[KernelAddressSanitizer] Make globals constructors compatible with kernel [v2]

[melver]

Summary

Note: The first version of this feature was reverted due to modpost causing failures. This v2 fixes this. More info:

https://github.com/ClangBuiltLinux/linux/issues/1045#issuecomment-640381783

This makes -fsanitize=kernel-address emit the correct globals
constructors for the kernel. We had to do the following:

• Disable generation of constructors that rely on linker features such as dead-global elimination.

• Only instrument globals *not* in explicit sections. The kernel uses sections for special globals, which we should not touch.

• Do not instrument globals that are prefixed with "" nor that are aliased by a symbol that is prefixed with "". For example, modpost relies on specially named aliases to find globals and checks their contents. Unfortunately modpost relies on size stored as ELF debug info and any padding of globals currently causes the debug info to cause size reported to be *with* redzone which throws modpost off.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=203493

Tested:

• With 'clang/test/CodeGen/asan-globals.cpp'.

• With test_kasan.ko, we can see:
  
  BUG: KASAN: global-out-of-bounds in kasan_global_oob+0xb3/0xba [test_kasan]

• allyesconfig, allmodconfig (x86_64)

[melver]

Also ignore non-alias globals prefixed by __.

[nathanchance]

I do not know enough about KASAN enough to review this patch but I can say that against mainline at https://git.kernel.org/linus/af7b4801030c07637840191c69eb666917e4135d, there appear to be no visible regressions with this version of the patch on top of caa2fddce72f2e8ca3d6346cc2c8fe85252b91d8.

[melver]

In D81390#2081067, @nathanchance wrote:

I do not know enough about KASAN enough to review this patch but I can say that against mainline at https://git.kernel.org/linus/af7b4801030c07637840191c69eb666917e4135d, there appear to be no visible regressions with this version of the patch on top of caa2fddce72f2e8ca3d6346cc2c8fe85252b91d8.

Thank you for testing this!

[glider]

clang/test/CodeGen/asan-globals.cpp

16

Need a comment explaining this case a bit.

llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

759

UseGlobalsGC assumes !this->CompileKernel already, doesn't it?

1796

Maybe it's better to call this function only if CompileKernel is true?
I don't think we need it except for the kernel.

1942

This change looks unrelated to the rest.

[melver]

Address comments.

[melver]

Thanks! PTAL.

llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

759

I experimented a bit and found that even if one of them is enabled things break (say if you remove UseGlobalsGC here). This is more explicit and less error-prone in case somebody removes UseGlobalsGC from UseCtorComdat. And there is no real penalty here for having it on both.

1796

Done, though the previous version was cleaner. I guarded the call but now we need an assert and a comment to make sure the check is moved when people decide to use this for more than the kernel.

[melver]

Fix test broken by linter.

[melver]

Fix typos.

[melver]

Fix test on windows.

[glider]

LGTM assuming allyesconfig builds.

llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

759

That's strange, but ok.

[thakis]

This breaks mac again: http://45.33.8.238/mac/15259/step_7.txt

clang/test/CodeGen/asan-globals.cpp

 // RUN: echo "int extra_global;" > %t.extra-source.cpp
 // RUN: echo "global:*blacklisted_global*" > %t.blacklist
-// RUN: %clang_cc1 -include %t.extra-source.cpp -fsanitize=address -fsanitize-blacklist=%t.blacklist -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -include %t.extra-source.cpp -fsanitize=address -fsanitize-blacklist=%t.blacklist -emit-llvm -o - %s | FileCheck %s --check-prefixes=CHECK,ASAN
+// RUN: %clang_cc1 -include %t.extra-source.cpp -fsanitize=kernel-address -fsanitize-blacklist=%t.blacklist -emit-llvm -o - %s | FileCheck %s --check-prefixes=CHECK,KASAN
 // The blacklist file uses regexps, so Windows path backslashes.
 // RUN: echo "src:%s" | sed -e 's/\\/\\\\/g' > %t.blacklist-src
 // RUN: %clang_cc1 -include %t.extra-source.cpp -fsanitize=address -fsanitize-blacklist=%t.blacklist-src -emit-llvm -o - %s | FileCheck %s --check-prefix=BLACKLIST-SRC
+// RUN: %clang_cc1 -include %t.extra-source.cpp -fsanitize=kernel-address -fsanitize-blacklist=%t.blacklist-src -emit-llvm -o - %s | FileCheck %s --check-prefix=BLACKLIST-SRC
 
 int global;
 int dyn_init_global = global;
 int __attribute__((no_sanitize("address"))) attributed_global;
 int blacklisted_global;
 
