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    :  #include "syzygy/block_graph/block_util.h"
  16    :  
  17    :  #include <algorithm>
  18    :  #include <vector>
  19    :  
  20    :  namespace block_graph {
  21    :  
  22    :  bool CodeBlockAttributesAreBasicBlockSafe(
  23  E :      const block_graph::BlockGraph::Block* block) {
  24  E :    DCHECK(block != NULL);
  25  E :    DCHECK_EQ(BlockGraph::CODE_BLOCK, block->type());
  26    :  
  27    :    // If the block was built by our toolchain it's inherently safe. This
  28    :    // attribute is used to whitelist a block.
  29  E :    if (block->attributes() & BlockGraph::BUILT_BY_SYZYGY)
  30  E :      return true;
  31    :  
  32    :    // Any of the following attributes make it unsafe to basic-block
  33    :    // decompose the code block.
  34    :    static const BlockGraph::BlockAttributes kInvalidAttributes =
  35    :        BlockGraph::GAP_BLOCK |
  36    :        BlockGraph::PADDING_BLOCK |
  37    :        BlockGraph::HAS_INLINE_ASSEMBLY |
  38    :        BlockGraph::BUILT_BY_UNSUPPORTED_COMPILER |
  39    :        BlockGraph::ERRORED_DISASSEMBLY |
  40    :        BlockGraph::HAS_EXCEPTION_HANDLING |
  41    :        BlockGraph::DISASSEMBLED_PAST_END;
  42  E :    if ((block->attributes() & kInvalidAttributes) != 0)
  43  E :      return false;
  44    :  
  45  E :    return true;
  46  E :  }
  47    :  
  48    :  bool GetBasicBlockSourceRange(const BasicCodeBlock& bb,
  49  E :                                BlockGraph::Block::SourceRange* source_range) {
  50  E :    DCHECK(source_range != NULL);
  51    :  
  52    :    typedef BlockGraph::Block::SourceRange SourceRange;
  53  E :    std::vector<SourceRange> ranges;
  54    :  
  55    :    // Collect all the instruction and successor source ranges.
  56  E :    BasicBlock::Instructions::const_iterator inst_it(bb.instructions().begin());
  57  E :    for (; inst_it != bb.instructions().end(); ++inst_it) {
  58  E :      const SourceRange& range = inst_it->source_range();
  59  E :      if (range.size() > 0)
  60  E :        ranges.push_back(range);
  61  E :    }
  62  E :    BasicBlock::Successors::const_iterator succ_it(bb.successors().begin());
  63  E :    for (; succ_it != bb.successors().end(); ++succ_it) {
  64  E :      const SourceRange& range = succ_it->source_range();
  65  E :      if (range.size() > 0)
  66  E :        ranges.push_back(range);
  67  E :    }
  68    :  
  69  E :    if (ranges.size() == 0)
  70  E :      return false;
  71    :  
  72    :    // Sort the ranges.
  73  E :    std::sort(ranges.begin(), ranges.end());
  74    :  
  75    :    // Test that they're all contiguous, while computing their total length.
  76  E :    SourceRange::Size size = ranges[0].size();
  77  E :    for (size_t i = 0; i < ranges.size() - 1; ++i) {
  78  E :      size += ranges[i + 1].size();
  79  E :      if (ranges[i].start() + ranges[i].size() != ranges[i + 1].start())
  80  E :        return false;
  81  E :    }
  82  E :    *source_range = SourceRange(ranges[0].start(), size);
  83    :  
  84  E :    return true;
  85  E :  }
  86    :  
  87    :  bool IsUnsafeReference(const BlockGraph::Block* referrer,
  88  E :                         const BlockGraph::Reference& ref) {
  89    :    // Skip references with a non-zero offset if we're
  90    :    // not instrumenting unsafe references.
  91  E :    if (ref.offset() != 0)
  92  E :      return true;
  93    :  
  94    :    BlockGraph::BlockAttributes kUnsafeAttribs =
  95    :        BlockGraph::HAS_INLINE_ASSEMBLY |
  96  E :        BlockGraph::BUILT_BY_UNSUPPORTED_COMPILER;
  97    :  
  98  E :    bool unsafe_referrer = false;
  99    :    if (referrer->type() == BlockGraph::CODE_BLOCK &&
 100  E :        (referrer->attributes() & kUnsafeAttribs) != 0) {
 101  E :      unsafe_referrer = true;
 102    :    }
 103    :  
 104  E :    DCHECK_EQ(BlockGraph::CODE_BLOCK, ref.referenced()->type());
 105  E :    bool unsafe_block = (ref.referenced()->attributes() & kUnsafeAttribs) != 0;
 106    :  
 107    :    // If both the referrer and the referenced blocks are unsafe, we can't
 108    :    // safely assume that this reference represents a call semantics,
 109    :    // e.g. where a return address is at the top of stack at entry.
 110    :    // Ideally we'd decide this on the basis of a full stack analysis, but
 111    :    // beggers can't be choosers, plus for hand-coded assembly that's
 112    :    // the halting problem :).
 113    :    // For instrumentation that uses return address swizzling, instrumenting
 114    :    // an unsafe reference leads to crashes, so better to back off and get
 115    :    // slightly less coverage.
 116  E :    return unsafe_referrer && unsafe_block;
 117  E :  }
 118    :  
 119    :  }  // namespace block_graph