Linux Kernel Architecture

Mauerer runapp05.tex V1 - 09/04/2008 6:13pm Page 1255

Appendix E: The ELF Binary Format

As you can see in the following code, a similar data structure is defined for 64-bit architectures. The only

difference as compared to the 32-bit variant is that other data types are used. Nevertheless, the meaning

of the entries is the same:

<elf.h>

typedef struct elf64_phdr {

Elf64_Word p_type;

Elf64_Word p_flags;

Elf64_Off p_offset; /* Segment file offset */

Elf64_Addr p_vaddr; /* Segment virtual address */

Elf64_Addr p_paddr; /* Segment physical address */

Elf64_Xword p_filesz; /* Segment size in file */

Elf64_Xword p_memsz; /* Segment size in memory */

Elf64_Xword p_align; /* Segment alignment, file & memory */

} Elf64_Phdr;

SectionHeader

The section header table is implemented by means of an array in which each entry contains a section. The

individual sections form the contents of the segments defined in the program header table. The following

data structure represents a section:

<elf.h>

typedef struct {

Elf32_Word sh_name;

Elf32_Word sh_type;

Elf32_Word sh_flags;

Elf32_Addr sh_addr;

Elf32_Off sh_offset;

Elf32_Word sh_size;

Elf32_Word sh_link;

Elf32_Word sh_info;

Elf32_Word sh_addralign;

Elf32_Word sh_entsize;

} Elf32_Shdr;

The elements have the following meanings:

❑ sh_namespecifies the name of the section. Its value is not the string itself but an index into the

section header string table.

❑ sh_typespecifies the section type. The following section types are available:

❑ SH_NULLindicates that the section is not used. Its data are ignored.

❑ SH_PROGBITSholds program-specific information whose format is undefined and is irrele-

vant to this discussion.

❑ SH_SYMTABholds a symbol table whose structure is discussed in Section E.2.4.SH_DYNSYM

also holds a symbol table. The difference between these two types is discussed later in this

appendix.

❑ SH_STRTABindicates a section that contains a string table.

❑ SH_RELAandSHT_RELAhold relocation sections whose structure is discussed in

Section E.2.5.