[PATCH] D132691: [clang] Do not instrument the rtti_proxies under hwasan

[Leonard Chan via Phabricator via cfe-commits]

leonardchan created this revision.
leonardchan added reviewers: mcgrathr, phosek.
leonardchan added a project: clang.
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leonardchan requested review of this revision.

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 <https://reviews.llvm.org/D132425> we can just disable hwasan for the proxies for now.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D132691

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


Index: clang/test/CodeGenCXX/RelativeVTablesABI/relative-vtables-hwasan.cpp
===================================================================
--- clang/test/CodeGenCXX/RelativeVTablesABI/relative-vtables-hwasan.cpp
+++ 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 @@
 /// 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:
Index: clang/lib/CodeGen/CGVTables.h
===================================================================
--- clang/lib/CodeGen/CGVTables.h
+++ clang/lib/CodeGen/CGVTables.h
@@ -155,8 +155,8 @@
   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
Index: clang/lib/CodeGen/CGVTables.cpp
===================================================================
--- clang/lib/CodeGen/CGVTables.cpp
+++ clang/lib/CodeGen/CGVTables.cpp
@@ -664,6 +664,12 @@
         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 different tags from different
+      // 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 @@
 // 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);
   }
 }
 


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