[PATCH] D15642: [asan] Use private aliases for global variables (LLVM part).

[Maxim Ostapenko via llvm-commits]

m.ostapenko set the repository for this revision to rL LLVM.
m.ostapenko updated this revision to Diff 45279.
m.ostapenko added a comment.

Back here. Hide using private aliases for globals behind -asan-use-private-alias compile option. Generate ODR indicator symbol if use aliases and pass it's address to Global structure, pass 0 otherwise. Tested on Chromium (build chrome itself, build and run unit tests).


Repository:
  rL LLVM

http://reviews.llvm.org/D15642

Files:
  lib/Transforms/Instrumentation/AddressSanitizer.cpp

Index: lib/Transforms/Instrumentation/AddressSanitizer.cpp
===================================================================
--- lib/Transforms/Instrumentation/AddressSanitizer.cpp
+++ lib/Transforms/Instrumentation/AddressSanitizer.cpp
@@ -101,6 +101,7 @@
 static const char *const kAsanStackMallocNameTemplate = "__asan_stack_malloc_";
 static const char *const kAsanStackFreeNameTemplate = "__asan_stack_free_";
 static const char *const kAsanGenPrefix = "__asan_gen_";
+static const char *const kODRGenPrefix = "__odr_gen_";
 static const char *const kSanCovGenPrefix = "__sancov_gen_";
 static const char *const kAsanPoisonStackMemoryName =
     "__asan_poison_stack_memory";
@@ -226,6 +227,12 @@
     cl::desc("Force optimization experiment (for testing)"), cl::Hidden,
     cl::init(0));
 
+static cl::opt<bool>
+    ClUsePrivateAliasForGlobals("asan-use-private-alias",
+                                cl::desc("Use private aliases for global"
+                                         " variables"),
+                                cl::Hidden, cl::init(false));
+
 // Debug flags.
 static cl::opt<int> ClDebug("asan-debug", cl::desc("debug"), cl::Hidden,
                             cl::init(0));
@@ -815,7 +822,8 @@
 
 static bool GlobalWasGeneratedByAsan(GlobalVariable *G) {
   return G->getName().find(kAsanGenPrefix) == 0 ||
-         G->getName().find(kSanCovGenPrefix) == 0;
+         G->getName().find(kSanCovGenPrefix) == 0 ||
+         G->getName().find(kODRGenPrefix) == 0;
 }
 
 Value *AddressSanitizer::memToShadow(Value *Shadow, IRBuilder<> &IRB) {
@@ -1307,6 +1315,7 @@
 
   // A global is described by a structure
   //   size_t beg;
+  //   size_t odr_indicator;
   //   size_t size;
   //   size_t size_with_redzone;
   //   const char *name;
@@ -1316,7 +1325,7 @@
   // We initialize an array of such structures and pass it to a run-time call.
   StructType *GlobalStructTy =
       StructType::get(IntptrTy, IntptrTy, IntptrTy, IntptrTy, IntptrTy,
-                      IntptrTy, IntptrTy, nullptr);
+                      IntptrTy, IntptrTy, IntptrTy, nullptr);
   SmallVector<Constant *, 16> Initializers(n);
 
   bool HasDynamicallyInitializedGlobals = false;
@@ -1332,10 +1341,11 @@
     GlobalVariable *G = GlobalsToChange[i];
 
     auto MD = GlobalsMD.get(G);
+    StringRef NameForGlobal = G->getName();
     // Create string holding the global name (use global name from metadata
     // if it's available, otherwise just write the name of global variable).
     GlobalVariable *Name = createPrivateGlobalForString(
-        M, MD.Name.empty() ? G->getName() : MD.Name,
+        M, MD.Name.empty() ? NameForGlobal : MD.Name,
         /*AllowMerging*/ true);
 
     Type *Ty = G->getValueType();
@@ -1383,8 +1393,33 @@
       SourceLoc = ConstantInt::get(IntptrTy, 0);
     }
 
+    Constant *ODRIndicator = ConstantExpr::getNullValue(IntptrTy);
+    GlobalValue *InstrumentedGlobal = NewGlobal;
+
+    if (ClUsePrivateAliasForGlobals) {
+      // Create local alias for NewGlobal to avoid crash on ODR between
+      // instrumented and non-instrumented libraries.
+      auto *GA = GlobalAlias::create(GlobalValue::InternalLinkage,
+                                     NameForGlobal + M.getName(), NewGlobal);
+
+      // With local aliases, we need to provide another externally visible
+      // symbol
+      // _odr_genXXX to detect ODR violation.
+      auto *ODRIndicatorSym =
+          new GlobalVariable(M, IRB.getInt8Ty(), false, Linkage,
+                             Constant::getNullValue(IRB.getInt8Ty()),
+                             kODRGenPrefix + NameForGlobal, nullptr,
+                             NewGlobal->getThreadLocalMode());
+
+      ODRIndicatorSym->copyAttributesFrom(NewGlobal);
+      ODRIndicator = ODRIndicatorSym;
+      InstrumentedGlobal = GA;
+    }
+
     Initializers[i] = ConstantStruct::get(
-        GlobalStructTy, ConstantExpr::getPointerCast(NewGlobal, IntptrTy),
+        GlobalStructTy,
+        ConstantExpr::getPointerCast(InstrumentedGlobal, IntptrTy),
+        ConstantExpr::getPointerCast(ODRIndicator, IntptrTy),
         ConstantInt::get(IntptrTy, SizeInBytes),
         ConstantInt::get(IntptrTy, SizeInBytes + RightRedzoneSize),
         ConstantExpr::getPointerCast(Name, IntptrTy),


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