1 : // Copyright 2012 Google Inc. All Rights Reserved.
2 : //
3 : // Licensed under the Apache License, Version 2.0 (the "License");
4 : // you may not use this file except in compliance with the License.
5 : // You may obtain a copy of the License at
6 : //
7 : // http://www.apache.org/licenses/LICENSE-2.0
8 : //
9 : // Unless required by applicable law or agreed to in writing, software
10 : // distributed under the License is distributed on an "AS IS" BASIS,
11 : // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 : // See the License for the specific language governing permissions and
13 : // limitations under the License.
14 : //
15 : // Implementation of basic block decomposer.
16 :
17 : #include "syzygy/block_graph/basic_block_decomposer.h"
18 :
19 : #include <algorithm>
20 : #include <vector>
21 :
22 : #include "base/logging.h"
23 : #include "base/strings/stringprintf.h"
24 : #include "syzygy/block_graph/basic_block.h"
25 : #include "syzygy/block_graph/basic_block_subgraph.h"
26 : #include "syzygy/block_graph/block_graph.h"
27 : #include "syzygy/block_graph/block_util.h"
28 :
29 : #include "mnemonics.h" // NOLINT
30 :
31 : namespace block_graph {
32 :
33 : namespace {
34 :
35 : using block_graph::BasicBlock;
36 : using block_graph::BasicBlockReference;
37 : using block_graph::BasicBlockReferrer;
38 : using block_graph::BasicBlockSubGraph;
39 : using block_graph::BlockGraph;
40 : using block_graph::Instruction;
41 : using block_graph::Successor;
42 : using core::Disassembler;
43 :
44 : typedef BlockGraph::Block Block;
45 : typedef BlockGraph::Offset Offset;
46 : typedef BlockGraph::Size Size;
47 : typedef core::AddressSpace<Offset, size_t, BasicBlock*> BBAddressSpace;
48 : typedef BBAddressSpace::Range Range;
49 : typedef BBAddressSpace::RangeMap RangeMap;
50 : typedef BBAddressSpace::RangeMapConstIter RangeMapConstIter;
51 : typedef BBAddressSpace::RangeMapIter RangeMapIter;
52 :
53 : const size_t kPointerSize = BlockGraph::Reference::kMaximumSize;
54 :
55 : // We use a (somewhat) arbitrary value as the disassembly address for a block
56 : // so we can tell the difference between a reference to the beginning of the
57 : // block (offset=0) and a null address.
58 : const size_t kDisassemblyAddress = 65536;
59 :
60 : // Look up the reference made from an instruction's byte range within the
61 : // given block. The reference should start AFTER the instruction starts
62 : // and there should be exactly 1 reference in the byte range.
63 : // Returns true if the reference was found, false otherwise.
64 : bool GetReferenceOfInstructionAt(const Block* block,
65 : Offset instr_offset,
66 : Size instr_size,
67 E : BlockGraph::Reference* ref) {
68 E : DCHECK(block != NULL);
69 E : DCHECK_LE(0, instr_offset);
70 E : DCHECK_LT(0U, instr_size);
71 E : DCHECK(ref != NULL);
72 :
73 : // Find the first reference following the instruction offset.
74 : Block::ReferenceMap::const_iterator ref_iter =
75 E : block->references().upper_bound(instr_offset);
76 :
77 : // If no reference is found then we're done.
78 E : if (ref_iter == block->references().end())
79 E : return false;
80 :
81 : // If the reference occurs outside the instruction then we're done.
82 E : Offset next_instr_offset = instr_offset + instr_size;
83 E : if (ref_iter->first >= next_instr_offset)
84 E : return false;
85 :
86 : // Otherwise, the reference should fit into the instruction.
87 : CHECK_LE(static_cast<size_t>(next_instr_offset),
88 E : ref_iter->first + ref_iter->second.size());
89 :
90 : // And it should be the only reference in the instruction.
91 E : if (ref_iter != block->references().begin()) {
92 E : Block::ReferenceMap::const_iterator prev_iter = ref_iter;
93 E : --prev_iter;
94 : CHECK_GE(static_cast<size_t>(instr_offset),
95 E : prev_iter->first + prev_iter->second.size());
96 : }
97 E : Block::ReferenceMap::const_iterator next_iter = ref_iter;
98 E : ++next_iter;
99 : CHECK(next_iter == block->references().end() ||
100 E : next_iter->first >= next_instr_offset);
101 :
102 E : *ref = ref_iter->second;
103 E : return true;
104 E : }
105 :
106 : // Transfer instructions from original to tail, starting with the instruction
107 : // starting at offset.
108 : bool SplitInstructionListAt(Offset offset,
109 : BasicBlock::Instructions* original,
110 E : BasicBlock::Instructions* tail) {
111 E : DCHECK(original != NULL);
112 E : DCHECK(tail != NULL && tail->empty());
113 :
114 E : BasicBlock::Instructions::iterator it(original->begin());
115 E : while (offset > 0 && it != original->end()) {
116 E : offset -= it->size();
117 E : ++it;
118 E : }
119 :
120 : // Did we terminate at an instruction boundary?
121 E : if (offset != 0)
122 i : return false;
123 :
124 E : tail->splice(tail->end(), *original, it, original->end());
125 E : return true;
126 E : }
127 :
128 : } // namespace
129 :
130 : BasicBlockDecomposer::BasicBlockDecomposer(const BlockGraph::Block* block,
131 : BasicBlockSubGraph* subgraph)
132 : : block_(block),
133 : subgraph_(subgraph),
134 : current_block_start_(0),
135 : check_decomposition_results_(true),
136 E : contains_unsupported_instructions_(false) {
137 : // TODO(rogerm): Once we're certain this is stable for all input binaries
138 : // turn on check_decomposition_results_ by default only ifndef NDEBUG.
139 E : DCHECK(block != NULL);
140 E : DCHECK(block->type() == BlockGraph::CODE_BLOCK);
141 :
142 : // If no subgraph was provided then use a scratch one.
143 E : if (subgraph == NULL) {
144 E : scratch_subgraph_.reset(new BasicBlockSubGraph());
145 E : subgraph_ = scratch_subgraph_.get();
146 : }
147 E : }
148 :
149 E : bool BasicBlockDecomposer::Decompose() {
150 E : DCHECK(subgraph_->basic_blocks().empty());
151 E : DCHECK(subgraph_->block_descriptions().empty());
152 E : DCHECK(original_address_space_.empty());
153 E : subgraph_->set_original_block(block_);
154 :
155 E : bool disassembled = Disassemble();
156 E : if (contains_unsupported_instructions_) {
157 E : CHECK(!disassembled);
158 E : return false;
159 : }
160 E : CHECK(disassembled);
161 :
162 : // Don't bother with the following bookkeeping work if the results aren't
163 : // being looked at.
