From 9d2f0da138d9b2ea42b61b3545032f1403e4273e Mon Sep 17 00:00:00 2001
From: Rafael Espindola <rafael.espindola@gmail.com>
Date: Thu, 26 Mar 2015 21:11:00 +0000
Subject: [PATCH] Fix PR23025.

There is something in link.exe that requires a relocation to use a
global symbol. Not doing so breaks the chrome build on windows.

This patch sets isWeak for that to work. To compensate,
we then need to look past those symbols when not creating relocations.

This patch includes an ELF test that matches GNU as behaviour.

I am still reducing the chrome build issue and will add a test
once that is done.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233318 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/MC/MCExpr.h       |  7 +++++++
 lib/MC/MCAssembler.cpp         |  2 +-
 lib/MC/MCExpr.cpp              | 17 +++++++++++++----
 lib/MC/WinCOFFObjectWriter.cpp |  8 ++++++++
 test/MC/X86/expand-var.s       |  6 ++++++
 5 files changed, 35 insertions(+), 5 deletions(-)

diff --git a/include/llvm/MC/MCExpr.h b/include/llvm/MC/MCExpr.h
index 11da711ab9c..d5a68be3ec6 100644
--- a/include/llvm/MC/MCExpr.h
+++ b/include/llvm/MC/MCExpr.h
@@ -105,6 +105,13 @@ public:
   bool EvaluateAsRelocatable(MCValue &Res, const MCAsmLayout *Layout,
                              const MCFixup *Fixup) const;
 
+  /// \brief Try to evaluate the expression to the form (a - b + constant) where
+  /// neither a nor b are variables.
+  ///
+  /// This is a more aggressive variant of EvaluateAsRelocatable. The intended
+  /// use is for when relocations are not available, like the .size directive.
+  bool evaluateAsValue(MCValue &Res, const MCAsmLayout &Layout) const;
+
   /// FindAssociatedSection - Find the "associated section" for this expression,
   /// which is currently defined as the absolute section for constants, or
   /// otherwise the section associated with the first defined symbol in the
diff --git a/lib/MC/MCAssembler.cpp b/lib/MC/MCAssembler.cpp
index 6345bd53417..857eafc0b7e 100644
--- a/lib/MC/MCAssembler.cpp
+++ b/lib/MC/MCAssembler.cpp
@@ -188,7 +188,7 @@ const MCSymbol *MCAsmLayout::getBaseSymbol(const MCSymbol &Symbol) const {
 
   const MCExpr *Expr = Symbol.getVariableValue();
   MCValue Value;
-  if (!Expr->EvaluateAsRelocatable(Value, this, nullptr))
+  if (!Expr->evaluateAsValue(Value, *this))
     llvm_unreachable("Invalid Expression");
 
   const MCSymbolRefExpr *RefB = Value.getSymB();
diff --git a/lib/MC/MCExpr.cpp b/lib/MC/MCExpr.cpp
index 7508ef67123..8a64403362c 100644
--- a/lib/MC/MCExpr.cpp
+++ b/lib/MC/MCExpr.cpp
@@ -584,7 +584,15 @@ bool MCExpr::EvaluateAsRelocatable(MCValue &Res,
                                    false);
 }
 
-static bool canExpand(const MCSymbol &Sym, const MCAssembler *Asm) {
+bool MCExpr::evaluateAsValue(MCValue &Res, const MCAsmLayout &Layout) const {
+  MCAssembler *Assembler = &Layout.getAssembler();
+  return EvaluateAsRelocatableImpl(Res, Assembler, &Layout, nullptr, nullptr,
+                                   true);
+}
+
+static bool canExpand(const MCSymbol &Sym, const MCAssembler *Asm, bool InSet) {
+  if (InSet)
+    return true;
   if (!Asm)
     return false;
   const MCSymbolData &SD = Asm->getSymbolData(Sym);
@@ -613,10 +621,11 @@ bool MCExpr::EvaluateAsRelocatableImpl(MCValue &Res, const MCAssembler *Asm,
 
     // Evaluate recursively if this is a variable.
     if (Sym.isVariable() && SRE->getKind() == MCSymbolRefExpr::VK_None &&
-        canExpand(Sym, Asm)) {
+        canExpand(Sym, Asm, InSet)) {
+      bool IsMachO = SRE->hasSubsectionsViaSymbols();
       if (Sym.getVariableValue()->EvaluateAsRelocatableImpl(
-              Res, Asm, Layout, Fixup, Addrs, true)) {
-        if (!SRE->hasSubsectionsViaSymbols())
+              Res, Asm, Layout, Fixup, Addrs, InSet || IsMachO)) {
+        if (!IsMachO)
           return true;
 
         const MCSymbolRefExpr *A = Res.getSymA();
diff --git a/lib/MC/WinCOFFObjectWriter.cpp b/lib/MC/WinCOFFObjectWriter.cpp
index c519a9d6d5e..c6bc81ddc56 100644
--- a/lib/MC/WinCOFFObjectWriter.cpp
+++ b/lib/MC/WinCOFFObjectWriter.cpp
@@ -175,6 +175,8 @@ public:
                                               const MCFragment &FB, bool InSet,
                                               bool IsPCRel) const override;
 
+  bool isWeak(const MCSymbolData &SD) const override;
+
   void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
                         const MCFragment *Fragment, const MCFixup &Fixup,
                         MCValue Target, bool &IsPCRel,
@@ -661,6 +663,12 @@ bool WinCOFFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
                                                                 InSet, IsPCRel);
 }
 
+bool WinCOFFObjectWriter::isWeak(const MCSymbolData &SD) const {
+  // FIXME: this is for PR23025. Write a good description on
+  // why this is needed.
+  return SD.isExternal();
+}
+
 void WinCOFFObjectWriter::RecordRelocation(
     MCAssembler &Asm, const MCAsmLayout &Layout, const MCFragment *Fragment,
     const MCFixup &Fixup, MCValue Target, bool &IsPCRel, uint64_t &FixedValue) {
diff --git a/test/MC/X86/expand-var.s b/test/MC/X86/expand-var.s
index b3311b4a844..ef62d8a260f 100644
--- a/test/MC/X86/expand-var.s
+++ b/test/MC/X86/expand-var.s
@@ -10,3 +10,9 @@ a:
         d = a
         .weak d
         .long d + (b - c)
+
+
+a2:
+        .weak b2
+        b2 = a2
+        c2 = b2 - a2