $0, %eax movl %ebp,%esp popl %ebp ret The output would be "Hello World!". Now I try to get a number from the user , and then print it out on the screen , but it doesn't work (code compile,but I did something wrong) . Where is my mistake ? .section .rodata input: .long 2 ######

问题 Given the following code : .section .rodata str: .string "Hello World!\n" input: .long 2 ######## .text .globl main .type main, @function main: pushl %ebp movl %esp, %ebp pushl $str call printf #return from printf: movl $0, %eax movl %ebp,%esp popl %ebp ret The output would be "Hello World!". Now I try to get a number from the user , and then print it out on the screen , but it doesn't work (code compile,but I did something wrong) . Where is my mistake ? .section .rodata input: .long 2 ######

问题 I just started programming in assembly so I am a beginner. To practice, I am trying to rewrite a basic libc in assembly (NASM Intel syntax). But I'm stuck on the strcmp function: ;; Compare two C-style NUL-terminated strings ;; Inputs : ESI = address of s1, EDI = address of s2 ;; Outputs : EAX = return an integer less than, equal to, or greater than zero if s1 is found, respectively, to be less than, to match, or be greater than s2 strcmp: call strlen mov ecx, eax ; ecx = length of the string

问题 I'm currently learning assembly programming by following Kip Irvine's "assembly language x86 programming" book. In the book, the authors tries to explain the concept of data label A data label identifies the location of a variable, providing a convenient way to reference the variable in code. The following, for example, defines a variable named count: count DWORD 100 The assembler assigns a numeric address to each label. So my understanding of what data label does is: data label count is a

问题 1) Is there a way to efficiently implement sign function using SSE3 (no SSE4) with the following characteristics? the input is a float vector __m128 . the output should be also __m128 with [-1.0f, 0.0f, 1.0f] as its values I tried this, but it didn't work (though I think it should): inputVal = _mm_set_ps(-0.5, 0.5, 0.0, 3.0); comp1 = _mm_cmpgt_ps(_mm_setzero_ps(), inputVal); comp2 = _mm_cmpgt_ps(inputVal, _mm_setzero_ps()); comp1 = _mm_castsi128_ps(_mm_castps_si128(comp1)); comp2 = _mm

问题 A lot of questions SO and articles/books such as https://mirrors.edge.kernel.org/pub/linux/kernel/people/paulmck/perfbook/perfbook.2018.12.08a.pdf, Preshing's articles such as https://preshing.com/20120710/memory-barriers-are-like-source-control-operations/ and his entire series of articles, talk about memory ordering abstractly, in terms of the ordering and visibility guarantees provided by different barriers types. My question is how are these barriers and memory ordering semantics

问题 section .text global _start ;must be declared for using gcc _start: ;tell linker entry point mov edx, len ;message length mov ecx, msg ;message to write mov ebx, 1 ;file descriptor (stdout) mov eax, 4 ;system call number (sys_write) int 0x80 ;call kernel mov eax, 1 ;system call number (sys_exit) int 0x80 ;call kernel section .data msg db 'Hello, world!',0xa ;our dear string len equ $ - msg ;length of our dear string This is a basic 32-bit x86 Linux assembly code to print "Hello, World!" on

问题 section .text global _start ;must be declared for using gcc _start: ;tell linker entry point mov edx, len ;message length mov ecx, msg ;message to write mov ebx, 1 ;file descriptor (stdout) mov eax, 4 ;system call number (sys_write) int 0x80 ;call kernel mov eax, 1 ;system call number (sys_exit) int 0x80 ;call kernel section .data msg db 'Hello, world!',0xa ;our dear string len equ $ - msg ;length of our dear string This is a basic 32-bit x86 Linux assembly code to print "Hello, World!" on