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ELF notes

Structure of an ELF file.

  • An ELF file is made up of both Sections and Segments (also called programs) that overlap in the actual binary
  • The sizes and space are defined by sequential headers
  • The start of the ELF file has a single ELF header that defines things like the binary size and entry point
    • More notably, the ELF header also specifies the number of program headers and section headers
  • A program header will point to where the program starts in memory. These are your assembly blocks
    • EX .text, .data -- these are the only two we used in this program
    • A segment called .shstrtab stores the names of the other segments for tools like readelf to show
  • You don't have to have any sections -- we didn't need for our hello world program

Unix commands

  • During development, I found the following unix commands helpful:
    • file - the values shown here are pulled from the ELF header, useful for showing if the ELF header is right
    • readelf -a - will show the ELF header values and a bunch of other useful info
    • hexdump -C - shows the bytes in hex from a file, as well as the "artwork", which is really useful
    • objdump -S - see the assembly instructions and accompanying binary commands
      • This mostly helped when comparing to an actual compiled assembly file

Resources

If you want to try a project like this yourself, these are the main resources I used online that helped me out here.