mu - Soul of a tiny new machine. More thorough tests → More comprehensible and rewrite-friendly software → More resilient society.

# A stack looks like this:
#   top: int
#   data: (array byte)  # prefixed by size as usual
#
# TODO: is it confusing that the push opcodes grow memory downward, but the
# push function grows stacks upward?

== code
#   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

clear-stack:  # s: (addr stack)
    # . prologue
    55/push-ebp
    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
    # . save registers
    50/push-eax
    51/push-ecx
    # eax = s
    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           0/r32/eax   8/disp8         .                 # copy *(ebp+8) to eax
    # var max/ecx: (addr byte) = &s->data[s->size]
    8b/copy                         1/mod/*+disp8   0/rm32/eax    .           .             .           1/r32/ecx   4/disp8         .                 # copy *(eax+4) to eax
    8d/copy-address                 1/mod/*+disp8   4/rm32/sib    0/base/eax  1/index/ecx   .           1/r32/ecx   8/disp8         .                 # copy eax+ecx+8 to ecx
    # s->top = 0
    c7          0/subop/copy        0/mod/direct    0/rm32/eax    .           .             .           .           .               0/imm32           # copy to *eax
    # var curr/eax: (addr byte) = s->data
    81          0/subop/add         3/mod/direct    0/rm32/eax    .           .             .           .           .               8/imm32           # add to eax
$clear-stack:loop:
    # if (curr >= max) break
    39/compare                      3/mod/direct    0/rm32/eax    .           .             .           1/r32/ecx   .               .                 # compare eax with ecx
    73/jump-if-addr>=  $clear-stack:end/disp8
    # *curr = 0
    c6          0/subop/copy-byte   0/mod/direct    0/rm32/eax    .           .             .           .           .               0/imm8            # copy byte to *eax
    # ++curr
    40/increment-eax
    eb/jump $clear-stack:loop/disp8
$clear-stack:end:
    # . restore registers
    59/pop-to-ecx
    58/pop-to-eax
    # . epilogue
    89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
    5d/pop-to-ebp
    c3/return

test-clear-stack:
    # . prologue
    55/push-ebp
    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
    # var stack/ecx = stack of size 8 with random data in it
    68/push 34/imm32
    68/push 35/imm32
    68/push 8/imm32/size
    68/push 14/imm32/top
    89/copy                         3/mod/direct    1/rm32/ecx    .           .             .           4/r32/esp   .               .                 # copy esp to ecx
    # clear(stack)
    # . . push args
    51/push-ecx
    # . . call
    e8/call  clear-stack/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # top should be 0
    58/pop-to-eax
    # . check-ints-equal(eax, 0, msg)
    # . . push args
    68/push  "F - test-clear-stack: top"/imm32
    68/push  0/imm32
    50/push-eax
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    # size should remain 8
    58/pop-to-eax
    # . check-ints-equal(eax, 8, msg)
    # . . push args
    68/push  "F - test-clear-stack: size"/imm32
    68/push  8/imm32
    50/push-eax
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    # first word is 0
    58/pop-to-eax
    # . check-ints-equal(eax, 0, msg)
    # . . push args
    68/push  "F - test-clear-stack: data[0..3]"/imm32
    68/push  0/imm32
    50/push-eax
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    # second word is 0
    58/pop-to-eax
    # . check-ints-equal(eax, 0, msg)
    # . . push args
    68/push  "F - test-clear-stack: data[4..7]"/imm32
    68/push  0/imm32
    50/push-eax
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    # . epilogue
    89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
    5d/pop-to-ebp
    c3/return

