Add more methods to gather target specific elf stuff

Support for .text relocations, implementing TargetELFWriter overloaded methods for x86/x86_64.
Use a map to track global values to their symbol table indexes
Code cleanup and small fixes



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73894 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/BinaryObject.h

@@ -61,6 +61,11 @@ public:
     return Relocations;
   }
 
+  /// hasRelocations - Return true if 'Relocations' is not empty
+  bool hasRelocations() const {
+    return !Relocations.empty();
+  }
+
   /// emitByte - This callback is invoked when a byte needs to be
   /// written to the data stream.
   inline void emitByte(uint8_t B) {
@@ -317,6 +322,7 @@ public:
   void addRelocation(const MachineRelocation& relocation) {
     Relocations.push_back(relocation);
   }
+
 };
 
 } // end namespace llvm

include/llvm/Target/TargetELFWriterInfo.h

@@ -78,11 +78,32 @@ namespace llvm {
 
     /// Symbol Table Info
     unsigned getSymTabEntrySize() const { return is64Bit ? 24 : 16; }
-    unsigned getSymTabAlignment() const { return is64Bit ? 8 : 4; }
+
+    /// getPrefELFAlignment - Returns the preferred alignment for ELF. This
+    /// is used to align some sections.
+    unsigned getPrefELFAlignment() const { return is64Bit ? 8 : 4; }
+
+    /// getRelocationEntrySize - Entry size used in the relocation section
+    unsigned getRelocationEntrySize() const {
+      return is64Bit ? (hasRelocationAddend() ? 24 : 16)
+                     : (hasRelocationAddend() ? 12 : 8);
+    }
 
     /// getFunctionAlignment - Returns the alignment for function 'F', targets
     /// with different alignment constraints should overload this method
     virtual unsigned getFunctionAlignment(const Function *F) const;
+
+    /// getRelocationType - Returns the target specific ELF Relocation type.
+    /// 'MachineRelTy' contains the object code independent relocation type
+    virtual unsigned getRelocationType(unsigned MachineRelTy) const = 0;
+
+    /// hasRelocationAddend - True if the target uses an addend in the
+    /// ELF relocation entry.
+    virtual bool hasRelocationAddend() const = 0;
+
+    /// getAddendForRelTy - Gets the addend value for an ELF relocation entry
+    /// based on the target relocation type. If addend is not used returns 0.
+    virtual long int getAddendForRelTy(unsigned RelTy) const = 0;
   };
 
 } // end llvm namespace

lib/CodeGen/ELF.h

@@ -128,7 +128,13 @@ namespace llvm {
   /// added to logical symbol table for the module.  This is eventually
   /// turned into a real symbol table in the file.
   struct ELFSym {
-    const GlobalValue *GV;    // The global value this corresponds to.
+    // The global value this corresponds to. Global symbols can be on of the 
+    // 3 types : if this symbol has a zero initializer, it is common or should
+    // be placed in bss section otherwise it's a constant.
+    const GlobalValue *GV;
+    bool IsCommon;
+    bool IsBss;
+    bool IsConstant;
 
     // ELF specific fields
     unsigned NameIdx;         // Index in .strtab of name, once emitted.
@@ -159,8 +165,9 @@ namespace llvm {
       STV_PROTECTED = 3 // Visible in other components but not preemptable
     };
 
-    ELFSym(const GlobalValue *gv) : GV(gv), NameIdx(0), Value(0),
+    ELFSym(const GlobalValue *gv) : GV(gv), IsCommon(false), IsBss(false),
-                                    Size(0), Info(0), Other(0),
+                                    IsConstant(false), NameIdx(0), Value(0),
+                                    Size(0), Info(0), Other(STV_DEFAULT),
                                     SectionIdx(ELFSection::SHN_UNDEF) {
       if (!GV)
         return;
@@ -180,16 +187,47 @@ namespace llvm {
       }
     }
 
-    void SetBind(unsigned X) {
+    unsigned getBind() {
+      return (Info >> 4) & 0xf;
+    }
+
+    void setBind(unsigned X) {
       assert(X == (X & 0xF) && "Bind value out of range!");
       Info = (Info & 0x0F) | (X << 4);
     }
-    void SetType(unsigned X) {
+    void setType(unsigned X) {
       assert(X == (X & 0xF) && "Type value out of range!");
       Info = (Info & 0xF0) | X;
     }
   };
 
