1 files changed, 118 insertions, 0 deletions

diff --git a/lib/MC/MachObjectWriter.cpp b/lib/MC/MachObjectWriter.cpp
index f81862e9ab..02a5575606 100644
--- a/lib/MC/MachObjectWriter.cpp
+++ b/lib/MC/MachObjectWriter.cpp
@@ -75,6 +75,86 @@ static bool doesSymbolRequireExternRelocation(MCSymbolData *SD) {
   return false;
 }
 
+static bool isScatteredFixupFullyResolved(const MCAssembler &Asm,
+                                          const MCValue Target,
+                                          const MCSymbolData *BaseSymbol) {
+  // The effective fixup address is
+  //     addr(atom(A)) + offset(A)
+  //   - addr(atom(B)) - offset(B)
+  //   - addr(BaseSymbol) + <fixup offset from base symbol>
+  // and the offsets are not relocatable, so the fixup is fully resolved when
+  //  addr(atom(A)) - addr(atom(B)) - addr(BaseSymbol) == 0.
+  //
+  // Note that "false" is almost always conservatively correct (it means we emit
+  // a relocation which is unnecessary), except when it would force us to emit a
+  // relocation which the target cannot encode.
+
+  const MCSymbolData *A_Base = 0, *B_Base = 0;
+  if (const MCSymbolRefExpr *A = Target.getSymA()) {
+    // Modified symbol references cannot be resolved.
+    if (A->getKind() != MCSymbolRefExpr::VK_None)
+      return false;
+
+    A_Base = Asm.getAtom(&Asm.getSymbolData(A->getSymbol()));
+    if (!A_Base)
+      return false;
+  }
+
+  if (const MCSymbolRefExpr *B = Target.getSymB()) {
+    // Modified symbol references cannot be resolved.
+    if (B->getKind() != MCSymbolRefExpr::VK_None)
+      return false;
+
+    B_Base = Asm.getAtom(&Asm.getSymbolData(B->getSymbol()));
+    if (!B_Base)
+      return false;
+  }
+
+  // If there is no base, A and B have to be the same atom for this fixup to be
+  // fully resolved.
+  if (!BaseSymbol)
+    return A_Base == B_Base;
+
+  // Otherwise, B must be missing and A must be the base.
+  return !B_Base && BaseSymbol == A_Base;
+}
+
+static bool isScatteredFixupFullyResolvedSimple(const MCAssembler &Asm,
+                                                const MCValue Target,
+                                                const MCSection *BaseSection) {
+  // The effective fixup address is
+  //     addr(atom(A)) + offset(A)
+  //   - addr(atom(B)) - offset(B)
+  //   - addr(<base symbol>) + <fixup offset from base symbol>
+  // and the offsets are not relocatable, so the fixup is fully resolved when
+  //  addr(atom(A)) - addr(atom(B)) - addr(<base symbol>)) == 0.
+  //
+  // The simple (Darwin, except on x86_64) way of dealing with this was to
+  // assume that any reference to a temporary symbol *must* be a temporary
+  // symbol in the same atom, unless the sections differ. Therefore, any PCrel
+  // relocation to a temporary symbol (in the same section) is fully
+  // resolved. This also works in conjunction with absolutized .set, which
+  // requires the compiler to use .set to absolutize the differences between
+  // symbols which the compiler knows to be assembly time constants, so we don't
+  // need to worry about considering symbol differences fully resolved.
+
+  // Non-relative fixups are only resolved if constant.
+  if (!BaseSection)
+    return Target.isAbsolute();
+
+  // Otherwise, relative fixups are only resolved if not a difference and the
+  // target is a temporary in the same section.
+  if (Target.isAbsolute() || Target.getSymB())
+    return false;
+
+  const MCSymbol *A = &Target.getSymA()->getSymbol();
+  if (!A->isTemporary() || !A->isInSection() ||
+      &A->getSection() != BaseSection)
+    return false;
+
+  return true;
+}
+
 namespace {
 
 class MachObjectWriterImpl {
@@ -1038,6 +1118,36 @@ public:
                        UndefinedSymbolData);
   }
 
+
+  bool IsFixupFullyResolved(const MCAssembler &Asm,
+                            const MCValue Target,
+                            bool IsPCRel,
+                            const MCFragment *DF) const {
+    // If we are using scattered symbols, determine whether this value is
+    // actually resolved; scattering may cause atoms to move.
+    if (Asm.getBackend().hasScatteredSymbols()) {
+      if (Asm.getBackend().hasReliableSymbolDifference()) {
+        // If this is a PCrel relocation, find the base atom (identified by its
+        // symbol) that the fixup value is relative to.
+        const MCSymbolData *BaseSymbol = 0;
+        if (IsPCRel) {
+          BaseSymbol = DF->getAtom();
+          if (!BaseSymbol)
+            return false;
+        }
+
+        return isScatteredFixupFullyResolved(Asm, Target, BaseSymbol);
+      } else {
+        const MCSection *BaseSection = 0;
+        if (IsPCRel)
+          BaseSection = &DF->getParent()->getSection();
+
+        return isScatteredFixupFullyResolvedSimple(Asm, Target, BaseSection);
+      }
+    }
+    return true;
+  }
+
   void WriteObject(const MCAssembler &Asm, const MCAsmLayout &Layout) {
     unsigned NumSections = Asm.size();
 
@@ -1224,6 +1334,14 @@ void MachObjectWriter::RecordRelocation(const MCAssembler &Asm,
                                                    Target, FixedValue);
 }
 
+bool MachObjectWriter::IsFixupFullyResolved(const MCAssembler &Asm,
+                                           const MCValue Target,
+                                           bool IsPCRel,
+                                           const MCFragment *DF) const {
+  return ((MachObjectWriterImpl*) Impl)->IsFixupFullyResolved(Asm, Target,
+                                                              IsPCRel, DF);
+}
+
 void MachObjectWriter::WriteObject(const MCAssembler &Asm,
                                    const MCAsmLayout &Layout) {
   ((MachObjectWriterImpl*) Impl)->WriteObject(Asm, Layout);