llvm-mc/Mach-O: Preliminary support for indirect symbols.

- The indirect table itself isn't being filled in yet.

 - This isn't factored properly and is rather FIXMEd, but at the moment I'm more
   focused on figuring out what it needs to do.

llvm-svn: 79910

llvm/include/llvm/MC/MCAssembler.h

@@ -16,6 +16,7 @@
 #include "llvm/MC/MCValue.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/DataTypes.h"
+#include <vector> // FIXME: Shouldn't be needed.
 
 namespace llvm {
 class raw_ostream;
@@ -360,6 +361,12 @@ public:
   /// @}  
 };
 
+// FIXME: This really doesn't belong here. See comments below.
+struct IndirectSymbolData {
+  MCSymbol *Symbol;
+  MCSectionData *SectionData;
+};
+
 class MCAssembler {
 public:
   typedef iplist<MCSectionData> SectionDataListType;
@@ -371,6 +378,8 @@ public:
   typedef SymbolDataListType::const_iterator const_symbol_iterator;
   typedef SymbolDataListType::iterator symbol_iterator;
 
+  typedef std::vector<IndirectSymbolData>::iterator indirect_symbol_iterator;
+
 private:
   MCAssembler(const MCAssembler&);    // DO NOT IMPLEMENT
   void operator=(const MCAssembler&); // DO NOT IMPLEMENT
@@ -381,6 +390,8 @@ private:
 
   iplist<MCSymbolData> Symbols;
 
+  std::vector<IndirectSymbolData> IndirectSymbols;
+
 private:
   /// LayoutSection - Assign offsets and sizes to the fragments in the section
   /// \arg SD, and update the section size. The section file offset should
@@ -431,6 +442,27 @@ public:
 
   size_t symbol_size() const { return Symbols.size(); }
 
+  /// @}
+  /// @name Indirect Symbol List Access
+  /// @{
+
+  // FIXME: This is a total hack, this should not be here. Once things are
+  // factored so that the streamer has direct access to the .o writer, it can
+  // disappear.
+  std::vector<IndirectSymbolData> &getIndirectSymbols() {
+    return IndirectSymbols;
+  }
+
+  indirect_symbol_iterator indirect_symbol_begin() {
+    return IndirectSymbols.begin();
+  }
+
+  indirect_symbol_iterator indirect_symbol_end() {
+    return IndirectSymbols.end();
+  }
+
+  size_t indirect_symbol_size() const { return IndirectSymbols.size(); }
+
   /// @}
 };
 

llvm/lib/MC/MCAssembler.cpp

@@ -311,12 +311,68 @@ public:
     Write32(0); // FIXME: Value
   }
 
+  void BindIndirectSymbols(MCAssembler &Asm) {
+    // This is the point where 'as' creates actual symbols for indirect symbols
+    // (in the following two passes). It would be easier for us to do this
+    // sooner when we see the attribute, but that makes getting the order in the
+    // symbol table much more complicated than it is worth.
+    //
+    // FIXME: Revisit this when the dust settles.
+
+    // FIXME: This should not be needed.
+    DenseMap<MCSymbol*, MCSymbolData *> SymbolMap;
+
+    for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
+           ie = Asm.symbol_end(); it != ie; ++it)
+      SymbolMap[&it->getSymbol()] = it;
+
+    // Bind non lazy symbol pointers first.
+    for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
+           ie = Asm.indirect_symbol_end(); it != ie; ++it) {
+      // FIXME: cast<> support!
+      const MCSectionMachO &Section =
+        static_cast<const MCSectionMachO&>(it->SectionData->getSection());
+
+      unsigned Type =
+        Section.getTypeAndAttributes() & MCSectionMachO::SECTION_TYPE;
+      if (Type != MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS)
+        continue;
+
+      MCSymbolData *&Entry = SymbolMap[it->Symbol];
+      if (!Entry)
+        Entry = new MCSymbolData(*it->Symbol, 0, 0, &Asm);
+    }
+
+    // Then lazy symbol pointers and symbol stubs.
+    for (MCAssembler::indirect_symbol_iterator it = Asm.indirect_symbol_begin(),
+           ie = Asm.indirect_symbol_end(); it != ie; ++it) {
+      // FIXME: cast<> support!
+      const MCSectionMachO &Section =
+        static_cast<const MCSectionMachO&>(it->SectionData->getSection());
+
+      unsigned Type =
+        Section.getTypeAndAttributes() & MCSectionMachO::SECTION_TYPE;
+      if (Type != MCSectionMachO::S_LAZY_SYMBOL_POINTERS &&
+          Type != MCSectionMachO::S_SYMBOL_STUBS)
+        continue;
+
+      MCSymbolData *&Entry = SymbolMap[it->Symbol];
+      if (!Entry) {
+        Entry = new MCSymbolData(*it->Symbol, 0, 0, &Asm);
+
+        // Set the symbol type to undefined lazy, but only on construction.
+        //
+        // FIXME: Do not hardcode.
+        Entry->setFlags(Entry->getFlags() | 0x0001);
+      }
+    }
+  }
+
   /// ComputeSymbolTable - Compute the symbol table data
   ///
   /// \param StringTable [out] - The string table data.
   /// \param StringIndexMap [out] - Map from symbol names to offsets in the
   /// string table.
-
   void ComputeSymbolTable(MCAssembler &Asm, SmallString<256> &StringTable,
                           std::vector<MachSymbolData> &LocalSymbolData,
                           std::vector<MachSymbolData> &ExternalSymbolData,
@@ -414,6 +470,8 @@ public:
   void WriteObject(MCAssembler &Asm) {
     unsigned NumSections = Asm.size();
 
