From 78f7e6d8d7956cb96d0fa0fd606192ca0218eee1 Mon Sep 17 00:00:00 2001
From: Evgenii Stepanov <eugenis@google.com>
Date: Tue, 22 Jun 2021 16:27:11 -0700
Subject: [PATCH] [hwasan] Respect llvm.asan.globals.

This enable no_sanitize C++ attribute to exclude globals from hwasan
testing, and automatically excludes other sanitizers' globals (such as
ubsan location descriptors).

Differential Revision: https://reviews.llvm.org/D104825
---
 .../Instrumentation/HWAddressSanitizer.cpp    | 27 +++++++++++++++++++
 .../HWAddressSanitizer/globals.ll             |  6 +++++
 2 files changed, 33 insertions(+)

diff --git a/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp b/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
index a1f7486b010b..ada6d5ff18cb 100644
--- a/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
@@ -1467,9 +1467,36 @@ void HWAddressSanitizer::instrumentGlobal(GlobalVariable *GV, uint8_t Tag) {
   GV->eraseFromParent();
 }
 
+static DenseSet<GlobalVariable *> getExcludedGlobals(Module &M) {
+  NamedMDNode *Globals = M.getNamedMetadata("llvm.asan.globals");
+  if (!Globals)
+    return DenseSet<GlobalVariable *>();
+  DenseSet<GlobalVariable *> Excluded(Globals->getNumOperands());
+  for (auto MDN : Globals->operands()) {
+    // Metadata node contains the global and the fields of "Entry".
+    assert(MDN->getNumOperands() == 5);
+    auto *V = mdconst::extract_or_null<Constant>(MDN->getOperand(0));
+    // The optimizer may optimize away a global entirely.
+    if (!V)
+      continue;
+    auto *StrippedV = V->stripPointerCasts();
+    auto *GV = dyn_cast<GlobalVariable>(StrippedV);
+    if (!GV)
+      continue;
+    ConstantInt *IsExcluded = mdconst::extract<ConstantInt>(MDN->getOperand(4));
+    if (IsExcluded->isOne())
+      Excluded.insert(GV);
+  }
+  return Excluded;
+}
+
 void HWAddressSanitizer::instrumentGlobals() {
   std::vector<GlobalVariable *> Globals;
+  auto ExcludedGlobals = getExcludedGlobals(M);
   for (GlobalVariable &GV : M.globals()) {
+    if (ExcludedGlobals.count(&GV))
+      continue;
+
     if (GV.isDeclarationForLinker() || GV.getName().startswith("llvm.") ||
         GV.isThreadLocal())
       continue;
diff --git a/llvm/test/Instrumentation/HWAddressSanitizer/globals.ll b/llvm/test/Instrumentation/HWAddressSanitizer/globals.ll
index 548c41e4ab33..a3fc6808843e 100644
--- a/llvm/test/Instrumentation/HWAddressSanitizer/globals.ll
+++ b/llvm/test/Instrumentation/HWAddressSanitizer/globals.ll
@@ -3,6 +3,8 @@
 
 ; CHECK29: @four = global
 
+; CHECK: @specialcaselisted = global i16 2
+
 ; CHECK: @__start_hwasan_globals = external hidden constant [0 x i8]
 ; CHECK: @__stop_hwasan_globals = external hidden constant [0 x i8]
 
@@ -34,3 +36,7 @@ source_filename = "foo"
 @four = global i32 1
 @sixteen = global [16 x i8] zeroinitializer
 @huge = global [16777232 x i8] zeroinitializer
+@specialcaselisted = global i16 2
+
+!llvm.asan.globals = !{!0}
+!0 = !{i16* @specialcaselisted, null, null, i1 false, i1 true}
-- 
2.32.0.93.g670b81a890-goog