From 53b2b7364385b2f2d98c0052df73a637a81c2288 Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Sat, 13 Aug 2011 01:04:44 +0000
Subject: [PATCH] Remove the last improper use of getGlobalContext() from LLVM.

This caused a race condition where a thread calls ~LLVMContextImpl which calls
Module::dropAllReferences which calls begin() on an empty ilist that would
create the sentinel, which racily accesses the global context.

This can not be fixed by locking inside createSentinel because the lock would
need to be shared with all users of the global context, including those that
reside outside LLVM's own code.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@137546 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/Module.h | 26 ++++++++++++++++++++++----
 lib/VMCore/Module.cpp | 19 +------------------
 2 files changed, 23 insertions(+), 22 deletions(-)

diff --git a/include/llvm/Module.h b/include/llvm/Module.h
index 7eb34b68961..8ce5ec4f1d1 100644
--- a/include/llvm/Module.h
+++ b/include/llvm/Module.h
@@ -50,17 +50,35 @@ template<> struct ilist_traits<Function>
 private:
   mutable ilist_node<Function> Sentinel;
 };
+
 template<> struct ilist_traits<GlobalVariable>
   : public SymbolTableListTraits<GlobalVariable, Module> {
   // createSentinel is used to create a node that marks the end of the list.
-  static GlobalVariable *createSentinel();
-  static void destroySentinel(GlobalVariable *GV) { delete GV; }
+  GlobalVariable *createSentinel() const {
+    return static_cast<GlobalVariable*>(&Sentinel);
+  }
+  static void destroySentinel(GlobalVariable*) {}
+
+  GlobalVariable *provideInitialHead() const { return createSentinel(); }
+  GlobalVariable *ensureHead(GlobalVariable*) const { return createSentinel(); }
+  static void noteHead(GlobalVariable*, GlobalVariable*) {}
+private:
+  mutable ilist_node<GlobalVariable> Sentinel;
 };
+
 template<> struct ilist_traits<GlobalAlias>
   : public SymbolTableListTraits<GlobalAlias, Module> {
   // createSentinel is used to create a node that marks the end of the list.
-  static GlobalAlias *createSentinel();
-  static void destroySentinel(GlobalAlias *GA) { delete GA; }
+  GlobalAlias *createSentinel() const {
+    return static_cast<GlobalAlias*>(&Sentinel);
+  }
+  static void destroySentinel(GlobalAlias*) {}
+
+  GlobalAlias *provideInitialHead() const { return createSentinel(); }
+  GlobalAlias *ensureHead(GlobalAlias*) const { return createSentinel(); }
+  static void noteHead(GlobalAlias*, GlobalAlias*) {}
+private:
+  mutable ilist_node<GlobalAlias> Sentinel;
 };
 
 template<> struct ilist_traits<NamedMDNode>
diff --git a/lib/VMCore/Module.cpp b/lib/VMCore/Module.cpp
index ee63d696d54..c29029bf6c0 100644
--- a/lib/VMCore/Module.cpp
+++ b/lib/VMCore/Module.cpp
@@ -32,25 +32,10 @@ using namespace llvm;
 // Methods to implement the globals and functions lists.
 //
 
-GlobalVariable *ilist_traits<GlobalVariable>::createSentinel() {
-  GlobalVariable *Ret = new GlobalVariable(Type::getInt32Ty(getGlobalContext()),
-                                           false, GlobalValue::ExternalLinkage);
-  // This should not be garbage monitored.
-  LeakDetector::removeGarbageObject(Ret);
-  return Ret;
-}
-GlobalAlias *ilist_traits<GlobalAlias>::createSentinel() {
-  GlobalAlias *Ret = new GlobalAlias(Type::getInt32Ty(getGlobalContext()),
-                                     GlobalValue::ExternalLinkage);
-  // This should not be garbage monitored.
-  LeakDetector::removeGarbageObject(Ret);
-  return Ret;
-}
-
 // Explicit instantiations of SymbolTableListTraits since some of the methods
 // are not in the public header file.
-template class llvm::SymbolTableListTraits<GlobalVariable, Module>;
 template class llvm::SymbolTableListTraits<Function, Module>;
+template class llvm::SymbolTableListTraits<GlobalVariable, Module>;
 template class llvm::SymbolTableListTraits<GlobalAlias, Module>;
 
 //===----------------------------------------------------------------------===//
@@ -552,5 +537,3 @@ namespace {
 void Module::findUsedStructTypes(std::vector<StructType*> &StructTypes) const {
   TypeFinder(StructTypes).run(*this);
 }
-
-