3 files changed, 28 insertions, 4 deletions
diff --git a/llvm/lib/MC/MCExpr.cpp b/llvm/lib/MC/MCExpr.cpp
index 995f4c96ee6..8a64403362c 100644
--- a/llvm/lib/MC/MCExpr.cpp
+++ b/llvm/lib/MC/MCExpr.cpp
@@ -775,9 +775,6 @@ const MCSection *MCExpr::FindAssociatedSection() const {
     if (RHS_S == MCSymbol::AbsolutePseudoSection)
       return LHS_S;
 
-    if (BE->getOpcode() == MCBinaryExpr::Sub)
-      return MCSymbol::AbsolutePseudoSection;
-
     // Otherwise, return the first non-null section.
     return LHS_S ? LHS_S : RHS_S;
   }
diff --git a/llvm/lib/MC/MCSymbol.cpp b/llvm/lib/MC/MCSymbol.cpp
index 6582574ae94..24165254e56 100644
--- a/llvm/lib/MC/MCSymbol.cpp
+++ b/llvm/lib/MC/MCSymbol.cpp
@@ -55,7 +55,13 @@ void MCSymbol::setVariableValue(const MCExpr *Value) {
   assert(!IsUsed && "Cannot set a variable that has already been used.");
   assert(Value && "Invalid variable value!");
   this->Value = Value;
-  this->Section = nullptr;
+
+  // Variables should always be marked as in the same "section" as the value.
+  const MCSection *Section = Value->FindAssociatedSection();
+  if (Section)
+    setSection(*Section);
+  else
+    setUndefined();
 }
 
 void MCSymbol::print(raw_ostream &OS) const {
diff --git a/llvm/lib/MC/MachObjectWriter.cpp b/llvm/lib/MC/MachObjectWriter.cpp
index 56cccab1d39..5e9e86f18a0 100644
--- a/llvm/lib/MC/MachObjectWriter.cpp
+++ b/llvm/lib/MC/MachObjectWriter.cpp
@@ -649,12 +649,33 @@ void MachObjectWriter::computeSectionAddresses(const MCAssembler &Asm,
   }
 }
 
+void MachObjectWriter::markAbsoluteVariableSymbols(MCAssembler &Asm,
+                                                   const MCAsmLayout &Layout) {
+  for (MCSymbolData &SD : Asm.symbols()) {
+    if (!SD.getSymbol().isVariable())
+      continue;
+
+    // Is the variable is a symbol difference (SA - SB + C) expression,
+    // and neither symbol is external, mark the variable as absolute.
+    const MCExpr *Expr = SD.getSymbol().getVariableValue();
+    MCValue Value;
+    if (Expr->EvaluateAsRelocatable(Value, &Layout, nullptr)) {
+      if (Value.getSymA() && Value.getSymB())
+        const_cast<MCSymbol*>(&SD.getSymbol())->setAbsolute();
+    }
+  }
+}
+
 void MachObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
                                                 const MCAsmLayout &Layout) {
   computeSectionAddresses(Asm, Layout);
 
   // Create symbol data for any indirect symbols.
   BindIndirectSymbols(Asm);
+
+  // Mark symbol difference expressions in variables (from .set or = directives)
+  // as absolute.
+  markAbsoluteVariableSymbols(Asm, Layout);
 }
 
 bool MachObjectWriter::