elf

ElfN_Addr	Unsigned program address, uintN_t
ElfN_Off	Unsigned file offset, uintN_t
ElfN_Section	Unsigned section index, uint16_t
ElfN_Versym	Unsigned version symbol information, uint16_t
Elf_Byte	unsigned char
ElfN_Half	uint16_t
ElfN_Sword	int32_t
ElfN_Word	uint32_t
ElfN_Sxword	int64_t
ElfN_Xword	uint64_t

#define EI_NIDENT 16

typedef struct {
    unsigned char e_ident[EI_NIDENT];
    uint16_t      e_type;
    uint16_t      e_machine;
    uint32_t      e_version;
    ElfN_Addr     e_entry;
    ElfN_Off      e_phoff;
    ElfN_Off      e_shoff;
    uint32_t      e_flags;
    uint16_t      e_ehsize;
    uint16_t      e_phentsize;
    uint16_t      e_phnum;
    uint16_t      e_shentsize;
    uint16_t      e_shnum;
    uint16_t      e_shstrndx;
} ElfN_Ehdr;

• e_ident This array of bytes specifies to interpret the file, independent of the processor or the file's remaining contents. Within this array everything is named by macros, which start with the prefix and may contain values which start with the prefix The following macros are defined:
• • EI_MAG0 The first byte of the magic number. It must be filled with (0: 0x7f)
  • EI_MAG1 The second byte of the magic number. It must be filled with (1: 'E')
  • EI_MAG2 The third byte of the magic number. It must be filled with (2: 'L')
  • EI_MAG3 The fourth byte of the magic number. It must be filled with (3: 'F')
  • EI_CLASS The fifth byte identifies the architecture for this binary:

• ELFCLASSNONE This class is invalid.
• ELFCLASS32 This defines the 32-bit architecture. It supports machines with files and virtual address spaces up to 4 Gigabytes.
• ELFCLASS64 This defines the 64-bit architecture.

• ELFDATANONE Unknown data format.
• ELFDATA2LSB Two's complement, little-endian.
• ELFDATA2MSB Two's complement, big-endian.

• EV_NONE Invalid version.
• EV_CURRENT Current version.

• ELFOSABI_NONE Same as ELFOSABI_SYSV
• ELFOSABI_SYSV UNIX System V ABI.
• ELFOSABI_HPUX HP-UX ABI.
• ELFOSABI_NETBSD NetBSD ABI.
• ELFOSABI_LINUX Linux ABI.
• ELFOSABI_SOLARIS Solaris ABI.
• ELFOSABI_IRIX IRIX ABI.
• ELFOSABI_FREEBSD FreeBSD ABI.
• ELFOSABI_TRU64 TRU64 UNIX ABI.
• ELFOSABI_ARM ARM architecture ABI.
• ELFOSABI_STANDALONE Stand-alone (embedded) ABI.

• ET_NONE An unknown type.
• ET_REL A relocatable file.
• ET_EXEC An executable file.
• ET_DYN A shared object.
• ET_CORE A core file.

• EM_NONE An unknown machine.
• EM_M32 AT&T WE 32100.
• EM_SPARC Sun Microsystems SPARC.
• EM_386 Intel 80386.
• EM_68K Motorola 68000.
• EM_88K Motorola 88000.
• EM_860 Intel 80860.
• EM_MIPS MIPS RS3000 (big-endian only).
• EM_PARISC HP/PA.
• EM_SPARC32PLUS SPARC with enhanced instruction set.
• EM_PPC PowerPC.
• EM_PPC64 PowerPC 64-bit.
• EM_S390 IBM S/390
• EM_ARM Advanced RISC Machines
• EM_SH Renesas SuperH
• EM_SPARCV9 SPARC v9 64-bit.
• EM_IA_64 Intel Itanium
• EM_X86_64 AMD x86-64
• EM_VAX DEC Vax.

• EV_NONE Invalid version.
• EV_CURRENT Current version.

typedef struct {
    uint32_t   p_type;
    Elf32_Off  p_offset;
    Elf32_Addr p_vaddr;
    Elf32_Addr p_paddr;
    uint32_t   p_filesz;
    uint32_t   p_memsz;
    uint32_t   p_flags;
    uint32_t   p_align;
} Elf32_Phdr;

typedef struct {
    uint32_t   p_type;
    uint32_t   p_flags;
    Elf64_Off  p_offset;
    Elf64_Addr p_vaddr;
    Elf64_Addr p_paddr;
    uint64_t   p_filesz;
    uint64_t   p_memsz;
    uint64_t   p_align;
} Elf64_Phdr;

• p_type This member of the Phdr struct tells what kind of segment this array element describes or how to interpret the array element's information.
• • PT_NULL The array element is unused and the other members' values are undefined. This lets the program header have ignored entries.
  • PT_LOAD The array element specifies a loadable segment, described by and The bytes from the file are mapped to the beginning of the memory segment. If the segment's memory size

• PF_X An executable segment.
• PF_W A writable segment.
• PF_R A readable segment.

