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