3 files changed, 20 insertions, 33 deletions

diff --git a/llvm/lib/MC/ELFObjectWriter.cpp b/llvm/lib/MC/ELFObjectWriter.cpp
index a92b049d898..e6552beefd0 100644
--- a/llvm/lib/MC/ELFObjectWriter.cpp
+++ b/llvm/lib/MC/ELFObjectWriter.cpp
@@ -1046,28 +1046,17 @@ void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
   WriteWord(EntrySize); // sh_entsize
 }
 
-// ELF doesn't require relocations to be in any order. We sort by the Offset,
-// just to match gnu as for easier comparison. The use type is an arbitrary way
-// of making the sort deterministic.
-static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) {
-  const ELFRelocationEntry &A = *AP;
-  const ELFRelocationEntry &B = *BP;
-  if (A.Offset != B.Offset)
-    return B.Offset - A.Offset;
-  if (B.Type != A.Type)
-    return A.Type - B.Type;
-  llvm_unreachable("ELFRelocs might be unstable!");
-  return 0;
-}
-
 void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
                                        const MCSectionELF &Sec) {
   std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
 
-  array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel);
+  // We record relocations by pushing to the end of a vector. Reverse the vector
+  // to get the relocations in the order they were created.
+  // In most cases that is not important, but it can be for special sections
+  // (.eh_frame) or specific relocations (TLS optimizations on SystemZ).
+  std::reverse(Relocs.begin(), Relocs.end());
 
-  // Sort the relocation entries. Most targets just sort by Offset, but some
-  // (e.g., MIPS) have additional constraints.
+  // Sort the relocation entries. MIPS needs this.
   TargetObjectWriter->sortRelocs(Asm, Relocs);
 
   for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
diff --git a/llvm/lib/Target/Mips/MCTargetDesc/MipsELFObjectWriter.cpp b/llvm/lib/Target/Mips/MCTargetDesc/MipsELFObjectWriter.cpp
index a01c2f8afe0..5b9f02b89be 100644
--- a/llvm/lib/Target/Mips/MCTargetDesc/MipsELFObjectWriter.cpp
+++ b/llvm/lib/Target/Mips/MCTargetDesc/MipsELFObjectWriter.cpp
@@ -327,11 +327,25 @@ static void setMatch(MipsRelocationEntry &Hi, MipsRelocationEntry &Lo) {
 //   matching LO;
 // - prefer LOs without a pair;
 // - prefer LOs with higher offset;
+
+static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) {
+  const ELFRelocationEntry &A = *AP;
+  const ELFRelocationEntry &B = *BP;
+  if (A.Offset != B.Offset)
+    return B.Offset - A.Offset;
+  if (B.Type != A.Type)
+    return A.Type - B.Type;
+  return 0;
+}
+
 void MipsELFObjectWriter::sortRelocs(const MCAssembler &Asm,
                                      std::vector<ELFRelocationEntry> &Relocs) {
   if (Relocs.size() < 2)
     return;
 
+  // Sorts entries by Offset in descending order.
+  array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel);
+
   // Init MipsRelocs from Relocs.
   std::vector<MipsRelocationEntry> MipsRelocs;
   for (unsigned I = 0, E = Relocs.size(); I != E; ++I)
diff --git a/llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCObjectWriter.cpp b/llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCObjectWriter.cpp
index 2f19127d686..ee1af023769 100644
--- a/llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCObjectWriter.cpp
+++ b/llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCObjectWriter.cpp
@@ -26,8 +26,6 @@ protected:
   // Override MCELFObjectTargetWriter.
   unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
                         bool IsPCRel) const override;
-  void sortRelocs(const MCAssembler &Asm,
-                  std::vector<ELFRelocationEntry> &Relocs) override;
 };
 } // end anonymous namespace
 
@@ -154,20 +152,6 @@ unsigned SystemZObjectWriter::GetRelocType(const MCValue &Target,
   }
 }
 
-void SystemZObjectWriter::sortRelocs(const MCAssembler &Asm,
-                                     std::vector<ELFRelocationEntry> &Relocs) {
-  // This is OK for SystemZ, except for R_390_TLS_GDCALL/LDCALL relocs.
-  // There is typically another reloc, a R_390_PLT32DBL, on the same
-  // instruction.  This other reloc must come *before* the GDCALL reloc,
-  // or else the TLS linker optimization may generate incorrect code.
-  for (unsigned i = 0, e = Relocs.size(); i + 1 < e; ++i) {
-    if ((Relocs[i + 1].Type == ELF::R_390_TLS_GDCALL ||
-         Relocs[i + 1].Type == ELF::R_390_TLS_LDCALL) &&
-        Relocs[i].Offset == Relocs[i + 1].Offset + 2)
-      std::swap(Relocs[i], Relocs[i + 1]);
-  }
-}
-
 MCObjectWriter *llvm::createSystemZObjectWriter(raw_pwrite_stream &OS,
                                                 uint8_t OSABI) {
   MCELFObjectTargetWriter *MOTW = new SystemZObjectWriter(OSABI);