+  /// ELFRelocation - This class contains all the information necessary to
+  /// to generate any 32-bit or 64-bit ELF relocation entry.
+  class ELFRelocation {
+    uint64_t r_offset;    // offset in the section of the object this applies to
+    uint32_t r_symidx;    // symbol table index of the symbol to use
+    uint32_t r_type;      // machine specific relocation type
+    int64_t  r_add;       // explicit relocation addend
+    bool     r_rela;      // if true then the addend is part of the entry
+                          // otherwise the addend is at the location specified
+                          // by r_offset
+  public:
+    uint64_t getInfo(bool is64Bit) const {
+      if (is64Bit)
+        return ((uint64_t)r_symidx << 32) + ((uint64_t)r_type & 0xFFFFFFFFL);
+      else
+        return (r_symidx << 8)  + (r_type & 0xFFL);
+    }
+
+    uint64_t getOffset() const { return r_offset; }
+    int64_t getAddend() const { return r_add; }
+
+    ELFRelocation(uint64_t off, uint32_t sym, uint32_t type,
+                  bool rela = true, int64_t addend = 0) :
+      r_offset(off), r_symidx(sym), r_type(type),
+      r_add(addend), r_rela(rela) {}
+  };
+
 } // end namespace llvm
 
 #endif

lib/CodeGen/ELFCodeEmitter.cpp

@@ -71,38 +71,37 @@ bool ELFCodeEmitter::finishFunction(MachineFunction &MF) {
   // Update Section Size
   ES->Size = CurBufferPtr - BufferBegin;
 
-  // Figure out the binding (linkage) of the symbol.
-  switch (MF.getFunction()->getLinkage()) {
-  default:
-    // appending linkage is illegal for functions.
-    assert(0 && "Unknown linkage type!");
-  case GlobalValue::ExternalLinkage:
-    FnSym.SetBind(ELFSym::STB_GLOBAL);
-    break;
-  case GlobalValue::LinkOnceAnyLinkage:
-  case GlobalValue::LinkOnceODRLinkage:
-  case GlobalValue::WeakAnyLinkage:
-  case GlobalValue::WeakODRLinkage:
-    FnSym.SetBind(ELFSym::STB_WEAK);
-    break;
-  case GlobalValue::PrivateLinkage:
-    assert (0 && "PrivateLinkage should not be in the symbol table.");
-  case GlobalValue::InternalLinkage:
-    FnSym.SetBind(ELFSym::STB_LOCAL);
-    break;
-  }
-
   // Set the symbol type as a function
-  FnSym.SetType(ELFSym::STT_FUNC);
+  FnSym.setType(ELFSym::STT_FUNC);
-
   FnSym.SectionIdx = ES->SectionIdx;
   FnSym.Size = CurBufferPtr-FnStartPtr;
 
   // Offset from start of Section
   FnSym.Value = FnStartPtr-BufferBegin;
 
-  // Finally, add it to the symtab.
+  // Figure out the binding (linkage) of the symbol.
-  EW.SymbolList.push_back(FnSym);
+  switch (MF.getFunction()->getLinkage()) {
+  default:
+    // appending linkage is illegal for functions.
+    assert(0 && "Unknown linkage type!");
+  case GlobalValue::ExternalLinkage:
+    FnSym.setBind(ELFSym::STB_GLOBAL);
+    EW.SymbolList.push_back(FnSym);
+    break;
+  case GlobalValue::LinkOnceAnyLinkage:
+  case GlobalValue::LinkOnceODRLinkage:
+  case GlobalValue::WeakAnyLinkage:
+  case GlobalValue::WeakODRLinkage:
+    FnSym.setBind(ELFSym::STB_WEAK);
+    EW.SymbolList.push_back(FnSym);
+    break;
+  case GlobalValue::PrivateLinkage:
+    assert (0 && "PrivateLinkage should not be in the symbol table.");
+  case GlobalValue::InternalLinkage:
+    FnSym.setBind(ELFSym::STB_LOCAL);
+    EW.SymbolList.push_front(FnSym);
+    break;
+  }
 
   // Relocations
   // -----------
@@ -113,7 +112,6 @@ bool ELFCodeEmitter::finishFunction(MachineFunction &MF) {
   for (unsigned i = 0, e = Relocations.size(); i != e; ++i) {
     MachineRelocation &MR = Relocations[i];
     intptr_t Addr;
-
     if (MR.isBasicBlock()) {
       Addr = getMachineBasicBlockAddress(MR.getBasicBlock());
       MR.setConstantVal(ES->SectionIdx);

lib/CodeGen/ELFWriter.cpp

@@ -136,105 +136,41 @@ bool ELFWriter::doInitialization(Module &M) {
   ElfHdr.emitWord16(0); // Placeholder
 
   // Add the null section, which is required to be first in the file.
-  getSection("", ELFSection::SHT_NULL, 0);
+  getNullSection();
-
-  // Start up the symbol table.  The first entry in the symtab is the null 
-  // entry.
-  SymbolList.push_back(ELFSym(0));
 
   return false;
 }
 
-void ELFWriter::EmitGlobal(GlobalVariable *GV) {
+unsigned ELFWriter::getGlobalELFLinkage(const GlobalVariable *GV) {
+  if (GV->hasInternalLinkage())
+    return ELFSym::STB_LOCAL;
 
-  // XXX: put local symbols *before* global ones!
+  if (GV->hasWeakLinkage())
+    return ELFSym::STB_WEAK;
+
+  return ELFSym::STB_GLOBAL;
+}
+
+// For global symbols without a section, return the Null section as a
+// placeholder
+ELFSection &ELFWriter::getGlobalSymELFSection(const GlobalVariable *GV,
+                                              ELFSym &Sym) {
   const Section *S = TAI->SectionForGlobal(GV);
-  DOUT << "Section " << S->getName() << " for global " << GV->getName() << "\n";
+  unsigned Flags = S->getFlags();
-
+  unsigned SectionType = ELFSection::SHT_PROGBITS;
-  // If this is an external global, emit it now.  TODO: Note that it would be
+  unsigned SHdrFlags = ELFSection::SHF_ALLOC;
-  // better to ignore the symbol here and only add it to the symbol table if
-  // referenced.
-  if (!GV->hasInitializer()) {
-    ELFSym ExternalSym(GV);
-    ExternalSym.SetBind(ELFSym::STB_GLOBAL);
-    ExternalSym.SetType(ELFSym::STT_NOTYPE);
-    ExternalSym.SectionIdx = ELFSection::SHN_UNDEF;
-    SymbolList.push_back(ExternalSym);
-    return;
-  }
-
   const TargetData *TD = TM.getTargetData();
   unsigned Align = TD->getPreferredAlignment(GV);
   Constant *CV = GV->getInitializer();
-  unsigned Size = TD->getTypeAllocSize(CV->getType());
 
-  // If this global has a zero initializer, go to .bss or common section.
+  DOUT << "Section " << S->getName() << " for global " << GV->getName() << "\n";
-  if (CV->isNullValue() || isa<UndefValue>(CV)) {
-    // If this global is part of the common block, add it now.  Variables are
-    // part of the common block if they are zero initialized and allowed to be
-    // merged with other symbols.
-    if (GV->hasLinkOnceLinkage() || GV->hasWeakLinkage() ||
-        GV->hasCommonLinkage()) {
-      ELFSym CommonSym(GV);
-      // Value for common symbols is the alignment required.
-      CommonSym.Value = Align;
-      CommonSym.Size  = Size;
-      CommonSym.SetBind(ELFSym::STB_GLOBAL);
-      CommonSym.SetType(ELFSym::STT_OBJECT);
-      CommonSym.SectionIdx = ELFSection::SHN_COMMON;
-      SymbolList.push_back(CommonSym);
-      getSection(S->getName(), ELFSection::SHT_NOBITS,
-        ELFSection::SHF_WRITE | ELFSection::SHF_ALLOC, 1);
-      return;
-    }
 
-    // Otherwise, this symbol is part of the .bss section.  Emit it now.
+  // If this is an external global, the symbol does not have a section.
-    // Handle alignment.  Ensure section is aligned at least as much as required
+  if (!GV->hasInitializer()) {
-    // by this symbol.
+    Sym.SectionIdx = ELFSection::SHN_UNDEF;
-    ELFSection &BSSSection = getBSSSection();
+    return getNullSection();
-    BSSSection.Align = std::max(BSSSection.Align, Align);
-
-    // Within the section, emit enough virtual padding to get us to an alignment
-    // boundary.
-    if (Align)
-      BSSSection.Size = (BSSSection.Size + Align - 1) & ~(Align-1);
-
-    ELFSym BSSSym(GV);
-    BSSSym.Value = BSSSection.Size;
-    BSSSym.Size = Size;
-    BSSSym.SetType(ELFSym::STT_OBJECT);
-
-    switch (GV->getLinkage()) {
-    default:  // weak/linkonce/common handled above
-      assert(0 && "Unexpected linkage type!");
-    case GlobalValue::AppendingLinkage:  // FIXME: This should be improved!
-    case GlobalValue::ExternalLinkage:
-      BSSSym.SetBind(ELFSym::STB_GLOBAL);
-      break;
-    case GlobalValue::InternalLinkage:
-      BSSSym.SetBind(ELFSym::STB_LOCAL);
-      break;
-    }
-
-    // Set the idx of the .bss section
-    BSSSym.SectionIdx = BSSSection.SectionIdx;
-    if (!GV->hasPrivateLinkage())
-      SymbolList.push_back(BSSSym);
-
-    // Reserve space in the .bss section for this symbol.
-    BSSSection.Size += Size;
-    return;
   }
 
-  /// Emit the Global symbol to the right ELF section
-  ELFSym GblSym(GV);
-  GblSym.Size = Size;
-  GblSym.SetType(ELFSym::STT_OBJECT);
-  GblSym.SetBind(ELFSym::STB_GLOBAL);
-  unsigned Flags = S->getFlags();
-  unsigned SectType = ELFSection::SHT_PROGBITS;
-  unsigned SHdrFlags = ELFSection::SHF_ALLOC;
-
   if (Flags & SectionFlags::Code)
     SHdrFlags |= ELFSection::SHF_EXECINSTR;
   if (Flags & SectionFlags::Writeable)
@@ -246,29 +182,78 @@ void ELFWriter::EmitGlobal(GlobalVariable *GV) {
   if (Flags & SectionFlags::Strings)
     SHdrFlags |= ELFSection::SHF_STRINGS;
 
-  // Remove tab from section name prefix
+  // If this global has a zero initializer, go to .bss or common section.
-  std::string SectionName(S->getName());
+  // Variables are part of the common block if they are zero initialized
-  size_t Pos = SectionName.find("\t");
+  // and allowed to be merged with other symbols.
-  if (Pos != std::string::npos)
+  if (CV->isNullValue() || isa<UndefValue>(CV)) {
-    SectionName.erase(Pos, 1);
+    SectionType = ELFSection::SHT_NOBITS;
+    ELFSection &ElfS = getSection(S->getName(), SectionType, SHdrFlags);
+    if (GV->hasLinkOnceLinkage() || GV->hasWeakLinkage() ||
+        GV->hasCommonLinkage()) {
+      Sym.SectionIdx = ELFSection::SHN_COMMON;
+      Sym.IsCommon = true;
+      return ElfS;
+    }
+    Sym.IsBss = true;
+    Sym.SectionIdx = ElfS.SectionIdx;
+    if (Align) ElfS.Size = (ElfS.Size + Align-1) & ~(Align-1);
+    ElfS.Align = std::max(ElfS.Align, Align);
+    return ElfS;
+  }
 
-  // The section alignment should be bound to the element with
+  Sym.IsConstant = true;
-  // the largest alignment
+  ELFSection &ElfS = getSection(S->getName(), SectionType, SHdrFlags);
-  ELFSection &ElfS = getSection(SectionName, SectType, SHdrFlags);
+  Sym.SectionIdx = ElfS.SectionIdx;
-  GblSym.SectionIdx = ElfS.SectionIdx;
+  ElfS.Align = std::max(ElfS.Align, Align);
-  if (Align > ElfS.Align)
+  return ElfS;
-    ElfS.Align = Align;
+}
 
-  // S.Value should contain the symbol index inside the section,
+void ELFWriter::EmitFunctionDeclaration(const Function *F) {
-  // and all symbols should start on their required alignment boundary
+  ELFSym GblSym(F);
-  GblSym.Value = (ElfS.size() + (Align-1)) & (-Align);
+  GblSym.setBind(ELFSym::STB_GLOBAL);
-  ElfS.emitAlignment(Align);
+  GblSym.setType(ELFSym::STT_NOTYPE);
-
+  GblSym.SectionIdx = ELFSection::SHN_UNDEF;
-  // Emit the constant symbol to its section
-  EmitGlobalConstant(CV, ElfS);
   SymbolList.push_back(GblSym);
 }
 
+void ELFWriter::EmitGlobalVar(const GlobalVariable *GV) {
+  unsigned SymBind = getGlobalELFLinkage(GV);
+  ELFSym GblSym(GV);
+  GblSym.setBind(SymBind);
+
+  if (GV->hasInitializer())
+    GblSym.setType(ELFSym::STT_OBJECT);
+  else
+    GblSym.setType(ELFSym::STT_NOTYPE);
+
+  ELFSection &GblSection = getGlobalSymELFSection(GV, GblSym);
+  const TargetData *TD = TM.getTargetData();
+  unsigned Align = TD->getPreferredAlignment(GV);
+  unsigned Size = TD->getTypeAllocSize(GV->getInitializer()->getType());
+  GblSym.Size = Size;
+
+  if (GblSym.IsCommon) {
+    GblSym.Value = Align;
+  } else if (GblSym.IsBss) {
+    GblSym.Value = GblSection.Size;
+    GblSection.Size += Size;
+  } else if (GblSym.IsConstant){
+    // GblSym.Value should contain the symbol index inside the section,
+    // and all symbols should start on their required alignment boundary
+    GblSym.Value = (GblSection.size() + (Align-1)) & (-Align);
+    GblSection.emitAlignment(Align);
+    EmitGlobalConstant(GV->getInitializer(), GblSection);
+  }
+
+  // Local symbols should come first on the symbol table.
+  if (!GV->hasPrivateLinkage()) {
+    if (SymBind == ELFSym::STB_LOCAL)
+      SymbolList.push_front(GblSym);
+    else
+      SymbolList.push_back(GblSym);
+  }
+}
+
 void ELFWriter::EmitGlobalConstantStruct(const ConstantStruct *CVS,
                                          ELFSection &GblS) {
 
