[clang] [clang][RelativeVTables] Make the rtti_proxy LinkOnceODR instead of External linkage (PR #67755)
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Tue Oct 3 15:56:04 PDT 2023
https://github.com/PiJoules updated https://github.com/llvm/llvm-project/pull/67755
>From 0e798f3fdd7dc8816a71e3e147ca14616ad4a123 Mon Sep 17 00:00:00 2001
From: Leonard Chan <leonardchan at google.com>
Date: Fri, 29 Sep 2023 00:25:44 +0000
Subject: [PATCH] [clang][RelativeVTables] Make the rtti_proxy LinkOnceODR
instead of External linkage
This way, it the rtti_proxies can be candidates for being replaced
altogether with GOTPCREL relocations because they are discardable.
Functionally, this shouldn't change the final ELF linkage of the
proxies.
---
clang/lib/CodeGen/CGVTables.cpp | 12 ++++++++++--
.../RelativeVTablesABI/child-vtable-in-comdat.cpp | 3 +--
.../RelativeVTablesABI/parent-vtable-in-comdat.cpp | 2 +-
.../RelativeVTablesABI/relative-vtables-hwasan.cpp | 4 ++--
.../RelativeVTablesABI/simple-vtable-definition.cpp | 2 +-
.../test/CodeGenCXX/RelativeVTablesABI/type-info.cpp | 4 ++--
6 files changed, 17 insertions(+), 10 deletions(-)
diff --git a/clang/lib/CodeGen/CGVTables.cpp b/clang/lib/CodeGen/CGVTables.cpp
index 23cfcdd138439f0..1eec9ab29133f5c 100644
--- a/clang/lib/CodeGen/CGVTables.cpp
+++ b/clang/lib/CodeGen/CGVTables.cpp
@@ -639,8 +639,16 @@ void CodeGenVTables::addRelativeComponent(ConstantArrayBuilder &builder,
// want the stub/proxy to be emitted for properly calculating the offset.
// Examples where there would be no symbol emitted are available_externally
// and private linkages.
- auto stubLinkage = vtableHasLocalLinkage ? llvm::GlobalValue::InternalLinkage
- : llvm::GlobalValue::ExternalLinkage;
+ //
+ // `internal` linkage results in LOCAL Elf linkage while still manifesting a
+ // local symbol.
+ //
+ // `linkonce_odr` linkage results in a DEFAULT Elf linkage but also allows for
+ // the rtti_proxy to be transparently replaced with a GOTPCREL reloc by a
+ // target that supports this replacement.
+ auto stubLinkage = vtableHasLocalLinkage
+ ? llvm::GlobalValue::InternalLinkage
+ : llvm::GlobalValue::LinkOnceODRLinkage;
llvm::Constant *target;
if (auto *func = dyn_cast<llvm::Function>(globalVal)) {
diff --git a/clang/test/CodeGenCXX/RelativeVTablesABI/child-vtable-in-comdat.cpp b/clang/test/CodeGenCXX/RelativeVTablesABI/child-vtable-in-comdat.cpp
index 48b1d8ed65d7e55..950921f67509f42 100644
--- a/clang/test/CodeGenCXX/RelativeVTablesABI/child-vtable-in-comdat.cpp
+++ b/clang/test/CodeGenCXX/RelativeVTablesABI/child-vtable-in-comdat.cpp
@@ -8,7 +8,6 @@
// CHECK-DAG: $_ZTS1B = comdat any
// CHECK-DAG: $_ZTI1B = comdat any
// CHECK-DAG: $_ZTI1B.rtti_proxy = comdat any
-// CHECK-DAG: $_ZTI1A.rtti_proxy = comdat any
// VTable for B is emitted here since we access it when creating an instance of B. The VTable is also linkonce_odr and in its own comdat.
// CHECK-DAG: @_ZTV1B.local = linkonce_odr hidden unnamed_addr constant { [3 x i32] } { [3 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr @_ZTI1B.rtti_proxy to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [3 x i32] }, ptr @_ZTV1B.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1B3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [3 x i32] }, ptr @_ZTV1B.local, i32 0, i32 0, i32 2) to i64)) to i32)] }, comdat($_ZTV1B), align 4
@@ -18,7 +17,7 @@
// CHECK-DAG: @_ZTS1B =
// CHECK-DAG: @_ZTI1A =
// CHECK-DAG: @_ZTI1B =
-// CHECK-DAG: @_ZTI1B.rtti_proxy = hidden unnamed_addr constant ptr @_ZTI1B, comdat
+// CHECK-DAG: @_ZTI1B.rtti_proxy = linkonce_odr hidden unnamed_addr constant ptr @_ZTI1B, comdat
// We will emit a vtable for B here, so it does have an alias, but we will not
// emit one for A.
