地址的含义0x8048080 [英] significance of address 0x8048080

问题描述

为什么当我在gdb中调试asm源时是0x8048080为代码的起始入口点选择的地址?这只是相对偏移量，而不是指令存储器中的实际偏移量，对吗?

解决方案

地址0x8048080没有特殊意义，但地址0x08048000有一个特殊含义.

后一个地址是默认地址，在Linux/x86上，ld在该默认地址上开始第一个PT_LOAD段.在Linux/x86_64上，默认值为0x400000，您可以使用自定义"链接描述文件来更改默认值.您还可以更改.text部分以-Wl,-Ttext,0xNNNNNNNN标志开头的位置.

ld从0x08048000开始后，它将为程序头添加空间，并根据其内置链接程序脚本继续链接可执行文件的其余部分，您可以查看是否将-Wl,--verbose传递给您的链接行.

对于您的程序，程序头的大小似乎始终为0x80，因此您的.text部分始终以0x8048080开头，但这绝不是通用的.

当我链接一个琐碎的int main() { return 0; }程序时，我会在0x8048300，0x8048178或0x8048360上得到&_start == &.text，这取决于我使用的是哪个编译器.

why when i debug asm source in gdb is 0x8048080 the address chosen for the starting entry point into code? this is just a relative offset, not an actual offset of into memory of an instruction, correct?

解决方案

There is no special significance to address 0x8048080, but there is one for address 0x08048000.

The latter address is the default address, on which ld starts the first PT_LOAD segment on Linux/x86. On Linux/x86_64, the default is 0x400000, and you can change the default by using a "custom" linker script. You can also change where .text section starts with -Wl,-Ttext,0xNNNNNNNN flag.

After ld starts at 0x08048000, it adds space for program headers, and proceeds to link the rest of the executable according to its built-in linker script, which you can see if you pass in -Wl,--verbose to your link line.

For your program, the size of program headers appears to always be 0x80, so your .text section always starts at 0x8048080, but that is by no means universal.

When I link a trivial int main() { return 0; } program, I get &_start == &.text at 0x8048300, 0x8048178 or 0x8048360, depending on which compiler I use.

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