@@ -306,6 +291,7 @@ void ELFWriter::EmitGlobalConstant(const Constant *CV, ELFSection &GblS) {
   if (const ConstantArray *CVA = dyn_cast<ConstantArray>(CV)) {
     if (CVA->isString()) {
       std::string GblStr = CVA->getAsString();
+      GblStr.resize(GblStr.size()-1);
       GblS.emitString(GblStr);
     } else { // Not a string.  Print the values in successive locations
       for (unsigned i = 0, e = CVA->getNumOperands(); i != e; ++i)
@@ -370,8 +356,31 @@ bool ELFWriter::doFinalization(Module &M) {
 
   // Build and emit data, bss and "common" sections.
   for (Module::global_iterator I = M.global_begin(), E = M.global_end();
-       I != E; ++I)
+       I != E; ++I) {
-    EmitGlobal(I);
+    EmitGlobalVar(I);
+    GblSymLookup[I] = 0;
+  }
+
+  // Emit all pending globals
+  // TODO: this should be done only for referenced symbols
+  for (SetVector<GlobalValue*>::const_iterator I = PendingGlobals.begin(),
+       E = PendingGlobals.end(); I != E; ++I) {
+
+    // No need to emit the symbol again
+    if (GblSymLookup.find(*I) != GblSymLookup.end())
+      continue;
+
+    if (GlobalVariable *GV = dyn_cast<GlobalVariable>(*I)) {
+      EmitGlobalVar(GV);
+    } else if (Function *F = dyn_cast<Function>(*I)) {
+      // If function is not in GblSymLookup, it doesn't have a body,
+      // so emit the symbol as a function declaration (no section associated)
+      EmitFunctionDeclaration(F);
+    } else {
+      assert("unknown howto handle pending global");
+    }
+    GblSymLookup[*I] = 0;
+  }
 
   // Emit non-executable stack note
   if (TAI->getNonexecutableStackDirective())
@@ -400,6 +409,67 @@ bool ELFWriter::doFinalization(Module &M) {
 
 /// EmitRelocations - Emit relocations
 void ELFWriter::EmitRelocations() {
+
+  // Create Relocation sections for each section which needs it.
+  for (std::list<ELFSection>::iterator I = SectionList.begin(),
+       E = SectionList.end(); I != E; ++I) {
+
+    // This section does not have relocations
+    if (!I->hasRelocations()) continue;
+
+    // Get the relocation section for section 'I'
+    bool HasRelA = TEW->hasRelocationAddend();
+    ELFSection &RelSec = getRelocSection(I->getName(), HasRelA);
+
+    // 'Link' - Section hdr idx of the associated symbol table
+    // 'Info' - Section hdr idx of the section to which the relocation applies
+    ELFSection &SymTab = getSymbolTableSection();
+    RelSec.Link = SymTab.SectionIdx;
+    RelSec.Info = I->SectionIdx;
+    RelSec.EntSize = TEW->getRelocationEntrySize();
+
+    // Get the relocations from Section
+    std::vector<MachineRelocation> Relos = I->getRelocations();
+    for (std::vector<MachineRelocation>::iterator MRI = Relos.begin(),
+         MRE = Relos.end(); MRI != MRE; ++MRI) {
+      MachineRelocation &MR = *MRI;
+
+      // Offset from the start of the section containing the symbol
+      unsigned Offset = MR.getMachineCodeOffset();
+
+      // Symbol index in the symbol table
+      unsigned SymIdx = 0;
+
+      // Target specific ELF relocation type
+      unsigned RelType = TEW->getRelocationType(MR.getRelocationType());
+
+      // Constant addend used to compute the value to be stored 
+      // into the relocatable field
+      int64_t Addend = TEW->getAddendForRelTy(RelType);
+
+      // There are several machine relocations types, and each one of
+      // them needs a different approach to retrieve the symbol table index.
+      if (MR.isGlobalValue()) {
+        const GlobalValue *G = MR.getGlobalValue();
+        SymIdx = GblSymLookup[G];
+      } else {
+        assert(0 && "dunno how to handle other relocation types");
+      }
+
+      // Get the relocation entry and emit to the relocation section
+      ELFRelocation Rel(Offset, SymIdx, RelType, HasRelA, Addend);
+      EmitRelocation(RelSec, Rel, HasRelA);
+    }
+  }
+}
+
+/// EmitRelocation - Write relocation 'Rel' to the relocation section 'Rel'
+void ELFWriter::EmitRelocation(BinaryObject &RelSec, ELFRelocation &Rel,
+                               bool HasRelA) {
+  RelSec.emitWord(Rel.getOffset());
+  RelSec.emitWord(Rel.getInfo(is64Bit));
+  if (HasRelA)
+    RelSec.emitWord(Rel.getAddend());
 }
 
