1ELF(5) Linux Programmer's Manual ELF(5)
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6 elf - format of Executable and Linking Format (ELF) files
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9 #include <elf.h>
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12 The header file <elf.h> defines the format of ELF executable binary
13 files. Amongst these files are normal executable files, relocatable
14 object files, core files, and shared objects.
15 An executable file using the ELF file format consists of an ELF header,
17 followed by a program header table or a section header table, or both.
18 The ELF header is always at offset zero of the file. The program
19 header table and the section header table's offset in the file are
20 defined in the ELF header. The two tables describe the rest of the
21 particularities of the file.
22 This header file describes the above mentioned headers as C structures
24 and also includes structures for dynamic sections, relocation sections
25 and symbol tables.
26 Basic types
28 The following types are used for N-bit architectures (N=32,64, ElfN
29 stands for Elf32 or Elf64, uintN_t stands for uint32_t or uint64_t):
30 ElfN_Addr Unsigned program address, uintN_t
32 ElfN_Off Unsigned file offset, uintN_t
33 ElfN_Section Unsigned section index, uint16_t
34 ElfN_Versym Unsigned version symbol information, uint16_t
35 Elf_Byte unsigned char
36 ElfN_Half uint16_t
37 ElfN_Sword int32_t
38 ElfN_Word uint32_t
39 ElfN_Sxword int64_t
40 ElfN_Xword uint64_t
41 (Note: the *BSD terminology is a bit different. There, Elf64_Half is
43 twice as large as Elf32_Half, and Elf64Quarter is used for uint16_t.
44 In order to avoid confusion these types are replaced by explicit ones
45 in the below.)
46 All data structures that the file format defines follow the "natural"
48 size and alignment guidelines for the relevant class. If necessary,
49 data structures contain explicit padding to ensure 4-byte alignment for
50 4-byte objects, to force structure sizes to a multiple of 4, and so on.
51 ELF header (Ehdr)
53 The ELF header is described by the type Elf32_Ehdr or Elf64_Ehdr:
54 #define EI_NIDENT 16
56 typedef struct {
58 unsigned char e_ident[EI_NIDENT];
59 uint16_t e_type;
60 uint16_t e_machine;
61 uint32_t e_version;
62 ElfN_Addr e_entry;
63 ElfN_Off e_phoff;
64 ElfN_Off e_shoff;
65 uint32_t e_flags;
66 uint16_t e_ehsize;
67 uint16_t e_phentsize;
68 uint16_t e_phnum;
69 uint16_t e_shentsize;
70 uint16_t e_shnum;
71 uint16_t e_shstrndx;
72 } ElfN_Ehdr;
73 The fields have the following meanings:
75 e_ident This array of bytes specifies how to interpret the file,
77 independent of the processor or the file's remaining