LLVM  4.0.0
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  constexpr Atom(uint16_t type, uint16_t form) : type(type), form(form) {}
130 #ifndef NDEBUG
131  void print(raw_ostream &O) {
132  O << "Type: " << dwarf::AtomTypeString(type) << "\n"
133  << "Form: " << dwarf::FormEncodingString(form) << "\n";
134  }
135  void dump() { print(dbgs()); }
136 #endif
137  };
138 
139 private:
140  struct TableHeaderData {
141  uint32_t die_offset_base;
142  SmallVector<Atom, 3> Atoms;
143 
144  TableHeaderData(ArrayRef<Atom> AtomList, uint32_t offset = 0)
145  : die_offset_base(offset), Atoms(AtomList.begin(), AtomList.end()) {}
146 
147 #ifndef NDEBUG
148  void print(raw_ostream &O) {
149  O << "die_offset_base: " << die_offset_base << "\n";
150  for (size_t i = 0; i < Atoms.size(); i++)
151  Atoms[i].print(O);
152  }
153  void dump() { print(dbgs()); }
154 #endif
155  };
156 
157  // The data itself consists of a str_offset, a count of the DIEs in the
158  // hash and the offsets to the DIEs themselves.
159  // On disk each data section is ended with a 0 KeyType as the end of the
160  // hash chain.
161  // On output this looks like:
162  // uint32_t str_offset
163  // uint32_t hash_data_count
164  // HashData[hash_data_count]
165 public:
167  const DIE *Die; // Offsets
168  char Flags; // Specific flags to output
169 
170  HashDataContents(const DIE *D, char Flags) : Die(D), Flags(Flags) {}
171 #ifndef NDEBUG
172  void print(raw_ostream &O) const {
173  O << " Offset: " << Die->getOffset() << "\n";
174  O << " Tag: " << dwarf::TagString(Die->getTag()) << "\n";
175  O << " Flags: " << Flags << "\n";
176  }
177 #endif
178  };
179 
180 private:
181  // String Data
182  struct DataArray {
184  std::vector<HashDataContents *> Values;
185  };
186  friend struct HashData;
187  struct HashData {
188  StringRef Str;
189  uint32_t HashValue;
190  MCSymbol *Sym;
191  DwarfAccelTable::DataArray &Data; // offsets
192  HashData(StringRef S, DwarfAccelTable::DataArray &Data)
193  : Str(S), Data(Data) {
194  HashValue = DwarfAccelTable::HashDJB(S);
195  }
196 #ifndef NDEBUG
197  void print(raw_ostream &O) {
198  O << "Name: " << Str << "\n";
199  O << " Hash Value: " << format("0x%x", HashValue) << "\n";
200  O << " Symbol: ";
201  if (Sym)
202  O << *Sym;
203  else
204  O << "<none>";
205  O << "\n";
206  for (HashDataContents *C : Data.Values) {
207  O << " Offset: " << C->Die->getOffset() << "\n";
208  O << " Tag: " << dwarf::TagString(C->Die->getTag()) << "\n";
209  O << " Flags: " << C->Flags << "\n";
210  }
211  }
212  void dump() { print(dbgs()); }
213 #endif
214  };
215 
216  DwarfAccelTable(const DwarfAccelTable &) = delete;
217  void operator=(const DwarfAccelTable &) = delete;
218 
219  // Internal Functions
220  void EmitHeader(AsmPrinter *);
221  void EmitBuckets(AsmPrinter *);
222  void EmitHashes(AsmPrinter *);
223  void emitOffsets(AsmPrinter *, const MCSymbol *);
224  void EmitData(AsmPrinter *, DwarfDebug *D);
225 
226  // Allocator for HashData and HashDataContents.
227  BumpPtrAllocator Allocator;
228 
229  // Output Variables
230  TableHeader Header;
231  TableHeaderData HeaderData;
232  std::vector<HashData *> Data;
233 
234  typedef StringMap<DataArray, BumpPtrAllocator &> StringEntries;
235  StringEntries Entries;
236 
237  // Buckets/Hashes/Offsets
238  typedef std::vector<HashData *> HashList;
239  typedef std::vector<HashList> BucketList;
240  BucketList Buckets;
241  HashList Hashes;
242 
243  // Public Implementation
244 public:
245  DwarfAccelTable(ArrayRef<DwarfAccelTable::Atom>);
246  void AddName(DwarfStringPoolEntryRef Name, const DIE *Die, char Flags = 0);
247  void FinalizeTable(AsmPrinter *, StringRef);
248  void emit(AsmPrinter *, const MCSymbol *, DwarfDebug *);
249 #ifndef NDEBUG
250  void print(raw_ostream &O);
251  void dump() { print(dbgs()); }
252 #endif
253 };
254 }
255 #endif
const_iterator end(StringRef path)
Get end iterator over path.
Definition: Path.cpp:241
size_t i
StringRef AtomTypeString(unsigned Atom)
Definition: Dwarf.cpp:307
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:233
struct fuzzer::@269 Flags
StringRef FormEncodingString(unsigned Encoding)
Definition: Dwarf.cpp:58
String pool entry reference.
static GCRegistry::Add< StatepointGC > D("statepoint-example","an example strategy for statepoint")
constexpr Atom(uint16_t type, uint16_t form)
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: APInt.h:33
void AddName(DwarfStringPoolEntryRef Name, const DIE *Die, char Flags=0)
LLVM_NODISCARD LLVM_ATTRIBUTE_ALWAYS_INLINE size_t size() const
size - Get the string size.
Definition: StringRef.h:135
dwarf::Tag getTag() const
Definition: DIE.h:692
format_object< Ts...> format(const char *Fmt, const Ts &...Vals)
These are helper functions used to produce formatted output.
Definition: Format.h:124
BumpPtrAllocatorImpl BumpPtrAllocator
The standard BumpPtrAllocator which just uses the default template paramaters.
Definition: Allocator.h:361
A structured debug information entry.
Definition: DIE.h:655
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:843
unsigned getOffset() const
Get the compile/type unit relative offset of this DIE.
Definition: DIE.h:694
void print(raw_ostream &O)
static GCRegistry::Add< ShadowStackGC > C("shadow-stack","Very portable GC for uncooperative code generators")
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:132
StringRef TagString(unsigned Tag)
Definition: Dwarf.cpp:21
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:44
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:47
void print(raw_ostream &O)