[FMV] Set default attributes on the resolver functions

[atrosinenko]

There is a number of attributes that is expected to be set on functions by default. This patch implements setting more such attributes on the FMV resolver functions generated by Clang. On AArch64, this makes the resolver functions use the default PAC and BTI hardening settings.

[llvmbot]

@llvm/pr-subscribers-clang-codegen

@llvm/pr-subscribers-clang

Author: Anatoly Trosinenko (atrosinenko)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/141573.diff

2 Files Affected:

• (modified) clang/lib/CodeGen/CodeGenModule.cpp (+9)
• (added) clang/test/CodeGen/ptrauth-resolver-attributes.c (+25)

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 16e010adbeb5f..af8d4cc60de57 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -4638,6 +4638,13 @@ llvm::Constant *CodeGenModule::GetOrCreateMultiVersionResolver(GlobalDecl GD) {
   if (FD->isTargetMultiVersion() || FD->isTargetClonesMultiVersion())
     AddDeferredMultiVersionResolverToEmit(GD);
 
+  auto SetResolverAttrs = [&](llvm::Function &Resolver) {
+    TargetInfo::BranchProtectionInfo BPI(getLangOpts());
+    TargetCodeGenInfo::setBranchProtectionFnAttributes(BPI, Resolver);
+    TargetCodeGenInfo::setPointerAuthFnAttributes(CodeGenOpts.PointerAuth,
+                                                  Resolver);
+  };
+
   // For cpu_specific, don't create an ifunc yet because we don't know if the
   // cpu_dispatch will be emitted in this translation unit.
   if (ShouldReturnIFunc) {
@@ -4652,6 +4659,7 @@ llvm::Constant *CodeGenModule::GetOrCreateMultiVersionResolver(GlobalDecl GD) {
                                   "", Resolver, &getModule());
     GIF->setName(ResolverName);
     SetCommonAttributes(FD, GIF);
+    SetResolverAttrs(cast<llvm::Function>(*Resolver));
     if (ResolverGV)
       replaceDeclarationWith(ResolverGV, GIF);
     return GIF;
@@ -4662,6 +4670,7 @@ llvm::Constant *CodeGenModule::GetOrCreateMultiVersionResolver(GlobalDecl GD) {
   assert(isa<llvm::GlobalValue>(Resolver) && !ResolverGV &&
          "Resolver should be created for the first time");
   SetCommonAttributes(FD, cast<llvm::GlobalValue>(Resolver));
+  SetResolverAttrs(cast<llvm::Function>(*Resolver));
   return Resolver;
 }
 
diff --git a/clang/test/CodeGen/ptrauth-resolver-attributes.c b/clang/test/CodeGen/ptrauth-resolver-attributes.c
new file mode 100644
index 0000000000000..8bdedd2c549be
--- /dev/null
+++ b/clang/test/CodeGen/ptrauth-resolver-attributes.c
@@ -0,0 +1,25 @@
+// RUN: %clang_cc1 -triple aarch64-linux-gnu -mbranch-target-enforce -msign-return-address=all      -emit-llvm %s -o - | FileCheck --check-prefixes=CHECK,BTI-SIGNRA %s
+// RUN: %clang_cc1 -triple arm64-apple-ios   -mbranch-target-enforce -msign-return-address=all      -emit-llvm %s -o - | FileCheck --check-prefixes=CHECK,BTI-SIGNRA %s
+// RUN: %clang_cc1 -triple aarch64-linux-gnu -fptrauth-calls -fptrauth-returns -fptrauth-auth-traps -emit-llvm %s -o - | FileCheck --check-prefixes=CHECK,PAUTHTEST %s
+// RUN: %clang_cc1 -triple arm64-apple-ios   -fptrauth-calls -fptrauth-returns -fptrauth-auth-traps -emit-llvm %s -o - | FileCheck --check-prefixes=CHECK,PAUTHTEST %s
+
+// Check that resolver functions generated by clang have the correct attributes.
+
+int __attribute__((target_clones("crc", "default"))) ftc(void) { return 0; }
+
+int __attribute__((target_version("crc")))     fmv(void) { return 0; }
+int __attribute__((target_version("default"))) fmv(void) { return 0; }
+
+// CHECK: define{{.*}} i32 @ftc._Mcrc() #0
+// CHECK: define{{.*}} ptr @ftc.resolver() #1
+// CHECK: define{{.*}} i32 @fmv._Mcrc() #0
+// CHECK: define{{.*}} i32 @fmv.default() #2
+// CHECK: define{{.*}} i32 @ftc.default() #2
+// CHECK: define{{.*}} ptr @fmv.resolver() #1
+
+// BTI-SIGNRA: attributes #0 = { {{.*}}"branch-target-enforcement" {{.*}}"sign-return-address"="all" "sign-return-address-key"="a_key"{{.*}} }
+// BTI-SIGNRA: attributes #1 = { {{.*}}"branch-target-enforcement" {{.*}}"sign-return-address"="all" "sign-return-address-key"="a_key"{{.*}} }
+// BTI-SIGNRA: attributes #2 = { {{.*}}"branch-target-enforcement" {{.*}}"sign-return-address"="all" "sign-return-address-key"="a_key"{{.*}} }
+// PAUTHTEST: attributes #0 = { {{.*}}"ptrauth-auth-traps" "ptrauth-calls" "ptrauth-returns"{{.*}} }
+// PAUTHTEST: attributes #1 = { {{.*}}"ptrauth-auth-traps" "ptrauth-calls" "ptrauth-returns"{{.*}} }
+// PAUTHTEST: attributes #2 = { {{.*}}"ptrauth-auth-traps" "ptrauth-calls" "ptrauth-returns"{{.*}} }

[labrinea]

Seems somewhat related to #84704. @jroelofs mind taking a look?

[atrosinenko]

I have rebased this PR onto current main branch and moved the new test to AArch64/ subdirectory. There are no unresolved comments anymore, as far as I can see.

[labrinea]

We need this instead as I explained on the other thread.

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 2d37e0f13199..e26a540a8cb4 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -4586,6 +4586,8 @@ void CodeGenModule::emitMultiVersionFunctions() {
         });
     CodeGenFunction CGF(*this);
     CGF.EmitMultiVersionResolver(ResolverFunc, Options);
+    SetFunctionAttributes(GD, ResolverFunc, /*IsIncompleteFunction=*/false,
+                          /*IsThunk=*/false);
   }

   // Ensure that any additions to the deferred decls list caused by emitting a

Also a test to check that hidden is added to the resolver if specified on the commnad line

[labrinea]

ping @atrosinenko

[atrosinenko]

@labrinea I'm sorry for disappearing, I will update this PR this week.

[efriedma-quic]

LGTM

[labrinea]

Please update the description before you merge.

[atrosinenko]

Sorry for disappearing once again, now the PR description reflects the current state of the patch. Additionally, the handling of comdats is fixed in 4eafbe4 and f25b5c5.

[labrinea]

Please do not force-push so that we can see what changed from the last review otherwise we have to start over.