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

[Anatoly Trosinenko via llvm-commits]

================
@@ -30,6 +30,51 @@ EXCEPTION_DISPOSITION _GCC_specific_handler(PEXCEPTION_RECORD, void *, PCONTEXT,
                                             _Unwind_Personality_Fn);
 #endif
 
+#if __has_feature(ptrauth_calls)
+#include <ptrauth.h>
+
+#if __has_feature(ptrauth_restricted_intptr_qualifier)
+#define __ptrauth_gcc_personality_intptr(key, addressDiscriminated,            \
+                                         discriminator)                        \
+  __ptrauth_restricted_intptr(key, addressDiscriminated, discriminator)
+#else
+#define __ptrauth_gcc_personality_intptr(key, addressDiscriminated,            \
+                                         discriminator)                        \
+  __ptrauth(key, addressDiscriminated, discriminator)
+#endif
+#else
+#define __ptrauth_gcc_personality_intptr(...)
+#endif
+
+#define __ptrauth_gcc_personality_func_key ptrauth_key_function_pointer
+
+// ptrauth_string_discriminator("__gcc_personality_v0'funcStart") == 0xDFEB
+#define __ptrauth_gcc_personality_func_start                                   \
+  __ptrauth_gcc_personality_intptr(__ptrauth_gcc_personality_func_key, 1,      \
+                                   0xDFEB)
----------------
atrosinenko wrote:

(As an illustration for the "cover letter" of this review) I assume many such macroses define purely internal signing schemas. In such cases it should be possible to compute the discriminator automatically - it could probably improve readability to use something like

```cpp
    PTRAUTH_INTPTR(uintptr_t, start) = readEncodedPointer(&p, callSiteEncoding);
```

instead of 

```cpp
    uintptr_t __ptrauth_gcc_personality_start start =
        readEncodedPointer(&p, callSiteEncoding);
```

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