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memory 中 ELF 文件的布局方式

[英]How ELF file is laid out in memory

原文 2020-05-15 01:59:18 1 1 linux/ elf

When an ELF file is run and its various segments are loaded into memory, is there a way to know in advance how the segments will be arranged in relation to each other?当运行 ELF 文件并将其各个段加载到 memory 中时，有没有办法提前知道这些段将如何相互排列？ That is, could I know, for example, that the rodata segment comes after the bss segment?也就是说，我是否可以知道，例如，rodata 段在 bss 段之后？

1 个解决方案

is there a way to know in advance how the segments will be arranged in relation to each other?有没有办法提前知道这些段将如何相互排列？

Yes.是的。 There are two types of ELF files: ET_EXEC and ER_DYN .有两种类型的 ELF 文件： ET_EXEC和ER_DYN 。 The former is for executables, the latter for PIE executables and shared libraries.前者用于可执行文件，后者用于 PIE 可执行文件和共享库。

An ET_EXEC segments will be in memory in exactly the location they were linked at. ET_EXEC段将位于 memory 中，与它们链接的位置完全相同。 The executable will not work if its segments are loaded anywhere else.如果它的段被加载到其他任何地方，则可执行文件将无法工作。

You can examine the linked-at addresses with readelf -Wl a.out .您可以使用readelf -Wl a.out检查链接地址。

For ET_DYN , the segments will be loaded at a single fixed offset of where they were linked.对于ET_DYN ，段将在它们链接位置的单个固定偏移量处加载。 That is, if the first PT_LOAD segment is linked at address 0x0 , and loaded at address 0x1234000 , then you can add 0x1234000 to the p_vaddr of every subsequent segment to determine where it is loaded in memory.也就是说，如果第一个PT_LOAD段链接在地址0x0并加载到地址0x1234000 ，那么您可以将0x1234000添加到每个后续段的p_vaddr以确定它在 memory 中的加载位置。

could I know, for example, that the rodata segment comes after the bss segment?例如，我可以知道rodata 段在bss 段之后吗？

There is no such thing as rodata and bss segment -- they are sections .没有rodata和bss段这样的东西——它们是段。 To see which segment these sections are assigned to, use readelf -Wl .要查看这些部分分配到哪个段，请使用readelf -Wl 。