1  // -*- mode: C++ -*-
  2  
  3  // Copyright 2010 Google LLC
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 30  
 31  // Original author: Jim Blandy <jimb@mozilla.com> <jimb@red-bean.com>
 32  
 33  // cfi_frame_info-inl.h: Definitions for cfi_frame_info.h inlined functions.
 34  
 35  #ifndef PROCESSOR_CFI_FRAME_INFO_INL_H_
 36  #define PROCESSOR_CFI_FRAME_INFO_INL_H_
 37  
 38  #include <string.h>
 39  
 40  namespace google_breakpad {
 41  
 42  template <typename RegisterType, class RawContextType>
 43  bool SimpleCFIWalker<RegisterType, RawContextType>::FindCallerRegisters(
 44      const MemoryRegion& memory,
 45      const CFIFrameInfo& cfi_frame_info,
 46      const RawContextType& callee_context,
 47      int callee_validity,
 48      RawContextType* caller_context,
 49      int* caller_validity) const {
 50    typedef CFIFrameInfo::RegisterValueMap<RegisterType> ValueMap;
 51    ValueMap callee_registers;
 52    ValueMap caller_registers;
 53    // Just for brevity.
 54    typename ValueMap::const_iterator caller_none = caller_registers.end();
 55  
 56    // Populate callee_registers with register values from callee_context.
 57    for (size_t i = 0; i < map_size_; i++) {
 58      const RegisterSet& r = register_map_[i];
 59      if (callee_validity & r.validity_flag)
 60        callee_registers[r.name] = callee_context.*r.context_member;
 61    }
 62  
 63    // Apply the rules, and see what register values they yield.
 64    if (!cfi_frame_info.FindCallerRegs<RegisterType>(callee_registers, memory,
 65                                                     &caller_registers))
 66      return false;
 67  
 68    // Populate *caller_context with the values the rules placed in
 69    // caller_registers.
 70    memset(caller_context, 0xda, sizeof(*caller_context));
 71    *caller_validity = 0;
 72    for (size_t i = 0; i < map_size_; i++) {
 73      const RegisterSet& r = register_map_[i];
 74      typename ValueMap::const_iterator caller_entry;
 75  
 76      // Did the rules provide a value for this register by its name?
 77      caller_entry = caller_registers.find(r.name);
 78      if (caller_entry != caller_none) {
 79        caller_context->*r.context_member = caller_entry->second;
 80        *caller_validity |= r.validity_flag;
 81        continue;
 82      }
 83  
 84      // Did the rules provide a value for this register under its
 85      // alternate name?
 86      if (r.alternate_name) {
 87        caller_entry = caller_registers.find(r.alternate_name);
 88        if (caller_entry != caller_none) {
 89          caller_context->*r.context_member = caller_entry->second;
 90          *caller_validity |= r.validity_flag;
 91          continue;
 92        }
 93      }
 94  
 95      // Is this a callee-saves register? The walker assumes that these
 96      // still hold the caller's value if the CFI doesn't mention them.
 97      //
 98      // Note that other frame walkers may fail to recover callee-saves
 99      // registers; for example, the x86 "traditional" strategy only
100      // recovers %eip, %esp, and %ebp, even though %ebx, %esi, and %edi
101      // are callee-saves, too. It is not correct to blindly set the
102      // valid bit for all callee-saves registers, without first
103      // checking its validity bit in the callee.
104      if (r.callee_saves && (callee_validity & r.validity_flag) != 0) {
105        caller_context->*r.context_member = callee_context.*r.context_member;
106        *caller_validity |= r.validity_flag;
107        continue;
108      }
109  
110      // Otherwise, the register's value is unknown.
111    }
112  
113    return true;
114  }
115  
116  } // namespace google_breakpad
117  
118  #endif // PROCESSOR_CFI_FRAME_INFO_INL_H_