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# A sketch of Mu-style handles or kinda-safe pointers, that add a modicum of
# checking to dynamically allocated memory.
#
# This approach avoids using 'allocate' directly in favor of two primitives:
#   - 'new', which allocates some space (the 'payload'), stores the address
#     along with an opaque 'alloc id' in a 'handle', and prepends the same
#     alloc id to the payload.
#   - 'lookup', which checks that the alloc id at the start of a handle matches
#     the alloc id at the start of the payload before returning the address.
#
# Layout of a handle:
#   offset 0: alloc id
#   offset 4: address
#
# To run (from the subx directory):
#   $ ./subx translate *.subx apps/handle.subx -o apps/handle
#   $ ./subx run apps/handle
# Expected result is a hard abort:
#   ........lookup failed
# (This file is a prototype, so the tests in this file aren't real tests. Don't
# expect to run anything in the same process after they've completed.)

== 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

# no Entry; the standard library runs all tests by default

new:  # ad : (address allocation-descriptor), n : int, out : (address handle)
    # . prolog
    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
    52/push-EDX
    # ECX = n+4
    8b/copy                         1/mod/*+disp8   5/rm32/EBP    .           .             .           1/r32/ECX   0xc/disp8       .                 # copy *(EBP+12) to ECX
    81          0/subop/add         3/mod/direct    1/rm32/ECX    .           .             .           .           .               4/imm32           # add to ECX
    # EAX = allocate(ad, ECX)
    # . . push args
    51/push-ECX
    ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           8/disp8         .                 # push *(EBP+8)
    # . . call
    e8/call  allocate/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    # EDX = out
    8b/copy                         1/mod/*+disp8   5/rm32/EBP    .           .             .           2/r32/EDX   0x10/disp8      .                 # copy *(EBP+16) to EDX
    # out->address = EAX
    89/copy                         1/mod/*+disp8   2/rm32/EDX    .           .             .           0/r32/EAX   4/disp8         .                 # copy EAX to *(EDX+4)
    # if (EAX == 0) out->alloc_id = 0, return
    3d/compare-EAX-and  0/imm32
    75/jump-if-not-equal  $new:continue/disp8
    c7          0/subop/copy        0/mod/indirect  2/rm32/EDX    .           .             .           .           .               0/imm32           # copy to *EDX
    eb/jump  $new:end/disp8
$new:continue:
    # otherwise:
    # ECX = *Next-alloc-id
    8b/copy                         0/mod/indirect  5/rm32/.disp32            .             .           1/r32/ECX   Next-alloc-id/disp32              # copy *Next-alloc-id to ECX
    # *EAX = *Next-alloc-id/ECX
    89/copy                         0/mod/indirect  0/rm32/EAX    .           .             .           1/r32/ECX   .               .                 # copy ECX to *EAX
    # out->alloc_id = *Next-alloc-id
    89/copy                         0/mod/indirect  2/rm32/EDX    .           .             .           1/r32/ECX   .               .                 # copy ECX to *EDX
    # increment *Next-alloc-id
    ff          0/subop/increment   0/mod/indirect  5/rm32/.disp32            .             .           .           Next-alloc-id/disp32              # increment *Next-alloc-id
$new:end:
    # . restore registers
    5a/pop-to-EDX
    59/pop-to-ECX
    58/pop-to-EAX
    # . epilog
    89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
    5d/pop-to-EBP
    c3/return

test-new:
    # . prolog
    55/push-EBP
    89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
    # *Next-alloc-id = 0x34
    c7          0/subop/copy        0/mod/indirect  5/rm32/.disp32            .             .           .     Next-alloc-id/disp32  0x34/imm32        # copy to *Next-alloc-id
    # var handle/ECX = {0, 0}
    68/push  0/imm32/address
    68/push  0/imm32/alloc-id
    89/copy                         3/mod/direct    1/rm32/ECX    .           .             .           4/r32/ESP   .               .                 # copy ESP to ECX
    # new(Heap, 2, handle/ECX)
    # . . push args
    51/push-ECX
    68/push  2/imm32/size
    68/push  Heap/imm32
    # . . call
    e8/call  new/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
    # check-ints-equal(handle->alloc_id, 0x34, msg)
    # . . push args
    68/push  "F - test-new: alloc id of handle"/imm32
    68/push  0x34/imm32
    ff          6/subop/push        0/mod/indirect  1/rm32/ECX    .           .             .           .           .               .                 # push *ECX
    # . . 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-ints-equal(*handle->address, 0x34, msg)
    # . . push args
    68/push  "F - test-new: alloc id of payload"/imm32
    68/push  0x34/imm32
    8b/copy                         1/mod/*+disp8   1/rm32/ECX    .           .             .           2/r32/EDX   4/disp8         .                 # copy *(ECX+4) to EDX
    ff          6/subop/push        0/mod/indirect  2/rm32/EDX    .           .             .           .           .               .                 # push *EDX
    # . . 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-ints-equal(*Next-alloc-id, 0x35)
    # . . push args
    68/push  "F - test-new: next alloc id"/imm32
    68/push  0x35/imm32
    ff          6/subop/push        0/mod/indirect  5/rm32/.disp32            .             .           .           Next-alloc-id/disp32              # copy to *Next-alloc-id
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
    # clean up
    # . *Next-alloc-id = 1
    c7          0/subop/copy        0/mod/indirect  5/rm32/.disp32            .             .           .     Next-alloc-id/disp32  1/imm32           # copy to *Next-alloc-id
    # . epilog
    89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
    5d/pop-to-EBP
    c3/return