+int __attribute__((section("__DATA, __common"))) sectioned_global; // [KASAN] ignore globals in a section
+extern "C" {
+int aliased_global;                                                 // [KASAN] ignore globals prefixed by aliases with __-prefix [below]
+extern int __attribute__((alias("aliased_global"))) __global_alias; // [KASAN] aliased_global ignored
+int __special_global;                                               // [KASAN] ignore globals with __-prefix
+}
+
 void func() {
   static int static_var = 0;
   const char *literal = "Hello, world!";
 }
 
-// CHECK: !llvm.asan.globals = !{![[EXTRA_GLOBAL:[0-9]+]], ![[GLOBAL:[0-9]+]], ![[DYN_INIT_GLOBAL:[0-9]+]], ![[ATTR_GLOBAL:[0-9]+]], ![[BLACKLISTED_GLOBAL:[0-9]+]], ![[STATIC_VAR:[0-9]+]], ![[LITERAL:[0-9]+]]}
+// ASAN: sectioned_global{{.*}}{ i32, [60 x i8] }{{.*}}align 32
+// KASAN: sectioned_global{{.*}}i32
+// ASAN: @aliased_global{{.*}}{ i32, [60 x i8] }{{.*}}align 32
+// KASAN: @aliased_global{{.*}}i32
+// ASAN: @__special_global{{.*}}{ i32, [60 x i8] }{{.*}}align 32
+// KASAN: @__special_global{{.*}}i32
+
+// CHECK-LABEL: define internal void @asan.module_ctor
+// ASAN-NEXT: call void @__asan_init
+// ASAN-NEXT: call void @__asan_version_mismatch_check
+// KASAN-NOT: call void @__asan_init
+// KASAN-NOT: call void @__asan_version_mismatch_check
+// ASAN-NEXT: call void @__asan_register_globals({{.*}}, i{{32|64}} 8)
+// KASAN-NEXT: call void @__asan_register_globals({{.*}}, i{{32|64}} 5)
+// CHECK-NEXT: ret void
+
+// CHECK-LABEL: define internal void @asan.module_dtor
+// CHECK-NEXT: call void @__asan_unregister_globals
+// CHECK-NEXT: ret void
+
+// CHECK: !llvm.asan.globals = !{![[EXTRA_GLOBAL:[0-9]+]], ![[GLOBAL:[0-9]+]], ![[DYN_INIT_GLOBAL:[0-9]+]], ![[ATTR_GLOBAL:[0-9]+]], ![[BLACKLISTED_GLOBAL:[0-9]+]], ![[SECTIONED_GLOBAL:[0-9]+]], ![[ALIASED_GLOBAL:[0-9]+]], ![[SPECIAL_GLOBAL:[0-9]+]], ![[STATIC_VAR:[0-9]+]], ![[LITERAL:[0-9]+]]}
 // CHECK: ![[EXTRA_GLOBAL]] = !{{{.*}} ![[EXTRA_GLOBAL_LOC:[0-9]+]], !"extra_global", i1 false, i1 false}
 // CHECK: ![[EXTRA_GLOBAL_LOC]] = !{!"{{.*}}extra-source.cpp", i32 1, i32 5}
 // CHECK: ![[GLOBAL]] = !{{{.*}} ![[GLOBAL_LOC:[0-9]+]], !"global", i1 false, i1 false}
-// CHECK: ![[GLOBAL_LOC]] = !{!"{{.*}}asan-globals.cpp", i32 8, i32 5}
+// CHECK: ![[GLOBAL_LOC]] = !{!"{{.*}}asan-globals.cpp", i32 10, i32 5}
 // CHECK: ![[DYN_INIT_GLOBAL]] = !{{{.*}} ![[DYN_INIT_LOC:[0-9]+]], !"dyn_init_global", i1 true, i1 false}
-// CHECK: ![[DYN_INIT_LOC]] = !{!"{{.*}}asan-globals.cpp", i32 9, i32 5}
+// CHECK: ![[DYN_INIT_LOC]] = !{!"{{.*}}asan-globals.cpp", i32 11, i32 5}
 // CHECK: ![[ATTR_GLOBAL]] = !{{{.*}}, null, null, i1 false, i1 true}
 // CHECK: ![[BLACKLISTED_GLOBAL]] = !{{{.*}}, null, null, i1 false, i1 true}
+// CHECK: ![[SECTIONED_GLOBAL]] = !{{{.*}} ![[SECTIONED_GLOBAL_LOC:[0-9]+]], !"sectioned_global", i1 false, i1 false}
+// CHECK: ![[SECTIONED_GLOBAL_LOC]] = !{!"{{.*}}asan-globals.cpp", i32 15, i32 50}
+// CHECK: ![[ALIASED_GLOBAL]] = !{{{.*}} ![[ALIASED_GLOBAL_LOC:[0-9]+]], !"aliased_global", i1 false, i1 false}
+// CHECK: ![[ALIASED_GLOBAL_LOC]] = !{!"{{.*}}asan-globals.cpp", i32 17, i32 5}
+// CHECK: ![[SPECIAL_GLOBAL]] = !{{{.*}} ![[SPECIAL_GLOBAL_LOC:[0-9]+]], !"__special_global", i1 false, i1 false}
+// CHECK: ![[SPECIAL_GLOBAL_LOC]] = !{!"{{.*}}asan-globals.cpp", i32 19, i32 5}
 // CHECK: ![[STATIC_VAR]] = !{{{.*}} ![[STATIC_LOC:[0-9]+]], !"static_var", i1 false, i1 false}
-// CHECK: ![[STATIC_LOC]] = !{!"{{.*}}asan-globals.cpp", i32 14, i32 14}
+// CHECK: ![[STATIC_LOC]] = !{!"{{.*}}asan-globals.cpp", i32 23, i32 14}
 // CHECK: ![[LITERAL]] = !{{{.*}} ![[LITERAL_LOC:[0-9]+]], !"<string literal>", i1 false, i1 false}
-// CHECK: ![[LITERAL_LOC]] = !{!"{{.*}}asan-globals.cpp", i32 15, i32 25}
+// CHECK: ![[LITERAL_LOC]] = !{!"{{.*}}asan-globals.cpp", i32 24, i32 25}
 
