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From wiki Executable and Linkable Format:
The segments contain information that is necessary for runtime execution of the file, while sections contain important data for linking and relocation. Any byte in the entire file can be owned by at most one section, and there can be orphan bytes which are not owned by any section.
But what is the difference between section and segment? In an executable ELF file, does a segment contain one or more sections?
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Thus, a segment is almost exactly the same as a section, and the two can be used interchangeably. However, segment carries a secondary meaning and so can also be used when specifically talking about lines and planes in geometry. So you can use part whenever you want to talk about any piece of a larger entity.
you can use readelf and objdump to read parts of an elf file. You can also use 'hexdump filename' to get a hexdump of the contents of a binary file (this is likely only useful if you like reading machine code or you are writing an assembler).
You can use the stat functions family ( stat() , lstat() , fstat() ) to get the size of any file (using the st_size member of the stat member). Do you need something more specific? If you really want to use the ELF structure, use the elf.
But what's difference between section and segment?
Exactly what you quoted: the segments contain information needed at runtime, while the sections contain information needed during linking.
does a segment contain one or more sections?
A segment can contain 0 or more sections. Example:
readelf -l /bin/date Elf file type is EXEC (Executable file) Entry point 0x402000 There are 9 program headers, starting at offset 64 Program Headers: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flags Align PHDR 0x0000000000000040 0x0000000000400040 0x0000000000400040 0x00000000000001f8 0x00000000000001f8 R E 8 INTERP 0x0000000000000238 0x0000000000400238 0x0000000000400238 0x000000000000001c 0x000000000000001c R 1 [Requesting program interpreter: /lib64/ld-linux-x86-64.so.2] LOAD 0x0000000000000000 0x0000000000400000 0x0000000000400000 0x000000000000d5ac 0x000000000000d5ac R E 200000 LOAD 0x000000000000de10 0x000000000060de10 0x000000000060de10 0x0000000000000440 0x0000000000000610 RW 200000 DYNAMIC 0x000000000000de38 0x000000000060de38 0x000000000060de38 0x00000000000001a0 0x00000000000001a0 RW 8 NOTE 0x0000000000000254 0x0000000000400254 0x0000000000400254 0x0000000000000044 0x0000000000000044 R 4 GNU_EH_FRAME 0x000000000000c700 0x000000000040c700 0x000000000040c700 0x00000000000002a4 0x00000000000002a4 R 4 GNU_STACK 0x0000000000000000 0x0000000000000000 0x0000000000000000 0x0000000000000000 0x0000000000000000 RW 8 GNU_RELRO 0x000000000000de10 0x000000000060de10 0x000000000060de10 0x00000000000001f0 0x00000000000001f0 R 1 Section to Segment mapping: Segment Sections... 00 01 .interp 02 .interp .note.ABI-tag .note.gnu.build-id .gnu.hash .dynsym .dynstr .gnu.version .gnu.version_r .rela.dyn .rela.plt .init .plt .text .fini .rodata .eh_frame_hdr .eh_frame 03 .ctors .dtors .jcr .dynamic .got .got.plt .data .bss 04 .dynamic 05 .note.ABI-tag .note.gnu.build-id 06 .eh_frame_hdr 07 08 .ctors .dtors .jcr .dynamic .got Here, PHDR segment contains 0 sections, INTERP segment contains .interp section, and the first LOAD segment contains a whole bunch of sections.
Further reading with a nice illustration:
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