6612 - reorganize layers

1 files changed, 992 insertions, 0 deletions

diff --git a/107trace.subx b/107trace.subx
new file mode 100644
index 00000000..cc6a7b43
--- /dev/null
+++ b/107trace.subx
@@ -0,0 +1,992 @@
+# primitives for emitting traces to a 'trace' stream, and for tests to make assertions on its contents
+#
+# A trace stream looks like a regular stream:
+#   write: int  # index at which writes go
+#   read: int  # index that we've read until
+#   data: (array byte)  # prefixed by size as usual
+# Usually the trace stream will be in a separate segment set aside for the purpose.
+#
+# primitives for operating on traces (arguments in quotes):
+#   - initialize-trace-stream: populates Trace-stream with a new segment of the given 'size'
+#   - trace: adds a 'line' to Trace-stream
+#   - check-trace-contains: scans from Trace-stream's start for a matching 'line', prints a 'message' to stderr on failure
+#   - check-trace-scans-to: scans from Trace-stream's read pointer for a matching 'line', prints a 'message' to stderr on failure
+
+== data
+
+# Handles are addresses created on the heap.
+# In safe Mu they'll be fat pointers. But in SubX they're just addresses, since
+# SubX programs never reclaim memory.
+
+Trace-stream:  # (handle stream byte)
+    0/imm32
+    # we don't have safe handles (fat pointers) yet
+
+Trace-segment:
+    0/imm32/curr
+    0/imm32/limit
+
+# Fake trace-stream for tests.
+# Also illustrates the layout of the real trace-stream (segment).
+_test-trace-stream:  # (stream byte)
+    # current write index
+    0/imm32
+    # current read index
+    0/imm32
+    # size
+    8/imm32
+    # data
+    00 00 00 00 00 00 00 00  # 8 bytes
+
+== 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
+
+# Allocate a new segment for the trace stream, initialize its size, and save its address to Trace-stream.
+# The Trace-stream segment will consist of variable-length lines separated by newlines (0x0a)
+initialize-trace-stream:  # 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
+    # ecx = n
+    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           1/r32/ecx   8/disp8         .                 # copy *(ebp+8) to ecx
+    # Trace-segment = new-segment(n)
+    # . . push args
+    68/push  Trace-segment/imm32
+    51/push-ecx
+    # . . call
+    e8/call  new-segment/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
+    # copy Trace-segment->curr to *Trace-stream
+    8b/copy                         0/mod/indirect  5/rm32/.disp32            .             .           0/r32/eax   Trace-segment/disp32              # copy *Trace-segment to eax
+#?     # watch point to catch Trace-stream leaks
+#? $watch-1:
+    89/copy                         0/mod/indirect  5/rm32/.disp32            .             .           0/r32/eax   Trace-stream/disp32               # copy eax to *Trace-stream
+    # Trace-stream->size = n - 12
+    # . ecx -= 12
+    81          5/subop/subtract    3/mod/direct    1/rm32/ecx    .           .             .           .           .               0xc/imm32         # subtract from ecx
+    # . Trace-stream->size = ecx
+    89/copy                         1/mod/*+disp8   0/rm32/eax    .           .             .           1/r32/ecx   8/disp8         .                 # copy ecx to *(eax+8)
+$initialize-trace-stream: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
+
+# Append a string to the given trace stream.
+# Silently give up if it's already full. Or truncate the string if there isn't enough room.
