108write.subx


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162

# write: like _write, but also support in-memory streams in addition to file
# descriptors.
#
# Our first dependency-injected and testable primitive. We can pass it either
# a file descriptor or an address to a stream. If a file descriptor is passed
# in, we _write to it using the right syscall. If a 'fake file descriptor' or
# stream is passed in, we append to the stream. This lets us redirect output
# in tests and check it later.
#
# We assume our data segment will never begin at an address shorter than
# 0x08000000, so any smaller arguments are assumed to be real file descriptors.
#
# A stream looks like this:
#   read: int  # index at which to read next
#   write: int  # index at which writes go
#   data: (array byte)  # prefixed by size as usual

== 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

# TODO: come up with a way to signal when a write to disk fails
write:  # f: fd or (addr stream byte), s: (addr array byte)
    # . prologue
    55/push-ebp
    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
    # if (s == 0) return
    81          7/subop/compare     1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       0/imm32           # compare *(ebp+12)
    74/jump-if-=  $write:end/disp8
    # if (f < 0x08000000) _write(f, s) and return  # f can't be a user-mode address, so treat it as a kernel file descriptor
    81          7/subop/compare     1/mod/*+disp8   5/rm32/ebp    .           .             .           .           8/disp8         0x08000000/imm32  # compare *(ebp+8)
    73/jump-if-addr>=  $write:fake/disp8
    # . . 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  _write/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    eb/jump  $write:end/disp8
$write:fake:
    # otherwise, treat 'f' as a stream to append to
    # . save registers
    50/push-eax
    51/push-ecx
    52/push-edx
    53/push-ebx
    # ecx = f
    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .                         1/r32/ecx   8/disp8         .                 # copy *(ebp+8) to ecx
    # edx = f->write
    8b/copy                         0/mod/indirect  1/rm32/ecx    .           .             .           2/r32/edx   .               .                 # copy *ecx to edx
    # ebx = f->size
    8b/copy                         1/mod/*+disp8   1/rm32/ecx    .           .             .           3/r32/ebx   8/disp8         .                 # copy *(ecx+8) to ebx
    # eax = _append-3(&f->data[f->write], &f->data[f->size], s)
    # . . push s
    ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       .                 # push *(ebp+12)
    # . . push &f->data[f->size]
    8d/copy-address                 1/mod/*+disp8   4/rm32/sib    1/base/ecx  3/index/ebx   .           3/r32/ebx   0xc/disp8       .                 # copy ecx+ebx+12 to ebx
    53/push-ebx
    # . . push &f->data[f->write]
    8d/copy-address                 1/mod/*+disp8   4/rm32/sib    1/base/ecx  2/index/edx   .           3/r32/ebx   0xc/disp8       .                 # copy ecx+edx+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
    # f->write += eax
    01/add                          0/mod/indirect  1/rm32/ecx    .           .             .           0/r32/eax   .               .                 # add eax to *ecx
    # . restore registers
    5b/pop-to-ebx
    5a/pop-to-edx
    59/pop-to-ecx
    58/pop-to-eax
$write:end:
    # . epilogue
    89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
    5d/pop-to-ebp
    c3/return

test-write-single:
    # clear-stream(_test-stream)
    # . . push args
    68/push  _test-stream/imm32
    # . . call
    e8/call  clear-stream/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # write(_test-stream, "Ab")
    # . . push args
    68/push  "Ab"/imm32
    68/push  _test-stream/imm32
    # . . call
    e8/call  write/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # check-ints-equal(*_test-stream->data, 41/A 62/b 00 00, msg)
    # . . push args
    68/push  "F - test-write-single"/imm32
    68/push  0x006241/imm32/Ab
    # . . push *_test-stream->data
    b8/copy-to-eax  _test-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-write-appends:
    # clear-stream(_test-stream)
    # . . push args
    68/push  _test-stream/imm32
    # . . call
    e8/call  clear-stream/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
    # write(_test-stream, "C")
    # . . push args
    68/push  "C"/imm32
    68/push  _test-stream/imm32
    # . . call
    e8/call  write/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # write(_test-stream, "D")
    # . . push args
    68/push  "D"/imm32
    68/push  _test-stream/imm32
    # . . call
    e8/call  write/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # check-ints-equal(*_test-stream->data, 43/C 44/D 00 00, msg)
    # . . push args
    68/push  "F - test-write-appends"/imm32
    68/push  0x00004443/imm32/C-D
    # . . push *_test-stream->data
    b8/copy-to-eax  _test-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

== data

_test-stream:  # (stream byte)
    # current write index
    0/imm32
    # current read index
    0/imm32
    # size
    0x10/imm32
    # data (2 lines x 8 bytes/line)
    00 00 00 00 00 00 00 00
    00 00 00 00 00 00 00 00

# . . vim:nowrap:textwidth=0
//: SubX mostly deals with instructions operating on 32-bit operands, but we
//: still need to deal with raw bytes for strings and so on.

