[clang] cdb30f7 - [clang] Do not instrument the rtti_proxies under hwasan

[Leonard Chan via cfe-commits]

Author: Leonard Chan
Date: 2022-08-26T18:22:17Z
New Revision: cdb30f7a26354b000310ebe30a6874f7737675ed

URL: https://github.com/llvm/llvm-project/commit/cdb30f7a26354b000310ebe30a6874f7737675ed
DIFF: https://github.com/llvm/llvm-project/commit/cdb30f7a26354b000310ebe30a6874f7737675ed.diff

LOG: [clang] Do not instrument the rtti_proxies under hwasan

We run into a duplicate symbol error when instrumenting the rtti_proxies
generated as part of the relative vtables ABI with hwasan:

```
ld.lld: error: duplicate symbol: typeinfo for icu_71::UObject
(.rtti_proxy)
>>> defined at brkiter.cpp
>>>
arm64-hwasan-shared/obj/third_party/icu/source/common/libicuuc.brkiter.cpp.o:(typeinfo
for icu_71::UObject (.rtti_proxy))
>>> defined at locavailable.cpp
>>>
arm64-hwasan-shared/obj/third_party/icu/source/common/libicuuc.locavailable.cpp.o:(.data.rel.ro..L_ZTIN6icu_717UObjectE.rtti_proxy.hwasan+0xE00000000000000)
```

The issue here is that the hwasan alias carries over the visibility and
linkage of the original proxy, so we have duplicate external symbols
that participate in linking. Similar to D132425 we can just disable
hwasan for the proxies for now.

Differential Revision: https://reviews.llvm.org/D132691

Added: 
    

Modified: 
    clang/lib/CodeGen/CGVTables.cpp
    clang/lib/CodeGen/CGVTables.h
    clang/test/CodeGenCXX/RelativeVTablesABI/relative-vtables-hwasan.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/CodeGen/CGVTables.cpp b/clang/lib/CodeGen/CGVTables.cpp
index c8b29aec917c..3f8835d80a9a 100644
--- a/clang/lib/CodeGen/CGVTables.cpp
+++ b/clang/lib/CodeGen/CGVTables.cpp
@@ -664,6 +664,12 @@ void CodeGenVTables::addRelativeComponent(ConstantArrayBuilder &builder,
         proxy->setVisibility(llvm::GlobalValue::HiddenVisibility);
         proxy->setComdat(module.getOrInsertComdat(rttiProxyName));
       }
+      // Do not instrument the rtti proxies with hwasan to avoid a duplicate
+      // symbol error. Aliases generated by hwasan will retain the same namebut
+      // the addresses they are set to may have 
diff erent tags from 
diff erent
+      // compilation units. We don't run into this without hwasan because the
+      // proxies are in comdat groups, but those aren't propagated to the alias.
+      RemoveHwasanMetadata(proxy);
     }
     target = proxy;
   }
@@ -938,13 +944,13 @@ llvm::GlobalVariable *CodeGenVTables::GenerateConstructionVTable(
 // relocations. A future alternative for this would be finding which usages of
 // the vtable can continue to use the untagged hwasan value without any loss of
 // value in hwasan.
-void CodeGenVTables::RemoveHwasanMetadata(llvm::GlobalValue *VTable) {
+void CodeGenVTables::RemoveHwasanMetadata(llvm::GlobalValue *GV) const {
   if (CGM.getLangOpts().Sanitize.has(SanitizerKind::HWAddress)) {
     llvm::GlobalValue::SanitizerMetadata Meta;
-    if (VTable->hasSanitizerMetadata())
-      Meta = VTable->getSanitizerMetadata();
+    if (GV->hasSanitizerMetadata())
+      Meta = GV->getSanitizerMetadata();
     Meta.NoHWAddress = true;
-    VTable->setSanitizerMetadata(Meta);
+    GV->setSanitizerMetadata(Meta);
   }
 }
 

diff  --git a/clang/lib/CodeGen/CGVTables.h b/clang/lib/CodeGen/CGVTables.h
index c044ecc9bc8c..eb6b00b7847b 100644
--- a/clang/lib/CodeGen/CGVTables.h
+++ b/clang/lib/CodeGen/CGVTables.h
@@ -155,8 +155,8 @@ class CodeGenVTables {
   void GenerateRelativeVTableAlias(llvm::GlobalVariable *VTable,
                                    llvm::StringRef AliasNameRef);
 
-  /// Specify a vtable should not be instrumented with hwasan.
-  void RemoveHwasanMetadata(llvm::GlobalValue *VTable);
+  /// Specify a global should not be instrumented with hwasan.
+  void RemoveHwasanMetadata(llvm::GlobalValue *GV) const;
 };
 
 } // end namespace CodeGen

diff  --git a/clang/test/CodeGenCXX/RelativeVTablesABI/relative-vtables-hwasan.cpp b/clang/test/CodeGenCXX/RelativeVTablesABI/relative-vtables-hwasan.cpp
index b414b8d8ea8a..d0777b0f1245 100644
--- a/clang/test/CodeGenCXX/RelativeVTablesABI/relative-vtables-hwasan.cpp
+++ b/clang/test/CodeGenCXX/RelativeVTablesABI/relative-vtables-hwasan.cpp
@@ -6,6 +6,7 @@
 /// hwasan-instrumented.
 // CHECK-DAG: @_ZTV1A.local = private unnamed_addr constant { [3 x i32] } { [3 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr @_ZTI1A.rtti_proxy to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [3 x i32] }, ptr @_ZTV1A.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1A3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [3 x i32] }, ptr @_ZTV1A.local, i32 0, i32 0, i32 2) to i64)) to i32)] }, no_sanitize_hwaddress, align 4
 // CHECK-DAG: @_ZTV1A = unnamed_addr alias { [3 x i32] }, ptr @_ZTV1A.local
+// CHECK-DAG: @_ZTI1A.rtti_proxy = hidden unnamed_addr constant ptr @_ZTI1A, no_sanitize_hwaddress, comdat
 
 class A {
 public:
@@ -21,6 +22,7 @@ void A_foo(A *a) {
 /// If the vtable happens to be hidden, then the alias is not needed. In this
 /// case, the original vtable struct itself should be unsanitized.
 // CHECK-DAG: @_ZTV1B = hidden unnamed_addr constant { [3 x i32] } { [3 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr @_ZTI1B.rtti_proxy to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [3 x i32] }, ptr @_ZTV1B, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1B3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [3 x i32] }, ptr @_ZTV1B, i32 0, i32 0, i32 2) to i64)) to i32)] }, no_sanitize_hwaddress, align 4
+// CHECK-DAG: @_ZTI1B.rtti_proxy = hidden unnamed_addr constant ptr @_ZTI1B, no_sanitize_hwaddress, comdat
 
 class __attribute__((visibility("hidden"))) B {
 public: