apps/ex5.mu


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# Draw a single line of ASCII text using the built-in font (GNU unifont)
# Also demonstrates bounds-checking _before_ drawing.
#
# To build a disk image:
#   ./translate apps/ex5.mu        # emits code.img
# To run:
#   qemu-system-i386 code.img
#
# Expected output: text in green near the top-left corner of screen

fn main screen: (addr screen), keyboard: (addr keyboard), data-disk: (addr disk) {
  var dummy/eax: int <- draw-text-rightward screen, "hello from baremetal Mu!", 0x10/x, 0x400/xmax, 0x10/y, 0xa/fg, 0/bg
  dummy <- draw-text-rightward screen, "you shouldn't see this", 0x10/x, 0xa0/xmax, 0x30/y, 3/fg, 0/bg  # xmax is too narrow
}
# 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 length as usual
# In a real trace the data will be in a special segment set aside for the purpose.
#
# primitives for operating on traces:
#   - initialize-trace-stream (update global variable)
#   - trace: stream, string
#   - die: stream (exit(1) if using real trace)
#   - check-trace-contains: stream, string/line, string/message (scans only from stream's read pointer, prints message to stderr on failure, updates stream's read pointer)
#   - scan-to-next-line: stream (advance read pointer past next newline)
#
# Traces are very fundamental, so many of the helpers we create here won't be
# used elsewhere; we'll switch to more bounds-checked variants. But here we get
# bounds-checking for free; we allocate a completely disjoint segment for trace
# data, and overflowing it will generate a page fault.

== data

# We'll save the address of the trace segment here.
Trace-stream:
    0/imm32

# Fake trace-stream for tests.
# Also illustrates the layout of the real trace-stream (segment).
_test-trace-stream:
    # current write index
    0/imm32
    # current read index
    0/imm32
    # length
    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 length, and save its address to Trace-stream.
# The Trace-stream segment will consist of variable-length lines separated by newlines (0x0a)
initialize-trace-stream:
    # EAX = new-segment(0x1000)
    # . . push args
    68/push  0x1000/imm32/N
    # . . call
    e8/call  new-segment/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
    # copy EAX to *Trace-stream
    89/copy                         0/mod/indirect  5/rm32/.disp32            .             .           0/r32/EAX   Trace-stream/disp32               # copy EAX to *Trace-stream
    # Trace-stream->length = 0x1000/N - 12
    c7          0/subop/copy        1/mod/*+disp8   0/rm32/EAX    .           .             .           .           8/disp8         0xff4/imm32       # copy 0xff4 to *(EAX+8)
    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:  # t : (address trace-stream), line : string
    # . 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
    53/push-EBX
    56/push-ESI
    57/push-EDI
    # EDI = t
    8b/copy                         1/mod/*+disp8   5/rm32/EBP    .           .                         7/r32/EDI   8/disp8         .                 # copy *(EBP+8) to EDI
    # ESI = line
    8b/copy                         1/mod/*+disp8   5/rm32/EBP    .           .                         6/r32/ESI   0xc/disp8       .                 # copy *(EBP+12) to ESI
    # ECX = t->write
    8b/copy                         0/mod/indirect  7/rm32/EDI    .           .             .           1/r32/ECX   .               .                 # copy *EDI to ECX
    # EDX = t->length
    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->length], line)
    # . . push line
    56/push-ESI
    # . . push &t->data[t->length]
    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-equal  $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->length], line)
    # . . push line
    68/push  Newline/imm32
    # . . push &t->data[t->length]
    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
    # . epilog
    89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
    5d/pop-to-EBP
    c3/return

clear-trace-stream:  # t : (address trace-stream)
    # . 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
    # EAX = t
    8b/copy                         1/mod/*+disp8   5/rm32/EBP    .           .                         0/r32/EAX   8/disp8         .                 # copy *(EBP+8) to EAX
    # ECX = t->length
    8b/copy                         1/mod/*+disp8   0/rm32/EAX    .           .             .           1/r32/ECX   8/disp8         .                 # copy *(EAX+8) to ECX
    # ECX = &t->data[t->length]
    8d/copy-address                 1/mod/*+disp8   4/rm32/sib    0/base/EAX  1/index/ECX   .           1/r32/ECX   0xc/disp8       .                 # copy EAX+ECX+12 to ECX
    # t->write = 0
    c7          0/subop/copy        0/mod/direct    0/rm32/EAX    .           .             .           .           .               0/imm32           # copy to *EAX
    # t->read = 0
    c7          0/subop/copy        1/mod/*+disp8   0/rm32/EAX    .           .             .           .           4/disp8         0/imm32           # copy to *(EAX+4)
    # EAX = t->data
    81          0/subop/add         3/mod/direct    0/rm32/EAX    .           .             .           .           .               0xc/imm32         # add to EAX
$clear-trace-stream:loop:
    # if (EAX >= ECX) break
    39/compare                      3/mod/direct    0/rm32/EAX    .           .             .           1/r32/ECX   .               .                 # compare EAX with ECX
    7d/jump-if-greater-or-equal  $clear-trace-stream:end/disp8
    # *EAX = 0
    c7          0/subop/copy        0/mod/direct    0/rm32/EAX    .           .             .           .           .               0/imm32           # copy to *EAX
    # EAX += 4
    81          0/subop/add         3/mod/direct    0/rm32/EAX    .           .             .           .           .               4/imm32           # add to EAX
    eb/jump  $clear-trace-stream:loop/disp8
$clear-trace-stream:end:
    # . restore registers
    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

# - tests

test-trace-single:
    # clear-trace-stream(_test-trace-stream)
    # . . push args
    68/push  _test-trace-stream/imm32
    # . . call
    e8/call  clear-trace-stream/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
    # trace(_test-trace-stream, "Ab")
    # . . push args
    68/push  "Ab"/imm32
    68/push  _test-trace-stream/imm32
    # . . call
    e8/call  trace/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/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
    # end
    c3/return

test-trace-appends:
    # clear-trace-stream(_test-trace-stream)
    # . . push args
    68/push  _test-trace-stream/imm32
    # . . call
    e8/call  clear-trace-stream/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
    # trace(_test-trace-stream, "C")
    # . . push args
    68/push  "C"/imm32
    68/push  _test-trace-stream/imm32
    # . . call
    e8/call  trace/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
    # trace(_test-trace-stream, "D")
    # . . push args
    68/push  "D"/imm32
    68/push  _test-trace-stream/imm32
    # . . call
    e8/call  trace/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/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
    # end
    c3/return

test-trace-empty-line:
    # clear-trace-stream(_test-trace-stream)
    # . . push args
    68/push  _test-trace-stream/imm32
    # . . call
    e8/call  clear-trace-stream/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
    # trace(_test-trace-stream, "")
    # . . push args
    68/push  ""/imm32
    68/push  _test-trace-stream/imm32
    # . . call
    e8/call  trace/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/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
    # end
    c3/return

# - helpers

# 3-argument variant of _append
_append-3:  # out : address, outend : address, s : (array byte) -> num_bytes_appended/EAX
    # . prolog
    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->length])
    # . . push &s->data[s->length]
    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
    # . epilog
    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 : address, outend : address, in : address, inend : address -> num_bytes_appended/EAX
    # . prolog
    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
    # EAX/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
    7d/jump-if-greater-or-equal  $_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
    7d/jump-if-greater-or-equal  $_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
    # . epilog
    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"/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
    b8/copy-to-EAX  1/imm32/exit
    cd/syscall  0x80/imm8
    # never gets here

# . . vim:nowrap:textwidth=0