32位计算机中用于0x08048000之前的内存是多少? [英] What's the memory before 0x08048000 used for in 32 bit machine?

问题描述

在Linux中，我了解到每个进程都在32位计算机中存储从0x08048000开始的数据(在64位计算机中存储从0x00400000开始的数据).

In Linux, I learned that every process stores data starting at 0x08048000 in 32 bit machine (and 0x00400000 in 64 bit machine).

但是我不知道为什么要从那里开始. 0x08048000 之前的内存是什么?

But I don't know the reason why starting from there. What's the memory before 0x08048000 used for?

更新: 有人认为它是为内核映射的.但是据我所知，Linux内核从用户堆栈之后开始使用高端内存.

Update: Some people think it's mapped for the kernel. However as far as I know, Linux kernel uses the high-end memory starting after the user stack.

推荐答案

答案确实是:一堆东西.可执行文件的加载地址没有神奇的含义，几乎所有内容都可以映射到较低的地址.常见示例包括:C库(例如C库)，动态加载程序ld.so和内核VDSO(内核映射动态代码库，提供了x86 Linux中内核的某些接口).但是，您可以使用mmap()系统调用将所需的内容映射到任何地方.

The answer is really: a bunch of things. There is no magical meaning to the load address of the executable and pretty much anything can be mapped to the lower addresses. Common examples including: C library (such as the C library), the dynamic loader ld.so and the kernel VDSO (kernel mapped dynamic code library that provides some of the interface to the kernel in x86 Linux). But you can pretty much map anything you desire there, using the mmap() system call.

例如，在我的特定计算机上，地图如下(已获得，但为"cat/proc/self/maps"):

For example on my specific machine the map is as follows (acquired but "cat /proc/self/maps"):

gby@watson:~$ cat /proc/self/maps 
001c0000-00317000 r-xp 00000000 08:01 245836     /lib/libc-2.12.1.so
00317000-00318000 ---p 00157000 08:01 245836     /lib/libc-2.12.1.so
00318000-0031a000 r--p 00157000 08:01 245836     /lib/libc-2.12.1.so
0031a000-0031b000 rw-p 00159000 08:01 245836     /lib/libc-2.12.1.so
0031b000-0031e000 rw-p 00000000 00:00 0 
00376000-00377000 r-xp 00000000 00:00 0          [vdso]
00852000-0086e000 r-xp 00000000 08:01 245783     /lib/ld-2.12.1.so
0086e000-0086f000 r--p 0001b000 08:01 245783     /lib/ld-2.12.1.so
0086f000-00870000 rw-p 0001c000 08:01 245783     /lib/ld-2.12.1.so
08048000-08051000 r-xp 00000000 08:01 2244617    /bin/cat
08051000-08052000 r--p 00008000 08:01 2244617    /bin/cat
08052000-08053000 rw-p 00009000 08:01 2244617    /bin/cat
09ab5000-09ad6000 rw-p 00000000 00:00 0          [heap]
b7502000-b7702000 r--p 00000000 08:01 4456455    /usr/lib/locale/locale-archive
b7702000-b7703000 rw-p 00000000 00:00 0 
b771b000-b771c000 r--p 002a1000 08:01 4456455    /usr/lib/locale/locale-archive
b771c000-b771e000 rw-p 00000000 00:00 0 
bfbd9000-bfbfa000 rw-p 00000000 00:00 0          [stack]

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