164 E : if (scratch_subgraph_.get() != NULL)
165 E : return true;
166 :
167 : // TODO(cseri): Decomposition of blocks with nonzero alignment offset is not
168 : // yet supported.
169 E : CHECK_EQ(0, block_->alignment_offset());
170 :
171 : typedef BasicBlockSubGraph::BlockDescription BlockDescription;
172 E : subgraph_->block_descriptions().push_back(BlockDescription());
173 E : BlockDescription& desc = subgraph_->block_descriptions().back();
174 E : desc.name = block_->name();
175 E : desc.compiland_name = block_->compiland_name();
176 E : desc.type = block_->type();
177 E : desc.alignment = block_->alignment();
178 E : desc.padding_before = block_->padding_before();
179 E : desc.attributes = block_->attributes();
180 E : desc.section = block_->section();
181 :
182 : // Add the basic blocks to the block descriptor.
183 E : Offset offset = 0;
184 E : RangeMapConstIter it = original_address_space_.begin();
185 E : for (; it != original_address_space_.end(); ++it) {
186 E : DCHECK_EQ(it->first.start(), offset);
187 E : desc.basic_block_order.push_back(it->second);
188 :
189 : // Any data basic blocks (jump and case tables) with 0 mod 4 alignment
190 : // are marked so that the alignment is preserved by the block builder.
191 : if (desc.alignment >= kPointerSize &&
192 : it->second->type() == BasicBlock::BASIC_DATA_BLOCK &&
193 E : (offset % kPointerSize) == 0) {
194 E : it->second->set_alignment(kPointerSize);
195 : }
196 :
197 E : offset += it->first.size();
198 E : }
199 :
200 E : return true;
201 E : }
202 :
203 : bool BasicBlockDecomposer::DecodeInstruction(Offset offset,
204 : Offset code_end_offset,
205 E : Instruction* instruction) const {
206 : // The entire offset range should fall within the extent of block_ and the
207 : // output instruction pointer must not be NULL.
208 E : DCHECK_LE(0, offset);
209 E : DCHECK_LT(offset, code_end_offset);
210 E : DCHECK_LE(static_cast<Size>(code_end_offset), block_->size());
211 E : DCHECK(instruction != NULL);
212 :
213 : // Decode the instruction.
214 E : const uint8* buffer = block_->data() + offset;
215 E : size_t max_length = code_end_offset - offset;
216 E : if (!Instruction::FromBuffer(buffer, max_length, instruction)) {
217 i : VLOG(1) << "Failed to decode instruction at offset " << offset
218 : << " of block '" << block_->name() << "'.";
219 :
220 : // Dump the bytes to aid in debugging.
221 i : std::string dump;
222 i : size_t dump_length = std::min(max_length, Instruction::kMaxSize);
223 i : for (size_t i = 0; i < dump_length; ++i)
224 i : base::StringAppendF(&dump, " %02X", buffer[i]);
225 i : VLOG(2) << ".text =" << dump << (dump_length < max_length ? "..." : ".");
226 :
227 : // Return false to indicate an error.
228 i : return false;
229 : }
230 :
231 E : VLOG(3) << "Disassembled " << instruction->GetName()
232 : << " instruction (" << instruction->size()
233 : << " bytes) at offset " << offset << ".";
234 :
235 : // Track the source range.
236 : instruction->set_source_range(
237 E : GetSourceRange(offset, instruction->size()));
238 :
239 : // If the block is labeled, preserve the label.
240 E : BlockGraph::Label label;
241 E : if (block_->GetLabel(offset, &label)) {
242 : // If this instruction has run into known data, then we have a problem!
243 E : CHECK(!label.has_attributes(BlockGraph::DATA_LABEL))
244 : << "Disassembling into data at offset " << offset << " of "
245 : << block_->name() << ".";
246 E : instruction->set_label(label);
247 : }
248 :
249 E : return true;
250 E : }
251 :
252 : BasicBlockDecomposer::SourceRange BasicBlockDecomposer::GetSourceRange(
253 E : Offset offset, Size size) const {
254 : // Find the source range for the original bytes. We may not have a data
255 : // range for bytes that were synthesized in other transformations. As a
256 : // rule, however, there should be a covered data range for each instruction,
257 : // successor, that relates back to the original image.
258 : const Block::SourceRanges::RangePair* range_pair =
259 E : block_->source_ranges().FindRangePair(offset, size);
260 : // Return an empty range if we found nothing.
261 E : if (range_pair == NULL)
262 E : return SourceRange();
263 :
264 E : const Block::DataRange& data_range = range_pair->first;
265 E : const Block::SourceRange& source_range = range_pair->second;
266 E : if (offset == data_range.start() && size == data_range.size()) {
267 : // We match a data range exactly, so let's use the entire
268 : // matching source range.
269 E : return source_range;
270 : }
271 :
272 : // The data range doesn't match exactly, so let's slice the corresponding
273 : // source range. The assumption here is that no transformation will ever
274 : // slice the data or source ranges for an instruction, so we should always
275 : // have a covering data and source ranges.
276 E : DCHECK_GE(offset, data_range.start());
277 E : DCHECK_LE(offset + size, data_range.start() + data_range.size());
278 :
279 E : Offset start_offs = offset - data_range.start();
280 E : return SourceRange(source_range.start() + start_offs, size);
281 E : }
282 :
283 : bool BasicBlockDecomposer::FindBasicBlock(Offset offset,
284 : BasicBlock** basic_block,
285 E : Range* range) const {
286 E : DCHECK_LE(0, offset);
287 E : DCHECK(basic_block != NULL);
288 E : DCHECK(range != NULL);
289 E : DCHECK(subgraph_->original_block() != NULL);
290 E : DCHECK_GE(subgraph_->original_block()->size(), static_cast<size_t>(offset));
291 :
292 : RangeMapConstIter bb_iter =
293 E : original_address_space_.FindFirstIntersection(Range(offset, 1));
294 :
295 E : if (bb_iter == original_address_space_.end())
296 i : return false;
297 :
298 E : *basic_block = bb_iter->second;
299 E : *range = bb_iter->first;
300 E : return true;
301 E : }
302 :
303 E : BasicBlock* BasicBlockDecomposer::GetBasicBlockAt(Offset offset) const {
304 E : DCHECK_LE(0, offset);
305 E : DCHECK(subgraph_->original_block() != NULL);
306 E : DCHECK_GE(subgraph_->original_block()->size(), static_cast<size_t>(offset));
307 :
308 E : BasicBlock* bb = NULL;
309 E : Range range;
310 E : CHECK(FindBasicBlock(offset, &bb, &range));
311 E : DCHECK(bb != NULL);
312 E : DCHECK_EQ(offset, range.start());
313 E : return bb;
314 E : }
315 :
316 E : void BasicBlockDecomposer::InitJumpTargets(Offset code_end_offset) {
317 E : DCHECK_LE(static_cast<Size>(code_end_offset), block_->size());
318 :
319 : // Make sure the jump target set is empty.
