1//=-- llvm/CodeGen/DwarfAccelTable.cpp - 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#include "DwarfAccelTable.h"
15#include "DwarfCompileUnit.h"
16#include "DwarfDebug.h"
17#include "llvm/ADT/STLExtras.h"
18#include "llvm/ADT/Twine.h"
19#include "llvm/CodeGen/AsmPrinter.h"
20#include "llvm/CodeGen/DIE.h"
21#include "llvm/MC/MCExpr.h"
22#include "llvm/MC/MCStreamer.h"
23#include "llvm/MC/MCSymbol.h"
24#include "llvm/Support/Debug.h"
25
26using namespace llvm;
27
28// The length of the header data is always going to be 4 + 4 + 4*NumAtoms.
29DwarfAccelTable::DwarfAccelTable(ArrayRef<DwarfAccelTable::Atom> atomList)
30    : Header(8 + (atomList.size() * 4)), HeaderData(atomList),
31      Entries(Allocator) {}
32
33void DwarfAccelTable::AddName(DwarfStringPoolEntryRef Name, const DIE *die,
34                              char Flags) {
35  assert(Data.empty() && "Already finalized!");
36  // If the string is in the list already then add this die to the list
37  // otherwise add a new one.
38  DataArray &DIEs = Entries[Name.getString()];
39  assert(!DIEs.Name || DIEs.Name == Name);
40  DIEs.Name = Name;
41  DIEs.Values.push_back(new (Allocator) HashDataContents(die, Flags));
42}
43
44void DwarfAccelTable::ComputeBucketCount() {
45  // First get the number of unique hashes.
46  std::vector<uint32_t> uniques(Data.size());
47  for (size_t i = 0, e = Data.size(); i < e; ++i)
48    uniques[i] = Data[i]->HashValue;
49  array_pod_sort(uniques.begin(), uniques.end());
50  std::vector<uint32_t>::iterator p =
51      std::unique(uniques.begin(), uniques.end());
52  uint32_t num = std::distance(uniques.begin(), p);
53
54  // Then compute the bucket size, minimum of 1 bucket.
55  if (num > 1024)
56    Header.bucket_count = num / 4;
57  else if (num > 16)
58    Header.bucket_count = num / 2;
59  else
60    Header.bucket_count = num > 0 ? num : 1;
61
62  Header.hashes_count = num;
63}
64
65// compareDIEs - comparison predicate that sorts DIEs by their offset.
66static bool compareDIEs(const DwarfAccelTable::HashDataContents *A,
67                        const DwarfAccelTable::HashDataContents *B) {
68  return A->Die->getOffset() < B->Die->getOffset();
69}
70
71void DwarfAccelTable::FinalizeTable(AsmPrinter *Asm, StringRef Prefix) {
72  // Create the individual hash data outputs.
73  Data.reserve(Entries.size());
74  for (StringMap<DataArray>::iterator EI = Entries.begin(), EE = Entries.end();
75       EI != EE; ++EI) {
76
77    // Unique the entries.
78    std::stable_sort(EI->second.Values.begin(), EI->second.Values.end(), compareDIEs);
79    EI->second.Values.erase(
80        std::unique(EI->second.Values.begin(), EI->second.Values.end()),
81        EI->second.Values.end());
82
83    HashData *Entry = new (Allocator) HashData(EI->getKey(), EI->second);
84    Data.push_back(Entry);
85  }
86
87  // Figure out how many buckets we need, then compute the bucket
88  // contents and the final ordering. We'll emit the hashes and offsets
89  // by doing a walk during the emission phase. We add temporary
90  // symbols to the data so that we can reference them during the offset
91  // later, we'll emit them when we emit the data.
92  ComputeBucketCount();
93
94  // Compute bucket contents and final ordering.
95  Buckets.resize(Header.bucket_count);
96  for (size_t i = 0, e = Data.size(); i < e; ++i) {
97    uint32_t bucket = Data[i]->HashValue % Header.bucket_count;
98    Buckets[bucket].push_back(Data[i]);
99    Data[i]->Sym = Asm->createTempSymbol(Prefix);
100  }
101
102  // Sort the contents of the buckets by hash value so that hash
103  // collisions end up together. Stable sort makes testing easier and
104  // doesn't cost much more.