+    BindIndirectSymbols(Asm);
+
     // Compute symbol table information.
     SmallString<256> StringTable;
     std::vector<MachSymbolData> LocalSymbolData;
@@ -467,22 +525,32 @@ public:
 
     // Write the symbol table load command, if used.
     if (NumSymbols) {
-      // The string table is written after all the section data.
-      uint64_t SymbolTableOffset = SectionDataStartOffset + SectionDataSize;
-      uint64_t StringTableOffset =
-        SymbolTableOffset + NumSymbols * Nlist32Size;
-      WriteSymtabLoadCommand(SymbolTableOffset, NumSymbols,
-                             StringTableOffset, StringTable.size());
-
       unsigned FirstLocalSymbol = 0;
       unsigned NumLocalSymbols = LocalSymbolData.size();
       unsigned FirstExternalSymbol = FirstLocalSymbol + NumLocalSymbols;
       unsigned NumExternalSymbols = ExternalSymbolData.size();
       unsigned FirstUndefinedSymbol = FirstExternalSymbol + NumExternalSymbols;
       unsigned NumUndefinedSymbols = UndefinedSymbolData.size();
-      // FIXME: Get correct symbol indices and counts for indirect symbols.
-      unsigned IndirectSymbolOffset = 0;
-      unsigned NumIndirectSymbols = 0;
+      unsigned NumIndirectSymbols = Asm.indirect_symbol_size();
+      unsigned NumSymTabSymbols =
+        NumLocalSymbols + NumExternalSymbols + NumUndefinedSymbols;
+      uint64_t IndirectSymbolSize = NumIndirectSymbols * 4;
+      uint64_t IndirectSymbolOffset = 0;
+
+      // If used, the indirect symbols are written after the section data.
+      if (NumIndirectSymbols)
+        IndirectSymbolOffset = SectionDataStartOffset + SectionDataSize;
+
+      // The symbol table is written after the indirect symbol data.
+      uint64_t SymbolTableOffset =
+        SectionDataStartOffset + SectionDataSize + IndirectSymbolSize;
+
+      // The string table is written after symbol table.
+      uint64_t StringTableOffset =
+        SymbolTableOffset + NumSymTabSymbols * Nlist32Size;
+      WriteSymtabLoadCommand(SymbolTableOffset, NumSymTabSymbols,
+                             StringTableOffset, StringTable.size());
+
       WriteDysymtabLoadCommand(FirstLocalSymbol, NumLocalSymbols,
                                FirstExternalSymbol, NumExternalSymbols,
                                FirstUndefinedSymbol, NumUndefinedSymbols,
@@ -495,9 +563,13 @@ public:
 
     // Write the symbol table data, if used.
     if (NumSymbols) {
-      // FIXME: Check that offsets match computed ones.
+      // Write the indirect symbol entries.
+      //
+      // FIXME: We need the symbol index map for this.
+      for (unsigned i = 0, e = Asm.indirect_symbol_size(); i != e; ++i)
+        Write32(0);
 
-      // FIXME: Some of these are ordered by name to help the linker.
+      // FIXME: Check that offsets match computed ones.
 
       // Write the symbol table entries.
       for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)

llvm/lib/MC/MCMachOStreamer.cpp

@@ -165,6 +165,16 @@ void MCMachOStreamer::EmitAssignment(MCSymbol *Symbol,
 
 void MCMachOStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
                                           SymbolAttr Attribute) {
+  // Indirect symbols are handled differently, to match how 'as' handles
+  // them. This makes writing matching .o files easier.
+  if (Attribute == MCStreamer::IndirectSymbol) {
+    IndirectSymbolData ISD;
+    ISD.Symbol = Symbol;
+    ISD.SectionData = CurSectionData;
+    Assembler.getIndirectSymbols().push_back(ISD);
+    return;
+  }
+
   // Adding a symbol attribute always introduces the symbol, note that an
   // important side effect of calling getSymbolData here is to register the
   // symbol with the assembler.
@@ -177,6 +187,7 @@ void MCMachOStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
   // In the future it might be worth trying to make these operations more well
   // defined.
   switch (Attribute) {
+  case MCStreamer::IndirectSymbol:
   case MCStreamer::Hidden:
   case MCStreamer::Internal:
   case MCStreamer::Protected:
@@ -195,10 +206,6 @@ void MCMachOStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
       SD.setFlags(SD.getFlags() | SF_ReferenceTypeUndefinedLazy);
     break;
 
-  case MCStreamer::IndirectSymbol:
-    llvm_unreachable("FIXME: Not yet implemented!");
-    break;
-
     // Since .reference sets the no dead strip bit, it is equivalent to
     // .no_dead_strip in practice.
   case MCStreamer::Reference: