“DS:[40207A]"是什么意思?在组装中的意思? [英] What does "DS:[40207A]" mean in assembly?

问题描述

0040103A   CALL DWORD PTR DS:[40207A]                USER32.MessageBoxA

DS: 是什么意思?

推荐答案

该指令正在从位于 ds:[40207A] 的内存中加载新的 EIP 值.即在地址 40207A 处有一个函数指针.(它推送一个返回地址，因为这是一个 call 而不仅仅是一个 jmp.)

The instruction is loading a new EIP value from memory at ds:[40207A]. i.e. there's a function pointer at address 40207A. (And it pushes a return address because this is a call not just a jmp.)

ds: 表示指令正在引用数据段中的内存 - 在现代操作系统上几乎可以被忽略，因为它们以平面地址空间模型(代码、数据和堆栈段)运行都指向同一个内存范围，内存保护通过分页处理).

The ds: means the instruction is referencing memory in the Data Segment - and can pretty much be ignored on modern OSes, since they run with a flat address space model (code, data and stack segments all refer to the same memory range, and memory protection is handled with paging).

ds: 是为了向您展示它绝对是一个内存操作数，并提醒您它使用哪个段/表明没有段覆盖前缀(可能除了 ds 前缀，因为这已经是默认值).

The ds: is there to show you it's definitely a memory operand, and to remind you which segment it uses / show that there were no segment override prefixes (except maybe a ds prefix because that's already the default).

稍微详细说明 - 请注意，为了简单起见，这是在运行 Windows 的 32 位保护模式的上下文中.

A little elaboration - note that, to keep things simple, this is in the context of 32bit protected mode running Windows.

一个段寄存器(CS、DS、SS、ES、FS、GS)持有一个指向描述符的selector.有两个描述符表:全局(GDT)和本地(LDT)，并且选择器有一点指示要使用哪个.Windows(几乎?)专门使用全局表.

A segment register (CS,DS,SS,ES,FS,GS) holds a selector pointing to a descriptor. There's two descriptor tables: global (GDT) and local (LDT), and the selector has a bit indicating which to use. Windows (almost?) exclusively uses the global table.

一个描述符基本上是一个{beginning-address, size}对——还有更多，但这超出了本文的范围发布.

A descriptor is basically a {beginning-address, size} pair - there's more to it, but that's outside the scope of this post.

Windows 使用 平面内存模型:每个进程都有一个 4GB 的地址空间，从内存地址开始0，并使用分页来隔离进程.

Windows uses a Flat Memory Model: each process has a 4GB address space starting at memory address 0, and uses paging to isolate processes from eachother.

由于进程具有这种平面视图，它们使用 {0, 4GB} 描述符与所有段一起运行 - 因此，Windows 可以只使用少数全局描述符，而不是为每个进程分配描述符，并让所有进程使用

Since processes have this flat view of the world, they run with all segments using {0, 4GB} descriptors - and thus, instead of allocating per-process descriptors, Windows can use only a few global descriptors and have all processes use those.

Portable Executable 格式定义了 sections，与x86 segments - 即使有一些概念上的重叠.PE EXE 几乎可以有您想要的任何部分布局，但通常情况下是分成(至少)代码(读/执行)、数据(读/写)、资源(只读?).将可执行文件拆分为多个部分可以将 x86 页面级内存保护应用于内存范围.

The Portable Executable format defines sections, which are unrelated to the x86 segments - even if there's some conceptual overlap. The PE EXEs can have pretty much any section layout you wish, but the normal is to split into (at least) code (read/execute), data (read/write), resources (readonly?). Splitting the executable into sections makes it possible to apply x86 page-level memory protection to the memory ranges.

虽然普通段不会改变每个进程，但 Windows 使用 FS 寄存器来指向每个线程 TIB 结构.

While the normal segments don't change per-process, Windows uses the FS register to point to the per-thread TIB structure.

有关概述，请参阅此.这是 80386 上的旧文档，但信息仍然适用.

See this for an overview. This is from an old document on the 80386, but the information still applies.

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