//: Unfortunately the register encodings when dealing with bytes are a mess.
//: We need a special case for them.
:(code)
string rname_8bit(uint8_t r) {
  switch (r) {
  case 0: return "AL";  // lowest byte of EAX
  case 1: return "CL";  // lowest byte of ECX
  case 2: return "DL";  // lowest byte of EDX
  case 3: return "BL";  // lowest byte of EBX
  case 4: return "AH";  // second lowest byte of EAX
  case 5: return "CH";  // second lowest byte of ECX
  case 6: return "DH";  // second lowest byte of EDX
  case 7: return "BH";  // second lowest byte of EBX
  default: raise << "invalid 8-bit register " << r << '\n' << end();  return "";
  }
}

uint8_t* effective_byte_address(uint8_t modrm) {
  uint8_t mod = (modrm>>6);
  uint8_t rm = modrm & 0x7;
  if (mod == 3) {
    // select an 8-bit register
    trace(Callstack_depth+1, "run") << "r/m8 is " << rname_8bit(rm) << end();
    return reg_8bit(rm);
  }
  // the rest is as usual
  return mem_addr_u8(effective_address_number(modrm));
}

uint8_t* reg_8bit(uint8_t rm) {
  uint8_t* result = reinterpret_cast<uint8_t*>(&Reg[rm & 0x3].i);  // _L register
  if (rm & 0x4)
    ++result;  // _H register;  assumes host is little-endian
  return result;
}

:(before "End Initialize Op Names")
put_new(Name, "88", "copy r8 to r8/m8-at-r32");

:(code)
void test_copy_r8_to_mem_at_r32() {
  Reg[EBX].i = 0x224488ab;
  Reg[EAX].i = 0x2000;
  run(
      "== code 0x1\n"
      // op     ModR/M  SIB   displacement  immediate
      "  88     18                                      \n"  // copy BL to the byte at *EAX
      // ModR/M in binary: 00 (indirect mode) 011 (src BL) 000 (dest EAX)
      "== data 0x2000\n"
      "f0 cc bb aa\n"
  );
  CHECK_TRACE_CONTENTS(
      "run: copy BL to r8/m8-at-r32\n"
      "run: effective address is 0x00002000 (EAX)\n"
      "run: storing 0xab\n"
  );
  CHECK_EQ(0xaabbccab, read_mem_u32(0x2000));
}

:(before "End Single-Byte Opcodes")
case 0x88: {  // copy r8 to r/m8
  const uint8_t modrm = next();
  const uint8_t rsrc = (modrm>>3)&0x7;
  trace(Callstack_depth+1, "run") << "copy " << rname_8bit(rsrc) << " to r8/m8-at-r32" << end();
  // use unsigned to zero-extend 8-bit value to 32 bits
  uint8_t* dest = effective_byte_address(modrm);
  const uint8_t* src = reg_8bit(rsrc);
  *dest = *src;  // Read/write multiple elements of vector<uint8_t> at once. Assumes sizeof(int) == 4 on the host as well.
  trace(Callstack_depth+1, "run") << "storing 0x" << HEXBYTE << NUM(*dest) << end();
  break;
}

//:

:(before "End Initialize Op Names")
put_new(Name, "8a", "copy r8/m8-at-r32 to r8");

:(code)
void test_copy_mem_at_r32_to_r8() {
  Reg[EBX].i = 0xaabbcc0f;  // one nibble each of lowest byte set to all 0s and all 1s, to maximize value of this test
  Reg[EAX].i = 0x2000;
  run(
      "== code 0x1\n"
      // op     ModR/M  SIB   displacement  immediate
      "  8a     18                                      \n"  // copy just the byte at *EAX to BL
      // ModR/M in binary: 00 (indirect mode) 011 (dest EBX) 000 (src EAX)
      "== data 0x2000\n"
      "ab ff ff ff\n"  // 0xab with more data in following bytes
  );
  CHECK_TRACE_CONTENTS(
      "run: copy r8/m8-at-r32 to BL\n"
      "run: effective address is 0x00002000 (EAX)\n"
      "run: storing 0xab\n"
      // remaining bytes of EBX are *not* cleared
      "run: EBX now contains 0xaabbccab\n"
  );
}

