Object files

Data representation

As described here, the object file format supports various processors with 8-bit bytes and 32-bit or 64-bit architectures. Nevertheless, it is intended to be extensible to larger (or smaller) architectures. Object files therefore represent some control data with a machine-independent format, making it possible to identify object files and interpret their contents in a common way. Remaining data in an object file use the encoding of the target processor, regardless of the machine on which the file was created.

Name Size Alignment Purpose
Elf32_Addr 4 4 Unsigned program address
Elf32_Off 4 4 Unsigned file offset
Elf32_Half 2 2 Unsigned medium integer
Elf32_Word 4 4 Unsigned integer
Elf32_Sword 4 4 Signed integer
unsigned char 1 1 Unsigned small integer

32-Bit data types

Name Size Alignment Purpose
Elf64_Addr 8 8 Unsigned program address
Elf64_Off 8 8 Unsigned file offset
Elf64_Half 2 2 Unsigned medium integer
Elf64_Word 4 4 Unsigned integer
Elf64_Sword 4 4 Signed integer
Elf64_Xword 8 8 Unsigned long integer
Elf64_Sxword 8 8 Signed long integer
unsigned char 1 1 Unsigned small integer

64-Bit data types

All data structures that the object file format defines follow the ``natural'' size and alignment guidelines for the relevant class. If necessary, data structures contain explicit padding to ensure 8-byte alignment for 8-byte objects, 4-byte alignment for 4-byte objects, to force structure sizes to a multiple of 4 or 8, and so forth. Data also have suitable alignment from the beginning of the file. Thus, for example, a structure containing an Elf32_Addr member will be aligned on a 4-byte boundary within the file.

For portability reasons, ELF uses no bit-fields.

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UnixWare 7 Release 7.1.4 - 27 April 2004