320 E : jump_targets_.clear();
321 :
322 : // For each referrer, check if it references code. If so, it's a jump target.
323 : BlockGraph::Block::ReferrerSet::const_iterator ref_iter =
324 E : block_->referrers().begin();
325 E : for (; ref_iter != block_->referrers().end(); ++ref_iter) {
326 E : BlockGraph::Reference ref;
327 E : bool found = ref_iter->first->GetReference(ref_iter->second, &ref);
328 E : DCHECK(found);
329 E : DCHECK_EQ(block_, ref.referenced());
330 E : DCHECK_LE(0, ref.base());
331 E : DCHECK_LE(static_cast<size_t>(ref.base()), block_->size());
332 :
333 : // Ignore references to the data portion of the block.
334 E : if (ref.base() >= code_end_offset)
335 E : continue;
336 :
337 E : jump_targets_.insert(ref.base());
338 E : }
339 E : }
340 :
341 : bool BasicBlockDecomposer::HandleInstruction(const Instruction& instruction,
342 E : Offset offset) {
343 : // We do not handle the SYS* instructions. These should ONLY occur inside
344 : // the OS system libraries, mediated by an OS system call. We expect that
345 : // they NEVER occur in application code.
346 E : if (instruction.IsSystemCall()) {
347 i : VLOG(1) << "Encountered an unexpected " << instruction.GetName()
348 : << " instruction at offset " << offset << " of block '"
349 : << block_->name() << "'.";
350 i : return false;
351 : }
352 :
353 : // Calculate the offset of the next instruction. We'll need this if this
354 : // instruction marks the end of a basic block.
355 E : Offset next_instruction_offset = offset + instruction.size();
356 :
357 : // If the instruction is not a branch then it needs to be appended to the
358 : // current basic block... which we close if the instruction is a return or
359 : // a call to a non-returning function.
360 E : if (!instruction.IsBranch()) {
361 E : current_instructions_.push_back(instruction);
362 E : if (instruction.IsReturn()) {
363 E : EndCurrentBasicBlock(next_instruction_offset);
364 E : } else if (instruction.IsCall()) {
365 E : BlockGraph::Reference ref;
366 : bool found = GetReferenceOfInstructionAt(
367 E : block_, offset, instruction.size(), &ref);
368 : if (found && Instruction::IsCallToNonReturningFunction(
369 E : instruction.representation(), ref.referenced(), ref.offset())) {
370 E : EndCurrentBasicBlock(next_instruction_offset);
371 : }
372 : }
373 E : return true;
374 : }
375 :
376 : // If the branch is not PC-Relative then it also needs to be appended to
377 : // the current basic block... which we then close.
378 E : if (!instruction.HasPcRelativeOperand(0)) {
379 E : current_instructions_.push_back(instruction);
380 E : EndCurrentBasicBlock(next_instruction_offset);
381 E : return true;
382 : }
383 :
384 : // Otherwise, we're dealing with a branch whose destination is explicit.
385 E : DCHECK(instruction.IsBranch());
386 E : DCHECK(instruction.HasPcRelativeOperand(0));
387 :
388 : // Make sure we understand the branching condition. If we don't, then
389 : // there's an instruction we have failed (or are unable) to consider.
390 : // This failure is by design, as we can't represent instructions like
391 : // JECZX or LOOPZ, as discussed in basic_block.cc.
392 : Successor::Condition condition = Successor::OpCodeToCondition(
393 E : instruction.opcode());
394 E : if (condition == Successor::kInvalidCondition) {
395 E : VLOG(1) << "Received unknown condition for branch instruction: "
396 : << instruction.GetName() << ".";
397 E : contains_unsupported_instructions_ = true;
398 E : return false;
399 : }
400 :
401 : // If this is a conditional branch add the inverse conditional successor
402 : // to represent the fall-through. If we don't understand the inverse, then
403 : // there's an instruction we have failed to consider.
404 E : if (instruction.IsConditionalBranch()) {
405 : Successor::Condition inverse_condition =
406 E : Successor::InvertCondition(condition);
407 E : CHECK_NE(Successor::kInvalidCondition, inverse_condition)
408 : << "Non-invertible condition seen for branch instruction: "
409 : << instruction.GetName() << ".";
410 :
411 : // Create an (unresolved) successor pointing to the next instruction.
412 : BasicBlockReference ref(BlockGraph::PC_RELATIVE_REF,
413 : 1, // The size is irrelevant in successors.
414 : const_cast<Block*>(block_),
415 : next_instruction_offset,
416 E : next_instruction_offset);
417 E : current_successors_.push_front(Successor(inverse_condition, ref, 0));
418 E : jump_targets_.insert(next_instruction_offset);
419 E : }
420 :
421 : // Attempt to figure out where the branch is going by finding a
422 : // reference inside the instruction's byte range.
423 E : BlockGraph::Reference ref;
424 : bool found = GetReferenceOfInstructionAt(
425 E : block_, offset, instruction.size(), &ref);
426 :
427 : // If a reference was found, prefer its destination information to the
428 : // information conveyed by the bytes in the instruction. This should
429 : // handle all inter-block jumps (thunks, tail-call elimination, etc).
430 : // Otherwise, create a reference into the current block.
431 E : if (found) {
432 : // This is an explicit branching instruction so we expect the reference to
433 : // be direct.