 /// EmitSymbol - Write symbol 'Sym' to the symbol table 'SymbolTable'
@@ -451,25 +521,27 @@ void ELFWriter::EmitSectionHeader(BinaryObject &SHdrTab,
 /// EmitSymbolTable - If the current symbol table is non-empty, emit the string
 /// table for it and then the symbol table itself.
 void ELFWriter::EmitSymbolTable() {
-  if (SymbolList.size() == 1) return;  // Only the null entry.
+  if (!SymbolList.size()) return;  // Empty symbol table.
 
-  // FIXME: compact all local symbols to the start of the symtab.
   unsigned FirstNonLocalSymbol = 1;
-
   ELFSection &StrTab = getStringTableSection();
 
   // Set the zero'th symbol to a null byte, as required.
   StrTab.emitByte(0);
 
+  // Walk on the symbol list and write symbol names into the
+  // string table.
   unsigned Index = 1;
-  for (unsigned i = 1, e = SymbolList.size(); i != e; ++i) {
+  for (std::list<ELFSym>::iterator I = SymbolList.begin(),
+       E = SymbolList.end(); I != E; ++I) {
+
     // Use the name mangler to uniquify the LLVM symbol.
-    std::string Name = Mang->getValueName(SymbolList[i].GV);
+    std::string Name = Mang->getValueName(I->GV);
 
     if (Name.empty()) {
-      SymbolList[i].NameIdx = 0;
+      I->NameIdx = 0;
     } else {
-      SymbolList[i].NameIdx = Index;
+      I->NameIdx = Index;
       StrTab.emitString(Name);
 
       // Keep track of the number of bytes emitted to this section.
@@ -482,16 +554,33 @@ void ELFWriter::EmitSymbolTable() {
   // Now that we have emitted the string table and know the offset into the
   // string table of each symbol, emit the symbol table itself.
   ELFSection &SymTab = getSymbolTableSection();
-  SymTab.Align = TEW->getSymTabAlignment();
+  SymTab.Align = TEW->getPrefELFAlignment();
   SymTab.Link  = StrTab.SectionIdx;      // Section Index of .strtab.
-  SymTab.Info  = FirstNonLocalSymbol;    // First non-STB_LOCAL symbol.
 
   // Size of each symtab entry.
   SymTab.EntSize = TEW->getSymTabEntrySize();
 
-  for (unsigned i = 0, e = SymbolList.size(); i != e; ++i)
+  // The first entry in the symtab is the null symbol
-    EmitSymbol(SymTab, SymbolList[i]);
+  ELFSym NullSym = ELFSym(0);
+  EmitSymbol(SymTab, NullSym);
 
+  // Emit all the symbols to the symbol table. Skip the null
+  // symbol, cause it's emitted already
+  Index = 1;
+  for (std::list<ELFSym>::iterator I = SymbolList.begin(),
+       E = SymbolList.end(); I != E; ++I, ++Index) {
+    // Keep track of the first non-local symbol
+    if (I->getBind() == ELFSym::STB_LOCAL)
+      FirstNonLocalSymbol++;
+
+    // Emit symbol to the symbol table
+    EmitSymbol(SymTab, *I);
+
+    // Record the symbol table index for each global value
+    GblSymLookup[I->GV] = Index;
+  }
+
+  SymTab.Info = FirstNonLocalSymbol;
   SymTab.Size = SymTab.size();
 }
 
@@ -559,7 +648,7 @@ void ELFWriter::OutputSectionsAndSectionTable() {
   }
 
   // Align Section Header.
-  unsigned TableAlign = is64Bit ? 8 : 4;
+  unsigned TableAlign = TEW->getPrefELFAlignment();
   FileOff = (FileOff+TableAlign-1) & ~(TableAlign-1);
 
   // Now that we know where all of the sections will be emitted, set the e_shnum

lib/CodeGen/ELFWriter.h

@@ -16,7 +16,7 @@
 
 #include "llvm/ADT/SetVector.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
-#include "llvm/Support/OutputBuffer.h"
+#include "llvm/Support/Debug.h"
 #include "llvm/Target/TargetAsmInfo.h"
 #include "llvm/Target/TargetELFWriterInfo.h"
 #include "ELF.h"
@@ -89,7 +89,7 @@ namespace llvm {
     bool doFinalization(Module &M);
 
   private:
-    // Blob containing the Elf header
+    /// Blob containing the Elf header
     BinaryObject ElfHdr;
 
