Address review feedback: clarify core info usage and use size() helper

- Added comments explaining the semantics of AArch64PauthAbiCoreInfo and the reserved (0, 0) value.
- Replaced hardcoded sizeof(uint64_t) * 2 with AArch64PauthAbiCoreInfo::size().

Author: sivan-shani

lld/ELF/Config.h

@@ -139,9 +139,13 @@ enum class GcsPolicy { Implicit, Never, Always };
 // For some options that resemble -z bti-report={none,warning,error}
 enum class ReportPolicy { None, Warning, Error };
 
+// Describes the signing schema for a file using the PAuth ABI extension.
+// Two files are considered compatible when both `platform` and `version` match.
+// The pair (0, 0) is reserved to indicate incompatibility with the PAuth ABI.
 struct AArch64PauthAbiCoreInfo {
   uint64_t platform;
   uint64_t version;
+  // Returns true if the core info is not the reserved (0, 0) value.
   bool isValid() const { return platform || version; }
   static constexpr size_t size() { return sizeof(platform) + sizeof(version); }
   bool operator==(const AArch64PauthAbiCoreInfo &other) const {

lld/ELF/SyntheticSections.cpp

@@ -357,7 +357,7 @@ size_t GnuPropertySection::getSize() const {
   if (ctx.arg.andFeatures != 0)
     contentSize += ctx.arg.is64 ? 16 : 12;
   if (ctx.aarch64PauthAbiCoreInfo)
-    contentSize += 4 + 4 + sizeof(uint64_t) * 2;
+    contentSize += 4 + 4 + AArch64PauthAbiCoreInfo::size();
   assert(contentSize != 0);
   return contentSize + 16;
 }