MC-COFF: Drop empty sections, and label symbols. Convert relocations

targeted at symbols into relocations relative to the containing section.

Patch by Nathan Jeffords!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@114823 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 163 insertions, 82 deletions

diff --git a/lib/MC/WinCOFFObjectWriter.cpp b/lib/MC/WinCOFFObjectWriter.cpp
index eeb2b96..d686098 100644
--- a/lib/MC/WinCOFFObjectWriter.cpp
+++ b/lib/MC/WinCOFFObjectWriter.cpp
@@ -55,6 +55,9 @@ struct AuxSymbol {
   COFF::Auxiliary Aux;
 };
 
+class COFFSymbol;
+class COFFSection;
+
 class COFFSymbol {
 public:
   COFF::symbol Data;
@@ -65,12 +68,16 @@ public:
   size_t           Index;
   AuxiliarySymbols Aux;
   COFFSymbol      *Other;
+  COFFSection     *Section;
+  int              Relocations;
 
   MCSymbolData const *MCData;
 
-  COFFSymbol(llvm::StringRef name, size_t index);
+  COFFSymbol(llvm::StringRef name);
   size_t size() const;
   void set_name_offset(uint32_t Offset);
+
+  bool should_keep() const;
 };
 
 // This class contains staging data for a COFF relocation entry.
@@ -91,10 +98,10 @@ public:
   std::string          Name;
   size_t               Number;
   MCSectionData const *MCData;
-  COFFSymbol              *Symb;
+  COFFSymbol          *Symbol;
   relocations          Relocations;
 
-  COFFSection(llvm::StringRef name, size_t Index);
+  COFFSection(llvm::StringRef name);
   static size_t size();
 };
 
@@ -141,18 +148,20 @@ public:
   COFFSymbol *createSymbol(llvm::StringRef Name);
   COFFSection *createSection(llvm::StringRef Name);
 
-  void InitCOFFEntity(COFFSymbol &Symbol);
-  void InitCOFFEntity(COFFSection &Section);
-
   template <typename object_t, typename list_t>
   object_t *createCOFFEntity(llvm::StringRef Name, list_t &List);
 
   void DefineSection(MCSectionData const &SectionData);
   void DefineSymbol(MCSymbolData const &SymbolData, MCAssembler &Assembler);
 
-  bool ExportSection(COFFSection *S);
+  void MakeSymbolReal(COFFSymbol &S, size_t Index);
+  void MakeSectionReal(COFFSection &S, size_t Number);
+
+  bool ExportSection(COFFSection const *S);
   bool ExportSymbol(MCSymbolData const &SymbolData, MCAssembler &Asm);
 
+  bool IsPhysicalSection(COFFSection *S);
+
   // Entity writing methods.
 
   void WriteFileHeader(const COFF::header &Header);
@@ -198,9 +207,12 @@ static inline void write_uint8_le(void *Data, uint8_t const &Value) {
 //------------------------------------------------------------------------------
 // Symbol class implementation
 
-COFFSymbol::COFFSymbol(llvm::StringRef name, size_t index)
-      : Name(name.begin(), name.end()), Index(-1)
-      , Other(NULL), MCData(NULL) {
+COFFSymbol::COFFSymbol(llvm::StringRef name)
+  : Name(name.begin(), name.end())
+  , Other(NULL)
+  , Section(NULL)
+  , Relocations(0)
+  , MCData(NULL) {
   memset(&Data, 0, sizeof(Data));
 }
 
@@ -216,12 +228,41 @@ void COFFSymbol::set_name_offset(uint32_t Offset) {
   write_uint32_le(Data.Name + 4, Offset);
 }
 
+/// logic to decide if the symbol should be reported in the symbol table
+bool COFFSymbol::should_keep() const {
+  // no section means its external, keep it
+  if (Section == NULL)
+    return true;
+
+  // if it has relocations pointing at it, keep it
+  if (Relocations > 0)   {
+    assert(Section->Number != -1 && "Sections with relocations must be real!");
+    return true;
+  }
+
+  // if the section its in is being droped, drop it
+  if (Section->Number == -1)
+      return false;
+
+  // if it is the section symbol, keep it
+  if (Section->Symbol == this)
+    return true;
+
+  // if its temporary, drop it
+  if (MCData && MCData->getSymbol().isTemporary())
+      return false;
+
+  // otherwise, keep it
+  return true;
+}
+
 //------------------------------------------------------------------------------
 // Section class implementation
 