• SHN_UNDEF This value marks an undefined, missing, irrelevant or otherwise meaningless section reference.
• SHN_LORESERVE This value specifies the lower bound of the range of reserved indices.
• SHN_LOPROC Values greater than or equal to are reserved for processor-specific semantics.
• SHN_HIPROC Values less than or equal to are reserved for processor-specific semantics.
• SHN_ABS This value specifies the absolute value for the corresponding reference. For example, a symbol defined relative to section number has an absolute value and is not affected by relocation.
• SHN_COMMON Symbols defined relative to this section are common symbols, such as FORTRAN COMMON or unallocated C external variables.
• SHN_HIRESERVE This value specifies the upper bound of the range of reserved indices. The system reserves indices between and inclusive. The section header table does not contain entries for the reserved indices.

typedef struct {
    uint32_t   sh_name;
    uint32_t   sh_type;
    uint32_t   sh_flags;
    Elf32_Addr sh_addr;
    Elf32_Off  sh_offset;
    uint32_t   sh_size;
    uint32_t   sh_link;
    uint32_t   sh_info;
    uint32_t   sh_addralign;
    uint32_t   sh_entsize;
} Elf32_Shdr;

typedef struct {
    uint32_t   sh_name;
    uint32_t   sh_type;
    uint64_t   sh_flags;
    Elf64_Addr sh_addr;
    Elf64_Off  sh_offset;
    uint64_t   sh_size;
    uint32_t   sh_link;
    uint32_t   sh_info;
    uint64_t   sh_addralign;
    uint64_t   sh_entsize;
} Elf64_Shdr;

• sh_name This member specifies the name of the section. Its value is an index into the section header string table section, giving the location of a null-terminated string.
• sh_type This member categorizes the section's contents and semantics.
• • SHT_NULL This value marks the section header as inactive. It does not have an associated section. Other members of the section header have undefined values.
  • SHT_PROGBITS This section holds information defined by the program, whose format and meaning are determined solely by the program.
  • SHT_SYMTAB This section holds a symbol table. Typically, provides symbols for link editing, though it may also be used for dynamic linking. As a complete symbol table, it may contain many symbols unnecessary for dynamic linking. An object file can also contain a section.
  • SHT_STRTAB This section holds a string table. An object file may have multiple string table sections.
  • SHT_RELA This section holds relocation entries with explicit addends, such as type for the 32-bit class of object files. An object may have multiple relocation sections.
  • SHT_HASH This section holds a symbol hash table. An object participating in dynamic linking must contain a symbol hash table. An object file may have only one hash table.
  • SHT_DYNAMIC This section holds information for dynamic linking. An object file may have only one dynamic section.
  • SHT_NOTE This section holds information that marks the file in some way.
  • SHT_NOBITS A section of this type occupies no space in the file but otherwise resembles Although this section contains no bytes, the member contains the conceptual file offset.
  • SHT_REL This section holds relocation offsets without explicit addends, such as type for the 32-bit class of object files. An object file may have multiple relocation sections.
  • SHT_SHLIB This section is reserved but has unspecified semantics.
  • SHT_DYNSYM This section holds a minimal set of dynamic linking symbols. An object file can also contain a section.
  • SHT_LOPROC This value up to and including is reserved for processor-specific semantics.
  • SHT_HIPROC This value down to and including is reserved for processor-specific semantics.
  • SHT_LOUSER This value specifies the lower bound of the range of indices reserved for application programs.
  • SHT_HIUSER This value specifies the upper bound of the range of indices reserved for application programs. Section types between and may be used by the application, without conflicting with current or future system-defined section types.

• SHF_WRITE This section contains data that should be writable during process execution.
• SHF_ALLOC This section occupies memory during process execution. Some control sections do not reside in the memory image of an object file. This attribute is off for those sections.
• SHF_EXECINSTR This section contains executable machine instructions.
• SHF_MASKPROC All bits included in this mask are reserved for processor-specific semantics.