434 E : if (!ref.IsDirect()) {
435 i : VLOG(1) << "Encountered an explicit control flow instruction containing "
436 : << "an indirect reference.";
437 i : return false;
438 : }
439 E : } else {
440 : Offset target_offset =
441 E : next_instruction_offset + instruction.representation().imm.addr;
442 :
443 : // If we don't have a reference (coming from a fixup) for a PC-relative jump
444 : // then we expect its destination to be in the block. We only see otherwise
445 : // in assembly generated code where section contributions don't correspond
446 : // to entire function bodies.
447 : if (target_offset < 0 ||
448 E : static_cast<Size>(target_offset) >= block_->size()) {
449 i : VLOG(1) << "Unexpected PC-relative target offset is external to block.";
450 i : return false;
451 : }
452 :
453 : ref = BlockGraph::Reference(BlockGraph::PC_RELATIVE_REF,
454 : 1, // Size is irrelevant in successors.
455 : const_cast<Block*>(block_),
456 : target_offset,
457 E : target_offset);
458 : }
459 :
460 : // If the reference points to the current block, track the target offset.
461 E : if (ref.referenced() == block_)
462 E : jump_targets_.insert(ref.offset());
463 :
464 : // Create the successor, preserving the source range and label.
465 : BasicBlockReference bb_ref(
466 E : ref.type(), ref.size(), ref.referenced(), ref.offset(), ref.base());
467 E : Successor succ(condition, bb_ref, instruction.size());
468 E : succ.set_source_range(instruction.source_range());
469 E : succ.set_label(instruction.label());
470 E : current_successors_.push_front(succ);
471 :
472 : // Having just branched, we need to end the current basic block.
473 E : EndCurrentBasicBlock(next_instruction_offset);
474 E : return true;
475 E : }
476 :
477 E : bool BasicBlockDecomposer::EndCurrentBasicBlock(Offset end_offset) {
478 : // We have reached the end of the current walk or we handled a conditional
479 : // branch. Let's mark this as the end of a basic block.
480 E : int basic_block_size = end_offset - current_block_start_;
481 E : DCHECK_LT(0, basic_block_size);
482 : if (!InsertBasicBlockRange(current_block_start_,
483 : basic_block_size,
484 E : BasicBlock::BASIC_CODE_BLOCK)) {
485 i : return false;
486 : }
487 :
488 : // Remember the end offset as the start of the next basic block.
489 E : current_block_start_ = end_offset;
490 E : return true;
491 E : }
492 :
493 E : bool BasicBlockDecomposer::GetCodeRangeAndCreateDataBasicBlocks(Offset* end) {
494 E : DCHECK_NE(reinterpret_cast<Offset*>(NULL), end);
495 :
496 E : *end = 0;
497 :
498 : // By default, we assume the entire block is code.
499 E : Offset code_end = block_->size();
500 :
501 : // Iterate over all labels, looking for data labels.
502 : BlockGraph::Block::LabelMap::const_reverse_iterator it =
503 E : block_->labels().rbegin();
504 E : bool saw_non_data_label = false;
505 E : for (; it != block_->labels().rend(); ++it) {
506 E : const BlockGraph::Label& label = it->second;
507 E : if (label.has_attributes(BlockGraph::DATA_LABEL)) {
508 : // There should never be data labels beyond the end of the block.
509 E : if (it->first >= static_cast<Offset>(block_->size())) {
510 i : VLOG(1) << "Encountered a data label at offset " << it->first
511 : << "of block \"" << block_->name() << "\" of size "
512 : << block_->size() << ".";
513 i : return false;
514 : }
515 :
516 : // If a non-data label was already encountered, and now there's another
517 : // data label then bail: the block does not respect the 'code first,
518 : // data second' supported layout requirement.
519 E : if (saw_non_data_label) {
520 i : VLOG(1) << "Block \"" << block_->name() << "\" has an unsupported "
521 : << "code-data layout.";
522 i : VLOG(1) << "Unexpected data label at offset " << it->first << ".";
523 i : return false;
524 : }
525 :
526 : // Create a data block and update the end-of-code offset. This should
527 : // never fail because this is the first time blocks are being created and
528 : // they are strictly non-overlapping by the iteration logic of this
529 : // function.
530 E : size_t size = code_end - it->first;
531 : CHECK(InsertBasicBlockRange(it->first, size,
532 E : BasicBlock::BASIC_DATA_BLOCK));
533 E : code_end = it->first;
534 E : } else {
535 : // We ignore the debug-end label, as it can come after block data.
536 E : if (label.attributes() == BlockGraph::DEBUG_END_LABEL)
537 E : continue;
538 :
539 : // Remember that a non-data label was seen. No further data labels should
540 : // be encountered.
541 E : saw_non_data_label = true;
542 : }
543 E : }
544 :
545 E : *end = code_end;
546 :
547 E : return true;
548 E : }
549 :
550 E : bool BasicBlockDecomposer::ParseInstructions() {
551 : // Find the beginning and ending offsets of code bytes within the block.
552 E : Offset code_end_offset = 0;
553 E : if (!GetCodeRangeAndCreateDataBasicBlocks(&code_end_offset))
554 i : return false;
555 :
556 : // Initialize jump_targets_ to include un-discoverable targets.
557 E : InitJumpTargets(code_end_offset);
558 :
559 : // Disassemble the instruction stream into rudimentary basic blocks.
560 E : Offset offset = 0;
561 E : current_block_start_ = offset;
562 E : while (offset < code_end_offset) {
563 : // Decode the next instruction.
564 E : Instruction instruction;
565 E : if (!DecodeInstruction(offset, code_end_offset, &instruction))
566 i : return false;
567 :
568 : // Handle the decoded instruction.
569 E : if (!HandleInstruction(instruction, offset))
570 E : return false;
571 :
572 : // Advance the instruction offset.
573 E : offset += instruction.size();
574 E : }
575 :
576 : // If we get here then we must have successfully consumed the entire code
577 : // range; otherwise, we should have failed to decode a partial instruction.
578 E : CHECK_EQ(offset, code_end_offset);
579 :
580 : // If the last bb we were working on didn't end with a RET or branch then
581 : // we need to close it now. We can detect this if the current_block_start_
582 : // does not match the current (end) offset.
583 E : if (current_block_start_ != code_end_offset)
584 E : EndCurrentBasicBlock(code_end_offset);
585 :
586 E : return true;
587 E : }
588 :
589 E : bool BasicBlockDecomposer::Disassemble() {
590 : // Parse the code bytes into instructions and rudimentary basic blocks.
591 E : if (!ParseInstructions())
592 E : return false;
593 :
594 : // Everything below this point is simply book-keeping that can't fail. These
595 : // can safely be skipped in a dry-run.
