1 //: Labels are defined by ending names with a ':'. This layer will compute
  2 //: displacements for labels, and compute the offset for instructions using them.
  3 //:
  4 //: We won't check this, but our convention will be that jump targets will
  5 //: start with a '$', while functions will not. Function names will never be
  6 //: jumped to, and jump targets will never be called.
  7 
  8 //: We're introducing non-number names for the first time, so it's worth
  9 //: laying down some ground rules all transforms will follow, so things don't
 10 //: get too confusing:
 11 //:   - if it starts with a digit, it's treated as a number. If it can't be
 12 //:     parsed as hex it will raise an error.
 13 //:   - if it starts with '-' it's treated as a number.
 14 //:   - if it starts with '0x' it's treated as a number.
 15 //:   - if it's two characters long, it can't be a name. Either it's a hex
 16 //:     byte, or it raises an error.
 17 //: That's it. Names can start with any non-digit that isn't a dash. They can
 18 //: be a single character long. 'a' is not a hex number, it's a variable.
 19 //: Later layers may add more conventions partitioning the space of names. But
 20 //: the above rules will remain inviolate.
 21 
 22 //: One special label: the address to start running the program at.
 23 
 24 void test_entry_label() {
 25   run(
 26       "== code 0x1\n"
 27       "05 0x0d0c0b0a/imm32\n"
 28       "Entry:\n"
 29       "05 0x0d0c0b0a/imm32\n"
 30   );
 31   CHECK_TRACE_CONTENTS(
 32       "run: 0x00000006 opcode: 05\n"
 33   );
 34   CHECK_TRACE_DOESNT_CONTAIN("run: 0x00000001 opcode: 05");
 35 }
 36 
 37 :(before "End Globals")
 38 uint32_t Entry_address = 0;
 39 :(before "End Reset")
 40 Entry_address = 0;
 41 :(before "End Initialize EIP")
 42 if (Entry_address) EIP = Entry_address;
 43 :(after "Override e_entry")
 44 if (Entry_address) e_entry = Entry_address;
 45 
 46 :(before "End looks_like_hex_int(s) Detectors")
 47 if (SIZE(s) == 2) return true;
 48 
 49 :(code)
 50 void test_pack_immediate_ignores_single_byte_nondigit_operand() {
 51   Hide_errors = true;
 52   transform(
 53       "== code 0x1\n"
 54       "b9/copy  a/imm32\n"
 55   );
 56   CHECK_TRACE_CONTENTS(
 57       "transform: packing instruction 'b9/copy a/imm32'\n"
 58       // no change (we're just not printing metadata to the trace)
 59       "transform: instruction after packing: 'b9 a'\n"
 60   );
 61 }
 62 
 63 void test_pack_immediate_ignores_3_hex_digit_operand() {
 64   Hide_errors = true;
 65   transform(
 66       "== code 0x1\n"
 67       "b9/copy  aaa/imm32\n"
 68   );
 69   CHECK_TRACE_CONTENTS(
 70       "transform: packing instruction 'b9/copy aaa/imm32'\n"
 71       // no change (we're just not printing metadata to the trace)
 72       "transform: instruction after packing: 'b9 aaa'\n"
 73   );
 74 }
 75 
 76 void test_pack_immediate_ignores_non_hex_operand() {
 77   Hide_errors = true;
 78   transform(
 79       "== code 0x1\n"
 80       "b9/copy xxx/imm32\n"
 81   );
 82   CHECK_TRACE_CONTENTS(
 83       "transform: packing instruction 'b9/copy xxx/imm32'\n"
 84       // no change (we're just not printing metadata to the trace)
 85       "transform: instruction after packing: 'b9 xxx'\n"
 86   );
 87 }
 88 
 89 //: a helper we'll find handy later
 90 void check_valid_name(const string& s) {
 91   if (s.empty()) {
 92     raise << "empty name!\n" << end();
 93     return;
 94   }
 95   if (s.at(0) == '-')
 96     raise << "'" << s << "' starts with '-', which can be confused with a negative number; use a different name\n" << end();
 97   if (s.substr(0, 2) == "0x") {
 98     raise << "'" << s << "' looks like a hex number; use a different name\n" << end();
 99     return;
100   }
101   if (isdigit(s.at(0)))
102     raise << "'" << s << "' starts with a digit, and so can be confused with a negative number; use a different name.\n" << end();
103   if (SIZE(s) == 2)
104     raise << "'" << s << "' is two characters long which can look like raw hex bytes at a glance; use a different name\n" << end();
105 }
106 
107 //: Now that that's done, let's start using names as labels.
