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29 
30 // Original author: Jim Blandy <jimb@mozilla.com> <jimb@red-bean.com>
31 
32 // cfi_assembler.cc: Implementation of google_breakpad::CFISection class.
33 // See cfi_assembler.h for details.
34 
35 #include "common/dwarf/cfi_assembler.h"
36 
37 #include <assert.h>
38 #include <stdlib.h>
39 
40 namespace google_breakpad {
41 
42 using dwarf2reader::DwarfPointerEncoding;
43 
44 CFISection &CFISection::CIEHeader(uint64_t code_alignment_factor,
45                                   int data_alignment_factor,
46                                   unsigned return_address_register,
47                                   uint8_t version,
48                                   const string &augmentation,
49                                   bool dwarf64) {
50   assert(!entry_length_);
51   entry_length_ = new PendingLength();
52   in_fde_ = false;
53 
54   if (dwarf64) {
55     D32(kDwarf64InitialLengthMarker);
56     D64(entry_length_->length);
57     entry_length_->start = Here();
58     D64(eh_frame_ ? kEHFrame64CIEIdentifier : kDwarf64CIEIdentifier);
59   } else {
60     D32(entry_length_->length);
61     entry_length_->start = Here();
62     D32(eh_frame_ ? kEHFrame32CIEIdentifier : kDwarf32CIEIdentifier);
63   }
64   D8(version);
65   AppendCString(augmentation);
66   ULEB128(code_alignment_factor);
67   LEB128(data_alignment_factor);
68   if (version == 1)
69     D8(return_address_register);
70   else
71     ULEB128(return_address_register);
72   return *this;
73 }
74 
75 CFISection &CFISection::FDEHeader(Label cie_pointer,
76                                   uint64_t initial_location,
77                                   uint64_t address_range,
78                                   bool dwarf64) {
79   assert(!entry_length_);
80   entry_length_ = new PendingLength();
81   in_fde_ = true;
82   fde_start_address_ = initial_location;
83 
84   if (dwarf64) {
85     D32(0xffffffff);
86     D64(entry_length_->length);
87     entry_length_->start = Here();
88     if (eh_frame_)
89       D64(Here() - cie_pointer);
90     else
91       D64(cie_pointer);
92   } else {
93     D32(entry_length_->length);
94     entry_length_->start = Here();
95     if (eh_frame_)
96       D32(Here() - cie_pointer);
97     else
98       D32(cie_pointer);
99   }
100   EncodedPointer(initial_location);
101   // The FDE length in an .eh_frame section uses the same encoding as the
102   // initial location, but ignores the base address (selected by the upper
103   // nybble of the encoding), as it's a length, not an address that can be
104   // made relative.
105   EncodedPointer(address_range,
106                  DwarfPointerEncoding(pointer_encoding_ & 0x0f));
107   return *this;
108 }
109 
110 CFISection &CFISection::FinishEntry() {
111   assert(entry_length_);
112   Align(address_size_, dwarf2reader::DW_CFA_nop);
113   entry_length_->length = Here() - entry_length_->start;
114   delete entry_length_;
115   entry_length_ = NULL;
116   in_fde_ = false;
117   return *this;
118 }
119 
120 CFISection &CFISection::EncodedPointer(uint64_t address,
121                                        DwarfPointerEncoding encoding,
122                                        const EncodedPointerBases &bases) {
123   // Omitted data is extremely easy to emit.
124   if (encoding == dwarf2reader::DW_EH_PE_omit)
125     return *this;
126 
127   // If (encoding & dwarf2reader::DW_EH_PE_indirect) != 0, then we assume
128   // that ADDRESS is the address at which the pointer is stored --- in
129   // other words, that bit has no effect on how we write the pointer.
130   encoding = DwarfPointerEncoding(encoding & ~dwarf2reader::DW_EH_PE_indirect);
131 
132   // Find the base address to which this pointer is relative. The upper
133   // nybble of the encoding specifies this.
134   uint64_t base;
135   switch (encoding & 0xf0) {
136     case dwarf2reader::DW_EH_PE_absptr:  base = 0;                  break;
137     case dwarf2reader::DW_EH_PE_pcrel:   base = bases.cfi + Size(); break;
138     case dwarf2reader::DW_EH_PE_textrel: base = bases.text;         break;
139     case dwarf2reader::DW_EH_PE_datarel: base = bases.data;         break;
140     case dwarf2reader::DW_EH_PE_funcrel: base = fde_start_address_; break;
141     case dwarf2reader::DW_EH_PE_aligned: base = 0;                  break;
142     default: abort();
143   };
144 
145   // Make ADDRESS relative. Yes, this is appropriate even for "absptr"
146   // values; see gcc/unwind-pe.h.
147   address -= base;
148 
149   // Align the pointer, if required.
150   if ((encoding & 0xf0) == dwarf2reader::DW_EH_PE_aligned)
151     Align(AddressSize());
152 
153   // Append ADDRESS to this section in the appropriate form. For the
154   // fixed-width forms, we don't need to differentiate between signed and
155   // unsigned encodings, because ADDRESS has already been extended to 64
156   // bits before it was passed to us.
157   switch (encoding & 0x0f) {
158     case dwarf2reader::DW_EH_PE_absptr:
159       Address(address);
160       break;
161 
162     case dwarf2reader::DW_EH_PE_uleb128:
163       ULEB128(address);
164       break;
165 
166     case dwarf2reader::DW_EH_PE_sleb128:
167       LEB128(address);
168       break;
169 
170     case dwarf2reader::DW_EH_PE_udata2:
171     case dwarf2reader::DW_EH_PE_sdata2:
172       D16(address);
173       break;
174 
175     case dwarf2reader::DW_EH_PE_udata4:
176     case dwarf2reader::DW_EH_PE_sdata4:
177       D32(address);
178       break;
179 
180     case dwarf2reader::DW_EH_PE_udata8:
181     case dwarf2reader::DW_EH_PE_sdata8:
182       D64(address);
183       break;
184 
185     default:
186       abort();
187   }
188 
189   return *this;
190 };
191 
192 const uint32_t CFISection::kDwarf64InitialLengthMarker;
193 const uint32_t CFISection::kDwarf32CIEIdentifier;
194 const uint64_t CFISection::kDwarf64CIEIdentifier;
195 const uint32_t CFISection::kEHFrame32CIEIdentifier;
196 const uint64_t CFISection::kEHFrame64CIEIdentifier;
197 
198 } // namespace google_breakpad
199