[llvm] [PAC][llvm-readobj][AArch64][ELF] Support `GNU_PROPERTY_AARCH64_FEATURE_PAUTH` (PR #85231)

[Fangrui Song via llvm-commits]

================
@@ -5098,6 +5098,86 @@ template <class ELFT> void GNUELFDumper<ELFT>::printAddrsig() {
   }
 }
 
+template <class ELFT>
+static bool printAArch64PAuthABICoreInfo(raw_ostream &OS, uint32_t DataSize,
+                                         ArrayRef<uint8_t> Desc) {
+  OS << "    AArch64 PAuth ABI core info: ";
+  // DataSize - size without padding, Desc.size() - size with padding
+  if (DataSize != 16) {
+    OS << format("<corrupted size: expected 16, got %d>", DataSize);
+    return false;
+  }
+
+  uint64_t Platform =
+      support::endian::read64<ELFT::TargetEndianness>(Desc.data() + 0);
+  uint64_t Version =
+      support::endian::read64<ELFT::TargetEndianness>(Desc.data() + 8);
+
+  std::string PlatformDesc = [Platform]() {
+    switch (Platform) {
+    case AARCH64_PAUTH_PLATFORM_INVALID:
+      return "invalid";
+    case AARCH64_PAUTH_PLATFORM_BAREMETAL:
+      return "baremetal";
+    case AARCH64_PAUTH_PLATFORM_LLVM_LINUX:
+      return "llvm_linux";
+    default:
+      return "unknown";
+    }
+  }();
+
+  std::string VersionDesc = [Platform, Version]() -> std::string {
+    if (Platform != AARCH64_PAUTH_PLATFORM_LLVM_LINUX)
+      return "";
+    if (Version >= (1 << (AARCH64_PAUTH_PLATFORM_LLVM_LINUX_VERSION_LAST + 1)))
+      return "unknown";
+    return std::string("") +
----------------
MaskRay wrote:

Define a std::string, then do

```
if (...)
  Desc += ...
if (...)
  Desc += ...
```

is likely more readable

https://github.com/llvm/llvm-project/pull/85231