Change ELFCodeEmitter logic to emit the constant pool and jump tables to

their appropriate sections before the code itself. They need to be emitted
before the function because on some targets (x86 but not x86_64) the later
may reference a JT or CP entry address


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@76672 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Target/TargetELFWriterInfo.h

@@ -120,7 +120,7 @@ namespace llvm {
     virtual unsigned getAbsoluteLabelMachineRelTy() const = 0;
 
     /// computeRelocation - Some relocatable fields could be relocated
-    /// directly, avoiding the emission of a relocation symbol, compute the
+    /// directly, avoiding the relocation symbol emission, compute the
     /// final relocation value for this symbol.
     virtual long int computeRelocation(unsigned SymOffset, unsigned RelOffset,
                                        unsigned RelTy) const = 0;

lib/CodeGen/ELFCodeEmitter.cpp

@@ -54,6 +54,12 @@ void ELFCodeEmitter::startFunction(MachineFunction &MF) {
 
   // Record the function start offset
   FnStartOff = ES->getCurrentPCOffset();
+
+  // Emit constant pool and jump tables to their appropriate sections.
+  // They need to be emitted before the function because in some targets
+  // the later may reference JT or CP entry address.
+  emitConstantPool(MF.getConstantPool());
+  emitJumpTables(MF.getJumpTableInfo());
 }
 
 /// finishFunction - This callback is invoked after the function is completely
@@ -78,11 +84,17 @@ bool ELFCodeEmitter::finishFunction(MachineFunction &MF) {
   if (!F->hasPrivateLinkage())
     EW.SymbolList.push_back(FnSym);
 
-  // Emit constant pool to appropriate section(s)
-  emitConstantPool(MF.getConstantPool());
-
-  // Emit jump tables to appropriate section
-  emitJumpTables(MF.getJumpTableInfo());
+  // Patch up Jump Table Section relocations to use the real MBBs offsets
+  // now that the MBB label offsets inside the function are known.
+  ELFSection &JTSection = EW.getJumpTableSection();
+  for (std::vector<MachineRelocation>::iterator MRI = JTRelocations.begin(),
+       MRE = JTRelocations.end(); MRI != MRE; ++MRI) {
+    MachineRelocation &MR = *MRI;
+    unsigned MBBOffset = getMachineBasicBlockAddress(MR.getBasicBlock());
+    MR.setResultPointer((void*)MBBOffset);
+    MR.setConstantVal(ES->SectionIdx);
+    JTSection.addRelocation(MR);
+  }
 
   // Relocations
   // -----------
@@ -105,7 +117,7 @@ bool ELFCodeEmitter::finishFunction(MachineFunction &MF) {
       MR.setResultPointer((void*)Addr);
     } else if (MR.isJumpTableIndex()) {
       Addr = getJumpTableEntryAddress(MR.getJumpTableIndex());
-      MR.setConstantVal(JumpTableSectionIdx);
+      MR.setConstantVal(JTSection.SectionIdx);
       MR.setResultPointer((void*)Addr);
     } else {
       llvm_unreachable("Unhandled relocation type");
@@ -114,6 +126,7 @@ bool ELFCodeEmitter::finishFunction(MachineFunction &MF) {
   }
 
   // Clear per-function data structures.
+  JTRelocations.clear();
   Relocations.clear();
   CPLocations.clear();
   CPSections.clear();
@@ -159,21 +172,15 @@ void ELFCodeEmitter::emitJumpTables(MachineJumpTableInfo *MJTI) {
          "PIC codegen not yet handled for elf jump tables!");
 
   const TargetELFWriterInfo *TEW = TM.getELFWriterInfo();
+  unsigned EntrySize = MJTI->getEntrySize();
 
   // Get the ELF Section to emit the jump table
   ELFSection &JTSection = EW.getJumpTableSection();
-  JumpTableSectionIdx = JTSection.SectionIdx;
-
-  // Entries in the JT Section are relocated against the text section
-  ELFSection &TextSection = EW.getTextSection();
 
   // For each JT, record its offset from the start of the section
   for (unsigned i = 0, e = JT.size(); i != e; ++i) {
     const std::vector<MachineBasicBlock*> &MBBs = JT[i].MBBs;
 
-    DOUT << "JTSection.size(): " << JTSection.size() << "\n";
-    DOUT << "JTLocations.size: " << JTLocations.size() << "\n";
-
     // Record JT 'i' offset in the JT section
     JTLocations.push_back(JTSection.size());
 
@@ -182,19 +189,14 @@ void ELFCodeEmitter::emitJumpTables(MachineJumpTableInfo *MJTI) {
     for (unsigned mi = 0, me = MBBs.size(); mi != me; ++mi) {
       unsigned MachineRelTy = TEW->getAbsoluteLabelMachineRelTy();
       MachineRelocation MR =
-        MachineRelocation::getBB(JTSection.size(),
-                                 MachineRelTy,
-                                 MBBs[mi]);
-
-      // Offset of JT 'i' in JT section
-      MR.setResultPointer((void*)getMachineBasicBlockAddress(MBBs[mi]));
-      MR.setConstantVal(TextSection.SectionIdx);
+        MachineRelocation::getBB(JTSection.size(), MachineRelTy, MBBs[mi]);
 
       // Add the relocation to the Jump Table section
-      JTSection.addRelocation(MR);
+      JTRelocations.push_back(MR);
 
       // Output placeholder for MBB in the JT section
-      JTSection.emitWord(0);
+      for (unsigned s=0; s < EntrySize; ++s)
+        JTSection.emitByte(0);
     }
   }
 }

lib/CodeGen/ELFCodeEmitter.h

@@ -31,14 +31,14 @@ namespace llvm {
     /// Relocations - Record relocations needed by the current function 
     std::vector<MachineRelocation> Relocations;
 
+    /// JTRelocations - Record relocations needed by the relocation
+    /// section.
+    std::vector<MachineRelocation> JTRelocations;
+
     /// FnStartPtr - Function offset from the beginning of ELFSection 'ES'
     uintptr_t FnStartOff;
-
-    /// JumpTableSectionIdx - Holds the index of the Jump Table Section 
-    unsigned JumpTableSectionIdx;
   public:
-    explicit ELFCodeEmitter(ELFWriter &ew) : EW(ew), TM(EW.TM),
-                                             JumpTableSectionIdx(0) {}
+    explicit ELFCodeEmitter(ELFWriter &ew) : EW(ew), TM(EW.TM) {}
 
     /// addRelocation - Register new relocations for this function
     void addRelocation(const MachineRelocation &MR) {