Rollup merge of #105932 - MasterAwesome:aarch64-bti-llvm-15, r=nikic

Correct branch-protection ModFlagBehavior for Aarch64 on LLVM-15

When building with Fat LTO and BTI enabled on aarch64, the BTI is set to `Module::Min` for alloc shim but is set to `Module::Error` for the crate. This was fine when we were using LLVM-14 but LLVM-15 changes it's behaviour to support for compiling with different `mbranch-protection` flags.

Refer:
https://github.com/rust-lang/llvm-project/commit/b0343a38a5910e980bb031e4014655d77cd0c162

fixes https://github.com/rust-lang/rust/issues/102162

2 files changed, 11 insertions, 4 deletions

diff --git a/compiler/rustc_codegen_llvm/src/context.rs b/compiler/rustc_codegen_llvm/src/context.rs
index f3bff5d5716..d9ccba07a34 100644
--- a/compiler/rustc_codegen_llvm/src/context.rs
+++ b/compiler/rustc_codegen_llvm/src/context.rs
@@ -280,29 +280,35 @@ pub unsafe fn create_module<'ll>(
     }
 
     if let Some(BranchProtection { bti, pac_ret }) = sess.opts.unstable_opts.branch_protection {
+        let behavior = if llvm_version >= (15, 0, 0) {
+            llvm::LLVMModFlagBehavior::Min
+        } else {
+            llvm::LLVMModFlagBehavior::Error
+        };
+
         if sess.target.arch == "aarch64" {
             llvm::LLVMRustAddModuleFlag(
                 llmod,
-                llvm::LLVMModFlagBehavior::Error,
+                behavior,
                 "branch-target-enforcement\0".as_ptr().cast(),
                 bti.into(),
             );
             llvm::LLVMRustAddModuleFlag(
                 llmod,
-                llvm::LLVMModFlagBehavior::Error,
+                behavior,
                 "sign-return-address\0".as_ptr().cast(),
                 pac_ret.is_some().into(),
             );
             let pac_opts = pac_ret.unwrap_or(PacRet { leaf: false, key: PAuthKey::A });
             llvm::LLVMRustAddModuleFlag(
                 llmod,
-                llvm::LLVMModFlagBehavior::Error,
+                behavior,
                 "sign-return-address-all\0".as_ptr().cast(),
                 pac_opts.leaf.into(),
             );
             llvm::LLVMRustAddModuleFlag(
                 llmod,
-                llvm::LLVMModFlagBehavior::Error,
+                behavior,
                 "sign-return-address-with-bkey\0".as_ptr().cast(),
                 u32::from(pac_opts.key == PAuthKey::B),
             );
diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index e61dbe8b8fc..6c78966a98d 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
@@ -79,6 +79,7 @@ pub enum LLVMModFlagBehavior {
     Append = 5,
     AppendUnique = 6,
     Max = 7,
+    Min = 8,
 }
 
 // Consts for the LLVM CallConv type, pre-cast to usize.