path: root/105files.subx

== code

open:  # filename: (addr array byte), write?: boolean, out: (addr handle buffered-file)
    # hard-coded parameter: file-buffer-size of created buffered-file
    # . prologue
    55/push-ebp
    89/<- %ebp 4/r32/esp
    # . save registers
    50/push-eax
    51/push-ecx
    52/push-edx
    53/push-ebx
    56/push-esi
    57/push-edi
    # ecx = filename
    8b/-> *(ebp+8) 1/r32/ecx
    # var size/edx: int = filename->length + 1 for the trailing null character
    8b/-> *ecx 2/r32/edx
    42/increment-edx
    # var s/esi: (stream size)
    29/subtract-from %esp 2/r32/edx
    52/push-edx  # size
    68/push 0/imm32/read
    68/push 0/imm32/write
    89/<- %esi 4/r32/esp
    # copy filename and a final null character
    (clear-stream %esi)
    (write %esi %ecx)
    # spill edx
    52/push-edx
    # var fd/ecx: fd = open(filename)
    8d/copy-address *(esi+0xc) 3/r32/ebx
    8b/-> *(ebp+0xc) 1/r32/ecx/flags
    ba/copy-to-edx 0x180/imm32/permissions
    e8/call syscall_open/disp32
    89/<- %ecx 0/r32/eax
    # restore edx
    5a/pop-to-edx
    # allocate a buffered-file
    (allocate Heap 0x1010 *(ebp+0x10))  # file-buffer-size + 16 for other fields
    # var out-addr/edi: (addr buffered-file)
    8b/-> *(ebp+0x10) 7/r32/edi
    (lookup *edi *(edi+4))  # => eax
    89/<- %edi 0/r32/eax
    # out-addr->size = 4KB
    c7 0/subop/copy *(edi+0xc) 0x1000/imm32/file-buffer-size  # Stream-size + 4 for fd
    # out-addr->fd = fd
    89/<- *edi 1/r32/ecx
$open:end:
    # . reclaim locals
    01/add-to %esp 2/r32/edx
    81 0/subop/add %esp 0xc/imm32
    # . restore registers
    5f/pop-to-edi
    5e/pop-to-esi
    5b/pop-to-ebx
    5a/pop-to-edx
    59/pop-to-ecx
    58/pop-to-eax
    # . epilogue
    89/<- %esp 5/r32/ebp
    5d/pop-to-ebp
    c3/return