596 E : if (scratch_subgraph_.get() != NULL)
597 E : return true;
598 :
599 : // Split the basic blocks at branch targets.
600 E : SplitCodeBlocksAtBranchTargets();
601 :
602 : // At this point we have basic blocks for all code and data. Now create a
603 : // basic-block to represent the end of the block. This will potentially carry
604 : // labels and references beyond the end of the block.
605 E : CHECK(InsertBasicBlockRange(block_->size(), 0, BasicBlock::BASIC_END_BLOCK));
606 :
607 : // By this point, we should have basic blocks for all visited code.
608 E : CheckAllJumpTargetsStartABasicCodeBlock();
609 :
610 : // We should now have contiguous block ranges that cover every byte in the
611 : // macro block. Verify that this is so.
612 E : CheckHasCompleteBasicBlockCoverage();
613 :
614 : // We should have propagated all of the labels in the original block into
615 : // the basic-block subgraph.
616 E : CheckAllLabelsArePreserved();
617 :
618 : // Populate the referrers in the basic block data structures by copying
619 : // them from the original source block.
620 E : CopyExternalReferrers();
621 :
622 : // Populate the references in the basic block data structures by copying
623 : // them from the original source block. This does not handle the successor
624 : // references.
625 E : CopyReferences();
626 :
627 : // Wire up the basic-block successors. These are not handled by
628 : // CopyReferences(), above.
629 E : ResolveSuccessors();
630 :
631 : // All the control flow we have derived should be valid.
632 E : CheckAllControlFlowIsValid();
633 :
634 : // Mark all unreachable code blocks as padding.
635 E : MarkUnreachableCodeAsPadding();
636 :
637 : // ... and we're done.
638 E : return true;
639 E : }
640 :
641 E : void BasicBlockDecomposer::CheckAllJumpTargetsStartABasicCodeBlock() const {
642 E : if (!check_decomposition_results_)
643 i : return;
644 :
645 E : JumpTargets::const_iterator offset_iter(jump_targets_.begin());
646 E : for (; offset_iter != jump_targets_.end(); ++offset_iter) {
647 : // The target basic-block should be a code basic-block.
648 E : BasicBlock* target_bb = GetBasicBlockAt(*offset_iter);
649 E : CHECK(target_bb != NULL);
650 E : CHECK_EQ(BasicBlock::BASIC_CODE_BLOCK, target_bb->type());
651 E : }
652 E : }
653 :
654 E : void BasicBlockDecomposer::CheckHasCompleteBasicBlockCoverage() const {
655 E : if (!check_decomposition_results_)
656 i : return;
657 :
658 : // Walk through the basic-block address space.
659 E : Offset next_start = 0;
660 E : RangeMapConstIter it(original_address_space_.begin());
661 E : for (; it != original_address_space_.end(); ++it) {
662 E : CHECK_EQ(it->first.start(), next_start);
663 E : CHECK_EQ(it->first.start(), it->second->offset());
664 :
665 E : size_t size = it->first.size();
666 :
667 E : BasicDataBlock* data_block = BasicDataBlock::Cast(it->second);
668 E : if (data_block != NULL) {
669 : // Data block's size should match the address segment exactly.
670 E : CHECK_EQ(size, data_block->size());
671 : }
672 :
673 E : BasicCodeBlock* code_block = BasicCodeBlock::Cast(it->second);
674 E : if (code_block != NULL) {
675 : // Code blocks may be short the trailing successor instruction.
676 : BasicCodeBlock::Successors::const_iterator succ_it(
677 E : code_block->successors().begin());
678 E : Size block_size = code_block->GetInstructionSize();
679 E : for (; succ_it != code_block->successors().end(); ++succ_it)
680 E : block_size += succ_it->instruction_size();
681 :
682 E : CHECK_GE(size, block_size);
683 : }
684 :
685 E : BasicEndBlock* end_block = BasicEndBlock::Cast(it->second);
686 E : if (end_block != NULL) {
687 E : CHECK_EQ(0u, end_block->size());
688 E : size = 0;
689 : }
690 :
691 : // The basic-block must have parsed as one of the fundamental types.
692 E : CHECK(data_block != NULL || code_block != NULL || end_block != NULL);
693 :
694 E : next_start += size;
695 E : }
696 :
697 : // At this point, if there were no gaps, next start will be the same as the
698 : // full size of the block we're decomposing.
699 E : CHECK_EQ(block_->size(), static_cast<size_t>(next_start));
700 E : }
701 :
702 E : void BasicBlockDecomposer::CheckAllControlFlowIsValid() const {
703 E : if (!check_decomposition_results_)
704 i : return;
705 :
706 : // Check that the subgraph is valid. This will make sure that the
707 : // instructions and successors generally make sense.
708 E : CHECK(subgraph_->IsValid());
709 :
710 : // The only thing left to check is that synthesized flow-through
711 : // successors refer to the adjacent basic-blocks.
712 E : RangeMapConstIter it(original_address_space_.begin());
713 E : for (; it != original_address_space_.end(); ++it) {
714 E : const BasicCodeBlock* bb = BasicCodeBlock::Cast(it->second);
715 E : if (bb == NULL)
716 E : continue;
717 :
718 E : const BasicBlock::Successors& successors = bb->successors();
719 :
720 : // There may be at most 2 successors.
721 E : switch (successors.size()) {
722 : case 0:
723 E : break;
724 :
725 : case 1:
726 : // If the successor is synthesized, then flow is from this basic-block
727 : // to the next adjacent one.
728 E : if (successors.back().instruction_size() == 0) {
729 E : RangeMapConstIter next(it);
730 E : ++next;
731 E : CHECK(next != original_address_space_.end());
732 E : CHECK_EQ(successors.back().reference().basic_block(), next->second);
733 : }
734 E : break;
735 :
736 : case 2: {
737 : // Exactly one of the successors should have been synthesized.
738 E : bool front_synthesized = successors.front().instruction_size() == 0;
739 E : bool back_synthesized = successors.back().instruction_size() == 0;
740 E : CHECK_NE(front_synthesized, back_synthesized);
741 :
742 : // The synthesized successor flows from this basic-block to the next
743 : // adjacent one.
