From 45d81bdde87a38c21facf2ec3b82b0589e9de7e9 Mon Sep 17 00:00:00 2001
From: Jim Grosbach <grosbach@apple.com>
Date: Thu, 13 Sep 2012 23:11:25 +0000
Subject: [PATCH] MachO: Correctly mark symbol-difference variables as N_ABS.

.set a, b - c + CONSTANT
d = b - c + CONSTANT

Both 'a' and 'd' should be marked as absolute symbols (N_ABS).

rdar://12219394

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163853 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/MC/MCMachObjectWriter.h |  2 ++
 lib/MC/MachObjectWriter.cpp          | 35 ++++++++++++++++++++++++----
 2 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/include/llvm/MC/MCMachObjectWriter.h b/include/llvm/MC/MCMachObjectWriter.h
index 949d90700e0..da3b2491018 100644
--- a/include/llvm/MC/MCMachObjectWriter.h
+++ b/include/llvm/MC/MCMachObjectWriter.h
@@ -233,6 +233,8 @@ public:
   void computeSectionAddresses(const MCAssembler &Asm,
                                const MCAsmLayout &Layout);
 
+  void markAbsoluteVariableSymbols(MCAssembler &Asm,
+                                   const MCAsmLayout &Layout);
   void ExecutePostLayoutBinding(MCAssembler &Asm, const MCAsmLayout &Layout);
 
   virtual bool IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
diff --git a/lib/MC/MachObjectWriter.cpp b/lib/MC/MachObjectWriter.cpp
index c57b0d65c1d..904fbbfe83e 100644
--- a/lib/MC/MachObjectWriter.cpp
+++ b/lib/MC/MachObjectWriter.cpp
@@ -68,6 +68,11 @@ uint64_t MachObjectWriter::getSymbolAddress(const MCSymbolData* SD,
 
   // If this is a variable, then recursively evaluate now.
   if (S.isVariable()) {
+    if (const MCConstantExpr *C =
+          dyn_cast<const MCConstantExpr>(S.getVariableValue()))
+      return C->getValue();
+
+
     MCValue Target;
     if (!S.getVariableValue()->EvaluateAsRelocatable(Target, Layout))
       report_fatal_error("unable to evaluate offset for variable '" +
@@ -315,11 +320,7 @@ void MachObjectWriter::WriteNlist(MachSymbolData &MSD,
 
   // Compute the symbol address.
   if (Symbol.isDefined()) {
-    if (Symbol.isAbsolute()) {
-      Address = cast<MCConstantExpr>(Symbol.getVariableValue())->getValue();
-    } else {
-      Address = getSymbolAddress(&Data, Layout);
-    }
+    Address = getSymbolAddress(&Data, Layout);
   } else if (Data.isCommon()) {
     // Common symbols are encoded with the size in the address
     // field, and their alignment in the flags.
@@ -557,6 +558,26 @@ void MachObjectWriter::computeSectionAddresses(const MCAssembler &Asm,
   }
 }
 
+void MachObjectWriter::markAbsoluteVariableSymbols(MCAssembler &Asm,
+                                                   const MCAsmLayout &Layout) {
+  for (MCAssembler::symbol_iterator i = Asm.symbol_begin(),
+                                    e = Asm.symbol_end();
+      i != e; ++i) {
+    MCSymbolData &SD = *i;
+    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)) {
+      if (Value.getSymA() && Value.getSymB())
+        const_cast<MCSymbol*>(&SD.getSymbol())->setAbsolute();
+    }
+  }
+}
+
 void MachObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
                                                 const MCAsmLayout &Layout) {
   computeSectionAddresses(Asm, Layout);
@@ -564,6 +585,10 @@ void MachObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
   // Create symbol data for any indirect symbols.
   BindIndirectSymbols(Asm);
 
+  // Mark symbol difference expressions in variables (from .set or = directives)
+  // as absolute.
+  markAbsoluteVariableSymbols(Asm, Layout);
+
   // Compute symbol table information and bind symbol indices.
   ComputeSymbolTable(Asm, StringTable, LocalSymbolData, ExternalSymbolData,
                      UndefinedSymbolData);