[lld] Refactor storage of PAuth ABI core info (#141920)

Previously, the AArch64 PAuth ABI core values were stored as an
ArrayRef<uint8_t>, introducing unnecessary indirection.

This patch replaces the ArrayRef with two explicit uint64_t fields:
aarch64PauthAbiPlatform and aarch64PauthAbiVersion. This simplifies the
representation and improves readability.

No functional change intended, aside from improved error messages.

Author: sivan-shani

lld/ELF/Arch/AArch64.cpp

@@ -1043,8 +1043,7 @@ AArch64BtiPac::AArch64BtiPac(Ctx &ctx) : AArch64(ctx) {
   // instructions.
 
   if (ctx.arg.zPacPlt) {
-    if (llvm::any_of(ctx.aarch64PauthAbiCoreInfo,
-                     [](uint8_t c) { return c != 0; }))
+    if (ctx.aarch64PauthAbiCoreInfo && ctx.aarch64PauthAbiCoreInfo->isValid())
       pacEntryKind = PEK_Auth;
     else
       pacEntryKind = PEK_AuthHint;

lld/ELF/Config.h

@@ -139,6 +139,23 @@ 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 {
+    return platform == other.platform && version == other.version;
+  }
+  bool operator!=(const AArch64PauthAbiCoreInfo &other) const {
+    return !(*this == other);
+  }
+};
+
 struct SymbolVersion {
   llvm::StringRef name;
   bool isExternCpp;
@@ -699,7 +716,7 @@ struct Ctx : CommonLinkerContext {
 
   llvm::raw_fd_ostream openAuxiliaryFile(llvm::StringRef, std::error_code &);
 
-  ArrayRef<uint8_t> aarch64PauthAbiCoreInfo;
+  std::optional<AArch64PauthAbiCoreInfo> aarch64PauthAbiCoreInfo;
 };
 
 // The first two elements of versionDefinitions represent VER_NDX_LOCAL and

lld/ELF/Driver.cpp

@@ -2857,15 +2857,15 @@ static void readSecurityNotes(Ctx &ctx) {
   StringRef referenceFileName;
   if (ctx.arg.emachine == EM_AARCH64) {
     auto it = llvm::find_if(ctx.objectFiles, [](const ELFFileBase *f) {
-      return !f->aarch64PauthAbiCoreInfo.empty();
+      return f->aarch64PauthAbiCoreInfo.has_value();
     });
     if (it != ctx.objectFiles.end()) {
       ctx.aarch64PauthAbiCoreInfo = (*it)->aarch64PauthAbiCoreInfo;
       referenceFileName = (*it)->getName();
     }
   }
-  bool hasValidPauthAbiCoreInfo = llvm::any_of(
-      ctx.aarch64PauthAbiCoreInfo, [](uint8_t c) { return c != 0; });
+  bool hasValidPauthAbiCoreInfo =
+      ctx.aarch64PauthAbiCoreInfo && ctx.aarch64PauthAbiCoreInfo->isValid();
 
   auto report = [&](ReportPolicy policy) -> ELFSyncStream {
     return {ctx, toDiagLevel(policy)};
@@ -2952,10 +2952,10 @@ static void readSecurityNotes(Ctx &ctx) {
     }
     ctx.arg.andFeatures &= features;
 
-    if (ctx.aarch64PauthAbiCoreInfo.empty())
+    if (!ctx.aarch64PauthAbiCoreInfo)
       continue;
 
-    if (f->aarch64PauthAbiCoreInfo.empty()) {
+    if (!f->aarch64PauthAbiCoreInfo) {
       report(ctx.arg.zPauthReport)
           << f
           << ": -z pauth-report: file does not have AArch64 "
@@ -2965,11 +2965,18 @@ static void readSecurityNotes(Ctx &ctx) {
     }
 
     if (ctx.aarch64PauthAbiCoreInfo != f->aarch64PauthAbiCoreInfo)
-      Err(ctx) << "incompatible values of AArch64 PAuth core info found\n>>> "
-               << referenceFileName << ": 0x"
-               << toHex(ctx.aarch64PauthAbiCoreInfo, /*LowerCase=*/true)
-               << "\n>>> " << f << ": 0x"
-               << toHex(f->aarch64PauthAbiCoreInfo, /*LowerCase=*/true);
+      Err(ctx)
+          << "incompatible values of AArch64 PAuth core info found\n"
+          << "platform:\n"
+          << ">>> " << referenceFileName << ": 0x"
+          << toHex(ctx.aarch64PauthAbiCoreInfo->platform, /*LowerCase=*/true)
+          << "\n>>> " << f << ": 0x"
+          << toHex(f->aarch64PauthAbiCoreInfo->platform, /*LowerCase=*/true)
+          << "\nversion:\n"
+          << ">>> " << referenceFileName << ": 0x"
+          << toHex(ctx.aarch64PauthAbiCoreInfo->version, /*LowerCase=*/true)
+          << "\n>>> " << f << ": 0x"
+          << toHex(f->aarch64PauthAbiCoreInfo->version, /*LowerCase=*/true);
   }
 
