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Full context in https://bugs.fuchsia.dev/p/fuchsia/issues/detail?id=107017.
Instrumenting hwasan with globals results in a linker error under the relative
vtables abi:
ld.lld: error:
libunwind.cpp:(.rodata..L_ZTVN9libunwind12UnwindCursorINS_17LocalAddressSpaceENS_15Registers_arm64EEE.hwasan+0x8):
relocation R_AARCH64_PLT32 out of range: 6845471433603167792 is not in
[-2147483648, 2147483647]; references
libunwind::AbstractUnwindCursor::~AbstractUnwindCursor()
>>> defined in libunwind/src/CMakeFiles/unwind_shared.dir/libunwind.cpp.obj
This is because the tag is included in the vtable address when calculating
the offset between the vtable and virtual function. A temporary solution until
we can resolve this is to just disable hwasan instrumentation on relative
vtables specifically, which can be done in the frontend.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D132425
Files:
clang/lib/CodeGen/CGVTables.cpp
clang/lib/CodeGen/CGVTables.h
clang/lib/CodeGen/ItaniumCXXABI.cpp
clang/test/CodeGenCXX/RelativeVTablesABI/relative-vtables-hwasan.cpp
Index: clang/test/CodeGenCXX/RelativeVTablesABI/relative-vtables-hwasan.cpp
===================================================================
--- /dev/null
+++ clang/test/CodeGenCXX/RelativeVTablesABI/relative-vtables-hwasan.cpp
@@ -0,0 +1,34 @@
+// RUN: %clang_cc1 %s -triple=aarch64-unknown-fuchsia -S -o - -emit-llvm -fsanitize=hwaddress | FileCheck %s
+
+/// The usual vtable will have default visibility. In this case, the actual
+/// vtable is hidden and the alias is made public. With hwasan enabled, we want
+/// to ensure the local one self-referenced in the hidden vtable is not
+/// 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
+
+class A {
+public:
+ virtual void foo();
+};
+
+void A::foo() {}
+
+void A_foo(A *a) {
+ a->foo();
+}
+
+/// 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
+
+class __attribute__((visibility("hidden"))) B {
+public:
+ virtual void foo();
+};
+
+void B::foo() {}
+
+void B_foo(B *b) {
+ b->foo();
+}
Index: clang/lib/CodeGen/ItaniumCXXABI.cpp
===================================================================
--- clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -1769,8 +1769,11 @@
}
}
- if (VTContext.isRelativeLayout() && !VTable->isDSOLocal())
- CGVT.GenerateRelativeVTableAlias(VTable, VTable->getName());
+ if (VTContext.isRelativeLayout()) {
+ CGVT.RemoveHwasanMetadata(VTable);
+ if (!VTable->isDSOLocal())
+ CGVT.GenerateRelativeVTableAlias(VTable, VTable->getName());
+ }
}
bool ItaniumCXXABI::isVirtualOffsetNeededForVTableField(
Index: clang/lib/CodeGen/CGVTables.h
===================================================================
--- clang/lib/CodeGen/CGVTables.h
+++ clang/lib/CodeGen/CGVTables.h
@@ -154,6 +154,9 @@
/// when a vtable may not be dso_local.
void GenerateRelativeVTableAlias(llvm::GlobalVariable *VTable,
llvm::StringRef AliasNameRef);
+
+ /// Specify a vtable should not be instrumented with hwasan.
+ void RemoveHwasanMetadata(llvm::GlobalValue *VTable);
};
} // end namespace CodeGen
Index: clang/lib/CodeGen/CGVTables.cpp
===================================================================
--- clang/lib/CodeGen/CGVTables.cpp
+++ clang/lib/CodeGen/CGVTables.cpp
@@ -921,12 +921,25 @@
CGM.EmitVTableTypeMetadata(RD, VTable, *VTLayout.get());
- if (UsingRelativeLayout && !VTable->isDSOLocal())
- GenerateRelativeVTableAlias(VTable, OutName);
+ if (UsingRelativeLayout) {
+ RemoveHwasanMetadata(VTable);
+ if (!VTable->isDSOLocal())
+ GenerateRelativeVTableAlias(VTable, OutName);
+ }
return VTable;
}
+void CodeGenVTables::RemoveHwasanMetadata(llvm::GlobalValue *VTable) {
+ if (CGM.getLangOpts().Sanitize.has(SanitizerKind::HWAddress)) {
+ llvm::GlobalValue::SanitizerMetadata Meta;
+ if (VTable->hasSanitizerMetadata())
+ Meta = VTable->getSanitizerMetadata();
+ Meta.NoHWAddress = true;
+ VTable->setSanitizerMetadata(Meta);
+ }
+}
+
// If the VTable is not dso_local, then we will not be able to indicate that
// the VTable does not need a relocation and move into rodata. A frequent
// time this can occur is for classes that should be made public from a DSO
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