744 : const Successor& synthesized =
745 E : front_synthesized ? successors.front() : successors.back();
746 E : RangeMapConstIter next(it);
747 E : ++next;
748 E : CHECK(next != original_address_space_.end());
749 E : CHECK_EQ(synthesized.reference().basic_block(), next->second);
750 E : break;
751 : }
752 :
753 : default:
754 i : NOTREACHED();
755 : }
756 E : }
757 E : }
758 :
759 E : void BasicBlockDecomposer::CheckAllLabelsArePreserved() const {
760 E : if (!check_decomposition_results_)
761 i : return;
762 :
763 E : const Block* original_block = subgraph_->original_block();
764 E : if (original_block == NULL)
765 i : return;
766 :
767 : // Remove any labels that fall *after* the given block. This can happen for
768 : // scope and debug-end labels when the function has no epilog. It is rare, but
769 : // has been observed in the wild.
770 : // TODO(chrisha): Find a way to preserve these. We may need the notion of an
771 : // empty basic-block which gets assigned the label, or we may need to
772 : // augment BBs/instructions with the ability to have two labels: one tied
773 : // to the beginning of the object, and one to the end.
774 : Block::LabelMap::const_iterator it_past_block_end =
775 E : original_block->labels().lower_bound(original_block->size());
776 :
777 : // Grab a copy of the original labels (except any that are beyond the end of
778 : // the block data). We will be matching against these to ensure that they are
779 : // preserved in the BB decomposition.
780 : const Block::LabelMap original_labels(original_block->labels().begin(),
781 E : it_past_block_end);
782 E : if (original_labels.empty())
783 E : return;
784 :
785 : // A map to track which labels (by offset) have been found in the subgraph.
786 E : std::map<Offset, bool> labels_found;
787 :
788 : // Initialize the map of labels found in the subgraph.
789 E : Block::LabelMap::const_iterator label_iter = original_labels.begin();
790 E : for (; label_iter != original_labels.end(); ++label_iter)
791 E : labels_found.insert(std::make_pair(label_iter->first, false));
792 :
793 : // Walk through the subgraph and mark all of the labels found.
794 : BasicBlockSubGraph::BBCollection::const_iterator bb_iter =
795 E : subgraph_->basic_blocks().begin();
796 E : for (; bb_iter != subgraph_->basic_blocks().end(); ++bb_iter) {
797 E : const BasicDataBlock* data_block = BasicDataBlock::Cast(*bb_iter);
798 E : if (data_block != NULL) {
799 : // Account for labels attached to basic-blocks.
800 E : if (data_block->has_label()) {
801 E : BlockGraph::Label label;
802 E : CHECK(original_block->GetLabel(data_block->offset(), &label));
803 E : CHECK(data_block->label() == label);
804 E : labels_found[data_block->offset()] = true;
805 E : }
806 : }
807 :
808 E : const BasicCodeBlock* code_block = BasicCodeBlock::Cast(*bb_iter);
809 E : if (code_block != NULL) {
810 : // Account for labels attached to instructions.
811 : BasicBlock::Instructions::const_iterator inst_iter =
812 E : code_block->instructions().begin();
813 E : Offset inst_offset = code_block->offset();
814 E : for (; inst_iter != code_block->instructions().end(); ++inst_iter) {
815 E : const Instruction& inst = *inst_iter;
816 E : if (inst.has_label()) {
817 E : BlockGraph::Label label;
818 E : CHECK(original_block->GetLabel(inst_offset, &label));
819 E : CHECK(inst.label() == label);
820 E : labels_found[inst_offset] = true;
821 E : }
822 E : inst_offset += inst.size();
823 E : }
824 :
825 : // Account for labels attached to successors.
826 : BasicBlock::Successors::const_iterator succ_iter =
827 E : code_block->successors().begin();
828 E : for (; succ_iter != code_block->successors().end(); ++succ_iter) {
829 E : const Successor& succ = *succ_iter;
830 E : if (succ.has_label()) {
831 E : BlockGraph::Label label;
832 E : CHECK_NE(0U, succ.instruction_size());
833 E : CHECK(original_block->GetLabel(inst_offset, &label));
834 E : CHECK(succ.label() == label);
835 E : labels_found[inst_offset] = true;
836 E : }
837 E : inst_offset += succ.instruction_size();
838 E : }
839 : }
840 E : }
841 :
842 : // We should have the right number of labels_found (check if we added
843 : // something to the wrong place).
844 E : CHECK_EQ(original_labels.size(), labels_found.size());
845 :
846 : // Make sure all of the items in labels_found have been set to true.
847 E : std::map<Offset, bool>::const_iterator found_iter = labels_found.begin();
848 E : for (; found_iter != labels_found.end(); ++found_iter) {
849 E : CHECK(found_iter->second);
850 E : }
851 E : }
852 :
853 : bool BasicBlockDecomposer::InsertBasicBlockRange(Offset offset,
854 : size_t size,
855 E : BasicBlockType type) {
856 E : DCHECK_LE(0, offset);
857 E : DCHECK_LE(offset + size, block_->size());
858 E : DCHECK(type == BasicBlock::BASIC_CODE_BLOCK || current_instructions_.empty());
859 E : DCHECK(type == BasicBlock::BASIC_CODE_BLOCK || current_successors_.empty());
860 :
861 : // Find or create a name for this basic block. Reserve the label, if any,
862 : // to propagate to the basic block if there are no instructions in the
863 : // block to carry the label(s).
864 E : BlockGraph::Label label;
865 E : std::string basic_block_name;
866 E : bool have_label = block_->GetLabel(offset, &label);
867 E : if (have_label) {
868 E : basic_block_name = label.ToString();
869 E : } else {
870 : basic_block_name =
871 : base::StringPrintf("<%s+%04X-%s>",
872 : block_->name().c_str(),
873 : offset,
874 E : BasicBlock::BasicBlockTypeToString(type));
875 : }
876 :
877 : // Pre-flight address space insertion to make sure there's no
878 : // pre-existing conflicting range.
879 E : Range byte_range(offset, size);
880 : if (original_address_space_.FindFirstIntersection(byte_range) !=
881 E : original_address_space_.end()) {
882 i : LOG(ERROR) << "Attempted to insert overlapping basic block.";
883 i : return false;
884 : }
885 :
886 E : if (type == BasicBlock::BASIC_CODE_BLOCK) {
887 E : DCHECK_LT(0u, size);
888 :
889 : // Create the code block.
890 E : BasicCodeBlock* code_block = subgraph_->AddBasicCodeBlock(basic_block_name);
891 E : if (code_block == NULL)
892 i : return false;
893 E : CHECK(original_address_space_.Insert(byte_range, code_block));
894 :
895 : // Populate code basic-block with instructions and successors.