   // Force enable Shadow Stack.

lld/ELF/InputFiles.cpp

@@ -948,7 +948,7 @@ static void parseGnuPropertyNote(Ctx &ctx, ELFFileBase &f,
     } else if (ctx.arg.emachine == EM_AARCH64 &&
                type == GNU_PROPERTY_AARCH64_FEATURE_PAUTH) {
       ArrayRef<uint8_t> contents = data ? *data : desc;
-      if (!f.aarch64PauthAbiCoreInfo.empty()) {
+      if (f.aarch64PauthAbiCoreInfo) {
         return void(
             err(contents.data())
             << "multiple GNU_PROPERTY_AARCH64_FEATURE_PAUTH entries are "
@@ -959,7 +959,9 @@ static void parseGnuPropertyNote(Ctx &ctx, ELFFileBase &f,
                        "is invalid: expected 16 bytes, but got "
                     << size);
       }
-      f.aarch64PauthAbiCoreInfo = desc;
+      f.aarch64PauthAbiCoreInfo = {
+          support::endian::read64<ELFT::Endianness>(&desc[0]),
+          support::endian::read64<ELFT::Endianness>(&desc[8])};
     }
 
     // Padding is present in the note descriptor, if necessary.

lld/ELF/InputFiles.h

@@ -241,7 +241,7 @@ class ELFFileBase : public InputFile {
   StringRef sourceFile;
   uint32_t andFeatures = 0;
   bool hasCommonSyms = false;
-  ArrayRef<uint8_t> aarch64PauthAbiCoreInfo;
+  std::optional<AArch64PauthAbiCoreInfo> aarch64PauthAbiCoreInfo;
 };
 
 // .o file.

lld/ELF/SyntheticSections.cpp

@@ -354,20 +354,20 @@ void GnuPropertySection::writeTo(uint8_t *buf) {
     offset += 16;
   }
 
-  if (!ctx.aarch64PauthAbiCoreInfo.empty()) {
+  if (ctx.aarch64PauthAbiCoreInfo) {
     write32(ctx, buf + offset + 0, GNU_PROPERTY_AARCH64_FEATURE_PAUTH);
-    write32(ctx, buf + offset + 4, ctx.aarch64PauthAbiCoreInfo.size());
-    memcpy(buf + offset + 8, ctx.aarch64PauthAbiCoreInfo.data(),
-           ctx.aarch64PauthAbiCoreInfo.size());
+    write32(ctx, buf + offset + 4, AArch64PauthAbiCoreInfo::size());
+    write64(ctx, buf + offset + 8, ctx.aarch64PauthAbiCoreInfo->platform);
+    write64(ctx, buf + offset + 16, ctx.aarch64PauthAbiCoreInfo->version);
   }
 }
 
 size_t GnuPropertySection::getSize() const {
   uint32_t contentSize = 0;
   if (ctx.arg.andFeatures != 0)
     contentSize += ctx.arg.is64 ? 16 : 12;
-  if (!ctx.aarch64PauthAbiCoreInfo.empty())
-    contentSize += 4 + 4 + ctx.aarch64PauthAbiCoreInfo.size();
+  if (ctx.aarch64PauthAbiCoreInfo)
+    contentSize += 4 + 4 + AArch64PauthAbiCoreInfo::size();
   assert(contentSize != 0);
   return contentSize + 16;
 }
@@ -4967,7 +4967,7 @@ template <class ELFT> void elf::createSyntheticSections(Ctx &ctx) {
   ctx.in.iplt = std::make_unique<IpltSection>(ctx);
   add(*ctx.in.iplt);
 
-  if (ctx.arg.andFeatures || !ctx.aarch64PauthAbiCoreInfo.empty()) {
+  if (ctx.arg.andFeatures || ctx.aarch64PauthAbiCoreInfo) {
     ctx.in.gnuProperty = std::make_unique<GnuPropertySection>(ctx);
     add(*ctx.in.gnuProperty);
   }

lld/test/ELF/aarch64-feature-pauth.s

@@ -13,8 +13,12 @@
 # RUN: not ld.lld tag1.o tag1a.o tag2.o -o /dev/null 2>&1 | FileCheck --check-prefix ERR1 %s
 
 # ERR1:      error: incompatible values of AArch64 PAuth core info found
-# ERR1-NEXT: >>> tag1.o: 0x2a000000000000000{{1|2}}00000000000000
-# ERR1-NEXT: >>> tag2.o: 0x2a000000000000000{{1|2}}00000000000000
+# ERR1-NEXT: platform:
+# ERR1-NEXT: >>> tag1.o: 0x2a
+# ERR1-NEXT: >>> tag2.o: 0x2a
+# ERR1-NEXT: version:
+# ERR1-NEXT: >>> tag1.o: 0x01
+# ERR1-NEXT: >>> tag2.o: 0x02
 
 # RUN: llvm-mc -filetype=obj -triple=aarch64-linux-gnu abi-tag-short.s -o short.o
 # RUN: not ld.lld short.o -o /dev/null 2>&1 | FileCheck --check-prefix ERR2 %s