As described here, the object file format supports various processors with 8-bit bytes, 32-bit and 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.
Table 7-1 32-Bit Data Types
Name |
Size |
Alignment |
Purpose |
---|---|---|---|
Elf32_Addr |
4 |
4 |
Unsigned program address |
Elf32_Half |
2 |
2 |
Unsigned medium integer |
Elf32_Off |
4 |
4 |
Unsigned file offset |
Elf32_Sword |
4 |
4 |
Signed integer |
Elf32_Word |
4 |
4 |
Unsigned integer |
unsigned char |
1 |
1 |
Unsigned small integer |
Table 7-2 64-Bit Data Types
Name |
Size |
Alignment |
Purpose |
---|---|---|---|
Elf64_Addr |
8 |
8 |
Unsigned program address |
Elf64_Half |
2 |
2 |
Unsigned medium integer |
Elf64_Off |
8 |
8 |
Unsigned file offset |
Elf64_Sword |
4 |
4 |
Signed integer |
Elf64_Word |
4 |
4 |
Unsigned integer |
Elf64_Xword |
8 |
8 |
Unsigned long integer |
Elf64_Sxword |
8 |
8 |
Signed long integer |
unsigned char |
1 |
1 |
Unsigned small integer |
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 4-byte alignment for 4-byte objects, to force structure sizes to a multiple of 4, 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, and a structure containing an Elf64_Addr member will be aligned on an 8-byte boundary.
For portability, ELF uses no bit-fields.