Some useful gdb commands for debugging Scryer Prolog

These work in the present Rust release (1.76) with stable-gnu set to the default in rustup. They’ll of course break as the underlying Rust APIs shift with new Rust releases, but that is the reason for posting them here.

define print-rust-string
  printf "%s\n", $arg0.vec.buf.ptr.pointer.pointer
end

define cell-tag
  print $arg0.get_tag()
end

define cell-value
  print $arg0.get_value()
end

define index-cell
  print *($arg0.buf.ptr.pointer.pointer + $arg1)
end

define print-scryer-atom
  set $atom_table = scryer_prolog::atom_table::global_atom_table::GLOBAL_ATOM_TABLE
  set $inner_tbl  = $atom_table.value.value.value.value.data.value.ptr.pointer.data.inner.active_value.p.value
  set $block_base = $inner_tbl.block.base
  # 16 bytes is the size of &str on 64-bit machines, which are fat pointers
  set $STRINGS_len = sizeof(scryer_prolog::atom_table::STRINGS) / 16
  set $atom_idx = $arg0.index >> 3

  if $atom_idx < $STRINGS_len
    printf "%s\n", scryer_prolog::atom_table::STRINGS[$atom_idx]
  else
    printf "%s\n", $block_base + ($atom_idx - $STRINGS_len) * 8 + 8
  end
end