path: root/mu-init.subx

# Initialize the minimal runtime for Mu programs.
#
# See translate_mu for how this file is used.
#
# Mu programs start at a function called 'main' with this signature:
#   fn main args: (addr array (addr array byte)) -> exit-status/ebx: int
# If your program doesn't need commandline arguments you can drop it:
#   fn main -> exit-status/ebx: int
#
# Notice that the output must be in ebx, so that the exit() syscall can pick
# it up.

== code

Entry:
    # we don't use ebp in Entry; just initialize it
    bd/copy-to-ebp 0/imm32
    # - save argc and argv
    # var argc-and-argv/esi
    89/<- %esi 4/r32/esp
$Entry:initialize-heap:
    # - initialize the heap
    (new-segment *Heap-size Heap)
$Entry:initialize-args:
    # - convert argv from null-terminated 'kernel' strings to length-prefixed Mu strings
    # var argc/edx: int
    8b/-> *esi 2/r32/edx
    # argc is in words; convert it to bytes
    c1/shift 4/subop/left %edx 2/imm8
    # var args/edi: (addr array (addr array byte))
    (allocate-array Heap %edx)  # => eax
    89/<- %edi 0/r32/eax
    # var curr/ecx: (addr kernel-string) = argv
    8d/copy-address *(esi+4) 1/r32/ecx
    # var max/edx: (addr kernel-string) = argv+4+argc
    8d/copy-address *(ecx+edx) 2/r32/edx
    # var dest/esi: (addr (addr array byte)) = args+4
    8d/copy-address *(edi+4) 6/r32/esi
    {
      # if (curr >= max) break
      39/compare %ecx 2/r32/edx
      73/jump-if-addr>= break/disp8
      # *dest = kernel-string-to-string(*curr)
      (kernel-string-to-string Heap *ecx)  # => eax
      89/<- *esi 0/r32/eax
      # curr += 4
      81 0/subop/add %ecx 4/imm32
      # dest += 4
      81 0/subop/add %esi 4/imm32
      #
      eb/jump loop/disp8
    }
    # - run Mu program
    (main %edi)  # => ebx
    # - exit
    (syscall_exit)