     /// SectionList - This is the list of sections that we have emitted to the
@@ -102,14 +102,35 @@ namespace llvm {
     /// the SectionList.
     std::map<std::string, ELFSection*> SectionLookup;
 
+    /// GblSymLookup - This is a mapping from global value to a symbol index
+    /// in the symbol table. This is useful since relocations symbol references
+    /// must be quickly mapped to a symbol table index
+    std::map<const GlobalValue*, uint32_t> GblSymLookup;
+
+    /// SymbolList - This is the list of symbols emitted to the symbol table
+    /// Local symbols go to the front and Globals to the back.
+    std::list<ELFSym> SymbolList;
+
+    /// PendingGlobals - List of externally defined symbols that we have been
+    /// asked to emit, but have not seen a reference to.  When a reference
+    /// is seen, the symbol will move from this list to the SymbolList.
+    SetVector<GlobalValue*> PendingGlobals;
+
     /// getSection - Return the section with the specified name, creating a new
     /// section if one does not already exist.
-    ELFSection &getSection(const std::string &Name, unsigned Type, 
+    ELFSection &getSection(const std::string &Name, unsigned Type,
                            unsigned Flags = 0, unsigned Align = 0) {
       ELFSection *&SN = SectionLookup[Name];
       if (SN) return *SN;
 
-      SectionList.push_back(ELFSection(Name, isLittleEndian, is64Bit));
+      // Remove tab from section name prefix. This is necessary becase TAI 
+      // sometimes return a section name prefixed with a "\t" char.
+      std::string SectionName(Name);
+      size_t Pos = SectionName.find("\t");
+      if (Pos != std::string::npos)
+        SectionName.erase(Pos, 1);
+
+      SectionList.push_back(ELFSection(SectionName, isLittleEndian, is64Bit));
       SN = &SectionList.back();
       SN->SectionIdx = NumSections++;
       SN->Type = Type;
@@ -119,11 +140,25 @@ namespace llvm {
       return *SN;
     }
 
+    /// TODO: support mangled names here to emit the right .text section
+    /// for c++ object files.
     ELFSection &getTextSection() {
       return getSection(".text", ELFSection::SHT_PROGBITS,
                         ELFSection::SHF_EXECINSTR | ELFSection::SHF_ALLOC);
     }
 
+    /// Return the relocation section of section 'S'. 'RelA' is true
+    /// if the relocation section contains entries with addends.
+    ELFSection &getRelocSection(std::string SName, bool RelA) {
+      std::string RelSName(".rel");
+      unsigned SHdrTy = RelA ? ELFSection::SHT_RELA : ELFSection::SHT_REL;
+
+      if (RelA) RelSName.append("a");
+      RelSName.append(SName);
+
+      return getSection(RelSName, SHdrTy, 0, TEW->getPrefELFAlignment());
+    }
+
     ELFSection &getNonExecStackSection() {
       return getSection(".note.GNU-stack", ELFSection::SHT_PROGBITS, 0, 1);
     }
@@ -146,15 +181,9 @@ namespace llvm {
                         ELFSection::SHF_WRITE | ELFSection::SHF_ALLOC);
     }
 
-    /// SymbolList - This is the list of symbols we have emitted to the file.
+    ELFSection &getNullSection() {
-    /// This actually gets rearranged before emission to the file (to put the
+      return getSection("", ELFSection::SHT_NULL, 0);
-    /// local symbols first in the list).
+    }
-    std::vector<ELFSym> SymbolList;
-
-    /// PendingGlobals - List of externally defined symbols that we have been
-    /// asked to emit, but have not seen a reference to.  When a reference
-    /// is seen, the symbol will move from this list to the SymbolList.
-    SetVector<GlobalValue*> PendingGlobals;
 
     // As we complete the ELF file, we need to update fields in the ELF header
     // (e.g. the location of the section table).  These members keep track of
@@ -165,11 +194,15 @@ namespace llvm {
     unsigned ELFHdr_e_shnum_Offset;     // e_shnum    in ELF header.
 