• .bss This section holds uninitialized data that contributes to the program's memory image. By definition, the system initializes the data with zeros when the program begins to run. This section is of type The attribute types are and
• .comment This section holds version control information. This section is of type No attribute types are used.
• .ctors This section holds initialized pointers to the C++ constructor functions. This section is of type The attribute types are and
• .data This section holds initialized data that contribute to the program's memory image. This section is of type The attribute types are and
• .data1 This section holds initialized data that contribute to the program's memory image. This section is of type The attribute types are and
• .debug This section holds information for symbolic debugging. The contents are unspecified. This section is of type No attribute types are used.
• .dtors This section holds initialized pointers to the C++ destructor functions. This section is of type The attribute types are and
• .dynamic This section holds dynamic linking information. The section's attributes will include the bit. Whether the bit is set is processor-specific. This section is of type See the attributes above.
• .dynstr This section holds strings needed for dynamic linking, most commonly the strings that represent the names associated with symbol table entries. This section is of type The attribute type used is
• .dynsym This section holds the dynamic linking symbol table. This section is of type The attribute used is
• .fini This section holds executable instructions that contribute to the process termination code. When a program exits normally the system arranges to execute the code in this section. This section is of type The attributes used are and
• .got This section holds the global offset table. This section is of type The attributes are processor-specific.
• .hash This section holds a symbol hash table. This section is of type The attribute used is
• .init This section holds executable instructions that contribute to the process initialization code. When a program starts to run the system arranges to execute the code in this section before calling the main program entry point. This section is of type The attributes used are and
• .interp This section holds the pathname of a program interpreter. If the file has a loadable segment that includes the section, the section's attributes will include the bit. Otherwise, that bit will be off. This section is of type
• .line This section holds line number information for symbolic debugging, which describes the correspondence between the program source and the machine code. The contents are unspecified. This section is of type No attribute types are used.
• .note This section holds information in the format described below. This section is of type No attribute types are used. native executables usually contain a section to identify themselves, for the kernel to bypass any compatibility ELF binary emulation tests when loading the file.
• .plt This section holds the procedure linkage table. This section is of type The attributes are processor-specific.
• .relNAME This section holds relocation information as described below. If the file has a loadable segment that includes relocation, the section's attributes will include the bit. Otherwise the bit will be off. By convention, is supplied by the section to which the relocations apply. Thus a relocation section for normally would have the name This section is of type
• .relaNAME This section holds relocation information as described below. If the file has a loadable segment that includes relocation, the section's attributes will include the bit. Otherwise the bit will be off. By convention, is supplied by the section to which the relocations apply. Thus a relocation section for normally would have the name This section is of type
• .rodata This section holds read-only data that typically contributes to a non-writable segment in the process image. This section is of type The attribute used is
• .rodata1 This section holds read-only data that typically contributes to a non-writable segment in the process image. This section is of type The attribute used is
• .shstrtab This section holds section names. This section is of type No attribute types are used.
• .strtab This section holds strings, most commonly the strings that represent the names associated with symbol table entries. If the file has a loadable segment that includes the symbol string table, the section's attributes will include the bit. Otherwise the bit will be off. This section is of type
• .symtab This section holds a symbol table. If the file has a loadable segment that includes the symbol table, the section's attributes will include the bit. Otherwise the bit will be off. This section is of type
• .text This section holds the or executable instructions, of a program. This section is of type The attributes used are and

typedef struct {
    uint32_t      st_name;
    Elf32_Addr    st_value;
    uint32_t      st_size;
    unsigned char st_info;
    unsigned char st_other;
    uint16_t      st_shndx;
} Elf32_Sym;

typedef struct {
    uint32_t      st_name;
    unsigned char st_info;
    unsigned char st_other;
    uint16_t      st_shndx;
    Elf64_Addr    st_value;
    uint64_t      st_size;
} Elf64_Sym;

