Rollup merge of #132259 - mrkajetanp:branch-protection-pauth-lr, r=davidtwco

rustc_codegen_llvm: Add a new 'pc' option to branch-protection

Add a new 'pc' option to -Z branch-protection for aarch64 that enables the use of PC as a diversifier in PAC branch protection code.

When the pauth-lr target feature is enabled in combination with -Z branch-protection=pac-ret,pc, the new 9.5-a instructions (pacibsppc, retaasppc, etc) will be generated.

compiler/rustc_session/src/config.rs

@@ -1320,6 +1320,7 @@ pub enum PAuthKey {
 #[derive(Clone, Copy, Hash, Debug, PartialEq)]
 pub struct PacRet {
     pub leaf: bool,
+    pub pc: bool,
     pub key: PAuthKey,
 }
 

compiler/rustc_session/src/options.rs

@@ -442,8 +442,7 @@ mod desc {
     pub(crate) const parse_polonius: &str = "either no value or `legacy` (the default), or `next`";
     pub(crate) const parse_stack_protector: &str =
         "one of (`none` (default), `basic`, `strong`, or `all`)";
-    pub(crate) const parse_branch_protection: &str =
-        "a `,` separated combination of `bti`, `b-key`, `pac-ret`, or `leaf`";
+    pub(crate) const parse_branch_protection: &str = "a `,` separated combination of `bti`, `pac-ret`, followed by a combination of `pc`, `b-key`, or `leaf`";
     pub(crate) const parse_proc_macro_execution_strategy: &str =
         "one of supported execution strategies (`same-thread`, or `cross-thread`)";
     pub(crate) const parse_remap_path_scope: &str =
@@ -1401,7 +1400,7 @@ pub mod parse {
                     match opt {
                         "bti" => slot.bti = true,
                         "pac-ret" if slot.pac_ret.is_none() => {
-                            slot.pac_ret = Some(PacRet { leaf: false, key: PAuthKey::A })
+                            slot.pac_ret = Some(PacRet { leaf: false, pc: false, key: PAuthKey::A })
                         }
                         "leaf" => match slot.pac_ret.as_mut() {
                             Some(pac) => pac.leaf = true,
@@ -1411,6 +1410,10 @@ pub mod parse {
                             Some(pac) => pac.key = PAuthKey::B,
                             _ => return false,
                         },
+                        "pc" => match slot.pac_ret.as_mut() {
+                            Some(pac) => pac.pc = true,
+                            _ => return false,
+                        },
                         _ => return false,
                     };
                 }