-// BLACKLIST-SRC: !llvm.asan.globals = !{![[EXTRA_GLOBAL:[0-9]+]], ![[GLOBAL:[0-9]+]], ![[DYN_INIT_GLOBAL:[0-9]+]], ![[ATTR_GLOBAL:[0-9]+]], ![[BLACKLISTED_GLOBAL:[0-9]+]], ![[STATIC_VAR:[0-9]+]], ![[LITERAL:[0-9]+]]}
+// BLACKLIST-SRC: !llvm.asan.globals = !{![[EXTRA_GLOBAL:[0-9]+]], ![[GLOBAL:[0-9]+]], ![[DYN_INIT_GLOBAL:[0-9]+]], ![[ATTR_GLOBAL:[0-9]+]], ![[BLACKLISTED_GLOBAL:[0-9]+]], ![[SECTIONED_GLOBAL:[0-9]+]], ![[ALIASED_GLOBAL:[0-9]+]], ![[SPECIAL_GLOBAL:[0-9]+]], ![[STATIC_VAR:[0-9]+]], ![[LITERAL:[0-9]+]]}
 // BLACKLIST-SRC: ![[EXTRA_GLOBAL]] = !{{{.*}} ![[EXTRA_GLOBAL_LOC:[0-9]+]], !"extra_global", i1 false, i1 false}
 // BLACKLIST-SRC: ![[EXTRA_GLOBAL_LOC]] = !{!"{{.*}}extra-source.cpp", i32 1, i32 5}
 // BLACKLIST-SRC: ![[GLOBAL]] = !{{{.*}} null, null, i1 false, i1 true}
 // BLACKLIST-SRC: ![[DYN_INIT_GLOBAL]] = !{{{.*}} null, null, i1 true, i1 true}
 // BLACKLIST-SRC: ![[ATTR_GLOBAL]] = !{{{.*}}, null, null, i1 false, i1 true}
 // BLACKLIST-SRC: ![[BLACKLISTED_GLOBAL]] = !{{{.*}}, null, null, i1 false, i1 true}
+// BLACKLIST-SRC: ![[SECTIONED_GLOBAL]] = !{{{.*}} null, null, i1 false, i1 true}
+// BLACKLIST-SRC: ![[ALIASED_GLOBAL]] = !{{{.*}} null, null, i1 false, i1 true}
+// BLACKLIST-SRC: ![[SPECIAL_GLOBAL]] = !{{{.*}} null, null, i1 false, i1 true}
 // BLACKLIST-SRC: ![[STATIC_VAR]] = !{{{.*}} null, null, i1 false, i1 true}
 // BLACKLIST-SRC: ![[LITERAL]] = !{{{.*}} null, null, i1 false, i1 true}

