~ ~~
~ ~~ ELF header
~ ~~
~ ~~   This is the top-level ELF header, for the entire file. An ELF always
~ ~~ has exactly one of this header, which is always at the start of the file.
~ ~~
: elf-file-header
  0x7f pack8 s" ELF" pack-raw-string        ~ magic number
  2 pack8                                   ~ 64-bit
  1 pack8                                   ~ little-endian
  1 pack8                                   ~ ELF header format v1
  0 pack8                                   ~ System-V ABI
  0 pack64                                  ~ (padding)

  2 pack16                                  ~ executable
  0x3e pack16                               ~ Intel x86-64
  1 pack32                                  ~ ELF format version

  L' start use-label origin + pack64        ~ entry point
    ~ This includes the origin, intentionally.

  L' program-header use-label pack64        ~ program header offset
    ~ We place the program header immediately after the ELF header. This
    ~ offset is from the start of the file.
  0 pack64                                  ~ section header offset
  0 pack32                                  ~ processor flags
  64 pack16                                 ~ ELF header size
  56 pack16                                 ~ program header entry size
  1 pack16                                  ~ number of program header entries
  0 pack16                                  ~ section header entry size
  0 pack16                                  ~ number of section header entries
  0 pack16                                  ~ section name string table index
  ;

~ ~~
~ ~~ Program header
~ ~~
~ ~~   An ELF program header consists of any number of these entries; they are
~ ~~ always consecutive, but may be anywhere in the file. We always have
~ ~~ exactly one, and it's always right after the ELF file header.
~ ~~
: elf-program-header
  current-offset L' program-header set-label
  1 pack32                                  ~ "loadable" segment type
  0x05 pack32                               ~ read+execute permission
  0 pack64                                  ~ offset in file
  origin pack64                             ~ virtual address
    ~ required, but can be anything, subject to alignment
  0 pack64                                  ~ physical address (ignored)

  L' total-size use-label pack64            ~ size in file
  L' total-size use-label pack64            ~ size in memory

  0 pack64                                  ~ segment alignment
    ~ for relocation, but this doesn't apply to us
  ;