No branch protection metadata unless enabled

compiler/rustc_codegen_llvm/src/context.rs

@@ -269,36 +269,36 @@ pub unsafe fn create_module<'ll>(
         }
     }
 
-    if sess.target.arch == "aarch64" {
-        let BranchProtection { bti, pac_ret: pac } = sess.opts.debugging_opts.branch_protection;
-
-        llvm::LLVMRustAddModuleFlag(
-            llmod,
-            llvm::LLVMModFlagBehavior::Error,
-            "branch-target-enforcement\0".as_ptr().cast(),
-            bti.into(),
-        );
-
-        llvm::LLVMRustAddModuleFlag(
-            llmod,
-            llvm::LLVMModFlagBehavior::Error,
-            "sign-return-address\0".as_ptr().cast(),
-            pac.is_some().into(),
-        );
-        let pac_opts = pac.unwrap_or(PacRet { leaf: false, key: PAuthKey::A });
-        llvm::LLVMRustAddModuleFlag(
-            llmod,
-            llvm::LLVMModFlagBehavior::Error,
-            "sign-return-address-all\0".as_ptr().cast(),
-            pac_opts.leaf.into(),
-        );
-        let is_bkey: bool = pac_opts.key != PAuthKey::A;
-        llvm::LLVMRustAddModuleFlag(
-            llmod,
-            llvm::LLVMModFlagBehavior::Error,
-            "sign-return-address-with-bkey\0".as_ptr().cast(),
-            is_bkey.into(),
-        );
+    if let Some(BranchProtection { bti, pac_ret }) = sess.opts.debugging_opts.branch_protection {
+        if sess.target.arch != "aarch64" {
+            sess.err("-Zbranch-protection is only supported on aarch64");
+        } else {
+            llvm::LLVMRustAddModuleFlag(
+                llmod,
+                llvm::LLVMModFlagBehavior::Error,
+                "branch-target-enforcement\0".as_ptr().cast(),
+                bti.into(),
+            );
+            llvm::LLVMRustAddModuleFlag(
+                llmod,
+                llvm::LLVMModFlagBehavior::Error,
+                "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,
+                "sign-return-address-all\0".as_ptr().cast(),
+                pac_opts.leaf.into(),
+            );
+            llvm::LLVMRustAddModuleFlag(
+                llmod,
+                llvm::LLVMModFlagBehavior::Error,
+                "sign-return-address-with-bkey\0".as_ptr().cast(),
+                u32::from(pac_opts.key == PAuthKey::B),
+            );
+        }
     }
 
     // Pass on the control-flow protection flags to LLVM (equivalent to `-fcf-protection` in Clang).

compiler/rustc_interface/src/tests.rs

@@ -721,7 +721,10 @@ fn test_debugging_options_tracking_hash() {
     tracked!(binary_dep_depinfo, true);
     tracked!(
         branch_protection,
-        BranchProtection { bti: true, pac_ret: Some(PacRet { leaf: true, key: PAuthKey::B }) }
+        Some(BranchProtection {
+            bti: true,
+            pac_ret: Some(PacRet { leaf: true, key: PAuthKey::B })
+        })
     );
     tracked!(chalk, true);
     tracked!(codegen_backend, Some("abc".to_string()));

compiler/rustc_session/src/lib.rs

@@ -2,6 +2,7 @@
 #![feature(derive_default_enum)]
 #![feature(min_specialization)]
 #![feature(once_cell)]
+#![feature(option_get_or_insert_default)]
 #![recursion_limit = "256"]
 #![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 

compiler/rustc_session/src/options.rs

@@ -984,9 +984,10 @@ mod parse {
         true
     }
 
-    crate fn parse_branch_protection(slot: &mut BranchProtection, v: Option<&str>) -> bool {
+    crate fn parse_branch_protection(slot: &mut Option<BranchProtection>, v: Option<&str>) -> bool {
         match v {
             Some(s) => {
+                let slot = slot.get_or_insert_default();
                 for opt in s.split(',') {
                     match opt {
                         "bti" => slot.bti = true,
@@ -1161,7 +1162,7 @@ options! {
         (default: no)"),
     borrowck: String = ("migrate".to_string(), parse_string, [UNTRACKED],
         "select which borrowck is used (`mir` or `migrate`) (default: `migrate`)"),
-    branch_protection: BranchProtection = (BranchProtection::default(), parse_branch_protection, [TRACKED],
+    branch_protection: Option<BranchProtection> = (None, parse_branch_protection, [TRACKED],
         "set options for branch target identification and pointer authentication on AArch64"),
     cf_protection: CFProtection = (CFProtection::None, parse_cfprotection, [TRACKED],
         "instrument control-flow architecture protection"),

src/test/codegen/branch-protection.rs

@@ -1,12 +1,12 @@
 // Test that the correct module flags are emitted with different branch protection flags.
 
