pointers - Nasm - 按值和地址访问结构元素

Question

我最近开始使用 NASM 程序集编写代码，但我的问题是我不知道如何以正确的方式访问结构元素。我已经在这个网站和谷歌上搜索了解决方案，但我看到到处都有人说不同的话。我的程序崩溃了，我感觉问题出在访问结构上。

查看示例代码时:

STRUC Test
    .normalValue RESD 1
    .address RESD 1
ENDSTRUC

TestStruct:    
    istruc Test
        at Test.normalValue dd ffff0000h
        at Test.address dd 01234567h
    iend

;Example:
mov eax, TestStruct ; moves pointer to first element to eax

mov eax, [TestStruct] ; moves content of the dereferenced pointer to eax (same as mov eax, ffff0000h)

mov eax, TestStruct
add eax, 4
mov ebx, eax ; moves pointer to the second element (4 because RESD 1)

mov eax, [TestStruct+4] ; moves content of the dereferenced pointer to eax (same as mov eax, 01234567h)

mov ebx, [eax] ; moves content at the address 01234567h to ebx

是这样吗？

感谢帮助

Answer 1

我不知道你是否明白，但这是我们的代码，稍作修改就可以正常工作。除了最后一条 mov ebx, [eax] 之外，所有指令都是正确的，因为您正在尝试访问地址 0x1234567 处的内容，导致 SIGSEGV >

section .bss
  struc Test
    normalValue RESD 1
    address RESD 1
  endstruc

section .data
  TestStruct:
    istruc Test
      at normalValue, dd 0xffff0000
      at address, dd 0x01234567
    iend

section .text
  global _start

_start:

  mov eax, TestStruct ; moves pointer to first element to eax
  mov eax, [TestStruct] ; moves content of the dereferenced pointer to eax same as mov eax, ffff0000h
  mov eax, TestStruct
  add eax, 4
  mov ebx, eax ; moves pointer to the second element 4 because RESD 1
  mov eax, [TestStruct+4] ; moves content of the dereferenced pointer to eax same as mov eax, 01234567h
  mov ebx, [eax] ; moves content at the address 01234567h to ebx

使用nasm -f elf64 main.nasm -o main.o 逐步编译、链接和运行； ld main.o -o main; gdb 主程序