• st_name This member holds an index into the object file's symbol string table, which holds character representations of the symbol names. If the value is non-zero, it represents a string table index that gives the symbol name. Otherwise, the symbol table has no name.
• st_value This member gives the value of the associated symbol.
• st_size Many symbols have associated sizes. This member holds zero if the symbol has no size or an unknown size.
• st_info This member specifies the symbol's type and binding attributes:
• • STT_NOTYPE The symbol's type is not defined.
  • STT_OBJECT The symbol is associated with a data object.
  • STT_FUNC The symbol is associated with a function or other executable code.
  • STT_SECTION The symbol is associated with a section. Symbol table entries of this type exist primarily for relocation and normally have bindings.
  • STT_FILE By convention, the symbol's name gives the name of the source file associated with the object file. A file symbol has bindings, its section index is and it precedes the other symbols of the file, if it is present.
  • STT_LOPROC This value up to and including is reserved for processor-specific semantics.
  • STT_HIPROC This value down to and including is reserved for processor-specific semantics.
• • STB_LOCAL Local symbols are not visible outside the object file containing their definition. Local symbols of the same name may exist in multiple files without interfering with each other.
  • STB_GLOBAL Global symbols are visible to all object files being combined. One file's definition of a global symbol will satisfy another file's undefined reference to the same symbol.
  • STB_WEAK Weak symbols resemble global symbols, but their definitions have lower precedence.
  • STB_LOPROC This value up to and including is reserved for processor-specific semantics.
  • STB_HIPROC This value down to and including is reserved for processor-specific semantics.

typedef struct {
    Elf32_Addr r_offset;
    uint32_t   r_info;
} Elf32_Rel;

typedef struct {
    Elf64_Addr r_offset;
    uint64_t   r_info;
} Elf64_Rel;

typedef struct {
    Elf32_Addr r_offset;
    uint32_t   r_info;
    int32_t    r_addend;
} Elf32_Rela;

typedef struct {
    Elf64_Addr r_offset;
    uint64_t   r_info;
    int64_t    r_addend;
} Elf64_Rela;

r_offset
This member gives the location at which to apply the relocation action.
For a relocatable file, the value is the byte offset from the beginning
of the section to the storage unit affected by the relocation.
For an
executable file or shared object, the value is the virtual address of
the storage unit affected by the relocation.

r_info
This member gives both the symbol table index with respect to which the
relocation must be made and the type of relocation to apply.
Relocation
types are processor-specific.
When the text refers to a relocation
entry's relocation type or symbol table index, it means the result of
applying
or
respectively, to the entry's
member.

r_addend
This member specifies a constant addend used to compute the value to be
stored into the relocatable field.

typedef struct {
    Elf32_Sword    d_tag;
    union {
	Elf32_Word d_val;
	Elf32_Addr d_ptr;
    } d_un;
} Elf32_Dyn;
extern Elf32_Dyn _DYNAMIC[];

typedef struct {
    Elf64_Sxword    d_tag;
    union {
        Elf64_Xword d_val;
        Elf64_Addr  d_ptr;
    } d_un;
} Elf64_Dyn;
extern Elf64_Dyn _DYNAMIC[];
d_tag
This member may have any of the following values:

DT_NULL
Marks end of dynamic section

DT_NEEDED
String table offset to name of a needed library

DT_PLTRELSZ
Size in bytes of PLT relocs

DT_PLTGOT
Address of PLT and/or GOT

DT_HASH
Address of symbol hash table

DT_STRTAB
Address of string table

DT_SYMTAB
Address of symbol table

DT_RELA
Address of Rela relocs table

DT_RELASZ
Size in bytes of Rela table

DT_RELAENT
Size in bytes of a Rela table entry

DT_STRSZ
Size in bytes of string table

DT_SYMENT
Size in bytes of a symbol table entry

DT_INIT
Address of the initialization function

DT_FINI
Address of the termination function

DT_SONAME
String table offset to name of shared object

DT_RPATH
String table offset to library search path (deprecated)

DT_SYMBOLIC
Alert linker to search this shared object before the executable for symbols

DT_REL
Address of Rel relocs table

DT_RELSZ
Size in bytes of Rel table

DT_RELENT
Size in bytes of a Rel table entry

DT_PLTREL
Type of reloc the PLT refers (Rela or Rel)

DT_DEBUG
Undefined use for debugging

DT_TEXTREL
Absence of this indicates no relocs should apply to a non-writable segment

DT_JMPREL
Address of reloc entries solely for the PLT

DT_BIND_NOW
Instruct dynamic linker to process all relocs before transferring control to
the executable

DT_RUNPATH
String table offset to library search path

DT_LOPROC
Start of processor-specific semantics

DT_HIPROC
End of processor-specific semantics


d_val
This member represents integer values with various interpretations.

d_ptr
This member represents program virtual addresses.
When interpreting
these addresses, the actual address should be computed based on the
original file value and memory base address.
Files do not contain
relocation entries to fixup these addresses.

_DYNAMIC
Array containing all the dynamic structures in the .dynamic section.
This is automatically populated by the linker.