[ELF] Support --package-metadata

This was recently introduced in GNU linkers and it makes sense for
ld.lld to have the same support. This implementation omits checking if
the input string is valid json to reduce size bloat.

Differential Revision: https://reviews.llvm.org/D131439

lld/ELF/Config.h

@@ -291,6 +291,7 @@ struct Configuration {
   StringRef thinLTOJobs;
   unsigned timeTraceGranularity;
   int32_t splitStackAdjustSize;
+  StringRef packageMetadata;
 
   // The following config options do not directly correspond to any
   // particular command line options.

lld/ELF/Driver.cpp

@@ -1146,6 +1146,7 @@ static void readConfigs(opt::InputArgList &args) {
   config->optimize = args::getInteger(args, OPT_O, 1);
   config->orphanHandling = getOrphanHandling(args);
   config->outputFile = args.getLastArgValue(OPT_o);
+  config->packageMetadata = args.getLastArgValue(OPT_package_metadata);
   config->pie = args.hasFlag(OPT_pie, OPT_no_pie, false);
   config->printIcfSections =
       args.hasFlag(OPT_print_icf_sections, OPT_no_print_icf_sections, false);

lld/ELF/Options.td

@@ -503,6 +503,8 @@ def z: JoinedOrSeparate<["-"], "z">, MetaVarName<"<option>">,
 def visual_studio_diagnostics_format : FF<"vs-diagnostics">,
 HelpText<"Format diagnostics for Visual Studio compatibility">;
 
+def package_metadata: JJ<"package-metadata=">, HelpText<"Emit package metadata note">;
+
 // Aliases
 def: Separate<["-"], "f">, Alias<auxiliary>, HelpText<"Alias for --auxiliary">;
 def: F<"call_shared">, Alias<Bdynamic>, HelpText<"Alias for --Bdynamic">;

lld/ELF/SyntheticSections.cpp

@@ -3876,6 +3876,20 @@ size_t MemtagAndroidNote::getSize() const {
          /*descsz=*/sizeof(uint32_t);
 }
 
+void PackageMetadataNote::writeTo(uint8_t *buf) {
+  write32(buf, 4);
+  write32(buf + 4, config->packageMetadata.size() + 1);
+  write32(buf + 8, FDO_PACKAGING_METADATA);
+  memcpy(buf + 12, "FDO", 4);
+  memcpy(buf + 16, config->packageMetadata.data(),
+         config->packageMetadata.size());
+}
+
+size_t PackageMetadataNote::getSize() const {
+  return sizeof(llvm::ELF::Elf64_Nhdr) + 4 +
+         alignTo(config->packageMetadata.size() + 1, 4);
+}
+
 InStruct elf::in;
 
 std::vector<Partition> elf::partitions;

lld/ELF/SyntheticSections.h

@@ -1176,6 +1176,15 @@ public:
   size_t getSize() const override;
 };
 
+class PackageMetadataNote : public SyntheticSection {
+public:
+  PackageMetadataNote()
+      : SyntheticSection(llvm::ELF::SHF_ALLOC, llvm::ELF::SHT_NOTE,
+                         /*alignment=*/4, ".note.package") {}
+  void writeTo(uint8_t *buf) override;
+  size_t getSize() const override;
+};
+
 InputSection *createInterpSection();
 MergeInputSection *createCommentSection();
 template <class ELFT> void splitSections();
@@ -1208,6 +1217,7 @@ struct Partition {
   std::unique_ptr<GnuHashTableSection> gnuHashTab;
   std::unique_ptr<HashTableSection> hashTab;
   std::unique_ptr<MemtagAndroidNote> memtagAndroidNote;
+  std::unique_ptr<PackageMetadataNote> packageMetadataNote;
   std::unique_ptr<RelocationBaseSection> relaDyn;
   std::unique_ptr<RelrBaseSection> relrDyn;
   std::unique_ptr<VersionDefinitionSection> verDef;

lld/ELF/Writer.cpp

@@ -405,6 +405,11 @@ template <class ELFT> void elf::createSyntheticSections() {
       part.armExidx = std::make_unique<ARMExidxSyntheticSection>();
       add(*part.armExidx);
     }
+
+    if (!config->packageMetadata.empty()) {
+      part.packageMetadataNote = std::make_unique<PackageMetadataNote>();
+      add(*part.packageMetadataNote);
+    }
   }
 
   if (partitions.size() != 1) {

lld/docs/ReleaseNotes.rst

@@ -25,6 +25,8 @@ Non-comprehensive list of changes in this release
 
 ELF Improvements
 ----------------
+* ``--package-metadata=`` has been added to create package metadata notes
+  (`D131439 <https://reviews.llvm.org/D131439>`_)
 
 Breaking changes
 ----------------

lld/test/ELF/package-metadata.s

@@ -0,0 +1,19 @@
+# REQUIRES: x86
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %s -o %t.o
+
+# RUN: ld.lld %t.o -o %t --package-metadata='{}'
+# RUN: llvm-readelf -n %t | FileCheck %s --check-prefixes=NOTE,FIRST
+
+# RUN: ld.lld %t.o -o %t --package-metadata='{"abc":123}'
+# RUN: llvm-readelf -n %t | FileCheck %s --check-prefixes=NOTE,SECOND
+
+# NOTE: .note.package
+# NOTE-NEXT: Owner
+# NOTE-NEXT: FDO 0x{{.*}} Unknown note type: (0xcafe1a7e)
+# FIRST-NEXT: description data: 7b 7d 00
+# SECOND-NEXT: description data: 7b 22 61 62 63 22 3a 31 32 33 7d 00
+
+.globl _start
+_start:
+  ret

llvm/include/llvm/BinaryFormat/ELF.h

@@ -1598,6 +1598,7 @@ enum {
   NT_GNU_BUILD_ID = 3,
   NT_GNU_GOLD_VERSION = 4,
   NT_GNU_PROPERTY_TYPE_0 = 5,
+  FDO_PACKAGING_METADATA = 0xcafe1a7e,
 };
 
 // Android note types.