108 
109 void test_map_label() {
110   transform(
111       "== code 0x1\n"
112       "loop:\n"
113       "  05  0x0d0c0b0a/imm32\n"
114   );
115   CHECK_TRACE_CONTENTS(
116       "transform: label 'loop' is at address 1\n"
117   );
118 }
119 
120 :(before "End Level-2 Transforms")
121 Transform.push_back(rewrite_labels);
122 :(code)
123 void rewrite_labels(program& p) {
124   trace(3, "transform") << "-- rewrite labels" << end();
125   if (p.segments.empty()) return;
126   segment& code = *find(p, "code");
127   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
128   compute_byte_indices_for_labels(code, byte_index);
129   if (trace_contains_errors()) return;
130   drop_labels(code);
131   if (trace_contains_errors()) return;
132   replace_labels_with_displacements(code, byte_index);
133   if (contains_key(byte_index, "Entry"))
134     Entry_address = code.start + get(byte_index, "Entry");
135 }
136 
137 void compute_byte_indices_for_labels(const segment& code, map<string, int32_t>& byte_index) {
138   int current_byte = 0;
139   for (int i = 0;  i < SIZE(code.lines);  ++i) {
140     const line& inst = code.lines.at(i);
141     if (Source_lines_file.is_open() && !inst.original.empty() && /*not a label*/ *inst.words.at(0).data.rbegin() != ':')
142       Source_lines_file << "0x" << HEXWORD << (code.start + current_byte) << ' ' << inst.original << '\n';
143     for (int j = 0;  j < SIZE(inst.words);  ++j) {
144       const word& curr = inst.words.at(j);
145       // hack: if we have any operand metadata left after previous transforms,
146       // deduce its size
147       // Maybe we should just move this transform to before instruction
148       // packing, and deduce the size of *all* operands. But then we'll also
149       // have to deal with bitfields.
150       if (has_operand_metadata(curr, "disp32") || has_operand_metadata(curr, "imm32")) {
151         if (*curr.data.rbegin() == ':')
152           raise << "'" << to_string(inst) << "': don't use ':' when jumping to labels\n" << end();
153         current_byte += 4;
154       }
155       else if (has_operand_metadata(curr, "disp16")) {
156         if (*curr.data.rbegin() == ':')
157           raise << "'" << to_string(inst) << "': don't use ':' when jumping to labels\n" << end();
158         current_byte += 2;
159       }
160       // automatically handle /disp8 and /imm8 here
161       else if (*curr.data.rbegin() != ':') {
162         ++current_byte;
163       }
164       else {
165         string label = drop_last(curr.data);
166         // ensure labels look sufficiently different from raw hex
167         check_valid_name(label);
168         if (trace_contains_errors()) return;
169         if (contains_any_operand_metadata(curr))
170           raise << "'" << to_string(inst) << "': label definition (':') not allowed in operand\n" << end();
171         if (j > 0)
172           raise << "'" << to_string(inst) << "': labels can only be the first word in a line.\n" << end();
173         if (Labels_file.is_open())
174           Labels_file << "0x" << HEXWORD << (code.start + current_byte) << ' ' << label << '\n';
175         if (contains_key(byte_index, label) && label != "Entry") {
176           raise << "duplicate label '" << label << "'\n" << end();
177           return;
178         }
179         put(byte_index, label, current_byte);
180         trace(99, "transform") << "label '" << label << "' is at address " << (current_byte+code.start) << end();
181         // no modifying current_byte; label definitions won't be in the final binary
182       }
183     }
184   }
185 }
186 
187 :(before "End Globals")
188 bool Dump_debug_info = false;  // currently used only by 'subx translate'
189 ofstream Labels_file;
190 ofstream Source_lines_file;
191 :(before "End Commandline Options")
192 else if (is_equal(*arg, "--debug")) {
193   Dump_debug_info = true;
194   // End --debug Settings
195 }
196 //: wait to open "labels" for writing until we're sure we aren't trying to read it
197 :(after "Begin subx translate")
198 if (Dump_debug_info) {
199   cerr << "saving address->label information to 'labels'\n";
200   Labels_file.open("labels");
201   cerr << "saving address->source information to 'source_lines'\n";
202   Source_lines_file.open("source_lines");
203 }
204 :(before "End subx translate")
205 if (Dump_debug_info) {
206   Labels_file.close();
207   Source_lines_file.close();
208 }
209 
210 :(code)
211 void drop_labels(segment& code) {
212   for (int i = 0;  i < SIZE(code.lines);  ++i) {
213     line& inst = code.lines.at(i);
214     vector<word>::iterator new_end = remove_if(inst.words.begin(), inst.words.end(), is_label);
215     inst.words.erase(new_end, inst.words.end());
216   }
217 }
218 
219 bool is_label(const word& w) {
220   return *w.data.rbegin() == ':';
221 }
222 
223 void replace_labels_with_displacements(segment& code, const map<string, int32_t>& byte_index) {
224   int32_t byte_index_next_instruction_starts_at = 0;
225   for (int i = 0;  i < SIZE(code.lines);  ++i) {
226     line& inst = code.lines.at(i);
227     byte_index_next_instruction_starts_at += num_bytes(inst);
228     line new_inst;