105  for (size_t i = 0; i < Buckets.size(); ++i)
106    std::stable_sort(Buckets[i].begin(), Buckets[i].end(),
107                     [] (HashData *LHS, HashData *RHS) {
108                       return LHS->HashValue < RHS->HashValue;
109                     });
110}
111
112// Emits the header for the table via the AsmPrinter.
113void DwarfAccelTable::EmitHeader(AsmPrinter *Asm) {
114  Asm->OutStreamer->AddComment("Header Magic");
115  Asm->EmitInt32(Header.magic);
116  Asm->OutStreamer->AddComment("Header Version");
117  Asm->EmitInt16(Header.version);
118  Asm->OutStreamer->AddComment("Header Hash Function");
119  Asm->EmitInt16(Header.hash_function);
120  Asm->OutStreamer->AddComment("Header Bucket Count");
121  Asm->EmitInt32(Header.bucket_count);
122  Asm->OutStreamer->AddComment("Header Hash Count");
123  Asm->EmitInt32(Header.hashes_count);
124  Asm->OutStreamer->AddComment("Header Data Length");
125  Asm->EmitInt32(Header.header_data_len);
126  Asm->OutStreamer->AddComment("HeaderData Die Offset Base");
127  Asm->EmitInt32(HeaderData.die_offset_base);
128  Asm->OutStreamer->AddComment("HeaderData Atom Count");
129  Asm->EmitInt32(HeaderData.Atoms.size());
130  for (size_t i = 0; i < HeaderData.Atoms.size(); i++) {
131    Atom A = HeaderData.Atoms[i];
132    Asm->OutStreamer->AddComment(dwarf::AtomTypeString(A.type));
133    Asm->EmitInt16(A.type);
134    Asm->OutStreamer->AddComment(dwarf::FormEncodingString(A.form));
135    Asm->EmitInt16(A.form);
136  }
137}
138
139// Walk through and emit the buckets for the table. Each index is
140// an offset into the list of hashes.
141void DwarfAccelTable::EmitBuckets(AsmPrinter *Asm) {
142  unsigned index = 0;
143  for (size_t i = 0, e = Buckets.size(); i < e; ++i) {
144    Asm->OutStreamer->AddComment("Bucket " + Twine(i));
145    if (Buckets[i].size() != 0)
146      Asm->EmitInt32(index);
147    else
148      Asm->EmitInt32(UINT32_MAX);
149    // Buckets point in the list of hashes, not to the data. Do not
150    // increment the index multiple times in case of hash collisions.
151    uint64_t PrevHash = UINT64_MAX;
152    for (auto *HD : Buckets[i]) {
153      uint32_t HashValue = HD->HashValue;
154      if (PrevHash != HashValue)
155        ++index;
156      PrevHash = HashValue;
157    }
158  }
159}
160
161// Walk through the buckets and emit the individual hashes for each
162// bucket.
163void DwarfAccelTable::EmitHashes(AsmPrinter *Asm) {
164  uint64_t PrevHash = UINT64_MAX;
165  for (size_t i = 0, e = Buckets.size(); i < e; ++i) {
166    for (HashList::const_iterator HI = Buckets[i].begin(),
167                                  HE = Buckets[i].end();
168         HI != HE; ++HI) {
169      uint32_t HashValue = (*HI)->HashValue;
170      if (PrevHash == HashValue)
171        continue;
172      Asm->OutStreamer->AddComment("Hash in Bucket " + Twine(i));
173      Asm->EmitInt32(HashValue);
174      PrevHash = HashValue;
175    }
176  }
177}
178
179// Walk through the buckets and emit the individual offsets for each
180// element in each bucket. This is done via a symbol subtraction from the
181// beginning of the section. The non-section symbol will be output later
182// when we emit the actual data.