test-new-failure:
    # . prolog
    55/push-EBP
    89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
    # . *Next-alloc-id = 0x34
    c7          0/subop/copy        0/mod/indirect  5/rm32/.disp32            .             .           .           Next-alloc-id/disp32  0x34/imm32  # copy to *Next-alloc-id
    # define an allocation-descriptor with no space left
    # . var ad/EAX : (address allocation-descriptor) = {0x10, 0x10}
    68/push  0x10/imm32/limit
    68/push  0x10/imm32/curr
    89/copy                         3/mod/direct    0/rm32/EAX    .           .             .           4/r32/ESP   .               .                 # copy ESP to EAX
    # . var handle/ECX = {random, random}
    68/push  1234/imm32/address
    68/push  5678/imm32/alloc-id
    89/copy                         3/mod/direct    1/rm32/ECX    .           .             .           4/r32/ESP   .               .                 # copy ESP to ECX
    # try to allocate
    # . new(ad, 2, handle/ECX)
    # . . push args
    51/push-ECX
    68/push  2/imm32/size
    50/push-EAX
    # . . call
    e8/call  new/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
    # handle should be cleared
    # . check-ints-equal(handle->alloc_id, 0, msg)
    # . . push args
    68/push  "F - test-new-failure: alloc id of handle"/imm32
    68/push  0/imm32
    ff          6/subop/push        0/mod/indirect  1/rm32/ECX    .           .             .           .           .               .                 # push *ECX
    # . . 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-ints-equal(handle->address, 0, msg)
    # . . push args
    68/push  "F - test-new-failure: address of handle"/imm32
    68/push  0/imm32
    ff          6/subop/push        1/mod/*+disp8   1/rm32/ECX    .           .             .           .           4/disp8         .                 # push *(ECX+4)
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
    # Next-alloc-id should be unmodified
    # . check-ints-equal(*Next-alloc-id, 0x34)
    # . . push args
    68/push  "F - test-new-failure: next alloc id"/imm32
    68/push  0x34/imm32
    ff          6/subop/push        0/mod/indirect  5/rm32/.disp32            .             .           .           Next-alloc-id/disp32              # copy to *Next-alloc-id
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
    # clean up
    # . *Next-alloc-id = 1
    c7          0/subop/copy        0/mod/indirect  5/rm32/.disp32            .             .           .     Next-alloc-id/disp32  1/imm32           # copy to *Next-alloc-id
    # . epilog
    89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
    5d/pop-to-EBP
    c3/return

lookup:  # h : (handle T) -> EAX : (address T)
    # . prolog
    55/push-EBP
    89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
    # - as a proof of concept for future inlining, uses no general-purpose registers besides the output (EAX)
    # EAX = handle
    8b/copy                         1/mod/*+disp8   5/rm32/EBP    .           .             .           0/r32/EAX   8/disp8         .                 # copy *(EBP+8) to EAX
    # - inline {
    # push handle->address
    ff          6/subop/push        1/mod/*+disp8   1/rm32/ECX    .           .             .           .           4/disp8         .                 # push *(EAX+4)
    # EAX = handle->alloc_id
    8b/copy                         0/mod/indirect  0/rm32/EAX    .           .             .           .           .               .                 # copy *EAX to EAX
    # if (EAX != *ESP) abort
    39/compare                      0/mod/indirect  4/rm32/sib    4/base/ESP  4/index/none  .           0/r32/EAX   .               .                 # compare *ESP and EAX
    75/jump-if-not-equal  $lookup:fail/disp8
    # return ESP+4
    58/pop-to-EAX
    05/add-to-EAX  4/imm32
    # - }
    # . epilog
    89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
    5d/pop-to-EBP
    c3/return
$lookup:fail:
    # . _write(2/stderr, msg)
    # . . push args
    68/push  "lookup failed"/imm32
    68/push  2/imm32/stderr
    # . . call
    e8/call  _write/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    # . syscall(exit, 1)
    bb/copy-to-EBX  1/imm32/exit-status
    b8/copy-to-EAX  1/imm32/exit
    cd/syscall  0x80/imm8

