Re-enable target-specific relocation table sorting and use it for Mips

Some targets (ie. Mips) have additional rules for ordering the relocation
table entries. Allow them to override generic sortRelocs(), which sorts
entries by Offset.
Then override this function for Mips, to emit HI16 and GOT16 relocations
against the local symbol in pair with the corresponding LO16 relocation.

Patch by Vladimir Stefanovic.

Differential Revision: http://reviews.llvm.org/D7414

llvm-svn: 234883

1 files changed, 21 insertions, 0 deletions

diff --git a/llvm/lib/MC/MCELFObjectTargetWriter.cpp b/llvm/lib/MC/MCELFObjectTargetWriter.cpp
index 84176dc1e90..dc3d6c35489 100644
--- a/llvm/lib/MC/MCELFObjectTargetWriter.cpp
+++ b/llvm/lib/MC/MCELFObjectTargetWriter.cpp
@@ -28,3 +28,24 @@ bool MCELFObjectTargetWriter::needsRelocateWithSymbol(const MCSymbolData &SD,
                                                       unsigned Type) const {
   return false;
 }
+
+// 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
+MCELFObjectTargetWriter::sortRelocs(const MCAssembler &Asm,
+                                    std::vector<ELFRelocationEntry> &Relocs) {
+  array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel);
+}