:(before "End Single-Byte Opcodes")
case 0x8a: {  // copy r/m8 to r8
  const uint8_t modrm = next();
  const uint8_t rdest = (modrm>>3)&0x7;
  trace(Callstack_depth+1, "run") << "copy r8/m8-at-r32 to " << rname_8bit(rdest) << end();
  // use unsigned to zero-extend 8-bit value to 32 bits
  const uint8_t* src = effective_byte_address(modrm);
  uint8_t* dest = reg_8bit(rdest);
  trace(Callstack_depth+1, "run") << "storing 0x" << HEXBYTE << NUM(*src) << end();
  *dest = *src;  // Read/write multiple elements of vector<uint8_t> at once. Assumes sizeof(int) == 4 on the host as well.
  const uint8_t rdest_32bit = rdest & 0x3;
  trace(Callstack_depth+1, "run") << rname(rdest_32bit) << " now contains 0x" << HEXWORD << Reg[rdest_32bit].u << end();
  break;
}

:(code)
void test_cannot_copy_byte_to_ESP_EBP_ESI_EDI() {
  Reg[ESI].u = 0xaabbccdd;
  Reg[EBX].u = 0x11223344;
  run(
      "== code 0x1\n"
      // op     ModR/M  SIB   displacement  immediate
      "  8a     f3                                      \n"  // copy just the byte at *EBX to 8-bit register '6'
      // ModR/M in binary: 11 (direct mode) 110 (dest 8-bit 'register 6') 011 (src EBX)
  );
  CHECK_TRACE_CONTENTS(
      // ensure 8-bit register '6' is DH, not ESI
      "run: copy r8/m8-at-r32 to DH\n"
      "run: storing 0x44\n"
  );
  // ensure ESI is unchanged
  CHECK_EQ(Reg[ESI].u, 0xaabbccdd);
}

//:

:(before "End Initialize Op Names")
put_new(Name, "c6", "copy imm8 to r8/m8-at-r32 (mov)");

:(code)
void test_copy_imm8_to_mem_at_r32() {
  Reg[EAX].i = 0x2000;
  run(
      "== code 0x1\n"
      // op     ModR/M  SIB   displacement  immediate
      "  c6     00                          dd          \n"  // copy to the byte at *EAX
      // ModR/M in binary: 00 (indirect mode) 000 (unused) 000 (dest EAX)
      "== data 0x2000\n"
      "f0 cc bb aa\n"
  );
  CHECK_TRACE_CONTENTS(
      "run: copy imm8 to r8/m8-at-r32\n"
      "run: effective address is 0x00002000 (EAX)\n"
      "run: storing 0xdd\n"
  );
  CHECK_EQ(0xaabbccdd, read_mem_u32(0x2000));
}

:(before "End Single-Byte Opcodes")
case 0xc6: {  // copy imm8 to r/m8
  const uint8_t modrm = next();
  const uint8_t src = next();
  trace(Callstack_depth+1, "run") << "copy imm8 to r8/m8-at-r32" << end();
  trace(Callstack_depth+1, "run") << "imm8 is 0x" << HEXWORD << NUM(src) << end();
  const uint8_t subop = (modrm>>3)&0x7;  // middle 3 'reg opcode' bits
  if (subop != 0) {
    cerr << "unrecognized subop for opcode c6: " << NUM(subop) << " (only 0/copy currently implemented)\n";
    exit(1);
  }
  // use unsigned to zero-extend 8-bit value to 32 bits
  uint8_t* dest = effective_byte_address(modrm);
  *dest = src;  // Write multiple elements of vector<uint8_t> at once. Assumes sizeof(int) == 4 on the host as well.
  trace(Callstack_depth+1, "run") << "storing 0x" << HEXBYTE << NUM(*dest) << end();
  break;
}

//:: set flags (setcc)

:(before "End Initialize Op Names")
put_new(Name_0f, "94", "set r8/m8-at-rm32 to 1 if equal, if ZF is set, 0 otherwise (setcc/setz/sete)");
put_new(Name_0f, "95", "set r8/m8-at-rm32 to 1 if not equal, if ZF is not set, 0 otherwise (setcc/setnz/setne)");
put_new(Name_0f, "9f", "set r8/m8-at-rm32 to 1 if greater (signed), if ZF is unset and SF == OF, 0 otherwise (setcc/setg/setnle)");
put_new(Name_0f, "97", "set r8/m8-at-rm32 to 1 if greater (unsigned), if ZF is unset and CF is unset, 0 otherwise (setcc/seta/setnbe)");
put_new(Name_0f, "9d", "set r8/m8-at-rm32 to 1 if greater or equal (signed), if SF == OF, 0 otherwise (setcc/setge/setnl)");
put_new(Name_0f, "93", "set r8/m8-at-rm32 to 1 if greater or equal (unsigned), if CF is unset, 0 otherwise (setcc/setae/setnb)");
put_new(Name_0f, "9c", "set r8/m8-at-rm32 to 1 if lesser (signed), if SF != OF, 0 otherwise (setcc/setl/setnge)");
put_new(Name_0f, "92", "set r8/m8-at-rm32 to 1 if lesser (unsigned), if CF is set, 0 otherwise (setcc/setb/setnae)");
put_new(Name_0f, "9e", "set r8/m8-at-rm32 to 1 if lesser or equal (signed), if ZF is set or SF != OF, 0 otherwise (setcc/setle/setng)");
put_new(Name_0f, "96", "set r8/m8-at-rm32 to 1 if lesser or equal (unsigned), if ZF is set or CF is set, 0 otherwise (setcc/setbe/setna)");