-COFFSection::COFFSection(llvm::StringRef name, size_t Index)
-       : Name(name), Number(Index + 1)
-       , MCData(NULL), Symb(NULL) {
+COFFSection::COFFSection(llvm::StringRef name)
+  : Name(name)
+  , MCData(NULL)
+  , Symbol(NULL) {
   memset(&Header, 0, sizeof(Header));
 }
 
@@ -298,45 +339,12 @@ COFFSection *WinCOFFObjectWriter::createSection(llvm::StringRef Name) {
   return createCOFFEntity<COFFSection>(Name, Sections);
 }
 
-/// This function initializes a symbol by entering its name into the string
-/// table if it is too long to fit in the symbol table header.
-void WinCOFFObjectWriter::InitCOFFEntity(COFFSymbol &S) {
-  if (S.Name.size() > COFF::NameSize) {
-    size_t StringTableEntry = Strings.insert(S.Name.c_str());
-
-    S.set_name_offset(StringTableEntry);
-  } else
-    memcpy(S.Data.Name, S.Name.c_str(), S.Name.size());
-}
-
-/// This function initializes a section by entering its name into the string
-/// table if it is too long to fit in the section table header.
-void WinCOFFObjectWriter::InitCOFFEntity(COFFSection &S) {
-  if (S.Name.size() > COFF::NameSize) {
-    size_t StringTableEntry = Strings.insert(S.Name.c_str());
-
-    // FIXME: Why is this number 999999? This number is never mentioned in the
-    // spec. I'm assuming this is due to the printed value needing to fit into
-    // the S.Header.Name field. In which case why not 9999999 (7 9's instead of
-    // 6)? The spec does not state if this entry should be null terminated in
-    // this case, and thus this seems to be the best way to do it. I think I
-    // just solved my own FIXME...
-    if (StringTableEntry > 999999)
-      report_fatal_error("COFF string table is greater than 999999 bytes.");
-
-    sprintf(S.Header.Name, "/%d", (unsigned)StringTableEntry);
-  } else
-    memcpy(S.Header.Name, S.Name.c_str(), S.Name.size());
-}
-
 /// A template used to lookup or create a symbol/section, and initialize it if
 /// needed.
 template <typename object_t, typename list_t>
 object_t *WinCOFFObjectWriter::createCOFFEntity(llvm::StringRef Name,
                                                 list_t &List) {
-  object_t *Object = new object_t(Name, List.size());
-
-  InitCOFFEntity(*Object);
+  object_t *Object = new object_t(Name);
 
   List.push_back(Object);
 
@@ -353,15 +361,14 @@ void WinCOFFObjectWriter::DefineSection(MCSectionData const &SectionData) {
   COFFSection *coff_section = createSection(Sec.getSectionName());
   COFFSymbol  *coff_symbol = createSymbol(Sec.getSectionName());
 
-  coff_section->Symb = coff_symbol;
+  coff_section->Symbol = coff_symbol;
+  coff_symbol->Section = coff_section;
   coff_symbol->Data.StorageClass = COFF::IMAGE_SYM_CLASS_STATIC;
-  coff_symbol->Data.SectionNumber = coff_section->Number;
 
   // In this case the auxiliary symbol is a Section Definition.
   coff_symbol->Aux.resize(1);
   memset(&coff_symbol->Aux[0], 0, sizeof(coff_symbol->Aux[0]));
   coff_symbol->Aux[0].AuxType = ATSectionDefinition;
-  coff_symbol->Aux[0].Aux.SectionDefinition.Number = coff_section->Number;
   coff_symbol->Aux[0].Aux.SectionDefinition.Selection = Sec.getSelection();
 
