[lld] [llvm] [lld-macho] Implement ObjC category merging (-objc_category_merging) (PR #82928)

[via llvm-commits]

================
@@ -320,3 +332,929 @@ void objc::checkCategories() {
       }
   }
 }
+
+namespace {
+
+class ObjcCategoryMerger {
+  // Information about an input category
+  struct InfoInputCategory {
+    ConcatInputSection *catListIsec;
+    ConcatInputSection *catBodyIsec;
+    uint32_t offCatListIsec = 0;
+
+    bool wasMerged = false;
+  };
+
+  // To write new (merged) categories or classes, we will try make limited
+  // assumptions about the alignment and the sections the various class/category
+  // info are stored in and . So we'll just reuse the same sections and
+  // alignment as already used in existing (input) categories. To do this we
+  // have InfoCategoryWriter which contains the various sections that the
+  // generated categories will be written to.
+  template <typename T> struct InfroWriteSection {
+    bool valid = false; // Data has been successfully collected from input
+    uint32_t align = 0;
+    Section *inputSection;
+    Reloc relocTemplate;
+    T *outputSection;
+  };
+
+  struct InfoCategoryWriter {
+    InfroWriteSection<ConcatOutputSection> catListInfo;
+    InfroWriteSection<ConcatOutputSection> catBodyInfo;
+    InfroWriteSection<CStringSection> catNameInfo;
+    InfroWriteSection<ConcatOutputSection> catPtrListInfo;
+  };
+
+  // Information about a pointer list in the original categories (method lists,
+  // protocol lists, etc)
+  struct PointerListInfo {
+    PointerListInfo(const char *_categoryPrefix, uint32_t _categoryOffset,
+                    uint32_t _pointersPerStruct)
+        : categoryPrefix(_categoryPrefix), categoryOffset(_categoryOffset),
+          pointersPerStruct(_pointersPerStruct) {}
+    const char *categoryPrefix;
+    uint32_t categoryOffset = 0;
+
+    uint32_t pointersPerStruct = 0;
+
+    uint32_t structSize = 0;
+    uint32_t structCount = 0;
+
+    std::vector<Symbol *> allPtrs;
+  };
+
+  // Full information about all the categories that are extending a class. This
+  // will have all the additional methods, protocols, proprieties that are
+  // contained in all the categories that extend a particular class.
+  struct ClassExtensionInfo {
+    ClassExtensionInfo(CategoryLayout &_catLayout) : catLayout(_catLayout){};
+
+    // Merged names of containers. Ex: base|firstCategory|secondCategory|...
+    std::string mergedContainerName;
+    std::string baseClassName;
+    Symbol *baseClass = nullptr;
+    CategoryLayout &catLayout;
+
+    // In case we generate new data, mark the new data as belonging to this file
+    ObjFile *objFileForMergeData = nullptr;
+
+    PointerListInfo instanceMethods = {
+        objc::symbol_names::categoryInstanceMethods,
+        /*_categoryOffset=*/catLayout.instanceMethodsOffset,
+        /*pointersPerStruct=*/3};
+    PointerListInfo classMethods = {
+        objc::symbol_names::categoryClassMethods,
+        /*_categoryOffset=*/catLayout.classMethodsOffset,
+        /*pointersPerStruct=*/3};
+    PointerListInfo protocols = {objc::symbol_names::categoryProtocols,
+                                 /*_categoryOffset=*/catLayout.protocolsOffset,
+                                 /*pointersPerStruct=*/0};
+    PointerListInfo instanceProps = {
+        objc::symbol_names::listProprieties,
+        /*_categoryOffset=*/catLayout.instancePropsOffset,
+        /*pointersPerStruct=*/2};
+    PointerListInfo classProps = {
+        objc::symbol_names::klassPropList,
+        /*_categoryOffset=*/catLayout.classPropsOffset,
+        /*pointersPerStruct=*/2};
+  };
+
+public:
+  ObjcCategoryMerger(std::vector<ConcatInputSection *> &_allInputSections);
+  void doMerge();
+  static void doCleanup();
+
+private:
+  void collectAndValidateCategoriesData();
+  void
+  mergeCategoriesIntoSingleCategory(std::vector<InfoInputCategory> &categories);
+
+  void eraseISec(ConcatInputSection *isec);
+  void eraseMergedCategories();
+
+  void generateCatListForNonErasedCategories(
+      std::map<ConcatInputSection *, std::set<uint64_t>>
+          catListToErasedOffsets);
+  template <typename T>
+  void collectSectionWriteInfoFromIsec(const InputSection *isec,
+                                       InfroWriteSection<T> &catWriteInfo);
+  void collectCategoryWriterInfoFromCategory(const InfoInputCategory &catInfo);
+  void parseCatInfoToExtInfo(const InfoInputCategory &catInfo,
+                             ClassExtensionInfo &extInfo);
+
+  void parseProtocolListInfo(const ConcatInputSection *isec, uint32_t secOffset,
+                             PointerListInfo &ptrList);
+
+  void parsePointerListInfo(const ConcatInputSection *isec, uint32_t secOffset,
+                            PointerListInfo &ptrList);
+
+  void emitAndLinkPointerList(Defined *parentSym, uint32_t linkAtOffset,
+                              const ClassExtensionInfo &extInfo,
+                              const PointerListInfo &ptrList);
+
+  void emitAndLinkProtocolList(Defined *parentSym, uint32_t linkAtOffset,
+                               const ClassExtensionInfo &extInfo,
+                               const PointerListInfo &ptrList);
+
+  Defined *emitCategory(const ClassExtensionInfo &extInfo);
+  Defined *emitCatListEntrySec(const std::string &forCateogryName,
+                               const std::string &forBaseClassName,
+                               ObjFile *objFile);
+  Defined *emitCategoryBody(const std::string &name, const Defined *nameSym,
+                            const Symbol *baseClassSym,
+                            const std::string &baseClassName, ObjFile *objFile);
+  Defined *emitCategoryName(const std::string &name, ObjFile *objFile);
+  void createSymbolReference(Defined *refFrom, const Symbol *refTo,
+                             uint32_t offset, const Reloc &relocTemplate);
+  Symbol *tryGetSymbolAtIsecOffset(const ConcatInputSection *isec,
+                                   uint32_t offset);
+  Defined *tryGetDefinedAtIsecOffset(const ConcatInputSection *isec,
+                                     uint32_t offset);
+  void tryEraseDefinedAtIsecOffset(const ConcatInputSection *isec,
+                                   uint32_t offset, bool stringOnly = false);
+
+  CategoryLayout catLayout;
+  ClassLayout classLayout;
+  ROClassLayout roClassLayout;
+  ListHeaderLayout listHeaderLayout;
+  MethodLayout methodLayout;
+  ProtocolListHeaderLayout protocolListHeaderLayout;
+
+  InfoCategoryWriter infoCategoryWriter;
+  std::vector<ConcatInputSection *> &allInputSections;
+  // Map of base class Symbol to list of InfoInputCategory's for it
+  std::map<const Symbol *, std::vector<InfoInputCategory>> categoryMap;
+
+  // Normally, the binary data comes from the input files, but since we're
+  // generating binary data ourselves, we use the below arrays to store it in.
+  // Need this to be 'static' so the data survives past the ObjcCategoryMerger
+  // object, as the data will be read by the Writer when the final binary is
+  // generated.
+  static SmallVector<SmallString<0>> generatedNames;
+  static SmallVector<SmallVector<uint8_t>> generatedSectionData;
----------------
alx32 wrote:

Refactored everything into `generatedSectionData` + `newStringData`  + `newSectionData`

https://github.com/llvm/llvm-project/pull/82928