Sort relocation entries before they are written out to a file. MIPS ABI

imposes a constraint that GOT16 referring to a local symbol or HI16 has to be
followed immediately by a matching LO16 relocation.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153553 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/Mips/MCTargetDesc/MipsELFObjectWriter.cpp

@@ -7,17 +7,31 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "MCTargetDesc/MipsBaseInfo.h"
 #include "MCTargetDesc/MipsFixupKinds.h"
 #include "MCTargetDesc/MipsMCTargetDesc.h"
+#include "llvm/MC/MCAssembler.h"
 #include "llvm/MC/MCELFObjectWriter.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCValue.h"
 #include "llvm/Support/ErrorHandling.h"
+#include <list>
 
 using namespace llvm;
 
 namespace {
+  struct RelEntry {
+    RelEntry(const ELFRelocationEntry &R, const MCSymbol *S, int64_t O) :
+      Reloc(R), Sym(S), Offset(O) {}
+    ELFRelocationEntry Reloc;
+    const MCSymbol *Sym;
+    int64_t Offset;
+  };
+
+  typedef std::list<RelEntry> RelLs;
+  typedef RelLs::iterator RelLsIter;
+
   class MipsELFObjectWriter : public MCELFObjectTargetWriter {
   public:
     MipsELFObjectWriter(uint8_t OSABI);
@@ -33,6 +47,8 @@ namespace {
                                            const MCFragment &F,
                                            const MCFixup &Fixup,
                                            bool IsPCRel) const;
+    virtual void sortRelocs(const MCAssembler &Asm,
+                            std::vector<ELFRelocationEntry> &Relocs);
   };
 }
 
@@ -129,6 +145,93 @@ unsigned MipsELFObjectWriter::GetRelocType(const MCValue &Target,
   return Type;
 }
 
+// Return true if R is either a GOT16 against a local symbol or HI16.
+static bool NeedsMatchingLo(const MCAssembler &Asm, const RelEntry &R) {
+  if (!R.Sym)
+    return false;
+
+  MCSymbolData &SD = Asm.getSymbolData(R.Sym->AliasedSymbol());
+
+  return ((R.Reloc.Type == ELF::R_MIPS_GOT16) && !SD.isExternal()) ||
+    (R.Reloc.Type == ELF::R_MIPS_HI16);
+}
+
+static bool HasMatchingLo(const MCAssembler &Asm, RelLsIter I, RelLsIter Last) {
+  if (I == Last)
+    return false;
+
+  RelLsIter Hi = I++;
+
+  return (I->Reloc.Type == ELF::R_MIPS_LO16) && (Hi->Sym == I->Sym) &&
+    (Hi->Offset == I->Offset);
+}
+
+static bool HasSameSymbol(const RelEntry &R0, const RelEntry &R1) {
+  return R0.Sym == R1.Sym;
+}
+
+static int CompareOffset(const RelEntry &R0, const RelEntry &R1) {
+  return (R0.Offset > R1.Offset) ? 1 : ((R0.Offset == R1.Offset) ? 0 : -1);
+}
+
+void MipsELFObjectWriter::sortRelocs(const MCAssembler &Asm,
+                                     std::vector<ELFRelocationEntry> &Relocs) {
+  // Call the defualt function first. Relocations are sorted in descending
+  // order of r_offset.
+  MCELFObjectTargetWriter::sortRelocs(Asm, Relocs);
+  
+  RelLs RelocLs;
+  std::vector<RelLsIter> Unmatched;
+
+  // Fill RelocLs. Traverse Relocs backwards so that relocations in RelocLs
+  // are in ascending order of r_offset.
+  for (std::vector<ELFRelocationEntry>::reverse_iterator R = Relocs.rbegin();
+       R != Relocs.rend(); ++R) {
+     std::pair<const MCSymbolRefExpr*, int64_t> P =
+       MipsGetSymAndOffset(*R->Fixup);
+     RelocLs.push_back(RelEntry(*R, P.first ? &P.first->getSymbol() : 0,
+                                P.second));
+  }
+
+  // Get list of unmatched HI16 and GOT16.
+  for (RelLsIter R = RelocLs.begin(); R != RelocLs.end(); ++R)
+    if (NeedsMatchingLo(Asm, *R) && !HasMatchingLo(Asm, R, --RelocLs.end()))
+      Unmatched.push_back(R);
+
+  // Insert unmatched HI16 and GOT16 immediately before their matching LO16.
+  for (std::vector<RelLsIter>::iterator U = Unmatched.begin();
+       U != Unmatched.end(); ++U) {
+    RelLsIter LoPos = RelocLs.end(), HiPos = *U;
+    bool MatchedLo = false;
+
+    for (RelLsIter R = RelocLs.begin(); R != RelocLs.end(); ++R) {
+      if ((R->Reloc.Type == ELF::R_MIPS_LO16) && HasSameSymbol(*HiPos, *R) &&
+          (CompareOffset(*R, *HiPos) >= 0) &&
+          ((LoPos == RelocLs.end()) || ((CompareOffset(*R, *LoPos) < 0)) ||
+           (!MatchedLo && !CompareOffset(*R, *LoPos))))
+        LoPos = R;
+
+      MatchedLo = NeedsMatchingLo(Asm, *R) &&
+        HasMatchingLo(Asm, R, --RelocLs.end());
+    }
+
+    // If a matching LoPos was found, move HiPos and insert it before LoPos.
+    // Make the offsets of HiPos and LoPos match.
+    if (LoPos != RelocLs.end()) {
+      HiPos->Offset = LoPos->Offset;
+      RelocLs.insert(LoPos, *HiPos);
+      RelocLs.erase(HiPos);
+    }
+  }
+
+  // Put the sorted list back in reverse order.
+  assert(Relocs.size() == RelocLs.size());
+  unsigned I = RelocLs.size();
+
+  for (RelLsIter R = RelocLs.begin(); R != RelocLs.end(); ++R)
+    Relocs[--I] = R->Reloc;
+}
+
 MCObjectWriter *llvm::createMipsELFObjectWriter(raw_ostream &OS, uint8_t OSABI,
                                                 bool IsLittleEndian) {
   MCELFObjectTargetWriter *MOTW = new MipsELFObjectWriter(OSABI);