183void DwarfAccelTable::emitOffsets(AsmPrinter *Asm, const MCSymbol *SecBegin) {
184  uint64_t PrevHash = UINT64_MAX;
185  for (size_t i = 0, e = Buckets.size(); i < e; ++i) {
186    for (HashList::const_iterator HI = Buckets[i].begin(),
187                                  HE = Buckets[i].end();
188         HI != HE; ++HI) {
189      uint32_t HashValue = (*HI)->HashValue;
190      if (PrevHash == HashValue)
191        continue;
192      PrevHash = HashValue;
193      Asm->OutStreamer->AddComment("Offset in Bucket " + Twine(i));
194      MCContext &Context = Asm->OutStreamer->getContext();
195      const MCExpr *Sub = MCBinaryExpr::createSub(
196          MCSymbolRefExpr::create((*HI)->Sym, Context),
197          MCSymbolRefExpr::create(SecBegin, Context), Context);
198      Asm->OutStreamer->EmitValue(Sub, sizeof(uint32_t));
199    }
200  }
201}
202
203// Walk through the buckets and emit the full data for each element in
204// the bucket. For the string case emit the dies and the various offsets.
205// Terminate each HashData bucket with 0.
206void DwarfAccelTable::EmitData(AsmPrinter *Asm, DwarfDebug *D) {
207  for (size_t i = 0, e = Buckets.size(); i < e; ++i) {
208    uint64_t PrevHash = UINT64_MAX;
209    for (HashList::const_iterator HI = Buckets[i].begin(),
210                                  HE = Buckets[i].end();
211         HI != HE; ++HI) {
212      // Terminate the previous entry if there is no hash collision
213      // with the current one.
214      if (PrevHash != UINT64_MAX && PrevHash != (*HI)->HashValue)
215        Asm->EmitInt32(0);
216      // Remember to emit the label for our offset.
217      Asm->OutStreamer->EmitLabel((*HI)->Sym);
218      Asm->OutStreamer->AddComment((*HI)->Str);
219      Asm->emitDwarfStringOffset((*HI)->Data.Name);
220      Asm->OutStreamer->AddComment("Num DIEs");
221      Asm->EmitInt32((*HI)->Data.Values.size());
222      for (HashDataContents *HD : (*HI)->Data.Values) {
223        // Emit the DIE offset
224        DwarfCompileUnit *CU = D->lookupUnit(HD->Die->getUnit());
225        assert(CU && "Accelerated DIE should belong to a CU.");
226        Asm->EmitInt32(HD->Die->getOffset() + CU->getDebugInfoOffset());
227        // If we have multiple Atoms emit that info too.
228        // FIXME: A bit of a hack, we either emit only one atom or all info.
229        if (HeaderData.Atoms.size() > 1) {
230          Asm->EmitInt16(HD->Die->getTag());
231          Asm->EmitInt8(HD->Flags);
232        }
233      }
234      PrevHash = (*HI)->HashValue;
235    }
236    // Emit the final end marker for the bucket.
237    if (!Buckets[i].empty())
238      Asm->EmitInt32(0);
239  }
240}
241
242// Emit the entire data structure to the output file.
243void DwarfAccelTable::emit(AsmPrinter *Asm, const MCSymbol *SecBegin,
244                           DwarfDebug *D) {
245  // Emit the header.
246  EmitHeader(Asm);
247
248  // Emit the buckets.
249  EmitBuckets(Asm);
250
251  // Emit the hashes.
252  EmitHashes(Asm);
253
254  // Emit the offsets.
255  emitOffsets(Asm, SecBegin);
256
257  // Emit the hash data.
258  EmitData(Asm, D);
259}
260
261#ifndef NDEBUG
262void DwarfAccelTable::print(raw_ostream &O) {
263
264  Header.print(O);
265  HeaderData.print(O);
266
267  O << "Entries: \n";
268  for (StringMap<DataArray>::const_iterator EI = Entries.begin(),
269                                            EE = Entries.end();
270       EI != EE; ++EI) {
271    O << "Name: " << EI->getKeyData() << "\n";
272    for (HashDataContents *HD : EI->second.Values)
273      HD->print(O);
274  }
275
276  O << "Buckets and Hashes: \n";
277  for (size_t i = 0, e = Buckets.size(); i < e; ++i)
278    for (HashList::const_iterator HI = Buckets[i].begin(),
279                                  HE = Buckets[i].end();
280         HI != HE; ++HI)
281      (*HI)->print(O);
282
283  O << "Data: \n";
284  for (std::vector<HashData *>::const_iterator DI = Data.begin(),
285                                               DE = Data.end();
286       DI != DE; ++DI)
287    (*DI)->print(O);
288}
289#endif
290