+trace:  # line: (addr array byte)
+    # . 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
+    52/push-edx
+    53/push-ebx
+    56/push-esi
+    57/push-edi
+    # var edi: (addr stream byte) = *Trace-stream
+    8b/copy                         0/mod/indirect  5/rm32/.disp32            .             .           7/r32/edi   Trace-stream/disp32               # copy *Trace-stream to edi
+    # esi = line
+    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .                         6/r32/esi   8/disp8         .                 # copy *(ebp+8) to esi
+    # var ecx: int = t->write
+    8b/copy                         0/mod/indirect  7/rm32/edi    .           .             .           1/r32/ecx   .               .                 # copy *edi to ecx
+    # var edx: int = t->size
+    8b/copy                         1/mod/*+disp8   7/rm32/edi    .           .             .           2/r32/edx   8/disp8         .                 # copy *(edi+8) to edx
+    # eax = _append-3(&t->data[t->write], &t->data[t->size], line)
+    # . . push line
+    56/push-esi
+    # . . push &t->data[t->size]
+    8d/copy-address                 1/mod/*+disp8   4/rm32/sib    7/base/edi  2/index/edx   .           3/r32/ebx   0xc/disp8       .                 # copy edi+edx+12 to ebx
+    53/push-ebx
+    # . . push &t->data[t->write]
+    8d/copy-address                 1/mod/*+disp8   4/rm32/sib    7/base/edi  1/index/ecx   .           3/r32/ebx   0xc/disp8       .                 # copy edi+ecx+12 to ebx
+    53/push-ebx
+    # . . call
+    e8/call  _append-3/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
+    # if (eax == 0) return
+    3d/compare-eax-and  0/imm32
+    74/jump-if-=  $trace:end/disp8
+    # t->write += eax
+    01/add                          0/mod/indirect  7/rm32/edi    .           .             .           0/r32/eax   .               .                 # add eax to *edi
+    # refresh ecx = t->write
+    8b/copy                         0/mod/indirect  7/rm32/edi    .           .             .           1/r32/ecx   .               .                 # copy *edi to ecx
+    # eax = _append-3(&t->data[t->write], &t->data[t->size], line)
+    # . . push line
+    68/push  Newline/imm32
+    # . . push &t->data[t->size]
+    8d/copy-address                 1/mod/*+disp8   4/rm32/sib    7/base/edi  2/index/edx   .           3/r32/ebx   0xc/disp8       .                 # copy edi+edx+12 to ebx
+    53/push-ebx
+    # . . push &t->data[t->write]
+    8d/copy-address                 1/mod/*+disp8   4/rm32/sib    7/base/edi  1/index/ecx   .           3/r32/ebx   0xc/disp8       .                 # copy edi+ecx+12 to ebx
+    53/push-ebx
+    # . . call
+    e8/call  _append-3/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
+    # t->write += eax
+    01/add                          0/mod/indirect  7/rm32/edi    .           .             .           0/r32/eax   .               .                 # add eax to *edi
+$trace:end:
+    # . 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/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
+    5d/pop-to-ebp
+    c3/return
+
+test-trace-single:
+    # push *Trace-stream
+    ff          6/subop/push        0/mod/indirect  5/rm32/.disp32            .             .           .           Trace-stream/disp32               # push *Trace-stream
+    # *Trace-stream = _test-trace-stream
+    b8/copy-to-eax  _test-trace-stream/imm32
+    89/copy                         0/mod/indirect  5/rm32/.disp32            .             .           0/r32/eax   Trace-stream/disp32               # copy eax to *Trace-stream
+    # clear-trace-stream()
+    e8/call  clear-trace-stream/disp32
+    # trace("Ab")
+    # . . push args
+    68/push  "Ab"/imm32
+    # . . call
+    e8/call  trace/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # check-ints-equal(*_test-trace-stream->data, 41/A 62/b 0a/newline 00, msg)
+    # . . push args
+    68/push  "F - test-trace-single"/imm32
+    68/push  0x0a6241/imm32/Ab-newline
+    # . . push *_test-trace-stream->data
+    b8/copy-to-eax  _test-trace-stream/imm32
+    ff          6/subop/push        1/mod/*+disp8   0/rm32/eax    .           .             .           .           0xc/disp8       .                 # push *(eax+12)
+    # . . call
+    e8/call  check-ints-equal/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
+    # pop into *Trace-stream
+    8f          0/subop/pop         0/mod/indirect  5/rm32/.disp32            .             .           .           Trace-stream/disp32               # pop into *Trace-stream
+    # end
+    c3/return
+
+test-trace-appends:
+    # push *Trace-stream
+    ff          6/subop/push        0/mod/indirect  5/rm32/.disp32            .             .           .           Trace-stream/disp32               # push *Trace-stream
+    # *Trace-stream = _test-trace-stream
+    b8/copy-to-eax  _test-trace-stream/imm32
+    89/copy                         0/mod/indirect  5/rm32/.disp32            .             .           0/r32/eax   Trace-stream/disp32               # copy eax to *Trace-stream
+    # clear-trace-stream()
+    e8/call  clear-trace-stream/disp32
+    # trace("C")