llvm/include/llvm/Transforms/Utils/ModuleUtils.h

 
 /// Same as appendToGlobalCtors(), but for global dtors.
 void appendToGlobalDtors(Module &M, Function *F, int Priority,
                          Constant *Data = nullptr);
 
 FunctionCallee declareSanitizerInitFunction(Module &M, StringRef InitName,
                                             ArrayRef<Type *> InitArgTypes);
 
+/// Creates sanitizer constructor function.
+/// \return Returns pointer to constructor.
+Function *createSanitizerCtor(Module &M, StringRef CtorName);
+
 /// Creates sanitizer constructor function, and calls sanitizer's init
 /// function from it.
 /// \return Returns pair of pointers to constructor, and init functions
 /// respectively.
 std::pair<Function *, FunctionCallee> createSanitizerCtorAndInitFunctions(
     Module &M, StringRef CtorName, StringRef InitName,
     ArrayRef<Type *> InitArgTypes, ArrayRef<Value *> InitArgs,
     StringRef VersionCheckName = StringRef());

llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

 
 char ASanGlobalsMetadataWrapperPass::ID = 0;
 
 /// AddressSanitizer: instrument the code in module to find memory bugs.
 struct AddressSanitizer {
   AddressSanitizer(Module &M, const GlobalsMetadata *GlobalsMD,
                    bool CompileKernel = false, bool Recover = false,
                    bool UseAfterScope = false)
-      : UseAfterScope(UseAfterScope || ClUseAfterScope), GlobalsMD(*GlobalsMD) {
-    this->Recover = ClRecover.getNumOccurrences() > 0 ? ClRecover : Recover;
-    this->CompileKernel =
-        ClEnableKasan.getNumOccurrences() > 0 ? ClEnableKasan : CompileKernel;
-
+      : CompileKernel(ClEnableKasan.getNumOccurrences() > 0 ? ClEnableKasan
+                                                            : CompileKernel),
+        Recover(ClRecover.getNumOccurrences() > 0 ? ClRecover : Recover),
+        UseAfterScope(UseAfterScope || ClUseAfterScope), GlobalsMD(*GlobalsMD) {
     C = &(M.getContext());
     LongSize = M.getDataLayout().getPointerSizeInBits();
     IntptrTy = Type::getIntNTy(*C, LongSize);
     TargetTriple = Triple(M.getTargetTriple());
 
     Mapping = getShadowMapping(TargetTriple, LongSize, this->CompileKernel);
   }
 
private:
   bool UseAfterScope;
 };
 
