[patch/asan] Use lvm.global_ctors instead of symbol name matching to find constructors

[Nico Weber]

Hi,

here's how the global_ctors version would look. I haven't tested this
much (it's different in that it could now instrument multiple
constructors per module).

Feel free to play with this, and then land this with tweaks, land it
as-is, or don't land it, up to you :-)

Nico
-------------- next part --------------
Index: lib/Transforms/Instrumentation/AddressSanitizer.cpp
===================================================================
--- lib/Transforms/Instrumentation/AddressSanitizer.cpp	(revision 208141)
+++ lib/Transforms/Instrumentation/AddressSanitizer.cpp	(working copy)
@@ -390,6 +390,7 @@
   void initializeCallbacks(Module &M);
 
   bool ShouldInstrumentGlobal(GlobalVariable *G);
+  void poisonOneInitializer(Function &GlobalInit, GlobalValue *ModuleName);
   void createInitializerPoisonCalls(Module &M, GlobalValue *ModuleName);
   size_t MinRedzoneSizeForGlobal() const {
     return RedzoneSizeForScale(Mapping.Scale);
@@ -844,49 +845,35 @@
   Crash->setDebugLoc(OrigIns->getDebugLoc());
 }
 
-void AddressSanitizerModule::createInitializerPoisonCalls(
-    Module &M, GlobalValue *ModuleName) {
-  // We do all of our poisoning and unpoisoning within a global constructor.
-  // These are called _GLOBAL__(sub_)?I_.*.
-  // TODO: Consider looking through the functions in
-  // M.getGlobalVariable("llvm.global_ctors") instead of using this stringly
-  // typed approach.
-  Function *GlobalInit = nullptr;
-  for (auto &F : M.getFunctionList()) {
-    StringRef FName = F.getName();
-
-    const char kGlobalPrefix[] = "_GLOBAL__";
-    if (!FName.startswith(kGlobalPrefix))
-      continue;
-    FName = FName.substr(strlen(kGlobalPrefix));
-
-    const char kOptionalSub[] = "sub_";
-    if (FName.startswith(kOptionalSub))
-      FName = FName.substr(strlen(kOptionalSub));
-
-    if (FName.startswith("I_")) {
-      GlobalInit = &F;
-      break;
-    }
-  }
-  // If that function is not present, this TU contains no globals, or they have
-  // all been optimized away
-  if (!GlobalInit)
-    return;
-
+void AddressSanitizerModule::poisonOneInitializer(Function &GlobalInit,
+                                                  GlobalValue *ModuleName) {
   // Set up the arguments to our poison/unpoison functions.
-  IRBuilder<> IRB(GlobalInit->begin()->getFirstInsertionPt());
+  IRBuilder<> IRB(GlobalInit.begin()->getFirstInsertionPt());
 
   // Add a call to poison all external globals before the given function starts.
   Value *ModuleNameAddr = ConstantExpr::getPointerCast(ModuleName, IntptrTy);
   IRB.CreateCall(AsanPoisonGlobals, ModuleNameAddr);
 
   // Add calls to unpoison all globals before each return instruction.
-  for (Function::iterator I = GlobalInit->begin(), E = GlobalInit->end();
-       I != E; ++I) {
-    if (ReturnInst *RI = dyn_cast<ReturnInst>(I->getTerminator())) {
+  for (auto &BB : GlobalInit.getBasicBlockList())
+    if (ReturnInst *RI = dyn_cast<ReturnInst>(BB.getTerminator()))
       CallInst::Create(AsanUnpoisonGlobals, "", RI);
-    }
+}
+
+void AddressSanitizerModule::createInitializerPoisonCalls(
+    Module &M, GlobalValue *ModuleName) {
+  GlobalVariable *GV = M.getGlobalVariable("llvm.global_ctors");
+
+  ConstantArray *CA = cast<ConstantArray>(GV->getInitializer());
+  for (Use &OP : CA->operands()) {
+    if (isa<ConstantAggregateZero>(OP))
+      continue;
+    ConstantStruct *CS = cast<ConstantStruct>(OP);
+
+    // Must have a function or null ptr.
+    // (CS->getOperand(0) is the init priority.)
+    if (Function* F = dyn_cast<Function>(CS->getOperand(1)))
+      poisonOneInitializer(*F, ModuleName);
   }
 }
 
Index: test/Instrumentation/AddressSanitizer/instrument_initializer_metadata.ll
===================================================================
--- test/Instrumentation/AddressSanitizer/instrument_initializer_metadata.ll	(revision 208096)
+++ test/Instrumentation/AddressSanitizer/instrument_initializer_metadata.ll	(working copy)
@@ -23,6 +23,8 @@
   ret void
 }
 
+ at llvm.global_ctors = appending global [1 x { i32, void ()* }] [{ i32, void ()* } { i32 65535, void ()* @_GLOBAL__I_a }]
+
 define internal void @_GLOBAL__I_a() sanitize_address section ".text.startup" {
 entry:
   call void @__cxx_global_var_init()