896 E : code_block->set_offset(offset);
897 E : code_block->instructions().swap(current_instructions_);
898 E : code_block->successors().swap(current_successors_);
899 E : } else if (type == BasicBlock::BASIC_DATA_BLOCK) {
900 E : DCHECK_LT(0u, size);
901 :
902 : // Create the data block.
903 : BasicDataBlock* data_block = subgraph_->AddBasicDataBlock(
904 E : basic_block_name, size, block_->data() + offset);
905 E : if (data_block == NULL)
906 i : return false;
907 E : CHECK(original_address_space_.Insert(byte_range, data_block));
908 :
909 : // Capture the source range (if any) for the data block.
910 E : data_block->set_source_range(GetSourceRange(offset, size));
911 :
912 : // Data basic-blocks carry their labels at the head of the basic blocks.
913 : // A padding basic-block might also be labeled if the block contains
914 : // unreachable code (for example, INT3 or NOP instructions following a call
915 : // to a non-returning function).
916 E : data_block->set_offset(offset);
917 E : if (have_label)
918 E : data_block->set_label(label);
919 E : } else {
920 E : DCHECK_EQ(0u, size);
921 E : DCHECK_EQ(BasicBlock::BASIC_END_BLOCK, type);
922 :
923 : // Create the end block.
924 E : BasicEndBlock* end_block = subgraph_->AddBasicEndBlock();
925 E : if (end_block == NULL)
926 i : return false;
927 :
928 : // We insert the basic end block with a size of 1, as the address space
929 : // does not support empty blocks. However, the block itself has no length.
930 : // This is only for internal book-keeping, and does not affect the
931 : // BasicBlockSubGraph representation.
932 E : CHECK(original_address_space_.Insert(Range(offset, 1), end_block));
933 :
934 : // Set the offset and any labels.
935 E : end_block->set_offset(offset);
936 E : if (have_label)
937 E : end_block->set_label(label);
938 : }
939 :
940 E : return true;
941 E : }
942 :
943 E : void BasicBlockDecomposer::SplitCodeBlocksAtBranchTargets() {
944 E : JumpTargets::const_iterator jump_target_iter(jump_targets_.begin());
945 E : for (; jump_target_iter != jump_targets_.end(); ++jump_target_iter) {
946 : // Resolve the target basic-block.
947 E : Offset target_offset = *jump_target_iter;
948 E : BasicBlock* target_bb = NULL;
949 E : Range target_bb_range;
950 E : CHECK(FindBasicBlock(target_offset, &target_bb, &target_bb_range));
951 :
952 : // If we're jumping to the start of a basic block, there isn't any work
953 : // to do.
954 E : if (target_offset == target_bb_range.start())
955 E : continue;
956 :
957 : // The target must be a code block.
958 E : BasicCodeBlock* target_code_block = BasicCodeBlock::Cast(target_bb);
959 E : CHECK(target_code_block != NULL);
960 :
961 : // Otherwise, we have found a basic-block that we need to split.
962 : // Let's contract the range the original occupies in the basic-block
963 : // address space, then add a second block at the target offset.
964 E : size_t left_split_size = target_offset - target_bb_range.start();
965 E : bool removed = original_address_space_.Remove(target_bb_range);
966 E : DCHECK(removed);
967 :
968 E : Range left_split_range(target_bb_range.start(), left_split_size);
969 : bool inserted =
970 E : original_address_space_.Insert(left_split_range, target_code_block);
971 E : DCHECK(inserted);
972 :
973 : // Now we split up containing_range into two new ranges and replace
974 : // containing_range with the two new entries.
975 :
976 : // Slice the trailing half of the instructions and the successors
977 : // off the block.
978 E : DCHECK(current_instructions_.empty());
979 E : DCHECK(current_successors_.empty());
980 : bool split = SplitInstructionListAt(left_split_size,
981 : &target_code_block->instructions(),
982 E : ¤t_instructions_);
983 E : DCHECK(split);
984 E : target_code_block->successors().swap(current_successors_);
985 :
986 : // Set-up the flow-through successor for the first "half".
987 : BasicBlockReference ref(BlockGraph::PC_RELATIVE_REF,
988 : 1, // Size is immaterial in successors.
989 : const_cast<Block*>(block_),
990 : target_offset,
991 E : target_offset);
992 : target_code_block->successors().push_back(
993 E : Successor(Successor::kConditionTrue, ref, 0));
994 :
995 : // This shouldn't fail because the range used to exist, and we just resized
996 : // it.
997 : CHECK(InsertBasicBlockRange(target_offset,
998 : target_bb_range.size() - left_split_size,
999 E : target_code_block->type()));
1000 E : }
1001 E : }
1002 :
1003 E : void BasicBlockDecomposer::CopyExternalReferrers() {
1004 E : const BlockGraph::Block::ReferrerSet& referrers = block_->referrers();
1005 E : BlockGraph::Block::ReferrerSet::const_iterator iter = referrers.begin();
1006 E : for (; iter != referrers.end(); ++iter) {
1007 : // Find the reference this referrer record describes.
1008 E : const BlockGraph::Block* referrer = iter->first;
1009 E : DCHECK(referrer != NULL);
1010 :
1011 : // We only care about external referrers.
1012 E : if (referrer == block_)
1013 E : continue;
1014 :
1015 : // This is an external referrer. Find the reference in the referring block.
1016 E : Offset source_offset = iter->second;
1017 E : BlockGraph::Reference reference;
1018 E : bool found = referrer->GetReference(source_offset, &reference);
1019 E : DCHECK(found);
1020 :
1021 : // Find the basic block the reference refers to.
1022 E : BasicBlock* target_bb = GetBasicBlockAt(reference.base());
1023 E : DCHECK(target_bb != NULL);
1024 :
1025 : // Insert the referrer into the target bb's referrer set. Note that there
1026 : // is no corresponding reference update to the referring block. The
1027 : // target bb will track these so a BlockBuilder can properly update
1028 : // the referrers when merging a subgraph back into the block-graph.
1029 : bool inserted = target_bb->referrers().insert(
1030 E : BasicBlockReferrer(referrer, source_offset)).second;
1031 E : DCHECK(inserted);
1032 E : }
1033 E : }
1034 :
1035 : void BasicBlockDecomposer::CopyReferences(
1036 E : Offset item_offset, Size item_size, BasicBlockReferenceMap* refs) {
1037 E : DCHECK_LE(0, item_offset);
1038 E : DCHECK_LT(0U, item_size);
1039 E : DCHECK(refs != NULL);
1040 :
1041 : // Figure out the bounds of item.