229     for (int j = 0;  j < SIZE(inst.words);  ++j) {
230       const word& curr = inst.words.at(j);
231       if (contains_key(byte_index, curr.data)) {
232         int32_t displacement = static_cast<int32_t>(get(byte_index, curr.data)) - byte_index_next_instruction_starts_at;
233         if (has_operand_metadata(curr, "disp8")) {
234           if (displacement > 0x7f || displacement < -0x7f)
235             raise << "'" << to_string(inst) << "': label too far away for displacement " << std::hex << displacement << " to fit in 8 signed bits\n" << end();
236           else
237             emit_hex_bytes(new_inst, displacement, 1);
238         }
239         else if (has_operand_metadata(curr, "disp16")) {
240           if (displacement > 0x7fff || displacement < -0x7fff)
241             raise << "'" << to_string(inst) << "': label too far away for displacement " << std::hex << displacement << " to fit in 16 signed bits\n" << end();
242           else
243             emit_hex_bytes(new_inst, displacement, 2);
244         }
245         else if (has_operand_metadata(curr, "disp32")) {
246           emit_hex_bytes(new_inst, displacement, 4);
247         } else if (has_operand_metadata(curr, "imm32")) {
248           emit_hex_bytes(new_inst, code.start + get(byte_index, curr.data), 4);
249         }
250       }
251       else {
252         new_inst.words.push_back(curr);
253       }
254     }
255     inst.words.swap(new_inst.words);
256     trace(99, "transform") << "instruction after transform: '" << data_to_string(inst) << "'" << end();
257   }
258 }
259 
260 string data_to_string(const line& inst) {
261   ostringstream out;
262   for (int i = 0;  i < SIZE(inst.words);  ++i) {
263     if (i > 0) out << ' ';
264     out << inst.words.at(i).data;
265   }
266   return out.str();
267 }
268 
269 string drop_last(const string& s) {
270   return string(s.begin(), --s.end());
271 }
272 
273 //: Label definitions must be the first word on a line. No jumping inside
274 //: instructions.
275 //: They should also be the only word on a line.
276 //: However, you can absolutely have multiple labels map to the same address,
277 //: as long as they're on separate lines.
278 
279 void test_multiple_labels_at() {
280   transform(
281       "== code 0x1\n"
282       // address 1
283       "loop:\n"
284       " $loop2:\n"
285       // address 1 (labels take up no space)
286       "    05  0x0d0c0b0a/imm32\n"
287       // address 6
288       "    eb  $loop2/disp8\n"
289       // address 8
290       "    eb  $loop3/disp8\n"
291       // address 0xa
292       " $loop3:\n"
293   );
294   CHECK_TRACE_CONTENTS(
295       "transform: label 'loop' is at address 1\n"
296       "transform: label '$loop2' is at address 1\n"
297       "transform: label '$loop3' is at address a\n"
298       // first jump is to -7
299       "transform: instruction after transform: 'eb f9'\n"
300       // second jump is to 0 (fall through)
301       "transform: instruction after transform: 'eb 00'\n"
302   );
303 }
304 
305 void test_loading_label_as_imm32() {
306   transform(
307       "== code 0x1\n"
308       "label:\n"
309       "  be/copy-to-ESI  label/imm32\n"
310   );
311   CHECK_TRACE_CONTENTS(
312       "transform: label 'label' is at address 1\n"
313       "transform: instruction after transform: 'be 01 00 00 00'\n"
314   );
315 }
316 
317 void test_duplicate_label() {
318   Hide_errors = true;
319   transform(
320       "== code 0x1\n"
321       "loop:\n"
322       "loop:\n"
323       "    05  0x0d0c0b0a/imm32\n"
324   );
325   CHECK_TRACE_CONTENTS(
326       "error: duplicate label 'loop'\n"
327   );
328 }
329 
330 void test_label_too_short() {
331   Hide_errors = true;
332   transform(
333       "== code 0x1\n"
334       "xz:\n"
335       "  05  0x0d0c0b0a/imm32\n"
336   );
337   CHECK_TRACE_CONTENTS(
338       "error: 'xz' is two characters long which can look like raw hex bytes at a glance; use a different name\n"
339   );
340 }
341 
342 void test_label_hex() {
343   Hide_errors = true;
344   transform(
345       "== code 0x1\n"
346       "0xab:\n"
347       "  05  0x0d0c0b0a/imm32\n"
348   );
349   CHECK_TRACE_CONTENTS(
350       "error: '0xab' looks like a hex number; use a different name\n"
351   );
352 }
353 
354 void test_label_negative_hex() {
355   Hide_errors = true;
356   transform(
357       "== code 0x1\n"
358       "-a:\n"
359       "    05  0x0d0c0b0a/imm32\n"
360   );
361   CHECK_TRACE_CONTENTS(
362       "error: '-a' starts with '-', which can be confused with a negative number; use a different name\n"
363   );
364 }
365 
366 //: now that we have labels, we need to adjust segment size computation to
367 //: ignore them.
368 
369 void test_segment_size_ignores_labels() {
370   transform(
371       "== code 0x09000074\n"
372       "  05/add  0x0d0c0b0a/imm32\n"  // 5 bytes
373       "foo:\n"                        // 0 bytes
374       "== data 0x0a000000\n"
375       "bar:\n"
376       "  00\n"
377   );
378   CHECK_TRACE_CONTENTS(
379       "transform: segment 1 begins at address 0x0a000079\n"
380   );
381 }
382 
383 :(before "End size_of(word w) Special-cases")
384 else if (is_label(w))
385   return 0;