about summary refs log tree commit diff stats
path: root/subx/035labels.cc
blob: 75000233e0ccf76d23c1febbd04b09bbacd8f91b (plain) (blame)
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
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
//: Labels are defined by ending names with a ':'. This layer will compute
//: displacements for labels, and compute the offset for instructions using them.
//:
//: We won't check this, but our convention will be that jump targets will
//: start with a '$', while functions will not. Function names will never be
//: jumped to, and jump targets will never be called.

//: We're introducing non-number names for the first time, so it's worth
//: laying down some ground rules all transforms will follow, so things don't
//: get too confusing:
//:   - if it starts with a digit, it's treated as a number. If it can't be
//:     parsed as hex it will raise an error.
//:   - if it starts with '-' it's treated as a number.
//:   - if it starts with '0x' it's treated as a number.
//:   - if it's two characters long, it can't be a name. Either it's a hex
//:     byte, or it raises an error.
//: That's it. Names can start with any non-digit that isn't a dash. They can
//: be a single character long. 'a' is not a hex number, it's a variable.
//: Later layers may add more conventions partitioning the space of names. But
//: the above rules will remain inviolate.

:(before "End looks_like_hex_int(s) Detectors")
if (SIZE(s) == 2) return true;

:(scenarios transform)
:(scenario pack_immediate_ignores_single_byte_nondigit_operand)
== 0x1
b9/copy a/imm32  # copy to ECX
+transform: packing instruction 'b9/copy a/imm32'
# no change (we're just not printing metadata to the trace)
+transform: instruction after packing: 'b9 a'

:(scenario pack_immediate_ignores_3_hex_digit_operand)
== 0x1
b9/copy aaa/imm32  # copy to ECX
+transform: packing instruction 'b9/copy aaa/imm32'
# no change (we're just not printing metadata to the trace)
+transform: instruction after packing: 'b9 aaa'

:(scenario pack_immediate_ignores_non_hex_operand)
== 0x1
b9/copy xxx/imm32  # copy to ECX
+transform: packing instruction 'b9/copy xxx/imm32'
# no change (we're just not printing metadata to the trace)
+transform: instruction after packing: 'b9 xxx'

//: a helper we'll find handy later
:(code)
void check_valid_name(const string& s) {
  if (s.empty()) {
    raise << "empty name!\n" << end();
    return;
  }
  if (s.at(0) == '-')
    raise << "'" << s << "' starts with '-', which can be confused with a negative number; use a different name\n" << end();
  if (s.substr(0, 2) == "0x") {
    raise << "'" << s << "' looks like a hex number; use a different name\n" << end();
    return;
  }
  if (isdigit(s.at(0)))
    raise << "'" << s << "' starts with a digit, and so can be confused with a negative number; use a different name.\n" << end();
  if (SIZE(s) == 2)
    raise << "'" << s << "' is two characters long which can look like raw hex bytes at a glance; use a different name\n" << end();
}

//: Now that that's done, let's start using names as labels.

:(scenario map_label)
== 0x1
          # instruction                     effective address                                                   operand     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
loop:
            05                                                                                                                              0x0d0c0b0a/imm32  # add to EAX
+transform: label 'loop' is at address 1

:(before "End Level-2 Transforms")
Transform.push_back(rewrite_labels);
:(code)
void rewrite_labels(program& p) {
  trace(99, "transform") << "-- rewrite labels" << end();
  if (p.segments.empty()) return;
  segment& code = p.segments.at(0);
  map<string, int32_t> byte_index;  // values are unsigned, but we're going to do subtractions on them so they need to fit in 31 bits
  compute_byte_indices_for_labels(code, byte_index);
  if (trace_contains_errors()) return;
  drop_labels(code);
  if (trace_contains_errors()) return;
  replace_labels_with_displacements(code, byte_index);
}

void compute_byte_indices_for_labels(const segment& code, map<string, int32_t>& byte_index) {
  int current_byte = 0;
  for (int i = 0;  i < SIZE(code.lines);  ++i) {
    const line& inst = code.lines.at(i);
    for (int j = 0;  j < SIZE(inst.words);  ++j) {
      const word& curr = inst.words.at(j);
      // hack: if we have any operand metadata left after previous transforms,
      // deduce its size
      // Maybe we should just move this transform to before instruction
      // packing, and deduce the size of *all* operands. But then we'll also
      // have to deal with bitfields.
      if (has_operand_metadata(curr, "disp32") || has_operand_metadata(curr, "imm32")) {
        if (*curr.data.rbegin() == ':')
          raise << "'" << to_string(inst) << "': don't use ':' when jumping to labels\n" << end();
        current_byte += 4;
      }
      // automatically handle /disp8 and /imm8 here
      else if (*curr.data.rbegin() != ':') {
        ++current_byte;
      }
      else {
        string label = drop_last(curr.data);
        // ensure labels look sufficiently different from raw hex
        check_valid_name(label);
        if (trace_contains_errors()) return;
        if (contains_any_operand_metadata(curr))
          raise << "'" << to_string(inst) << "': label definition (':') not allowed in operand\n" << end();
        if (j > 0)
          raise << "'" << to_string(inst) << "': labels can only be the first word in a line.\n" << end();
        if (Dump_map)
          cerr << "0x" << HEXWORD << (code.start + current_byte) << ' ' << label << '\n';
        put(byte_index, label, current_byte);
        trace(99, "transform") << "label '" << label << "' is at address " << (current_byte+code.start) << end();
        // no modifying current_byte; label definitions won't be in the final binary
      }
    }
  }
}

