[PAC][AArch64] Support init/fini array signing (#96478)

If both `-fptrauth-init-fini` and `-fptrauth-calls` are passed, sign
function pointers in `llvm.global_ctors` and `llvm.global_dtors` with
constant discriminator 0xD9D4
(`ptrauth_string_discriminator("init_fini")`). Additionally, if
`-fptrauth-init-fini-address-discrimination` is passed, address
discrimination is used for signing (otherwise, just constant
discriminator is used).

For address discrimination, we use it's special form since uses of
`llvm.global_{c|d}tors` are disallowed (see
`Verifier::visitGlobalVariable`) and we can't emit `getelementptr`
expressions referencing these special arrays. A signed ctor/dtor pointer
with special address discrimination applied looks like the following:

```
ptr ptrauth (ptr @foo, i32 0, i64 55764, ptr inttoptr (i64 1 to ptr))
```

1 files changed, 43 insertions, 24 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 31f6632..1f2cbee 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -1218,10 +1218,13 @@ void CodeGenModule::Release() {
           (LangOpts.PointerAuthVTPtrTypeDiscrimination
            << AARCH64_PAUTH_PLATFORM_LLVM_LINUX_VERSION_VPTRTYPEDISCR) |
           (LangOpts.PointerAuthInitFini
-           << AARCH64_PAUTH_PLATFORM_LLVM_LINUX_VERSION_INITFINI);
-      static_assert(AARCH64_PAUTH_PLATFORM_LLVM_LINUX_VERSION_INITFINI ==
-                        AARCH64_PAUTH_PLATFORM_LLVM_LINUX_VERSION_LAST,
-                    "Update when new enum items are defined");
+           << AARCH64_PAUTH_PLATFORM_LLVM_LINUX_VERSION_INITFINI) |
+          (LangOpts.PointerAuthInitFiniAddressDiscrimination
+           << AARCH64_PAUTH_PLATFORM_LLVM_LINUX_VERSION_INITFINIADDRDISC);
+      static_assert(
+          AARCH64_PAUTH_PLATFORM_LLVM_LINUX_VERSION_INITFINIADDRDISC ==
+              AARCH64_PAUTH_PLATFORM_LLVM_LINUX_VERSION_LAST,
+          "Update when new enum items are defined");
       if (PAuthABIVersion != 0) {
         getModule().addModuleFlag(llvm::Module::Error,
                                   "aarch64-elf-pauthabi-platform",
@@ -2082,37 +2085,53 @@ void CodeGenModule::AddGlobalDtor(llvm::Function *Dtor, int Priority,
 void CodeGenModule::EmitCtorList(CtorList &Fns, const char *GlobalName) {
   if (Fns.empty()) return;
 
-  // Ctor function type is void()*.
-  llvm::FunctionType* CtorFTy = llvm::FunctionType::get(VoidTy, false);
-  llvm::Type *CtorPFTy = llvm::PointerType::get(CtorFTy,
-      TheModule.getDataLayout().getProgramAddressSpace());
+  const PointerAuthSchema &InitFiniAuthSchema =
+      getCodeGenOpts().PointerAuth.InitFiniPointers;
 
-  // Get the type of a ctor entry, { i32, void ()*, i8* }.
-  llvm::StructType *CtorStructTy = llvm::StructType::get(
-      Int32Ty, CtorPFTy, VoidPtrTy);
+  // Ctor function type is ptr.
+  llvm::PointerType *PtrTy = llvm::PointerType::get(
+      getLLVMContext(), TheModule.getDataLayout().getProgramAddressSpace());
+
+  // Get the type of a ctor entry, { i32, ptr, ptr }.
+  llvm::StructType *CtorStructTy = llvm::StructType::get(Int32Ty, PtrTy, PtrTy);
 
   // Construct the constructor and destructor arrays.
-  ConstantInitBuilder builder(*this);
-  auto ctors = builder.beginArray(CtorStructTy);
+  ConstantInitBuilder Builder(*this);
+  auto Ctors = Builder.beginArray(CtorStructTy);
   for (const auto &I : Fns) {
-    auto ctor = ctors.beginStruct(CtorStructTy);
-    ctor.addInt(Int32Ty, I.Priority);
-    ctor.add(I.Initializer);
+    auto Ctor = Ctors.beginStruct(CtorStructTy);
+    Ctor.addInt(Int32Ty, I.Priority);
+    if (InitFiniAuthSchema) {
+      llvm::Constant *StorageAddress =
+          (InitFiniAuthSchema.isAddressDiscriminated()
+               ? llvm::ConstantExpr::getIntToPtr(
+                     llvm::ConstantInt::get(
+                         IntPtrTy,
+                         llvm::ConstantPtrAuth::AddrDiscriminator_CtorsDtors),
+                     PtrTy)
+               : nullptr);
+      llvm::Constant *SignedCtorPtr = getConstantSignedPointer(
+          I.Initializer, InitFiniAuthSchema.getKey(), StorageAddress,
+          llvm::ConstantInt::get(
+              SizeTy, InitFiniAuthSchema.getConstantDiscrimination()));
+      Ctor.add(SignedCtorPtr);
+    } else {
+      Ctor.add(I.Initializer);
+    }
     if (I.AssociatedData)
-      ctor.add(I.AssociatedData);
+      Ctor.add(I.AssociatedData);
     else
-      ctor.addNullPointer(VoidPtrTy);
-    ctor.finishAndAddTo(ctors);
+      Ctor.addNullPointer(PtrTy);
+    Ctor.finishAndAddTo(Ctors);
   }
 
-  auto list =
-    ctors.finishAndCreateGlobal(GlobalName, getPointerAlign(),
-                                /*constant*/ false,
-                                llvm::GlobalValue::AppendingLinkage);
+  auto List = Ctors.finishAndCreateGlobal(GlobalName, getPointerAlign(),
+                                          /*constant*/ false,
+                                          llvm::GlobalValue::AppendingLinkage);
 
   // The LTO linker doesn't seem to like it when we set an alignment
   // on appending variables.  Take it off as a workaround.
-  list->setAlignment(std::nullopt);
+  List->setAlignment(std::nullopt);
 
   Fns.clear();
 }