 class ModuleAddressSanitizer {
 public:
   ModuleAddressSanitizer(Module &M, const GlobalsMetadata *GlobalsMD,
                          bool CompileKernel = false, bool Recover = false,
                          bool UseGlobalsGC = true, bool UseOdrIndicator = false)
-      : GlobalsMD(*GlobalsMD), UseGlobalsGC(UseGlobalsGC && ClUseGlobalsGC),
+      : GlobalsMD(*GlobalsMD),
+        CompileKernel(ClEnableKasan.getNumOccurrences() > 0 ? ClEnableKasan
+                                                            : CompileKernel),
+        Recover(ClRecover.getNumOccurrences() > 0 ? ClRecover : Recover),
+        UseGlobalsGC(UseGlobalsGC && ClUseGlobalsGC && !this->CompileKernel),
         // Enable aliases as they should have no downside with ODR indicators.
         UsePrivateAlias(UseOdrIndicator || ClUsePrivateAlias),
         UseOdrIndicator(UseOdrIndicator || ClUseOdrIndicator),
         // Not a typo: ClWithComdat is almost completely pointless without
         // ClUseGlobalsGC (because then it only works on modules without
         // globals, which are rare); it is a prerequisite for ClUseGlobalsGC;
         // and both suffer from gold PR19002 for which UseGlobalsGC constructor
         // argument is designed as workaround. Therefore, disable both
         // ClWithComdat and ClUseGlobalsGC unless the frontend says it's ok to
         // do globals-gc.
-        UseCtorComdat(UseGlobalsGC && ClWithComdat) {
-    this->Recover = ClRecover.getNumOccurrences() > 0 ? ClRecover : Recover;
-    this->CompileKernel =
-        ClEnableKasan.getNumOccurrences() > 0 ? ClEnableKasan : CompileKernel;
-
+        UseCtorComdat(UseGlobalsGC && ClWithComdat && !this->CompileKernel) {
     C = &(M.getContext());
     int LongSize = M.getDataLayout().getPointerSizeInBits();
     IntptrTy = Type::getIntNTy(*C, LongSize);
     TargetTriple = Triple(M.getTargetTriple());
     Mapping = getShadowMapping(TargetTriple, LongSize, this->CompileKernel);
   }
 
   bool instrumentModule(Module &);
InstrumentGlobalsWithMetadataArray(IRBuilder<> &IRB, Module &M,
                                      ArrayRef<Constant *> MetadataInitializers);
 
   GlobalVariable *CreateMetadataGlobal(Module &M, Constant *Initializer,
                                        StringRef OriginalName);
   void SetComdatForGlobalMetadata(GlobalVariable *G, GlobalVariable *Metadata,
                                   StringRef InternalSuffix);
   Instruction *CreateAsanModuleDtor(Module &M);
 
-  bool ShouldInstrumentGlobal(GlobalVariable *G);
+  bool canInstrumentAliasedGlobal(const GlobalAlias &GA) const;
+  bool shouldInstrumentGlobal(GlobalVariable *G) const;
   bool ShouldUseMachOGlobalsSection() const;
   StringRef getGlobalMetadataSection() const;
   void poisonOneInitializer(Function &GlobalInit, GlobalValue *ModuleName);
   void createInitializerPoisonCalls(Module &M, GlobalValue *ModuleName);
   size_t MinRedzoneSizeForGlobal() const {
     return RedzoneSizeForScale(Mapping.Scale);
   }
   int GetAsanVersion(const Module &M) const;
if (Function *F = dyn_cast<Function>(CS->getOperand(1))) {
       // Don't instrument CTORs that will run before asan.module_ctor.
       if (Priority->getLimitedValue() <= GetCtorAndDtorPriority(TargetTriple))
         continue;
       poisonOneInitializer(*F, ModuleName);
     }
   }
 }
 
-bool ModuleAddressSanitizer::ShouldInstrumentGlobal(GlobalVariable *G) {
+bool ModuleAddressSanitizer::canInstrumentAliasedGlobal(
+    const GlobalAlias &GA) const {
+  // In case this function should be expanded to include rules that do not just
+  // apply when CompileKernel is true, either guard all existing rules with an
+  // 'if (CompileKernel) { ... }' or be absolutely sure that all these rules
+  // should also apply to user space.
+  assert(CompileKernel && "Only expecting to be called when compiling kernel");
+
+  // When compiling the kernel, globals that are aliased by symbols prefixed
+  // by "__" are special and cannot be padded with a redzone.
+  if (GA.getName().startswith("__"))
+    return false;
+
+  return true;
+}
+
+bool ModuleAddressSanitizer::shouldInstrumentGlobal(GlobalVariable *G) const {
   Type *Ty = G->getValueType();
   LLVM_DEBUG(dbgs() << "GLOBAL: " << *G << "\n");
 