-// revisions: bti pac-ret leaf b-key
+// revisions: BTI PACRET LEAF BKEY NONE
 // min-llvm-version: 12.0.0
 // needs-llvm-components: aarch64
-// [bti] compile-flags: -Z branch-protection=bti
-// [pac-ret] compile-flags: -Z branch-protection=pac-ret
-// [leaf] compile-flags: -Z branch-protection=pac-ret,leaf
-// [b-key] compile-flags: -Z branch-protection=pac-ret,b-key
+// [BTI] compile-flags: -Z branch-protection=bti
+// [PACRET] compile-flags: -Z branch-protection=pac-ret
+// [LEAF] compile-flags: -Z branch-protection=pac-ret,leaf
+// [BKEY] compile-flags: -Z branch-protection=pac-ret,b-key
 // compile-flags: --target aarch64-unknown-linux-gnu
 
 #![crate_type = "lib"]
@@ -20,22 +20,27 @@ trait Sized { }
 pub fn test() {
 }
 
-// bti: !"branch-target-enforcement", i32 1
-// bti: !"sign-return-address", i32 0
-// bti: !"sign-return-address-all", i32 0
-// bti: !"sign-return-address-with-bkey", i32 0
-
-// pac-ret: !"branch-target-enforcement", i32 0
-// pac-ret: !"sign-return-address", i32 1
-// pac-ret: !"sign-return-address-all", i32 0
-// pac-ret: !"sign-return-address-with-bkey", i32 0
-
-// leaf: !"branch-target-enforcement", i32 0
-// leaf: !"sign-return-address", i32 1
-// leaf: !"sign-return-address-all", i32 1
-// leaf: !"sign-return-address-with-bkey", i32 0
-
-// b-key: !"branch-target-enforcement", i32 0
-// b-key: !"sign-return-address", i32 1
-// b-key: !"sign-return-address-all", i32 0
-// b-key: !"sign-return-address-with-bkey", i32 1
+// BTI: !"branch-target-enforcement", i32 1
+// BTI: !"sign-return-address", i32 0
+// BTI: !"sign-return-address-all", i32 0
+// BTI: !"sign-return-address-with-bkey", i32 0
+
+// PACRET: !"branch-target-enforcement", i32 0
+// PACRET: !"sign-return-address", i32 1
+// PACRET: !"sign-return-address-all", i32 0
+// PACRET: !"sign-return-address-with-bkey", i32 0
+
+// LEAF: !"branch-target-enforcement", i32 0
+// LEAF: !"sign-return-address", i32 1
+// LEAF: !"sign-return-address-all", i32 1
+// LEAF: !"sign-return-address-with-bkey", i32 0
+
+// BKEY: !"branch-target-enforcement", i32 0
+// BKEY: !"sign-return-address", i32 1
+// BKEY: !"sign-return-address-all", i32 0
+// BKEY: !"sign-return-address-with-bkey", i32 1
+
+// NONE-NOT: branch-target-enforcement
+// NONE-NOT: sign-return-address
+// NONE-NOT: sign-return-address-all
+// NONE-NOT: sign-return-address-with-bkey

src/test/ui/invalid-compile-flags/branch-protection-missing-pac-ret.BADTARGET.stderr

@@ -0,0 +1,4 @@
+error: -Zbranch-protection is only supported on aarch64
+
+error: aborting due to previous error
+

src/test/ui/invalid-compile-flags/branch-protection-missing-pac-ret.rs

@@ -1 +1,14 @@
-// compile-flags: -Z branch-protection=leaf
+// revisions: BADFLAGS BADTARGET
+// [BADFLAGS] compile-flags: --target=aarch64-unknown-linux-gnu -Zbranch-protection=leaf
+// [BADFLAGS] check-fail
+// [BADFLAGS] needs-llvm-components: aarch64
+// [BADTARGET] compile-flags: --target=x86_64-unknown-linux-gnu -Zbranch-protection=bti
+// [BADTARGET] build-fail
+// [BADTARGET] needs-llvm-components: x86
+
+#![crate_type = "lib"]
+#![feature(no_core, lang_items)]
+#![no_core]
+
+#[lang="sized"]
+trait Sized { }