[compiler-rt] [libcxxabi] [libunwind] [runtimes][PAC] Harden unwinding when possible (#138571) (PR #143230)

[Louis Dionne via llvm-commits]

================
@@ -126,6 +130,36 @@ _LIBUNWIND_HIDDEN int __unw_set_reg(unw_cursor_t *cursor, unw_regnum_t regNum,
       // First, get the FDE for the old location and then update it.
       co->getInfo(&info);
       co->setInfoBasedOnIPRegister(false);
+
+#if __has_feature(ptrauth_calls)
+      // It is only valid to set the IP within the current function.
+      // This is important for ptrauth, otherwise the IP cannot be correctly
+      // signed.
+      unw_word_t stripped_value =
+          (unw_word_t)ptrauth_strip((void *)value, ptrauth_key_return_address);
+      (void)stripped_value;
+      assert(stripped_value >= info.start_ip && stripped_value <= info.end_ip);
+#endif
+
+      pint_t sp = (pint_t)co->getReg(UNW_REG_SP);
----------------
ldionne wrote:

```suggestion
      pint_t sp = (pint_t)co->getReg(UNW_REG_SP);
      (void)sp;
```

This should quiet the unused variable warnings.

https://github.com/llvm/llvm-project/pull/143230