   private:
-    void EmitGlobal(GlobalVariable *GV);
+    void EmitFunctionDeclaration(const Function *F);
+    void EmitGlobalVar(const GlobalVariable *GV);
     void EmitGlobalConstant(const Constant *C, ELFSection &GblS);
     void EmitGlobalConstantStruct(const ConstantStruct *CVS,
                                   ELFSection &GblS);
+    unsigned getGlobalELFLinkage(const GlobalVariable *GV);
+    ELFSection &getGlobalSymELFSection(const GlobalVariable *GV, ELFSym &Sym);
     void EmitRelocations();
+    void EmitRelocation(BinaryObject &RelSec, ELFRelocation &Rel, bool HasRelA);
     void EmitSectionHeader(BinaryObject &SHdrTab, const ELFSection &SHdr);
     void EmitSectionTableStringTable();
     void EmitSymbol(BinaryObject &SymbolTable, ELFSym &Sym);

lib/Target/X86/X86ELFWriterInfo.cpp

@@ -12,11 +12,17 @@
 //===----------------------------------------------------------------------===//
 
 #include "X86ELFWriterInfo.h"
+#include "X86Relocations.h"
 #include "llvm/Function.h"
 #include "llvm/Target/TargetData.h"
 #include "llvm/Target/TargetMachine.h"
+
 using namespace llvm;
 
+//===----------------------------------------------------------------------===//
+//  Implementation of the X86ELFWriterInfo class
+//===----------------------------------------------------------------------===//
+
 X86ELFWriterInfo::X86ELFWriterInfo(TargetMachine &TM)
   : TargetELFWriterInfo(TM) {
     bool is64Bit = TM.getTargetData()->getPointerSizeInBits() == 64;
@@ -25,6 +31,34 @@ X86ELFWriterInfo::X86ELFWriterInfo(TargetMachine &TM)
 
 X86ELFWriterInfo::~X86ELFWriterInfo() {}
 
+unsigned X86ELFWriterInfo::getRelocationType(unsigned MachineRelTy) const {
+  if (is64Bit) {
+    switch(MachineRelTy) {
+    case X86::reloc_pcrel_word:
+      return R_X86_64_PC32;
+    case X86::reloc_absolute_word:
+      return R_X86_64_32;
+    case X86::reloc_absolute_dword:
+      return R_X86_64_64;
+    case X86::reloc_picrel_word:
+    default:
+      assert(0 && "unknown relocation type");
+    }
+  } else {
+    switch(MachineRelTy) {
+    case X86::reloc_pcrel_word:
+      return R_386_PC32;
+    case X86::reloc_absolute_word:
+      return R_386_32;
+    case X86::reloc_absolute_dword:
+    case X86::reloc_picrel_word:
+    default:
+      assert(0 && "unknown relocation type");
+    }
+  }
+  return 0;
+}
+
 unsigned X86ELFWriterInfo::getFunctionAlignment(const Function *F) const {
   unsigned FnAlign = 4;
 
@@ -36,3 +70,15 @@ unsigned X86ELFWriterInfo::getFunctionAlignment(const Function *F) const {
 
   return (1 << FnAlign);
 }
+
+long int X86ELFWriterInfo::getAddendForRelTy(unsigned RelTy) const {
+  if (is64Bit) {
+    switch(RelTy) {
+    case R_X86_64_PC32: return -4;
+      break;
+    default:
+      assert(0 && "unknown x86 relocation type");
+    }
+  }
+  return 0;
+}

lib/Target/X86/X86ELFWriterInfo.h

@@ -19,11 +19,43 @@
 namespace llvm {
 
   class X86ELFWriterInfo : public TargetELFWriterInfo {
+
+    // ELF Relocation types for X86
+    enum X86RelocationType {
+      R_386_NONE = 0,
+      R_386_32   = 1,
+      R_386_PC32 = 2
+    };
+
+    // ELF Relocation types for X86_64
+    enum X86_64RelocationType {
+      R_X86_64_NONE = 0,
+      R_X86_64_64   = 1,
+      R_X86_64_PC32 = 2,
+      R_X86_64_32   = 10,
+      R_X86_64_32S  = 11,
+      R_X86_64_PC64 = 24
+    };
+
   public:
     X86ELFWriterInfo(TargetMachine &TM);
     virtual ~X86ELFWriterInfo();
 
+    /// getFunctionAlignment - Returns the alignment for function 'F', targets
+    /// with different alignment constraints should overload this method
     virtual unsigned getFunctionAlignment(const Function *F) const;
+
+    /// getRelocationType - Returns the target specific ELF Relocation type.
+    /// 'MachineRelTy' contains the object code independent relocation type
+    virtual unsigned getRelocationType(unsigned MachineRelTy) const;
+
+    /// hasRelocationAddend - True if the target uses an addend in the
+    /// ELF relocation entry.
+    virtual bool hasRelocationAddend() const { return is64Bit ? true : false; }
+
+    /// getAddendForRelTy - Gets the addend value for an ELF relocation entry
+    /// based on the target relocation type
+    virtual long int getAddendForRelTy(unsigned RelTy) const;
   };
 
 } // end llvm namespace