   // FIXME: Metadata should be attched directly to the global directly instead
   // of being added to llvm.asan.globals.
   if (GlobalsMD.get(G).IsBlacklisted) return false;
   if (!Ty->isSized()) return false;
   if (!G->hasInitializer()) return false;
case Comdat::NoDuplicates:
       break;
     case Comdat::Largest:
     case Comdat::SameSize:
       return false;
     }
   }
 
   if (G->hasSection()) {
+    // The kernel uses explicit sections for mostly special global variables
+    // that we should not instrument. E.g. the kernel may rely on their layout
+    // without redzones, or remove them at link time ("discard.*"), etc.
+    if (CompileKernel)
+      return false;
+
     StringRef Section = G->getSection();
 
     // Globals from llvm.metadata aren't emitted, do not instrument them.
     if (Section == "llvm.metadata") return false;
     // Do not instrument globals from special LLVM sections.
     if (Section.find("__llvm") != StringRef::npos || Section.find("__LLVM") != StringRef::npos) return false;
 
     // Do not instrument function pointers to initialization and termination
if (TargetTriple.isOSBinFormatMachO()) {
       // trailing zeroes.
       if (ParsedSegment == "__TEXT" && (TAA & MachO::S_CSTRING_LITERALS)) {
         LLVM_DEBUG(dbgs() << "Ignoring a cstring literal: " << *G << "\n");
         return false;
       }
     }
   }
 
+  if (CompileKernel) {
+    // Globals that prefixed by "__" are special and cannot be padded with a
+    // redzone.
+    if (G->getName().startswith("__"))
+      return false;
+  }
+
   return true;
 }
 
 // On Mach-O platforms, we emit global metadata in a separate section of the
 // binary in order to allow the linker to properly dead strip. This is only
 // supported on recent versions of ld64.
 bool ModuleAddressSanitizer::ShouldUseMachOGlobalsSection() const {
   if (!TargetTriple.isOSBinFormatMachO())
     return false;
 
   if (TargetTriple.isMacOSX() && !TargetTriple.isMacOSXVersionLT(10, 11))
     return true;
   if (TargetTriple.isiOS() /* or tvOS */ && !TargetTriple.isOSVersionLT(9))
     return true;
   if (TargetTriple.isWatchOS() && !TargetTriple.isOSVersionLT(2))

 // trailing redzones. It also creates a function that poisons
 // redzones and inserts this function into llvm.global_ctors.
 // Sets *CtorComdat to true if the global registration code emitted into the
 // asan constructor is comdat-compatible.
 bool ModuleAddressSanitizer::InstrumentGlobals(IRBuilder<> &IRB, Module &M,
                                                bool *CtorComdat) {
   *CtorComdat = false;
 
-  SmallVector<GlobalVariable *, 16> GlobalsToChange;
+  // Build set of globals that are aliased by some GA, where
+  // canInstrumentAliasedGlobal(GA) returns false.
+  SmallPtrSet<const GlobalVariable *, 16> AliasedGlobalBlacklist;
+  if (CompileKernel) {
+    for (auto &GA : M.aliases()) {
+      if (const auto *GV = dyn_cast<GlobalVariable>(GA.getAliasee())) {
+        if (!canInstrumentAliasedGlobal(GA))
+          AliasedGlobalBlacklist.insert(GV);
+      }
+    }
+  }
 
+  SmallVector<GlobalVariable *, 16> GlobalsToChange;
   for (auto &G : M.globals()) {
-    if (ShouldInstrumentGlobal(&G)) GlobalsToChange.push_back(&G);
+    if (!AliasedGlobalBlacklist.count(&G) && shouldInstrumentGlobal(&G))
+      GlobalsToChange.push_back(&G);
   }
 
   size_t n = GlobalsToChange.size();
   if (n == 0) {
     *CtorComdat = true;
     return false;
   }
 
int ModuleAddressSanitizer::GetAsanVersion(const Module &M) const {
   // shadow.
   Version += (LongSize == 32 && isAndroid);
   return Version;
 }
 
 bool ModuleAddressSanitizer::instrumentModule(Module &M) {
   initializeCallbacks(M);
 