test-lookup-success:
    # . prolog
    55/push-EBP
    89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
    # . save registers
    # var handle/ECX = {0, 0}
    68/push  0/imm32/address
    68/push  0/imm32/alloc-id
    89/copy                         3/mod/direct    1/rm32/ECX    .           .             .           4/r32/ESP   .               .                 # copy ESP to ECX
    # var old_top/EDX = Heap->curr
    8b/copy                         0/mod/indirect  5/rm32/.disp32            .             .           2/r32/EDX   Heap/disp32     .                 # copy *Heap to EDX
    # new(Heap, 2, handle)
    # . . push args
    51/push-ECX
    68/push  2/imm32/size
    68/push  Heap/imm32
    # . . call
    e8/call  new/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
    # EAX = lookup(handle)
    # . . push args
    51/push-ECX
    # . . call
    e8/call  lookup/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
    # EAX contains old top of Heap, except skipping the alloc id in the payload
    # . check-ints-equal(EAX, old_top+4, msg)
    # . . push args
    68/push  "F - test-lookup-success"/imm32
    81          0/subop/add         3/mod/direct    2/rm32/EDX    .           .             .           .           .               4/imm32           # add to EDX
    52/push-EDX
    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
    # clean up
    # . *Next-alloc-id = 1
    c7          0/subop/copy        0/mod/indirect  5/rm32/.disp32            .             .           .     Next-alloc-id/disp32  1/imm32           # copy to *Next-alloc-id
    # . restore registers
    5a/pop-to-EDX
    59/pop-to-ECX
    # . epilog
    89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
    5d/pop-to-EBP
    c3/return

test-lookup-failure:
    # . prolog
    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
    52/push-EDX
    # var h1/ECX = {0, 0}
    68/push  0/imm32/address
    68/push  0/imm32/alloc-id
    89/copy                         3/mod/direct    1/rm32/ECX    .           .             .           4/r32/ESP   .               .                 # copy ESP to ECX
    # var old_top/EBX = Heap->curr
    8b/copy                         0/mod/indirect  5/rm32/.disp32            .             .           3/r32/EBX   Heap/disp32     .                 # copy *Heap to EBX
    # first allocation, to h1
    # . new(Heap, 2, h1)
    # . . push args
    51/push-ECX
    68/push  2/imm32/size
    68/push  Heap/imm32
    # . . call
    e8/call  new/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
    # reset Heap->curr to mimic reclamation
    89/copy                         0/mod/indirect  5/rm32/.disp32            .             .           3/r32/EBX   Heap/disp32     .                 # copy EBX to *Heap
    # second allocation that returns the same address as the first
    # var h2/EDX = {0, 0}
    68/push  0/imm32/address
    68/push  0/imm32/alloc-id
    89/copy                         3/mod/direct    2/rm32/EDX    .           .             .           4/r32/ESP   .               .                 # copy ESP to EDX
    # . new(Heap, 2, h2)
    # . . push args
    52/push-EDX
    68/push  2/imm32/size
    68/push  Heap/imm32
    # . . call
    e8/call  new/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
    # check-ints-equal(h1->address, h2->address, msg)
    # . . push args
    68/push  "F - test-lookup-failure"/imm32
    ff          6/subop/push        1/mod/*+disp8   2/rm32/ECX    .           .             .           .           4/disp8         .                 # push *(EDX+4)
    ff          6/subop/push        1/mod/*+disp8   1/rm32/ECX    .           .             .           .           4/disp8         .                 # push *(ECX+4)
    # . . call
    e8/call  check-ints-equal/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               0xc/imm32         # add to ESP
    # lookup(h1) should crash
    # . . push args
    51/push-ECX
    # . . call
    e8/call  lookup/disp32
    # should never get past this point
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
    # clean up
    # . *Next-alloc-id = 1
    c7          0/subop/copy        0/mod/indirect  5/rm32/.disp32            .             .           .     Next-alloc-id/disp32  1/imm32           # copy to *Next-alloc-id
    # . restore registers
    5a/pop-to-EDX
    59/pop-to-ECX
    58/pop-to-EAX
    # . epilog
    89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
    5d/pop-to-EBP
    c3/return

== data

# Monotonically increasing counter for calls to 'new'
Next-alloc-id:
    1/imm32

# . . vim:nowrap:textwidth=0