+    # . . push args
+    68/push  "C"/imm32
+    # . . call
+    e8/call  trace/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # trace("D")
+    # . . push args
+    68/push  "D"/imm32
+    # . . call
+    e8/call  trace/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # check-ints-equal(*_test-trace-stream->data, 43/C 0a/newline 44/D 0a/newline, msg)
+    # . . push args
+    68/push  "F - test-trace-appends"/imm32
+    68/push  0x0a440a43/imm32/C-newline-D-newline
+    # . . push *_test-trace-stream->data
+    b8/copy-to-eax  _test-trace-stream/imm32
+    ff          6/subop/push        1/mod/*+disp8   0/rm32/eax    .           .             .           .           0xc/disp8       .                 # push *(eax+12)
+    # . . call
+    e8/call  check-ints-equal/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
+    # pop into *Trace-stream
+    8f          0/subop/pop         0/mod/indirect  5/rm32/.disp32            .             .           .           Trace-stream/disp32               # pop into *Trace-stream
+    # end
+    c3/return
+
+test-trace-empty-line:
+    # push *Trace-stream
+    ff          6/subop/push        0/mod/indirect  5/rm32/.disp32            .             .           .           Trace-stream/disp32               # push *Trace-stream
+    # *Trace-stream = _test-trace-stream
+    b8/copy-to-eax  _test-trace-stream/imm32
+    89/copy                         0/mod/indirect  5/rm32/.disp32            .             .           0/r32/eax   Trace-stream/disp32               # copy eax to *Trace-stream
+    # clear-trace-stream()
+    e8/call  clear-trace-stream/disp32
+    # trace("")
+    # . . push args
+    68/push  ""/imm32
+    # . . call
+    e8/call  trace/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # check-ints-equal(*_test-trace-stream->data, 0, msg)
+    # . . push args
+    68/push  "F - test-trace-empty-line"/imm32
+    68/push  0/imm32
+    # . . push *_test-trace-stream->data
+    b8/copy-to-eax  _test-trace-stream/imm32
+    ff          6/subop/push        1/mod/*+disp8   0/rm32/eax    .           .             .           .           0xc/disp8       .                 # push *(eax+12)
+    # . . call
+    e8/call  check-ints-equal/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
+    # pop into *Trace-stream
+    8f          0/subop/pop         0/mod/indirect  5/rm32/.disp32            .             .           .           Trace-stream/disp32               # pop into *Trace-stream
+    # end
+    c3/return
+
+check-trace-contains:  # line: (addr string), msg: (addr string)
+    # . prologue
+    55/push-ebp
+    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
+    # rewind-stream(*Trace-stream)
+    # . . push args
+    ff          6/subop/push        0/mod/indirect  5/rm32/.disp32            .             .           .           Trace-stream/disp32               # push *Trace-stream
+    # . . call
+    e8/call  rewind-stream/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # check-trace-scans-to(line, msg)
+    # . . push args
+    ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       .                 # push *(ebp+12)
+    ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           8/disp8         .                 # push *(ebp+8)
+    # . . call
+    e8/call  check-trace-scans-to/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
+$check-trace-contains:end:
+    # . epilogue
+    89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
+    5d/pop-to-ebp
+    c3/return
+
+check-trace-scans-to:  # line: (addr string), msg: (addr string)
+    # . prologue
+    55/push-ebp
+    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
+    # . save registers
+    50/push-eax
+    # eax = trace-scan(line)
+    # . . push args
+    ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           8/disp8         .                 # push *(ebp+8)
+    # . . call
+    e8/call  trace-scan/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # check-ints-equal(eax, 1, msg)
+    # . . push args
+    ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       .                 # push *(ebp+12)
+    68/push  1/imm32
+    50/push-eax
+    # . . call
+    e8/call check-ints-equal/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
+$check-trace-scans-to:end:
+    # . restore registers
+    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
+
+# Start scanning from Trace-stream->read for 'line'. If found, update Trace-stream->read and return true.
+trace-scan:  # line: (addr array byte) -> result/eax: boolean
+    # pseudocode:
+    #   push Trace-stream->read
+    #   while true:
+    #     if Trace-stream->read >= Trace-stream->write
+    #       break
+    #     if next-line-matches?(Trace-stream, line)
+    #       skip-next-line(Trace-stream)
+    #       dump saved copy of Trace-stream->read
+    #       return true
+    #     skip-next-line(Trace-stream)
+    #   pop saved copy of Trace-stream->read
+    #   return false
+    #
+    # . 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 = *Trace-stream
+    8b/copy                         0/mod/indirect  5/rm32/.disp32            .             .           6/r32/esi   Trace-stream/disp32               # copy *Trace-stream to esi