1042 E : BlockGraph::Offset end_offset = item_offset + item_size;
1043 :
1044 : // Get iterators encompassing all references within the bounds of item.
1045 : BlockGraph::Block::ReferenceMap::const_iterator ref_iter =
1046 E : block_->references().lower_bound(item_offset);
1047 : BlockGraph::Block::ReferenceMap::const_iterator end_iter =
1048 E : block_->references().lower_bound(end_offset);
1049 :
1050 E : for (; ref_iter != end_iter; ++ref_iter) {
1051 : // Calculate the local offset of this reference within item.
1052 E : BlockGraph::Offset local_offset = ref_iter->first - item_offset;
1053 E : const BlockGraph::Reference& reference = ref_iter->second;
1054 :
1055 : // We expect long references for everything except flow control.
1056 E : CHECK_EQ(4U, reference.size());
1057 E : DCHECK_LE(local_offset + reference.size(), static_cast<Size>(end_offset));
1058 :
1059 E : if (reference.referenced() != block_) {
1060 : // For external references, we can directly reference the other block.
1061 : bool inserted = refs->insert(std::make_pair(
1062 : local_offset,
1063 : BasicBlockReference(reference.type(), reference.size(),
1064 : reference.referenced(), reference.offset(),
1065 E : reference.base()))).second;
1066 E : DCHECK(inserted);
1067 E : } else {
1068 : // For intra block_ references, find the corresponding basic block in
1069 : // the basic block address space.
1070 E : BasicBlock* target_bb = GetBasicBlockAt(reference.base());
1071 E : DCHECK(target_bb != NULL);
1072 :
1073 : // Create target basic-block relative values for the base and offset.
1074 : // TODO(chrisha): Make BasicBlockReferences handle indirect references.
1075 E : CHECK_EQ(reference.offset(), reference.base());
1076 :
1077 : // Insert a reference to the target basic block.
1078 : bool inserted = refs->insert(std::make_pair(
1079 : local_offset,
1080 : BasicBlockReference(reference.type(),
1081 : reference.size(),
1082 E : target_bb))).second;
1083 E : DCHECK(inserted);
1084 : }
1085 E : }
1086 E : }
1087 :
1088 E : void BasicBlockDecomposer::CopyReferences() {
1089 : // Copy the references for the source range of each basic-block (by
1090 : // instruction for code basic-blocks). External referrers and successors are
1091 : // handled in separate passes.
1092 : BasicBlockSubGraph::BBCollection::iterator bb_iter =
1093 E : subgraph_->basic_blocks().begin();
1094 E : for (; bb_iter != subgraph_->basic_blocks().end(); ++bb_iter) {
1095 E : BasicCodeBlock* code_block = BasicCodeBlock::Cast(*bb_iter);
1096 E : if (code_block != NULL) {
1097 E : DCHECK_EQ(BasicBlock::BASIC_CODE_BLOCK, code_block->type());
1098 :
1099 E : Offset inst_offset = code_block->offset();
1100 : BasicBlock::Instructions::iterator inst_iter =
1101 E : code_block->instructions().begin();
1102 E : for (; inst_iter != code_block->instructions().end(); ++inst_iter) {
1103 : CopyReferences(inst_offset,
1104 : inst_iter->size(),
1105 E : &inst_iter->references());
1106 E : inst_offset += inst_iter->size();
1107 E : }
1108 : }
1109 :
1110 E : BasicDataBlock* data_block = BasicDataBlock::Cast(*bb_iter);
1111 E : if (data_block != NULL) {
1112 E : DCHECK_NE(BasicBlock::BASIC_CODE_BLOCK, data_block->type());
1113 : CopyReferences(data_block->offset(),
1114 : data_block->size(),
1115 E : &data_block->references());
1116 : }
1117 E : }
1118 E : }
1119 :
1120 E : void BasicBlockDecomposer::ResolveSuccessors() {
1121 : BasicBlockSubGraph::BBCollection::iterator bb_iter =
1122 E : subgraph_->basic_blocks().begin();
1123 E : for (; bb_iter != subgraph_->basic_blocks().end(); ++bb_iter) {
1124 : // Only code basic-blocks have successors and instructions.
1125 E : BasicCodeBlock* code_block = BasicCodeBlock::Cast(*bb_iter);
1126 E : if (code_block == NULL)
1127 E : continue;
1128 :
1129 : BasicBlock::Successors::iterator succ_iter =
1130 E : code_block->successors().begin();
1131 : BasicBlock::Successors::iterator succ_iter_end =
1132 E : code_block->successors().end();
1133 E : for (; succ_iter != succ_iter_end; ++succ_iter) {
1134 E : if (succ_iter->reference().block() != block_)
1135 E : continue;
1136 :
1137 : // Find the basic block the successor references.
1138 : BasicBlock* target_code_block =
1139 E : GetBasicBlockAt(succ_iter->reference().offset());
1140 E : DCHECK(target_code_block != NULL);
1141 :
1142 : // We transform all successor branches into 4-byte pc-relative targets.
1143 : succ_iter->set_reference(
1144 : BasicBlockReference(
1145 E : BlockGraph::PC_RELATIVE_REF, 4, target_code_block));
1146 E : DCHECK(succ_iter->reference().IsValid());
1147 E : }
1148 E : }
1149 E : }
1150 :
1151 E : void BasicBlockDecomposer::MarkUnreachableCodeAsPadding() {
1152 E : BasicBlockSubGraph::ReachabilityMap rm;
1153 E : subgraph_->GetReachabilityMap(&rm);
1154 E : DCHECK_EQ(rm.size(), subgraph_->basic_blocks().size());
1155 : BasicBlockSubGraph::BBCollection::iterator bb_iter =
1156 E : subgraph_->basic_blocks().begin();
1157 E : for (; bb_iter != subgraph_->basic_blocks().end(); ++bb_iter) {
1158 E : BasicCodeBlock* code_bb = BasicCodeBlock::Cast(*bb_iter);
1159 E : if (code_bb != NULL) {
1160 E : if (!subgraph_->IsReachable(rm, code_bb))
1161 E : code_bb->MarkAsPadding();
1162 : }
1163 E : }
1164 E : }
1165 :
1166 : } // namespace block_graph
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