diff --git a/clang/test/CodeGenCXX/RelativeVTablesABI/parent-vtable-in-comdat.cpp b/clang/test/CodeGenCXX/RelativeVTablesABI/parent-vtable-in-comdat.cpp
index 5f5f9edf411a809..ee710100152bfac 100644
--- a/clang/test/CodeGenCXX/RelativeVTablesABI/parent-vtable-in-comdat.cpp
+++ b/clang/test/CodeGenCXX/RelativeVTablesABI/parent-vtable-in-comdat.cpp
@@ -18,7 +18,7 @@
// CHECK: @_ZTVN10__cxxabiv117__class_type_infoE = external global [0 x ptr]
// CHECK: @_ZTS1A = linkonce_odr constant [3 x i8] c"1A\00", comdat, align 1
// CHECK: @_ZTI1A = linkonce_odr constant { ptr, ptr } { ptr getelementptr inbounds (i8, ptr @_ZTVN10__cxxabiv117__class_type_infoE, i32 8), ptr @_ZTS1A }, comdat, align 8
-// CHECK: @_ZTI1A.rtti_proxy = hidden unnamed_addr constant ptr @_ZTI1A, comdat
+// CHECK: @_ZTI1A.rtti_proxy = linkonce_odr hidden unnamed_addr constant ptr @_ZTI1A, comdat
// CHECK: @_ZTV1A = linkonce_odr unnamed_addr alias { [3 x i32] }, ptr @_ZTV1A.local
// CHECK: define linkonce_odr void @_ZN1A3fooEv(ptr {{.*}}%this) unnamed_addr #{{[0-9]+}} comdat
diff --git a/clang/test/CodeGenCXX/RelativeVTablesABI/relative-vtables-hwasan.cpp b/clang/test/CodeGenCXX/RelativeVTablesABI/relative-vtables-hwasan.cpp
index d0777b0f1245b65..7657a3bd0efdee4 100644
--- a/clang/test/CodeGenCXX/RelativeVTablesABI/relative-vtables-hwasan.cpp
+++ b/clang/test/CodeGenCXX/RelativeVTablesABI/relative-vtables-hwasan.cpp
@@ -6,7 +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
+// CHECK-DAG: @_ZTI1A.rtti_proxy = linkonce_odr hidden unnamed_addr constant ptr @_ZTI1A, no_sanitize_hwaddress, comdat
class A {
public:
@@ -22,7 +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
+// CHECK-DAG: @_ZTI1B.rtti_proxy = linkonce_odr hidden unnamed_addr constant ptr @_ZTI1B, no_sanitize_hwaddress, comdat
class __attribute__((visibility("hidden"))) B {
public:
diff --git a/clang/test/CodeGenCXX/RelativeVTablesABI/simple-vtable-definition.cpp b/clang/test/CodeGenCXX/RelativeVTablesABI/simple-vtable-definition.cpp
index 76de83d9d2cd466..5ed4745b9a0691d 100644
--- a/clang/test/CodeGenCXX/RelativeVTablesABI/simple-vtable-definition.cpp
+++ b/clang/test/CodeGenCXX/RelativeVTablesABI/simple-vtable-definition.cpp
@@ -14,7 +14,7 @@
// CHECK: @_ZTI1A ={{.*}} constant { ptr, ptr } { ptr getelementptr inbounds (i8, ptr @_ZTVN10__cxxabiv117__class_type_infoE, i32 8), ptr @_ZTS1A }, align 8
// The rtti should be in a comdat
-// CHECK: @_ZTI1A.rtti_proxy = hidden unnamed_addr constant ptr @_ZTI1A, comdat
+// CHECK: @_ZTI1A.rtti_proxy = {{.*}}comdat
// The vtable symbol is exposed through an alias.
// @_ZTV1A = dso_local unnamed_addr alias { [3 x i32] }, ptr @_ZTV1A.local
diff --git a/clang/test/CodeGenCXX/RelativeVTablesABI/type-info.cpp b/clang/test/CodeGenCXX/RelativeVTablesABI/type-info.cpp
index 42f28a770e72770..bc10461187b758c 100644
--- a/clang/test/CodeGenCXX/RelativeVTablesABI/type-info.cpp
+++ b/clang/test/CodeGenCXX/RelativeVTablesABI/type-info.cpp
@@ -13,8 +13,8 @@
// CHECK: @_ZTVN10__cxxabiv120__si_class_type_infoE = external global [0 x ptr]
// CHECK: @_ZTS1B ={{.*}} constant [3 x i8] c"1B\00", align 1
// CHECK: @_ZTI1B ={{.*}} constant { ptr, ptr, ptr } { ptr getelementptr inbounds (i8, ptr @_ZTVN10__cxxabiv120__si_class_type_infoE, i32 8), ptr @_ZTS1B, ptr @_ZTI1A }, align 8
-// CHECK: @_ZTI1A.rtti_proxy = hidden unnamed_addr constant ptr @_ZTI1A, comdat
-// CHECK: @_ZTI1B.rtti_proxy = hidden unnamed_addr constant ptr @_ZTI1B, comdat
+// CHECK: @_ZTI1A.rtti_proxy = linkonce_odr hidden unnamed_addr constant ptr @_ZTI1A, comdat
+// CHECK: @_ZTI1B.rtti_proxy = linkonce_odr hidden unnamed_addr constant ptr @_ZTI1B, comdat
// CHECK: define {{.*}}ptr @_Z11getTypeInfov() local_unnamed_addr
// CHECK-NEXT: entry:
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