+    # ecx = Trace-stream->write
+    8b/copy                         0/mod/indirect  6/rm32/esi    .           .             .           1/r32/ecx                   .                 # copy *esi to ecx
+    # push Trace-stream->read
+    ff          6/subop/push        1/mod/*+disp8   6/rm32/esi    .           .             .           .           4/disp8         .                 # push *(esi+4)
+$trace-scan:loop:
+    # if (Trace-stream->read >= Trace-stream->write) return false
+    39/compare                      1/mod/*+disp8   6/rm32/esi    .           .             .           1/r32/ecx   4/disp8         .                 # compare ecx with *(esi+4)
+    7d/jump-if->=  $trace-scan:false/disp8
+    # eax = next-line-matches?(Trace-stream, line)
+    # . . push args
+    ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           8/disp8         .                 # push *(ebp+8)
+    56/push-esi
+    # . . call
+    e8/call  next-line-matches?/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
+    # if (eax == false) continue
+    3d/compare-eax-and  0/imm32/false
+    74/jump-if-=  $trace-scan:continue/disp8
+$trace-scan:true:
+    # skip-next-line(Trace-stream)
+    # . . push args
+    56/push-esi
+    # . . call
+    e8/call  skip-next-line/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # dump saved copy of Trace-stream->read
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # return true
+    b8/copy-to-eax  1/imm32/true
+    eb/jump  $trace-scan:end/disp8
+$trace-scan:continue:
+    # skip-next-line(Trace-stream)
+    # . . push args
+    56/push-esi
+    # . . call
+    e8/call  skip-next-line/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    eb/jump  $trace-scan:loop/disp8
+$trace-scan:false:
+    # restore saved copy of Trace-stream->read
+    8f          0/subop/pop         1/mod/*+disp8   6/rm32/esi    .           .             .           .           4/disp8         .                 # pop to *(esi+4)
+    # return false
+    b8/copy-to-eax  0/imm32/false
+$trace-scan:end:
+    # . restore registers
+    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
+
+test-trace-scan-first:
+    # push *Trace-stream
+    ff          6/subop/push        0/mod/indirect  5/rm32/.disp32            .             .           .           Trace-stream/disp32               # push *Trace-stream
+    # setup
+    # . *Trace-stream = _test-trace-stream
+    b8/copy-to-eax  _test-trace-stream/imm32
+    89/copy                         0/mod/indirect  5/rm32/.disp32            .             .           0/r32/eax   Trace-stream/disp32               # copy eax to *Trace-stream
+    # . clear-trace-stream()
+    e8/call  clear-trace-stream/disp32
+    # . trace("Ab")
+    # . . push args
+    68/push  "Ab"/imm32
+    # . . call
+    e8/call  trace/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # eax = trace-scan("Ab")
+    # . . push args
+    68/push  "Ab"/imm32
+    # . . call
+    e8/call  trace-scan/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # check-ints-equal(eax, 1, msg)
+    # . . push args
+    68/push  "F - test-trace-scan-first"/imm32
+    68/push  1/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
+    # pop into *Trace-stream
+    8f          0/subop/pop         0/mod/indirect  5/rm32/.disp32            .             .           .           Trace-stream/disp32               # pop into *Trace-stream
+    # . end
+    c3/return
+
+test-trace-scan-skips-lines-until-found:
+    # push *Trace-stream
+    ff          6/subop/push        0/mod/indirect  5/rm32/.disp32            .             .           .           Trace-stream/disp32               # push *Trace-stream
+    # setup
+    # . *Trace-stream = _test-trace-stream
+    b8/copy-to-eax  _test-trace-stream/imm32
+    89/copy                         0/mod/indirect  5/rm32/.disp32            .             .           0/r32/eax   Trace-stream/disp32               # copy eax to *Trace-stream
+    # . clear-trace-stream()
+    e8/call  clear-trace-stream/disp32
+    # . trace("Ab")
+    # . . push args
+    68/push  "Ab"/imm32
+    # . . call
+    e8/call  trace/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # . trace("cd")
+    # . . push args
+    68/push  "cd"/imm32
+    # . . call
+    e8/call  trace/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # eax = trace-scan("cd")
+    # . . push args
+    68/push  "cd"/imm32
+    # . . call
+    e8/call  trace-scan/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # check-ints-equal(eax, 1, msg)
+    # . . push args
+    68/push  "F - test-trace-scan-skips-lines-until-found"/imm32
+    68/push  1/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
+    # pop into *Trace-stream
+    8f          0/subop/pop         0/mod/indirect  5/rm32/.disp32            .             .           .           Trace-stream/disp32               # pop into *Trace-stream
+    # . end
+    c3/return
+
+test-trace-second-scan-starts-where-first-left-off:
+    # push *Trace-stream
+    ff          6/subop/push        0/mod/indirect  5/rm32/.disp32            .             .           .           Trace-stream/disp32               # push *Trace-stream