   coff_section->Header.Characteristics = Sec.getCharacteristics();
@@ -394,7 +401,9 @@ void WinCOFFObjectWriter::DefineSection(MCSectionData const &SectionData) {
 /// This function takes a section data object from the assembler
 /// and creates the associated COFF symbol staging object.
 void WinCOFFObjectWriter::DefineSymbol(MCSymbolData const &SymbolData,
-                                        MCAssembler &Assembler) {
+                                       MCAssembler &Assembler) {
+  assert(!SymbolData.getSymbol().isVariable()
+    && "Cannot define a symbol that is a variable!");
   COFFSymbol *coff_symbol = createSymbol(SymbolData.getSymbol().getName());
 
   coff_symbol->Data.Type         = (SymbolData.getFlags() & 0x0000FFFF) >>  0;
@@ -405,7 +414,7 @@ void WinCOFFObjectWriter::DefineSymbol(MCSymbolData const &SymbolData,
     bool external = SymbolData.isExternal() || (SymbolData.Fragment == NULL);
 
     coff_symbol->Data.StorageClass =
-      external ? COFF::IMAGE_SYM_CLASS_EXTERNAL : COFF::IMAGE_SYM_CLASS_STATIC;
+      external ? COFF::IMAGE_SYM_CLASS_EXTERNAL : COFF::IMAGE_SYM_CLASS_LABEL;
   }
 
   if (SymbolData.getFlags() & COFF::SF_WeakReference) {
@@ -438,14 +447,50 @@ void WinCOFFObjectWriter::DefineSymbol(MCSymbolData const &SymbolData,
                                         COFF::IMAGE_WEAK_EXTERN_SEARCH_LIBRARY;
   }
 
+  if (SymbolData.Fragment != NULL)
+    coff_symbol->Section = SectionMap[SymbolData.Fragment->getParent()];
+
   // Bind internal COFF symbol to MC symbol.
   coff_symbol->MCData = &SymbolData;
   SymbolMap[&SymbolData] = coff_symbol;
 }
 
-bool WinCOFFObjectWriter::ExportSection(COFFSection *S) {
-  return (S->Header.Characteristics
-         & COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA) == 0;
+/// making a section real involves assigned it a number and putting
+/// name into the string table if needed
+void WinCOFFObjectWriter::MakeSectionReal(COFFSection &S, size_t Number) {
+  if (S.Name.size() > COFF::NameSize) {
+    size_t StringTableEntry = Strings.insert(S.Name.c_str());
+
+    // FIXME: Why is this number 999999? This number is never mentioned in the
+    // spec. I'm assuming this is due to the printed value needing to fit into
+    // the S.Header.Name field. In which case why not 9999999 (7 9's instead of
+    // 6)? The spec does not state if this entry should be null terminated in
+    // this case, and thus this seems to be the best way to do it. I think I
+    // just solved my own FIXME...
+    if (StringTableEntry > 999999)
+      report_fatal_error("COFF string table is greater than 999999 bytes.");
+
+    std::sprintf(S.Header.Name, "/%d", unsigned(StringTableEntry));
+  } else
+    std::memcpy(S.Header.Name, S.Name.c_str(), S.Name.size());
+
+  S.Number = Number;
+  S.Symbol->Data.SectionNumber = S.Number;
+  S.Symbol->Aux[0].Aux.SectionDefinition.Number = S.Number;
+}
+
+void WinCOFFObjectWriter::MakeSymbolReal(COFFSymbol &S, size_t Index) {
+  if (S.Name.size() > COFF::NameSize) {
+    size_t StringTableEntry = Strings.insert(S.Name.c_str());
+
+    S.set_name_offset(StringTableEntry);
+  } else
+    std::memcpy(S.Data.Name, S.Name.c_str(), S.Name.size());
+  S.Index = Index;
+}
+
+bool WinCOFFObjectWriter::ExportSection(COFFSection const *S) {
+  return !S->MCData->getFragmentList().empty();
 }
 
 bool WinCOFFObjectWriter::ExportSymbol(MCSymbolData const &SymbolData,
@@ -455,8 +500,14 @@ bool WinCOFFObjectWriter::ExportSymbol(MCSymbolData const &SymbolData,
 
   // return Asm.isSymbolLinkerVisible (&SymbolData);
 
