[hwasan] Respect llvm.asan.globals.

[eugenis]

Summary

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

[eugenis]

ASan does very fancy things to run this logic only once and access it in a function pass.
HWASan is a module pass and it can simply run the code once in initialization.

[pcc]

LGTM

[eugenis]

inclusive language

llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp

void HWAddressSanitizer::instrumentGlobal(GlobalVariable *GV, uint8_t Tag) {
   auto *Alias = GlobalAlias::create(GV->getValueType(), GV->getAddressSpace(),
                                     GV->getLinkage(), "", Aliasee, &M);
   Alias->setVisibility(GV->getVisibility());
   Alias->takeName(GV);
   GV->replaceAllUsesWith(Alias);
   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;
 
     // Common symbols can't have aliases point to them, so they can't be tagged.
     if (GV.hasCommonLinkage())
       continue;
 

llvm/test/Instrumentation/HWAddressSanitizer/globals.ll

 ; RUN: opt < %s -S -hwasan -mtriple=aarch64--linux-android29 | FileCheck --check-prefixes=CHECK,CHECK29 %s
 ; RUN: opt < %s -S -hwasan -mtriple=aarch64--linux-android30 | FileCheck --check-prefixes=CHECK,CHECK30 %s
 
 ; 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]
 
 ; CHECK: @hwasan.note = private constant { i32, i32, i32, [8 x i8], i32, i32 } { i32 8, i32 8, i32 3, [8 x i8] c"LLVM\00\00\00\00", i32 trunc (i64 sub (i64 ptrtoint ([0 x i8]* @__start_hwasan_globals to i64), i64 ptrtoint ({ i32, i32, i32, [8 x i8], i32, i32 }* @hwasan.note to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([0 x i8]* @__stop_hwasan_globals to i64), i64 ptrtoint ({ i32, i32, i32, [8 x i8], i32, i32 }* @hwasan.note to i64)) to i32) }, section ".note.hwasan.globals", comdat($hwasan.module_ctor), align 4
 
 ; CHECK: @hwasan.dummy.global = private constant [0 x i8] zeroinitializer, section "hwasan_globals", comdat($hwasan.module_ctor), !associated [[NOTE:![0-9]+]]
 
 ; CHECK30: @four.hwasan = private global { i32, [12 x i8] } { i32 1, [12 x i8] c"\00\00\00\00\00\00\00\00\00\00\00\AC" }, align 16

 ; CHECK30: [[SIXTEEN]] = !{[16 x i8]* @sixteen.hwasan}
 ; CHECK30: [[HUGE]] = !{[16777232 x i8]* @huge.hwasan}
 
 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}