LLVM  3.7.0
DwarfAccelTable.h
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1 //==-- llvm/CodeGen/DwarfAccelTable.h - Dwarf Accelerator Tables -*- C++ -*-==//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file contains support for writing dwarf accelerator tables.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #ifndef LLVM_LIB_CODEGEN_ASMPRINTER_DWARFACCELTABLE_H
15 #define LLVM_LIB_CODEGEN_ASMPRINTER_DWARFACCELTABLE_H
16 
17 #include "llvm/ADT/ArrayRef.h"
18 #include "llvm/ADT/StringMap.h"
19 #include "llvm/CodeGen/DIE.h"
20 #include "llvm/MC/MCSymbol.h"
21 #include "llvm/Support/Compiler.h"
22 #include "llvm/Support/DataTypes.h"
23 #include "llvm/Support/Debug.h"
24 #include "llvm/Support/Dwarf.h"
26 #include "llvm/Support/Format.h"
28 #include <vector>
29 
30 // The dwarf accelerator tables are an indirect hash table optimized
31 // for null lookup rather than access to known data. They are output into
32 // an on-disk format that looks like this:
33 //
34 // .-------------.
35 // | HEADER |
36 // |-------------|
37 // | BUCKETS |
38 // |-------------|
39 // | HASHES |
40 // |-------------|
41 // | OFFSETS |
42 // |-------------|
43 // | DATA |
44 // `-------------'
45 //
46 // where the header contains a magic number, version, type of hash function,
47 // the number of buckets, total number of hashes, and room for a special
48 // struct of data and the length of that struct.
49 //
50 // The buckets contain an index (e.g. 6) into the hashes array. The hashes
51 // section contains all of the 32-bit hash values in contiguous memory, and
52 // the offsets contain the offset into the data area for the particular
53 // hash.
54 //
55 // For a lookup example, we could hash a function name and take it modulo the
56 // number of buckets giving us our bucket. From there we take the bucket value
57 // as an index into the hashes table and look at each successive hash as long
58 // as the hash value is still the same modulo result (bucket value) as earlier.
59 // If we have a match we look at that same entry in the offsets table and
60 // grab the offset in the data for our final match.
61 
62 namespace llvm {
63 
64 class AsmPrinter;
65 class DwarfDebug;
66 
68 
69  static uint32_t HashDJB(StringRef Str) {
70  uint32_t h = 5381;
71  for (unsigned i = 0, e = Str.size(); i != e; ++i)
72  h = ((h << 5) + h) + Str[i];
73  return h;
74  }
75 
76  // Helper function to compute the number of buckets needed based on
77  // the number of unique hashes.
78  void ComputeBucketCount(void);
79 
80  struct TableHeader {
81  uint32_t magic; // 'HASH' magic value to allow endian detection
82  uint16_t version; // Version number.
83  uint16_t hash_function; // The hash function enumeration that was used.
84  uint32_t bucket_count; // The number of buckets in this hash table.
85  uint32_t hashes_count; // The total number of unique hash values
86  // and hash data offsets in this table.
87  uint32_t header_data_len; // The bytes to skip to get to the hash
88  // indexes (buckets) for correct alignment.
89  // Also written to disk is the implementation specific header data.
90 
91  static const uint32_t MagicHash = 0x48415348;
92 
93  TableHeader(uint32_t data_len)
94  : magic(MagicHash), version(1),
95  hash_function(dwarf::DW_hash_function_djb), bucket_count(0),
96  hashes_count(0), header_data_len(data_len) {}
97 
98 #ifndef NDEBUG
99  void print(raw_ostream &O) {
100  O << "Magic: " << format("0x%x", magic) << "\n"
101  << "Version: " << version << "\n"
102  << "Hash Function: " << hash_function << "\n"
103  << "Bucket Count: " << bucket_count << "\n"
104  << "Header Data Length: " << header_data_len << "\n";
105  }
106  void dump() { print(dbgs()); }
107 #endif
108  };
109 
110 public:
111  // The HeaderData describes the form of each set of data. In general this
112  // is as a list of atoms (atom_count) where each atom contains a type
113  // (AtomType type) of data, and an encoding form (form). In the case of
114  // data that is referenced via DW_FORM_ref_* the die_offset_base is
115  // used to describe the offset for all forms in the list of atoms.
116  // This also serves as a public interface of sorts.
117  // When written to disk this will have the form:
118  //
119  // uint32_t die_offset_base
120  // uint32_t atom_count
121  // atom_count Atoms
122 
123  // Make these public so that they can be used as a general interface to
124  // the class.
125  struct Atom {
126  uint16_t type; // enum AtomType
127  uint16_t form; // DWARF DW_FORM_ defines
128 
129  LLVM_CONSTEXPR Atom(uint16_t type, uint16_t form)
130  : type(type), form(form) {}
131 #ifndef NDEBUG
132  void print(raw_ostream &O) {
133  O << "Type: " << dwarf::AtomTypeString(type) << "\n"
134  << "Form: " << dwarf::FormEncodingString(form) << "\n";
135  }
136  void dump() { print(dbgs()); }
137 #endif
138  };
139 
140 private:
141  struct TableHeaderData {
142  uint32_t die_offset_base;
143  SmallVector<Atom, 3> Atoms;
144 
145  TableHeaderData(ArrayRef<Atom> AtomList, uint32_t offset = 0)
146  : die_offset_base(offset), Atoms(AtomList.begin(), AtomList.end()) {}
147 
148 #ifndef NDEBUG
149  void print(raw_ostream &O) {
150  O << "die_offset_base: " << die_offset_base << "\n";
151  for (size_t i = 0; i < Atoms.size(); i++)
152  Atoms[i].print(O);
153  }
154  void dump() { print(dbgs()); }
155 #endif
156  };
157 
158  // The data itself consists of a str_offset, a count of the DIEs in the
159  // hash and the offsets to the DIEs themselves.
160  // On disk each data section is ended with a 0 KeyType as the end of the
161  // hash chain.
162  // On output this looks like:
163  // uint32_t str_offset
164  // uint32_t hash_data_count
165  // HashData[hash_data_count]
166 public:
168  const DIE *Die; // Offsets
169  char Flags; // Specific flags to output
170 
171  HashDataContents(const DIE *D, char Flags) : Die(D), Flags(Flags) {}
172 #ifndef NDEBUG
173  void print(raw_ostream &O) const {
174  O << " Offset: " << Die->getOffset() << "\n";
175  O << " Tag: " << dwarf::TagString(Die->getTag()) << "\n";
176  O << " Flags: " << Flags << "\n";
177  }
178 #endif
179  };
180 
181 private:
182  // String Data
183  struct DataArray {
185  std::vector<HashDataContents *> Values;
186  };
187  friend struct HashData;
188  struct HashData {
189  StringRef Str;
190  uint32_t HashValue;
191  MCSymbol *Sym;
192  DwarfAccelTable::DataArray &Data; // offsets
193  HashData(StringRef S, DwarfAccelTable::DataArray &Data)
194  : Str(S), Data(Data) {
195  HashValue = DwarfAccelTable::HashDJB(S);
196  }
197 #ifndef NDEBUG
198  void print(raw_ostream &O) {
199  O << "Name: " << Str << "\n";
200  O << " Hash Value: " << format("0x%x", HashValue) << "\n";
201  O << " Symbol: ";
202  if (Sym)
203  O << *Sym;
204  else
205  O << "<none>";
206  O << "\n";
207  for (HashDataContents *C : Data.Values) {
208  O << " Offset: " << C->Die->getOffset() << "\n";
209  O << " Tag: " << dwarf::TagString(C->Die->getTag()) << "\n";
210  O << " Flags: " << C->Flags << "\n";
211  }
212  }
213  void dump() { print(dbgs()); }
214 #endif
215  };
216 
217  DwarfAccelTable(const DwarfAccelTable &) = delete;
218  void operator=(const DwarfAccelTable &) = delete;
219 
220  // Internal Functions
221  void EmitHeader(AsmPrinter *);
222  void EmitBuckets(AsmPrinter *);
223  void EmitHashes(AsmPrinter *);
224  void emitOffsets(AsmPrinter *, const MCSymbol *);
225  void EmitData(AsmPrinter *, DwarfDebug *D);
226 
227  // Allocator for HashData and HashDataContents.
228  BumpPtrAllocator Allocator;
229 
230  // Output Variables
231  TableHeader Header;
232  TableHeaderData HeaderData;
233  std::vector<HashData *> Data;
234 
235  typedef StringMap<DataArray, BumpPtrAllocator &> StringEntries;
236  StringEntries Entries;
237 
238  // Buckets/Hashes/Offsets
239  typedef std::vector<HashData *> HashList;
240  typedef std::vector<HashList> BucketList;
241  BucketList Buckets;
242  HashList Hashes;
243 
244  // Public Implementation
245 public:
246  DwarfAccelTable(ArrayRef<DwarfAccelTable::Atom>);
247  void AddName(DwarfStringPoolEntryRef Name, const DIE *Die, char Flags = 0);
248  void FinalizeTable(AsmPrinter *, StringRef);
249  void emit(AsmPrinter *, const MCSymbol *, DwarfDebug *);
250 #ifndef NDEBUG
251  void print(raw_ostream &O);
252  void dump() { print(dbgs()); }
253 #endif
254 };
255 }
256 #endif
const_iterator end(StringRef path)
Get end iterator over path.
Definition: Path.cpp:240
size_t size() const
size - Get the string size.
Definition: StringRef.h:113
MCSymbol - Instances of this class represent a symbol name in the MC file, and MCSymbols are created ...
Definition: MCSymbol.h:39
void print(raw_ostream &O) const
void emit(AsmPrinter *, const MCSymbol *, DwarfDebug *)
const_iterator begin(StringRef path)
Get begin iterator over path.
Definition: Path.cpp:232
LLVM_CONSTEXPR Atom(uint16_t type, uint16_t form)
#define LLVM_CONSTEXPR
Definition: Compiler.h:98
const char * TagString(unsigned Tag)
Definition: Dwarf.cpp:21
String pool entry reference.
HashDataContents(const DIE *D, char Flags)
void FinalizeTable(AsmPrinter *, StringRef)
ArrayRef - Represent a constant reference to an array (0 or more elements consecutively in memory)...
Definition: ArrayRef.h:31
void AddName(DwarfStringPoolEntryRef Name, const DIE *Die, char Flags=0)
dwarf::Tag getTag() const
Definition: DIE.h:663
format_object< Ts...> format(const char *Fmt, const Ts &...Vals)
These are helper functions used to produce formatted output.
Definition: Format.h:111
const char * AtomTypeString(unsigned Atom)
Definition: Dwarf.cpp:516
BumpPtrAllocatorImpl BumpPtrAllocator
The standard BumpPtrAllocator which just uses the default template paramaters.
Definition: Allocator.h:342
DIE - A structured debug information entry.
Definition: DIE.h:623
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:861
unsigned getOffset() const
Definition: DIE.h:664
void print(raw_ostream &O)
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:123
const char * FormEncodingString(unsigned Encoding)
Definition: Dwarf.cpp:208
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:38
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:40
void print(raw_ostream &O)