-  // For now, all symbols are exported, the linker will sort it out for us.
-  return true;
+  // For now, all non-variable symbols are exported,
+  // the linker will sort the rest out for us.
+  return !SymbolData.getSymbol().isVariable();
+}
+
+bool WinCOFFObjectWriter::IsPhysicalSection(COFFSection *S) {
+  return (S->Header.Characteristics
+         & COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA) == 0;
 }
 
 //------------------------------------------------------------------------------
@@ -548,7 +599,7 @@ void WinCOFFObjectWriter::WriteRelocation(const COFF::relocation &R) {
 
 void WinCOFFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm) {
   // "Define" each section & symbol. This creates section & symbol
-  // entries in the staging area and gives them their final indexes.
+  // entries in the staging area.
 
   for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e; i++)
     DefineSection(*i);
@@ -600,7 +651,15 @@ void WinCOFFObjectWriter::RecordRelocation(const MCAssembler &Asm,
 
   Reloc.Data.SymbolTableIndex = 0;
   Reloc.Data.VirtualAddress = Layout.getFragmentOffset(Fragment);
-  Reloc.Symb = coff_symbol;
+
+  // turn relocations for temporary symbols into section relocations
+  if (coff_symbol->MCData->getSymbol().isTemporary()) {
+    Reloc.Symb = coff_symbol->Section->Symbol;
+    FixedValue += Layout.getFragmentOffset(coff_symbol->MCData->Fragment);
+  } else
+    Reloc.Symb = coff_symbol;
+
+  ++Reloc.Symb->Relocations;
 
   Reloc.Data.VirtualAddress += Fixup.getOffset();
 
@@ -634,6 +693,16 @@ void WinCOFFObjectWriter::RecordRelocation(const MCAssembler &Asm,
 void WinCOFFObjectWriter::WriteObject(const MCAssembler &Asm,
                                       const MCAsmLayout &Layout) {
   // Assign symbol and section indexes and offsets.
+  Header.NumberOfSections = 0;
+
+  for (sections::iterator i = Sections.begin(),
+                          e = Sections.end(); i != e; i++) {
+    if (Layout.getSectionSize((*i)->MCData) > 0) {
+      MakeSectionReal(**i, ++Header.NumberOfSections);
+    } else {
+      (*i)->Number = -1;
+    }
+  }
 
   Header.NumberOfSymbols = 0;
 
@@ -641,32 +710,35 @@ void WinCOFFObjectWriter::WriteObject(const MCAssembler &Asm,
     COFFSymbol *coff_symbol = *i;
     MCSymbolData const *SymbolData = coff_symbol->MCData;
 
-    coff_symbol->Index = Header.NumberOfSymbols++;
-
     // Update section number & offset for symbols that have them.
     if ((SymbolData != NULL) && (SymbolData->Fragment != NULL)) {
-      COFFSection *coff_section = SectionMap[SymbolData->Fragment->getParent()];
+      assert(coff_symbol->Section != NULL);
 
-      coff_symbol->Data.SectionNumber = coff_section->Number;
+      coff_symbol->Data.SectionNumber = coff_symbol->Section->Number;
       coff_symbol->Data.Value = Layout.getFragmentOffset(SymbolData->Fragment)
                               + SymbolData->Offset;
     }
 
-    // Update auxiliary symbol info.
-    coff_symbol->Data.NumberOfAuxSymbols = coff_symbol->Aux.size();
-    Header.NumberOfSymbols += coff_symbol->Data.NumberOfAuxSymbols;
+    if (coff_symbol->should_keep()) {
+      MakeSymbolReal(*coff_symbol, Header.NumberOfSymbols++);
+
+      // Update auxiliary symbol info.
+      coff_symbol->Data.NumberOfAuxSymbols = coff_symbol->Aux.size();
+      Header.NumberOfSymbols += coff_symbol->Data.NumberOfAuxSymbols;
+    } else
+      coff_symbol->Index = -1;
   }
 
