path: root/apps/random.subx

# Repeatedly read 32-bit numbers from /dev/random, print them to stdout.
#
# To run:
#   $ ./bootstrap translate init.linux 0*.subx apps/random.subx -o apps/random
#   $ ./bootstrap run apps/random

== code 0x09000000
#   instruction                     effective address                                                   register    displacement    immediate
# . op          subop               mod             rm32          base        index         scale       r32
# . 1-3 bytes   3 bits              2 bits          3 bits        3 bits      3 bits        2 bits      2 bits      0/1/2/4 bytes   0/1/2/4 bytes

Entry:
    # stream/esi = syscall(open, "/dev/null", O_RDONLY, 0)  # we can't use 'fd' because it looks like a hex byte
    bb/copy-to-ebx  Filename/imm32
    b9/copy-to-ecx  0/imm32/rdonly
    ba/copy-to-edx  0x180/imm32/fixed-perms
    b8/copy-to-eax  5/imm32/open
    cd/syscall  0x80/imm8
    # . stream = eax
    89/copy                         3/mod/direct    6/rm32/esi    .           .             .           0/r32/eax   .               .                 # copy eax to esi

$loop:

    # syscall(read, Stream, N, 4)
    89/copy                         3/mod/direct    3/rm32/ebx    .           .             .           6/r32/esi   .               .                 # copy esi to ebx
    b9/copy-to-ecx  N/imm32
    ba/copy-to-edx  4/imm32/size
    b8/copy-to-eax  3/imm32/read
    cd/syscall  0x80/imm8

    # print-int32-buffered(Stdout, *N)
    # . . push args
    ff          6/subop/push        0/mod/indirect  5/rm32/.disp32            .             .           .           N/disp32                          # push *N
    68/push  Stdout/imm32
    # . . call
    e8/call  print-int32-buffered/disp32

    # write-buffered(Stdout, Newline)
    # . . push args
    68/push  Newline/imm32
    68/push  Stdout/imm32
    # . . call
    e8/call  write-buffered/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp

    eb/jump  $loop/disp8

    # syscall(exit, 0)
    bb/copy-to-ebx  0/imm32
    b8/copy-to-eax  1/imm32/exit
    cd/syscall  0x80/imm8

== data 0x0a000000

N:
    0/imm32
Filename:
    2f 64 65 76 2f 72 61 6e 64 6f 6d 00
#   /  d  e  v  /  r  a  n  d  o  m  null

# . . vim:nowrap:textwidth=0