object_structure.md

The structure of the object files

Object:

• Header:
  • Parameters:
    • Opcode size - the number of bits in an opcode
    • Text byte - the number of bits in a byte of text
    • Data byte - the number of bits in a byte of data
    • Text address - the number of bits in a text address
    • Data address - the number of bits in a data address
  • Section table size - the number of sections in the segment
• Section table:
  • Section table entries, each:
    • Section type - data, text, symbol table or relocation table
    • Section size - the number of bytes in a section (for text or data) or the number of symbols (for Symbol table or Relocation table)
• Sections (Text, Data, Symbol table or Relocation table)

Text, Data:

• Just a sequence of bytes

Symbol table:

• Each symbol (a symbol is basically a label):
  • Section id - in which section the symbol is located
  • Offset - the offset (in bytes) in the section to the symbol
  • Name address - the location (in bits), where to find the name of the symbol in the String
• String - concatinated names of the symbols (in format: name1\0name2\0name3\0)

Relocation table:

• Each relocation:
  • Location:
    • Section - the id of section in which the relocation is located
    • Offset - the offset (in bytes) in the section to byt of the relocation
  • Name address - the location (in bits), where to find the name of the symbol in the String o the Symbol table
  • Symbol size - how many bits should be replaced
  • Symbol offset - the offset inside the byte, where the bits should be replaced
  • Relative - if the relocation is relative or absolute (if relative, it will make the relocation position independently)