   // Fixup weak external references.
   for (symbols::iterator i = Symbols.begin(), e = Symbols.end(); i != e; i++) {
-    COFFSymbol *symb = *i;
-
-    if (symb->Other != NULL) {
-      assert(symb->Aux.size() == 1 &&
+    COFFSymbol *coff_symbol = *i;
+    if (coff_symbol->Other != NULL) {
+      assert(coff_symbol->Index != -1);
+      assert(coff_symbol->Aux.size() == 1 &&
              "Symbol must contain one aux symbol!");
-      assert(symb->Aux[0].AuxType == ATWeakExternal &&
+      assert(coff_symbol->Aux[0].AuxType == ATWeakExternal &&
              "Symbol's aux symbol must be a Weak External!");
-      symb->Aux[0].Aux.WeakExternal.TagIndex = symb->Other->Index;
+      coff_symbol->Aux[0].Aux.WeakExternal.TagIndex = coff_symbol->Other->Index;
     }
   }
 
@@ -675,18 +747,19 @@ void WinCOFFObjectWriter::WriteObject(const MCAssembler &Asm,
   unsigned offset = 0;
 
   offset += COFF::HeaderSize;
-  offset += COFF::SectionSize * Asm.size();
-
-  Header.NumberOfSections = Sections.size();
+  offset += COFF::SectionSize * Header.NumberOfSections;
 
   for (MCAssembler::const_iterator i = Asm.begin(),
                                    e = Asm.end();
                                    i != e; i++) {
     COFFSection *Sec = SectionMap[i];
 
+    if (Sec->Number == -1)
+      continue;
+
     Sec->Header.SizeOfRawData = Layout.getSectionFileSize(i);
 
-    if (ExportSection(Sec)) {
+    if (IsPhysicalSection(Sec)) {
       Sec->Header.PointerToRawData = offset;
 
       offset += Sec->Header.SizeOfRawData;
@@ -700,13 +773,15 @@ void WinCOFFObjectWriter::WriteObject(const MCAssembler &Asm,
 
       for (relocations::iterator cr = Sec->Relocations.begin(),
                                  er = Sec->Relocations.end();
-                                 cr != er; cr++) {
+                                 cr != er; ++cr) {
+        assert((*cr).Symb->Index != -1);
         (*cr).Data.SymbolTableIndex = (*cr).Symb->Index;
       }
     }
 
-    assert(Sec->Symb->Aux.size() == 1 && "Section's symbol must have one aux!");
-    AuxSymbol &Aux = Sec->Symb->Aux[0];
+    assert(Sec->Symbol->Aux.size() == 1
+      && "Section's symbol must have one aux!");
+    AuxSymbol &Aux = Sec->Symbol->Aux[0];
     assert(Aux.AuxType == ATSectionDefinition &&
            "Section's symbol's aux symbol must be a Section Definition!");
     Aux.Aux.SectionDefinition.Length = Sec->Header.SizeOfRawData;
@@ -728,11 +803,16 @@ void WinCOFFObjectWriter::WriteObject(const MCAssembler &Asm,
     MCAssembler::const_iterator j, je;
 
     for (i = Sections.begin(), ie = Sections.end(); i != ie; i++)
-      WriteSectionHeader((*i)->Header);
+      if ((*i)->Number != -1)
+        WriteSectionHeader((*i)->Header);
 
     for (i = Sections.begin(), ie = Sections.end(),
          j = Asm.begin(), je = Asm.end();
-         (i != ie) && (j != je); i++, j++) {
+         (i != ie) && (j != je); ++i, ++j) {
+
+      if ((*i)->Number == -1)
+        continue;
+
       if ((*i)->Header.PointerToRawData != 0) {
         assert(OS.tell() == (*i)->Header.PointerToRawData &&
                "Section::PointerToRawData is insane!");
@@ -759,7 +839,8 @@ void WinCOFFObjectWriter::WriteObject(const MCAssembler &Asm,
          "Header::PointerToSymbolTable is insane!");
 
   for (symbols::iterator i = Symbols.begin(), e = Symbols.end(); i != e; i++)
-    WriteSymbol(*i);
+    if ((*i)->Index != -1)
+      WriteSymbol(*i);
 
   OS.write((char const *)&Strings.Data.front(), Strings.Data.size());
 }