-  if (CompileKernel)
-    return false;
-
   // Create a module constructor. A destructor is created lazily because not all
   // platforms, and not all modules need it.
+  if (CompileKernel) {
+    // The kernel always builds with its own runtime, and therefore does not
+    // need the init and version check calls.
+    AsanCtorFunction = createSanitizerCtor(M, kAsanModuleCtorName);
+  } else {
     std::string AsanVersion = std::to_string(GetAsanVersion(M));
     std::string VersionCheckName =
         ClInsertVersionCheck ? (kAsanVersionCheckNamePrefix + AsanVersion) : "";
-  std::tie(AsanCtorFunction, std::ignore) = createSanitizerCtorAndInitFunctions(
-      M, kAsanModuleCtorName, kAsanInitName, /*InitArgTypes=*/{},
+    std::tie(AsanCtorFunction, std::ignore) =
+        createSanitizerCtorAndInitFunctions(M, kAsanModuleCtorName,
+                                            kAsanInitName, /*InitArgTypes=*/{},
                                             /*InitArgs=*/{}, VersionCheckName);
+  }
 
   bool CtorComdat = true;
-  // TODO(glider): temporarily disabled globals instrumentation for KASan.
   if (ClGlobals) {
     IRBuilder<> IRB(AsanCtorFunction->getEntryBlock().getTerminator());
     InstrumentGlobals(IRB, M, &CtorComdat);
   }
 
   const uint64_t Priority = GetCtorAndDtorPriority(TargetTriple);
 
   // Put the constructor and destructor in comdat if both

llvm/lib/Transforms/Utils/ModuleUtils.cpp

llvm::declareSanitizerInitFunction(Module &M, StringRef InitName,
                                    ArrayRef<Type *> InitArgTypes) {
   assert(!InitName.empty() && "Expected init function name");
   return M.getOrInsertFunction(
       InitName,
       FunctionType::get(Type::getVoidTy(M.getContext()), InitArgTypes, false),
       AttributeList());
 }
 
+Function *llvm::createSanitizerCtor(Module &M, StringRef CtorName) {
+  Function *Ctor = Function::Create(
+      FunctionType::get(Type::getVoidTy(M.getContext()), false),
+      GlobalValue::InternalLinkage, CtorName, &M);
+  BasicBlock *CtorBB = BasicBlock::Create(M.getContext(), "", Ctor);
+  ReturnInst::Create(M.getContext(), CtorBB);
+  return Ctor;
+}
+
 std::pair<Function *, FunctionCallee> llvm::createSanitizerCtorAndInitFunctions(
     Module &M, StringRef CtorName, StringRef InitName,
     ArrayRef<Type *> InitArgTypes, ArrayRef<Value *> InitArgs,
     StringRef VersionCheckName) {
   assert(!InitName.empty() && "Expected init function name");
   assert(InitArgs.size() == InitArgTypes.size() &&
          "Sanitizer's init function expects different number of arguments");
   FunctionCallee InitFunction =
       declareSanitizerInitFunction(M, InitName, InitArgTypes);
-  Function *Ctor = Function::Create(
-      FunctionType::get(Type::getVoidTy(M.getContext()), false),
-      GlobalValue::InternalLinkage, CtorName, &M);
-  BasicBlock *CtorBB = BasicBlock::Create(M.getContext(), "", Ctor);
-  IRBuilder<> IRB(ReturnInst::Create(M.getContext(), CtorBB));
+  Function *Ctor = createSanitizerCtor(M, CtorName);
+  IRBuilder<> IRB(Ctor->getEntryBlock().getTerminator());
   IRB.CreateCall(InitFunction, InitArgs);
   if (!VersionCheckName.empty()) {
     FunctionCallee VersionCheckFunction = M.getOrInsertFunction(
         VersionCheckName, FunctionType::get(IRB.getVoidTy(), {}, false),
         AttributeList());
     IRB.CreateCall(VersionCheckFunction, {});
   }
   return std::make_pair(Ctor, InitFunction);