:(before "End Two-Byte Opcodes Starting With 0f")
case 0x94: {  // set r8/m8-at-rm32 if ZF
  const uint8_t modrm = next();
  trace(Callstack_depth+1, "run") << "set r8/m8-at-rm32" << end();
  uint8_t* dest = effective_byte_address(modrm);
  *dest = ZF;
  trace(Callstack_depth+1, "run") << "storing " << NUM(*dest) << end();
  break;
}
case 0x95: {  // set r8/m8-at-rm32 if !ZF
  const uint8_t modrm = next();
  trace(Callstack_depth+1, "run") << "set r8/m8-at-rm32" << end();
  uint8_t* dest = effective_byte_address(modrm);
  *dest = !ZF;
  trace(Callstack_depth+1, "run") << "storing " << NUM(*dest) << end();
  break;
}
case 0x9f: {  // set r8/m8-at-rm32 if !SF and !ZF
  const uint8_t modrm = next();
  trace(Callstack_depth+1, "run") << "set r8/m8-at-rm32" << end();
  uint8_t* dest = effective_byte_address(modrm);
  *dest = !ZF && SF == OF;
  trace(Callstack_depth+1, "run") << "storing " << NUM(*dest) << end();
  break;
}
case 0x97: {  // set r8/m8-at-rm32 if !CF and !ZF
  const uint8_t modrm = next();
  trace(Callstack_depth+1, "run") << "set r8/m8-at-rm32" << end();
  uint8_t* dest = effective_byte_address(modrm);
  *dest = (!CF && !ZF);
  trace(Callstack_depth+1, "run") << "storing " << NUM(*dest) << end();
  break;
}
case 0x9d: {  // set r8/m8-at-rm32 if !SF
  const uint8_t modrm = next();
  trace(Callstack_depth+1, "run") << "set r8/m8-at-rm32" << end();
  uint8_t* dest = effective_byte_address(modrm);
  *dest = (SF == OF);
  trace(Callstack_depth+1, "run") << "storing " << NUM(*dest) << end();
  break;
}
case 0x93: {  // set r8/m8-at-rm32 if !CF
  const uint8_t modrm = next();
  trace(Callstack_depth+1, "run") << "set r8/m8-at-rm32" << end();
  uint8_t* dest = effective_byte_address(modrm);
  *dest = !CF;
  trace(Callstack_depth+1, "run") << "storing " << NUM(*dest) << end();
  break;
}
case 0x9c: {  // set r8/m8-at-rm32 if SF and !ZF
  const uint8_t modrm = next();
  trace(Callstack_depth+1, "run") << "set r8/m8-at-rm32" << end();
  uint8_t* dest = effective_byte_address(modrm);
  *dest = (SF != OF);
  trace(Callstack_depth+1, "run") << "storing " << NUM(*dest) << end();
  break;
}
case 0x92: {  // set r8/m8-at-rm32 if CF
  const uint8_t modrm = next();
  trace(Callstack_depth+1, "run") << "set r8/m8-at-rm32" << end();
  uint8_t* dest = effective_byte_address(modrm);
  *dest = CF;
  trace(Callstack_depth+1, "run") << "storing " << NUM(*dest) << end();
  break;
}
case 0x9e: {  // set r8/m8-at-rm32 if SF or ZF
  const uint8_t modrm = next();
  trace(Callstack_depth+1, "run") << "set r8/m8-at-rm32" << end();
  uint8_t* dest = effective_byte_address(modrm);
  *dest = (ZF || SF != OF);
  trace(Callstack_depth+1, "run") << "storing " << NUM(*dest) << end();
  break;
}
case 0x96: {  // set r8/m8-at-rm32 if ZF or CF
  const uint8_t modrm = next();
  trace(Callstack_depth+1, "run") << "set r8/m8-at-rm32" << end();
  uint8_t* dest = effective_byte_address(modrm);
  *dest = (ZF || CF);
  trace(Callstack_depth+1, "run") << "storing " << NUM(*dest) << end();
  break;
}