[AArch64] PAC/BTI code generation for LLVM generated functions

PAC/BTI-related codegen in the AArch64 backend is controlled by a set
of LLVM IR function attributes, added to the function by Clang, based
on command-line options and GCC-style function attributes. However,
functions, generated in the LLVM middle end (for example,
asan.module.ctor or __llvm_gcov_write_out) do not get any attributes
and the backend incorrectly does not do any PAC/BTI code generation.

This patch record the default state of PAC/BTI codegen in a set of
LLVM IR module-level attributes, based on command-line options:

* "sign-return-address", with non-zero value means generate code to
  sign return addresses (PAC-RET), zero value means disable PAC-RET.

* "sign-return-address-all", with non-zero value means enable PAC-RET
  for all functions, zero value means enable PAC-RET only for
  functions, which spill LR.

* "sign-return-address-with-bkey", with non-zero value means use B-key
  for signing, zero value mean use A-key.

This set of attributes are always added for AArch64 targets (as
opposed, for example, to interpreting a missing attribute as having a
value 0) in order to be able to check for conflicts when combining
module attributed during LTO.

Module-level attributes are overridden by function level attributes.
All the decision making about whether to not to generate PAC and/or
BTI code is factored out into AArch64FunctionInfo, there shouldn't be
any places left, other than AArch64FunctionInfo, which directly
examine PAC/BTI attributes, except AArch64AsmPrinter.cpp, which
is/will-be handled by a separate patch.

Differential Revision: https://reviews.llvm.org/D85649

1 files changed, 19 insertions, 26 deletions

diff --git a/clang/lib/CodeGen/TargetInfo.cpp b/clang/lib/CodeGen/TargetInfo.cpp
index 5ebf432..2f3f4c2 100644
--- a/clang/lib/CodeGen/TargetInfo.cpp
+++ b/clang/lib/CodeGen/TargetInfo.cpp
@@ -5521,40 +5521,33 @@ public:
     if (!FD)
       return;
 
-    LangOptions::SignReturnAddressScopeKind Scope =
-        CGM.getLangOpts().getSignReturnAddressScope();
-    LangOptions::SignReturnAddressKeyKind Key =
-        CGM.getLangOpts().getSignReturnAddressKey();
-    bool BranchTargetEnforcement = CGM.getLangOpts().BranchTargetEnforcement;
-    if (const auto *TA = FD->getAttr<TargetAttr>()) {
-      ParsedTargetAttr Attr = TA->parse();
-      if (!Attr.BranchProtection.empty()) {
-        TargetInfo::BranchProtectionInfo BPI;
-        StringRef Error;
-        (void)CGM.getTarget().validateBranchProtection(Attr.BranchProtection,
-                                                       BPI, Error);
-        assert(Error.empty());
-        Scope = BPI.SignReturnAddr;
-        Key = BPI.SignKey;
-        BranchTargetEnforcement = BPI.BranchTargetEnforcement;
-      }
-    }
+    const auto *TA = FD->getAttr<TargetAttr>();
+    if (TA == nullptr)
+      return;
+
+    ParsedTargetAttr Attr = TA->parse();
+    if (Attr.BranchProtection.empty())
+      return;
+
+    TargetInfo::BranchProtectionInfo BPI;
+    StringRef Error;
+    (void)CGM.getTarget().validateBranchProtection(Attr.BranchProtection,
+                                                   BPI, Error);
+    assert(Error.empty());
 
     auto *Fn = cast<llvm::Function>(GV);
-    if (Scope != LangOptions::SignReturnAddressScopeKind::None) {
-      Fn->addFnAttr("sign-return-address",
-                    Scope == LangOptions::SignReturnAddressScopeKind::All
-                        ? "all"
-                        : "non-leaf");
+    static const char *SignReturnAddrStr[] = {"none", "non-leaf", "all"};
+    Fn->addFnAttr("sign-return-address", SignReturnAddrStr[static_cast<int>(BPI.SignReturnAddr)]);
 
+    if (BPI.SignReturnAddr != LangOptions::SignReturnAddressScopeKind::None) {
       Fn->addFnAttr("sign-return-address-key",
-                    Key == LangOptions::SignReturnAddressKeyKind::AKey
+                    BPI.SignKey == LangOptions::SignReturnAddressKeyKind::AKey
                         ? "a_key"
                         : "b_key");
     }
 
-    if (BranchTargetEnforcement)
-      Fn->addFnAttr("branch-target-enforcement");
+    Fn->addFnAttr("branch-target-enforcement",
+                  BPI.BranchTargetEnforcement ? "true" : "false");
   }
 };