+    # setup
+    # . *Trace-stream = _test-trace-stream
+    b8/copy-to-eax  _test-trace-stream/imm32
+    89/copy                         0/mod/indirect  5/rm32/.disp32            .             .           0/r32/eax   Trace-stream/disp32               # copy eax to *Trace-stream
+    # . clear-trace-stream()
+    e8/call  clear-trace-stream/disp32
+    # . trace("Ab")
+    # . . push args
+    68/push  "Ab"/imm32
+    # . . call
+    e8/call  trace/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # . eax = trace-scan("Ab")
+    # . . push args
+    68/push  "Ab"/imm32
+    # . . call
+    e8/call  trace-scan/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # second scan fails
+    # . eax = trace-scan("Ab")
+    # . . push args
+    68/push  "Ab"/imm32
+    # . . call
+    e8/call  trace-scan/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # check-ints-equal(eax, 0, msg)
+    # . . push args
+    68/push  "F - test-trace-second-scan-starts-where-first-left-off"/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
+    # pop into *Trace-stream
+    8f          0/subop/pop         0/mod/indirect  5/rm32/.disp32            .             .           .           Trace-stream/disp32               # pop into *Trace-stream
+    # . end
+    c3/return
+
+test-trace-scan-failure-leaves-read-index-untouched:
+    # push *Trace-stream
+    ff          6/subop/push        0/mod/indirect  5/rm32/.disp32            .             .           .           Trace-stream/disp32               # push *Trace-stream
+    # setup
+    # . *Trace-stream = _test-trace-stream
+    b8/copy-to-eax  _test-trace-stream/imm32
+    89/copy                         0/mod/indirect  5/rm32/.disp32            .             .           0/r32/eax   Trace-stream/disp32               # copy eax to *Trace-stream
+    # . clear-trace-stream()
+    e8/call  clear-trace-stream/disp32
+    # . trace("Ab")
+    # . . push args
+    68/push  "Ab"/imm32
+    # . . call
+    e8/call  trace/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # . check-ints-equal(_test-trace-stream->read, 0, msg)
+    # . . push args
+    68/push  "F - test-trace-second-scan-starts-where-first-left-off/precondition-failure"/imm32
+    68/push  0/imm32
+    b8/copy-to-eax  _test-trace-stream/imm32
+    ff          6/subop/push        1/mod/*+disp8   0/rm32/eax    .           .             .           .           4/disp8         .                 # push *(eax+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
+    # perform a failing scan
+    # . eax = trace-scan("Ax")
+    # . . push args
+    68/push  "Ax"/imm32
+    # . . call
+    e8/call  trace-scan/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # no change in read index
+    # . check-ints-equal(_test-trace-stream->read, 0, msg)
+    # . . push args
+    68/push  "F - test-trace-second-scan-starts-where-first-left-off"/imm32
+    68/push  0/imm32
+    b8/copy-to-eax  _test-trace-stream/imm32
+    ff          6/subop/push        1/mod/*+disp8   0/rm32/eax    .           .             .           .           4/disp8         .                 # push *(eax+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
+    # pop into *Trace-stream
+    8f          0/subop/pop         0/mod/indirect  5/rm32/.disp32            .             .           .           Trace-stream/disp32               # pop into *Trace-stream
+    # . end
+    c3/return
+
+next-line-matches?:  # t: (addr stream byte), line: (addr array byte) -> result/eax: boolean
+    # pseudocode:
+    #   while true:
+    #     if (currl >= maxl) break
+    #     if (currt >= maxt) return false
+    #     if (*currt != *currl) return false
+    #     ++currt
+    #     ++currl
+    #   return *currt == '\n'
+    #
+    # . prologue
+    55/push-ebp
+    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
+    # . save registers
+    51/push-ecx
+    52/push-edx
+    53/push-ebx
+    56/push-esi
+    57/push-edi
+    # edx = line
+    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .                         2/r32/edx   0xc/disp8       .                 # copy *(ebp+12) to edx
+    # var currl/esi: (addr byte) = line->data
+    # . esi = line/edx->data
+    8d/copy-address                 1/mod/*+disp8   2/rm32/edx    .           .             .           6/r32/esi   4/disp8         .                 # copy edx+4 to esi
+    # var maxl/ecx: (addr byte) = &line->data[line->size]
+    # . eax = line/edx->size
+    8b/copy                         0/mod/indirect  2/rm32/edx    .           .                         0/r32/eax   .               .                 # copy *edx to eax
+    # . maxl = &line->data[line->size]
+    8d/copy-address                 0/mod/indirect  4/rm32/sib    6/base/esi  0/index/eax   .           1/r32/ecx   .               .                 # copy edx+eax to ecx
+    # edi = t
+    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .                         7/r32/edi   8/disp8         .                 # copy *(ebp+8) to edi
+    # var ebx: (addr byte) = t->data
+    8d/copy-address                 1/mod/*+disp8   7/rm32/edi    .           .             .           3/r32/ebx   0xc/disp8       .                 # copy edi+12 to ebx
+    # var maxt/edx: (addr byte) = &t->data[t->write]
+    # . eax = t->write
+    8b/copy                         0/mod/indirect  7/rm32/edi    .           .                         0/r32/eax   .               .                 # copy *edi to eax
+    # . maxt = &t->data[t->write]
+    8d/copy-address                 0/mod/indirect  4/rm32/sib    3/base/ebx  0/index/eax   .           2/r32/edx   .               .                 # copy ebx+eax to edx
+    # var currt/edi: (addr byte) = &t->data[t->read]
+    # . eax = t/edi->read
+    8b/copy                         1/mod/*+disp8   7/rm32/edi    .           .                         0/r32/eax   4/disp8         .                 # copy *(edi+4) to eax
+    # . currt = &t->data[t->read]
+    8d/copy-address                 0/mod/indirect  4/rm32/sib    3/base/ebx  0/index/eax   .           7/r32/edi   .               .                 # copy ebx+eax to edi
+$next-line-matches?:loop:
+    # if (currl >= maxl) break
+    39/compare                      3/mod/direct    6/rm32/esi    .           .             .           1/r32/ecx   .               .                 # compare esi and ecx
+    73/jump-if-addr>=  $next-line-matches?:break/disp8
+    # if (currt >= maxt) return false
+    # . eax = false
+    b8/copy-to-eax  0/imm32/false
+    39/compare                      3/mod/direct    7/rm32/edi    .           .             .           2/r32/edx   .               .                 # compare edi and edx
+    73/jump-if-addr>=  $next-line-matches?:end/disp8
+    # if (*currt != *currl) return false
+    31/xor                          3/mod/direct    0/rm32/eax    .           .             .           0/r32/eax   .               .                 # clear eax
+    31/xor                          3/mod/direct    3/rm32/eax    .           .             .           3/r32/eax   .               .                 # clear ebx
+    # . eax: byte = *currt
+    8a/copy-byte                    0/mod/indirect  7/rm32/edi    .           .                         0/r32/eax   .               .                 # copy *edi to eax
+    # . ebx: byte = *currl
+    8a/copy-byte                    0/mod/indirect  6/rm32/esi    .           .                         3/r32/ebx   .               .                 # copy *esi to ebx
+    # . eax >= ebx
+    39/compare                      3/mod/direct    0/rm32/eax    .           .             .           3/r32/ebx   .               .                 # compare eax and ebx
+    # . eax = false
+    b8/copy-to-eax  0/imm32/false
+    75/jump-if-!=  $next-line-matches?:end/disp8
+    # ++currt
+    47/increment-edi
+    # ++currl
+    46/increment-esi
+    eb/jump  $next-line-matches?:loop/disp8
+$next-line-matches?:break:
+    # return *currt == '\n'
+    31/xor                          3/mod/direct    0/rm32/eax    .           .             .           0/r32/eax   .               .                 # clear eax
+    # . eax: byte = *currt
+    8a/copy-byte                    0/mod/indirect  7/rm32/edi    .           .                         0/r32/eax   .               .                 # copy *edi to eax
+    3d/compare-eax-and  0xa/imm32/newline
+    # . eax = false
+    b8/copy-to-eax  1/imm32/true
+    74/jump-if-=  $next-line-matches?:end/disp8
+    b8/copy-to-eax  0/imm32/true
+$next-line-matches?:end:
+    # . restore registers
+    5f/pop-to-edi
+    5e/pop-to-esi
+    5b/pop-to-ebx
+    5a/pop-to-edx
+    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
+
+test-next-line-matches?-no-match-1:
+    # next line of "ABABA" does not match "blah blah"
+    # . eax = next-line-matches?(_test-stream-line-ABABA, "blah blah")
+    # . . push args
+    68/push  "blah blah"/imm32
+    68/push  _test-stream-line-ABABA/imm32
+    # . . call
+    e8/call  next-line-matches?/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
+    # . check-ints-equal(eax, 0, msg)
+    # . . push args
+    68/push  "F - test-next-line-matches?-no-match-1"/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
+    c3/return
+
+test-next-line-matches?-no-match-2:
+    # next line of "ABABA" does not match ""
+    # . eax = next-line-matches?(_test-stream-line-ABABA, "")
+    # . . push args
+    68/push  ""/imm32
+    68/push  _test-stream-line-ABABA/imm32
+    # . . call
+    e8/call  next-line-matches?/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
+    # . check-ints-equal(eax, 0, msg)
+    # . . push args
+    68/push  "F - test-next-line-matches?-no-match-2"/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
+    c3/return
+
+test-next-line-matches?-no-match-3:
+    # next line of "ABABA" does not match  "AA"
+    # . eax = next-line-matches?(_test-stream-line-ABABA, "AA")
+    # . . push args
+    68/push  "AA"/imm32
+    68/push  _test-stream-line-ABABA/imm32
+    # . . call
+    e8/call  next-line-matches?/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
+    # . check-ints-equal(eax, 0, msg)
+    # . . push args
+    68/push  "F - test-next-line-matches?-no-match-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
+    c3/return
+
+test-next-line-matches?-match:
+    # next line of "ABABA" matches "ABABA"