# TODO: make this generic
push:  # s: (addr stack), n: int
    # . prologue
    55/push-ebp
    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
    # . save registers
    50/push-eax
    51/push-ecx
    56/push-esi
    # esi = s
    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           6/r32/esi   8/disp8         .                 # copy *(ebp+8) to esi
    # ecx = s->top
    8b/copy                         0/mod/indirect  6/rm32/esi    .           .             .           1/r32/ecx   .               .                 # copy *esi to ecx
    # if (s->top >= s->size) abort
    39/compare                      1/mod/*+disp8   6/rm32/esi    .           .             .           1/r32/ecx   4/disp8         .                 # compare *(esi+4) and ecx
    7e/jump-if-<=  $push:abort/disp8
    # s->data[s->top] = n
    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           0/r32/eax   0xc/disp8       .                 # copy *(ebp+12) to eax
    89/copy                         1/mod/*+disp8   4/rm32/sib    6/base/esi  1/index/ecx   .           0/r32/eax   8/disp8         .                 # copy eax to *(esi+ecx+8)
    # s->top += 4
    81          0/subop/add         0/mod/direct    6/rm32/esi    .           .             .           .           .               4/imm32           # subtract from *esi
$push:end:
    # . restore registers
    5e/pop-to-esi
    59/pop-to-ecx
    58/pop-to-eax
    # . epilogue
    89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
    5d/pop-to-ebp
    c3/return

$push:abort:
    # print(stderr, "error: push: no space left")
    # . write-buffered(Stderr, "error: push: no space left")
    # . . push args
    68/push  "error: push: no space left"/imm32
    68/push  Stderr/imm32
    # . . call
    e8/call  write-buffered/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # . flush(Stderr)
    # . . push args
    68/push  Stderr/imm32
    # . . call
    e8/call  flush/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # . syscall(exit, 1)
    bb/copy-to-ebx  1/imm32
    e8/call  syscall_exit/disp32
    # never gets here

test-push:
    # . prologue
    55/push-ebp
    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
    # var stack/ecx = empty stack of size 8
    68/push 0/imm32
    68/push 0/imm32
    68/push 8/imm32/size
    68/push 0/imm32/top
    89/copy                         3/mod/direct    1/rm32/ecx    .           .             .           4/r32/esp   .               .                 # copy esp to ecx
    # push(stack, 0x42)
    # . . push args
    68/push  0x42/imm32
    51/push-ecx
    # . . call
    e8/call  push/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # check top
    58/pop-to-eax
    # . check-ints-equal(eax, 4, msg)
    # . . push args
    68/push  "F - test-push: top"/imm32
    68/push  4/imm32
    50/push-eax
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    # check size
    58/pop-to-eax
    # . check-ints-equal(eax, 8, msg)
    # . . push args
    68/push  "F - test-push: size"/imm32
    68/push  8/imm32
    50/push-eax
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    # first word is 0x42
    58/pop-to-eax
    # . check-ints-equal(eax, 0x42, msg)
    # . . push args
    68/push  "F - test-push: data[0..3]"/imm32
    68/push  0x42/imm32
    50/push-eax
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    # second word is 0
    58/pop-to-eax
    # . check-ints-equal(eax, 0, msg)
    # . . push args
    68/push  "F - test-push: data[4..7]"/imm32
    68/push  0/imm32
    50/push-eax
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    # . epilogue
    89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
    5d/pop-to-ebp
    c3/return

# TODO: make this generic
pop:  # s: (addr stack) -> n/eax: int
    # . prologue
    55/push-ebp
    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
    # . save registers
    51/push-ecx
    56/push-esi
    # esi = s
    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           6/r32/esi   8/disp8         .                 # copy *(ebp+8) to esi
    # if (s->top <= 0) abort
    81          7/subop/compare     0/mod/indirect  6/rm32/esi    .           .             .           .           .               0/imm32           # compare *esi
    7e/jump-if-<=  $pop:abort/disp8
    # s->top -= 4
    81          5/subop/subtract    0/mod/direct    6/rm32/esi    .           .             .           .           .               4/imm32           # subtract from *esi
    # eax = s->data[s->top]
    8b/copy                         0/mod/indirect  6/rm32/esi    .           .             .           1/r32/ecx   .               .                 # copy *esi to ecx
    8b/copy                         1/mod/*+disp8   4/rm32/sib    6/base/esi  1/index/ecx   .           0/r32/eax   8/disp8         .                 # copy *(esi+ecx+8) to eax
    # s->data[s->top] = 0
    c7          0/subop/copy        1/mod/*+disp8   4/rm32/sib    6/base/esi  1/index/ecx   .           0/r32/eax   8/disp8         0/imm32           # copy to *(esi+ecx+8)
$pop:end:
    # . restore registers
    5e/pop-to-esi
    59/pop-to-ecx
    # . epilogue
    89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
    5d/pop-to-ebp
    c3/return

$pop:abort:
    # print(stderr, "error: pop: nothing left in stack")
    # . write-buffered(Stderr, "error: pop: nothing left in stack")
    # . . push args
    68/push  "error: pop: nothing left in stack"/imm32
    68/push  Stderr/imm32
    # . . call
    e8/call  write-buffered/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # . flush(Stderr)
    # . . push args
    68/push  Stderr/imm32
    # . . call
    e8/call  flush/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # . syscall(exit, 1)
    bb/copy-to-ebx  1/imm32
    e8/call  syscall_exit/disp32
    # never gets here

test-pop:
    # . prologue
    55/push-ebp
    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
    # var stack/ecx = stack of size 8 containing just 0x42
    68/push 0/imm32
    68/push 0x42/imm32
    68/push 8/imm32/size
    68/push 4/imm32/top
    89/copy                         3/mod/direct    1/rm32/ecx    .           .             .           4/r32/esp   .               .                 # copy esp to ecx
    # eax = pop(stack)
    # . . push args
    51/push-ecx
    # . . call
    e8/call  pop/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # check-ints-equal(eax, 0x42, msg)
    # . . push args
    68/push  "F - test-pop: result"/imm32
    68/push  0x42/imm32
    50/push-eax
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    # check top
    58/pop-to-eax
    # . check-ints-equal(eax, 0, msg)
    # . . push args
    68/push  "F - test-pop: top"/imm32
    68/push  0/imm32
    50/push-eax
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    # check size
    58/pop-to-eax
    # . check-ints-equal(eax, 8, msg)
    # . . push args
    68/push  "F - test-pop: size"/imm32
    68/push  8/imm32
    50/push-eax
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    # . epilogue
    89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
    5d/pop-to-ebp
    c3/return

# TODO: make this generic
top:  # s: (addr stack) -> n/eax: int
    # . prologue
    55/push-ebp
    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
    # . save registers
    51/push-ecx
    56/push-esi
    # esi = s
    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           6/r32/esi   8/disp8         .                 # copy *(ebp+8) to esi
    # if (s->top <= 0) abort
    81          7/subop/compare     0/mod/indirect  6/rm32/esi    .           .             .           .           .               0/imm32           # compare *esi
    7e/jump-if-<=  $top:abort/disp8
    # n = s->data[s->top - 4]
    8b/copy                         0/mod/indirect  6/rm32/esi    .           .             .           1/r32/ecx   .               .                 # copy *esi to ecx
    81          5/subop/subtract    3/mod/direct    1/rm32/ecx    .           .             .           .           .               4/imm32           # subtract from ecx
    8b/copy                         1/mod/*+disp8   4/rm32/sib    6/base/esi  1/index/ecx   .           0/r32/eax   8/disp8         .                 # copy *(esi+ecx+8) to eax
$top:end:
    # . restore registers
    5e/pop-to-esi
    59/pop-to-ecx
    # . epilogue
    89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
    5d/pop-to-ebp
    c3/return

$top:abort:
    # print(stderr, "error: top: nothing left in stack")
    # . write-buffered(Stderr, "error: top: nothing left in stack")
    # . . push args
    68/push  "error: top: nothing left in stack"/imm32
    68/push  Stderr/imm32
    # . . call
    e8/call  write-buffered/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # . flush(Stderr)
    # . . push args
    68/push  Stderr/imm32
    # . . call
    e8/call  flush/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # . syscall(exit, 1)
    bb/copy-to-ebx  1/imm32
    e8/call  syscall_exit/disp32
    # never gets here

test-top:
    # . prologue
    55/push-ebp
    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
    # var stack/ecx = stack of size 8 containing just 0x42
    68/push  0/imm32
    68/push  0x42/imm32
    68/push  8/imm32/size
    68/push  4/imm32/top
    89/copy                         3/mod/direct    1/rm32/ecx    .           .             .           4/r32/esp   .               .                 # copy esp to ecx
    # eax = top(stack)
    # . . push args
    51/push-ecx
    # . . call
    e8/call  top/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # check-ints-equal(eax, 42, msg")
    # . . push args
    68/push  "F - test-top: result"/imm32
    68/push  0x42/imm32
    50/push-eax
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
    # . epilogue
    89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
    5d/pop-to-ebp
    c3/return

# . . vim:nowrap:textwidth=0