:(before "End Globals")
bool Dump_map = false;  // currently used only by 'subx translate'
:(before "End Commandline Options")
else if (is_equal(*arg, "--map")) {
  Dump_map = true;
}

:(code)
void drop_labels(segment& code) {
  for (int i = 0;  i < SIZE(code.lines);  ++i) {
    line& inst = code.lines.at(i);
    vector<word>::iterator new_end = remove_if(inst.words.begin(), inst.words.end(), is_label);
    inst.words.erase(new_end, inst.words.end());
  }
}

bool is_label(const word& w) {
  return *w.data.rbegin() == ':';
}

void replace_labels_with_displacements(segment& code, const map<string, int32_t>& byte_index) {
  int32_t byte_index_next_instruction_starts_at = 0;
  for (int i = 0;  i < SIZE(code.lines);  ++i) {
    line& inst = code.lines.at(i);
    byte_index_next_instruction_starts_at += num_bytes(inst);
    line new_inst;
    for (int j = 0;  j < SIZE(inst.words);  ++j) {
      const word& curr = inst.words.at(j);
      if (contains_key(byte_index, curr.data)) {
        int32_t displacement = static_cast<int32_t>(get(byte_index, curr.data)) - byte_index_next_instruction_starts_at;
        if (has_operand_metadata(curr, "disp8")) {
          if (displacement > 0xff || displacement < -0x7f)
            raise << "'" << to_string(inst) << "': label too far away for displacement " << std::hex << displacement << " to fit in 8 bits\n" << end();
          else
            emit_hex_bytes(new_inst, displacement, 1);
        }
        else if (has_operand_metadata(curr, "disp16")) {
          if (displacement > 0xffff || displacement < -0x7fff)
            raise << "'" << to_string(inst) << "': label too far away for displacement " << std::hex << displacement << " to fit in 16 bits\n" << end();
          else
            emit_hex_bytes(new_inst, displacement, 2);
        }
        else if (has_operand_metadata(curr, "disp32")) {
          emit_hex_bytes(new_inst, displacement, 4);
        }
      }
      else {
        new_inst.words.push_back(curr);
      }
    }
    inst.words.swap(new_inst.words);
    trace(99, "transform") << "instruction after transform: '" << data_to_string(inst) << "'" << end();
  }
}

string data_to_string(const line& inst) {
  ostringstream out;
  for (int i = 0;  i < SIZE(inst.words);  ++i) {
    if (i > 0) out << ' ';
    out << inst.words.at(i).data;
  }
  return out.str();
}

string drop_last(const string& s) {
  return string(s.begin(), --s.end());
}

//: Label definitions must be the first word on a line. No jumping inside
//: instructions.
//: They should also be the only word on a line.
//: However, you can absolutely have multiple labels map to the same address,
//: as long as they're on separate lines.

:(scenario multiple_labels_at)
== 0x1
          # instruction                     effective address                                                   operand     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
# address 1
loop:
 $loop2:
# address 1 (labels take up no space)
            05                                                                                                                              0x0d0c0b0a/imm32  # add to EAX
# address 6
            eb                                                                                                              $loop2/disp8
# address 8
            eb                                                                                                              $loop3/disp8
# address 0xa
 $loop3:
+transform: label 'loop' is at address 1
+transform: label '$loop2' is at address 1
+transform: label '$loop3' is at address a
# first jump is to -7
+transform: instruction after transform: 'eb f9'
# second jump is to 0 (fall through)
+transform: instruction after transform: 'eb 00'

:(scenario label_too_short)
% Hide_errors = true;
== 0x1
          # instruction                     effective address                                                   operand     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
xz:
            05                                                                                                                              0x0d0c0b0a/imm32  # add to EAX
+error: 'xz' is two characters long which can look like raw hex bytes at a glance; use a different name

:(scenario label_hex)
% Hide_errors = true;
== 0x1
          # instruction                     effective address                                                   operand     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
0xab:
            05                                                                                                                              0x0d0c0b0a/imm32  # add to EAX
+error: '0xab' looks like a hex number; use a different name

:(scenario label_negative_hex)
% Hide_errors = true;
== 0x1
          # instruction                     effective address                                                   operand     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
 -a:  # indent to avoid looking like a trace_should_not_contain command for this scenario
            05                                                                                                                              0x0d0c0b0a/imm32  # add to EAX
+error: '-a' starts with '-', which can be confused with a negative number; use a different name

//: now that we have labels, we need to adjust segment size computation to
//: ignore them.

:(scenario segment_size_ignores_labels)
== code  # 0x08048074
05/add 0x0d0c0b0a/imm32  # 5 bytes
foo:                     # 0 bytes
== data  # 0x08049079
bar:
00
+transform: segment 1 begins at address 0x08049079

:(before "End num_bytes(curr) Special-cases")
else if (is_label(curr))
  ;  // don't count it