+    # . eax = next-line-matches?(_test-stream-line-ABABA, "ABABA")
+    # . . push args
+    68/push  "ABABA"/imm32
+    68/push  _test-stream-line-ABABA/imm32
+    # . . call
+    e8/call  next-line-matches?/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
+    # . check-ints-equal(eax, 1, msg)
+    # . . push args
+    68/push  "F - test-next-line-matches?-match"/imm32
+    68/push  1/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
+    c3/return
+
+# move t->read to _after_ next newline
+skip-next-line:  # t: (addr stream byte)
+    # pseudocode:
+    #   max = &t->data[t->write]
+    #   i = t->read
+    #   curr = &t->data[t->read]
+    #   while true
+    #     if (curr >= max) break
+    #     ++i
+    #     if (*curr == '\n') break
+    #     ++curr
+    #   t->read = i
+    #
+    # . 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
+    52/push-edx
+    53/push-ebx
+    # ecx = t
+    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .                         1/r32/ecx   8/disp8         .                 # copy *(ebp+8) to ecx
+    # edx = t->data
+    8d/copy-address                 1/mod/*+disp8   1/rm32/ecx    .           .             .           2/r32/edx   0xc/disp8       .                 # copy ecx+12 to edx
+    # eax = t->write
+    8b/copy                         0/mod/indirect  1/rm32/ecx    .           .             .           0/r32/eax   .               .                 # copy *ecx to eax
+    # var max/ebx: (addr byte) = &t->data[t->write]
+    8d/copy-address                 0/mod/indirect  4/rm32/sib    2/base/edx  0/index/eax   .           3/r32/ebx   .               .                 # copy edx+eax to ebx
+    # eax = t->read
+    8b/copy                         1/mod/*+disp8   1/rm32/ecx    .           .             .           0/r32/eax   4/disp8         .                 # copy *(ecx+4) to edx
+    # var curr/ecx: (addr byte) = &t->data[t->read]
+    8d/copy-address                 0/mod/indirect  4/rm32/sib    2/base/edx  0/index/eax   .           1/r32/ecx   .               .                 # copy edx+eax to ecx
+    # var i/edx: int = t->read
+    89/copy                         3/mod/direct    2/rm32/edx    .           .             .           0/r32/eax   .               .                 # copy eax to edx
+$skip-next-line:loop:
+    # if (curr >= max) break
+    39/compare                      3/mod/direct    1/rm32/ecx    .           .             .           3/r32/ebx   .               .                 # compare ecx and ebx
+    73/jump-if-addr>=  $skip-next-line:end/disp8
+    # ++i
+    42/increment-edx
+    # if (*curr == '\n') break
+    31/xor                          3/mod/direct    0/rm32/eax    .           .             .           0/r32/eax   .               .                 # clear eax
+    8a/copy-byte                    0/mod/indirect  1/rm32/ecx    .           .             .           0/r32/eax   .               .                 # copy *ecx to eax
+    3d/compare-eax-and  0a/imm32/newline
+    74/jump-if-=  $skip-next-line:end/disp8
+    # ++curr
+    41/increment-ecx
+    # loop
+    eb/jump  $skip-next-line:loop/disp8
+$skip-next-line:end:
+    # ecx = t
+    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .                         1/r32/ecx   8/disp8         .                 # copy *(ebp+8) to ecx
+    # t->read = i
+    89/copy                         1/mod/*+disp8   1/rm32/ecx    .           .             .           2/r32/edx   4/disp8         .                 # copy edx to *(ecx+4)
+    # . restore registers
+    5b/pop-to-ebx
+    5a/pop-to-edx
+    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-skip-next-line-empty:
+    # skipping next line in empty stream leaves read pointer at 0
+    # . skip-next-line(_test-stream-empty)
+    # . . push args
+    68/push  _test-stream-empty/imm32
+    # . . call
+    e8/call  skip-next-line/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # . check-ints-equal(_test-stream-empty->read, 0, msg)
+    # . . push args
+    68/push  "F - test-skip-next-line-empty"/imm32
+    68/push  0/imm32
+    b8/copy-to-eax  _test-stream-empty/imm32
+    8b/copy                         1/mod/*+disp8   0/rm32/eax    .           .             .           0/r32/eax   4/disp8         .                 # copy *(eax+4) to eax
+    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
+    c3/return
+
+test-skip-next-line-filled:
+    # skipping next line increments read pointer by length of line + 1 (for newline)
+    # . skip-next-line(_test-stream-filled)
+    # . . push args
+    68/push  _test-stream-filled/imm32
+    # . . call
+    e8/call  skip-next-line/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+    # . check-ints-equal(_test-stream-filled->read, 5, msg)
+    # . . push args
+    68/push  "F - test-skip-next-line-filled"/imm32
+    68/push  5/imm32
+    b8/copy-to-eax  _test-stream-filled/imm32
+    8b/copy                         1/mod/*+disp8   0/rm32/eax    .           .             .           0/r32/eax   4/disp8         .                 # copy *(eax+4) to eax
+    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
+    c3/return
+
+clear-trace-stream:
+    # . prologue
+    55/push-ebp
+    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
+    # clear-stream(*Trace-stream)
+    # . . push args
+    ff          6/subop/push        0/mod/indirect  5/rm32/.disp32            .             .           .           Trace-stream/disp32               # push *Trace-stream
+    # . . call
+    e8/call  clear-stream/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+$clear-trace-stream:end:
+    # . epilogue
+    89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
+    5d/pop-to-ebp
+    c3/return
+
+# - helpers
+
+# 3-argument variant of _append
+_append-3:  # out: (addr byte), outend: (addr byte), s: (addr array byte) -> num_bytes_appended/eax
+    # . prologue
+    55/push-ebp
+    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
+    # . save registers
+    51/push-ecx
+    # eax = _append-4(out, outend, &s->data[0], &s->data[s->size])
+    # . . push &s->data[s->size]
+    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .                         0/r32/eax   0x10/disp8      .                 # copy *(ebp+16) to eax
+    8b/copy                         0/mod/indirect  0/rm32/eax    .           .             .           1/r32/ecx   .               .                 # copy *eax to ecx
+    8d/copy-address                 1/mod/*+disp8   4/rm32/sib    0/base/eax  1/index/ecx   .           1/r32/ecx   4/disp8         .                 # copy eax+ecx+4 to ecx
+    51/push-ecx
+    # . . push &s->data[0]
+    8d/copy-address                 1/mod/*+disp8   0/rm32/eax    .           .             .           1/r32/ecx   4/disp8         .                 # copy eax+4 to ecx
+    51/push-ecx
+    # . . push outend
+    ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       .                 # push *(ebp+12)
+    # . . push out
+    ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           8/disp8         .                 # push *(ebp+8)
+    # . . call
+    e8/call  _append-4/disp32
+    # . . discard args
+    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0x10/imm32        # add to esp
+$_append-3:end:
+    # . restore registers
+    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
+
+# 4-argument variant of _append
+_append-4:  # out: (addr byte), outend: (addr byte), in: (addr byte), inend: (addr byte) -> num_bytes_appended/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
+    52/push-edx
+    53/push-ebx
+    56/push-esi
+    57/push-edi
+    # num_bytes_appended = 0
+    b8/copy-to-eax  0/imm32
+    # edi = out
+    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           7/r32/edi   8/disp8         .                 # copy *(ebp+8) to edi
+    # edx = outend
+    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           2/r32/edx   0xc/disp8       .                 # copy *(ebp+12) to edx
+    # esi = in
+    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           6/r32/esi   0x10/disp8      .                 # copy *(ebp+16) to esi
+    # ecx = inend
+    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           1/r32/ecx   0x14/disp8      .                 # copy *(ebp+20) to ecx
+$_append-4:loop:
+    # if (in >= inend) break
+    39/compare                      3/mod/direct    6/rm32/esi    .           .             .           1/r32/ecx   .               .                 # compare esi with ecx
+    73/jump-if-addr>=  $_append-4:end/disp8
+    # if (out >= outend) abort  # just to catch test failures fast
+    39/compare                      3/mod/direct    7/rm32/edi    .           .             .           2/r32/edx   .               .                 # compare edi with edx
+    73/jump-if-addr>=  $_append-4:abort/disp8
+    # *out = *in
+    8a/copy-byte                    0/mod/indirect  6/rm32/esi    .           .             .           3/r32/BL    .               .                 # copy byte at *esi to BL
+    88/copy-byte                    0/mod/indirect  7/rm32/edi    .           .             .           3/r32/BL    .               .                 # copy byte at BL to *edi
+    # ++num_bytes_appended
+    40/increment-eax
+    # ++in
+    46/increment-esi
+    # ++out
+    47/increment-edi
+    eb/jump  $_append-4:loop/disp8
+$_append-4:end:
+    # . restore registers
+    5f/pop-to-edi
+    5e/pop-to-esi
+    5b/pop-to-ebx
+    5a/pop-to-edx
+    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
+
+$_append-4:abort:
+    # . _write(2/stderr, error)
+    # . . push args
+    68/push  "stream overflow\n"/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
+    e8/call  syscall_exit/disp32
+    # never gets here
+
+== data
+
+_test-stream-line-ABABA:  # (stream byte)
+    # write
+    8/imm32
+    # read
+    0/imm32
+    # size
+    8/imm32
+    # data
+    41 42 41 42 41 0a 00 00  # 8 bytes
+
+_test-stream-empty:  # (stream byte)
+    # write
+    0/imm32
+    # read
+    0/imm32
+    # size
+    8/imm32
+    # data
+    00 00 00 00 00 00 00 00  # 8 bytes
+
+_test-stream-filled:  # (stream byte)
+    # write
+    8/imm32
+    # read
+    0/imm32
+    # size
+    8/imm32
+    # data
+    41 41 41 41 0a 41 41 41  # 8 bytes
+
+# . . vim:nowrap:textwidth=0