[lld-macho] Fix crash: ObjC category merge + relative method lists (#104081)

A crash was happening when both ObjC Category Merging and Relative
method lists were enabled.

ObjC Category Merging creates new data sections and adds them by calling
`addInputSection`. `addInputSection` uses the symbols within the added
section to determine which container to actually add the section to.

The issue is that ObjC Category merging is calling `addInputSection`
before actually adding the relevant symbols the the added section. This
causes `addInputSection` to add the `InputSection` to the wrong
container, eventually resulting in a crash.

To fix this, we ensure that ObjC Category Merging calls
`addInputSection` only after the symbols have been added to the
`InputSection`.

(cherry picked from commit 0df9189)

Author: alx32

lld/MachO/ObjC.cpp

@@ -873,7 +873,6 @@ Defined *ObjcCategoryMerger::emitAndLinkProtocolList(
       infoCategoryWriter.catPtrListInfo.align);
   listSec->parent = infoCategoryWriter.catPtrListInfo.outputSection;
   listSec->live = true;
-  addInputSection(listSec);
 
   listSec->parent = infoCategoryWriter.catPtrListInfo.outputSection;
 
@@ -889,6 +888,7 @@ Defined *ObjcCategoryMerger::emitAndLinkProtocolList(
 
   ptrListSym->used = true;
   parentSym->getObjectFile()->symbols.push_back(ptrListSym);
+  addInputSection(listSec);
 
   createSymbolReference(parentSym, ptrListSym, linkAtOffset,
                         infoCategoryWriter.catBodyInfo.relocTemplate);
@@ -933,7 +933,6 @@ void ObjcCategoryMerger::emitAndLinkPointerList(
       infoCategoryWriter.catPtrListInfo.align);
   listSec->parent = infoCategoryWriter.catPtrListInfo.outputSection;
   listSec->live = true;
-  addInputSection(listSec);
 
   listSec->parent = infoCategoryWriter.catPtrListInfo.outputSection;
 
@@ -949,6 +948,7 @@ void ObjcCategoryMerger::emitAndLinkPointerList(
 
   ptrListSym->used = true;
   parentSym->getObjectFile()->symbols.push_back(ptrListSym);
+  addInputSection(listSec);
 
   createSymbolReference(parentSym, ptrListSym, linkAtOffset,
                         infoCategoryWriter.catBodyInfo.relocTemplate);
@@ -974,7 +974,6 @@ ObjcCategoryMerger::emitCatListEntrySec(const std::string &forCategoryName,
                                bodyData, infoCategoryWriter.catListInfo.align);
   newCatList->parent = infoCategoryWriter.catListInfo.outputSection;
   newCatList->live = true;
-  addInputSection(newCatList);
 
   newCatList->parent = infoCategoryWriter.catListInfo.outputSection;
 
@@ -990,6 +989,7 @@ ObjcCategoryMerger::emitCatListEntrySec(const std::string &forCategoryName,
 
   catListSym->used = true;
   objFile->symbols.push_back(catListSym);
+  addInputSection(newCatList);
   return catListSym;
 }
 
@@ -1012,7 +1012,6 @@ Defined *ObjcCategoryMerger::emitCategoryBody(const std::string &name,
                                bodyData, infoCategoryWriter.catBodyInfo.align);
   newBodySec->parent = infoCategoryWriter.catBodyInfo.outputSection;
   newBodySec->live = true;
-  addInputSection(newBodySec);
 
   std::string symName =
       objc::symbol_names::category + baseClassName + "(" + name + ")";
@@ -1025,6 +1024,7 @@ Defined *ObjcCategoryMerger::emitCategoryBody(const std::string &name,
 
   catBodySym->used = true;
   objFile->symbols.push_back(catBodySym);
+  addInputSection(newBodySec);
 
   createSymbolReference(catBodySym, nameSym, catLayout.nameOffset,
                         infoCategoryWriter.catBodyInfo.relocTemplate);
@@ -1245,7 +1245,6 @@ void ObjcCategoryMerger::generateCatListForNonErasedCategories(
           infoCategoryWriter.catListInfo.align);
       listSec->parent = infoCategoryWriter.catListInfo.outputSection;
       listSec->live = true;
-      addInputSection(listSec);
 
       std::string slotSymName = "<__objc_catlist slot for category ";
       slotSymName += nonErasedCatBody->getName();
@@ -1260,6 +1259,7 @@ void ObjcCategoryMerger::generateCatListForNonErasedCategories(
 
       catListSlotSym->used = true;
       objFile->symbols.push_back(catListSlotSym);
+      addInputSection(listSec);
 
       // Now link the category body into the newly created slot
       createSymbolReference(catListSlotSym, nonErasedCatBody, 0,

lld/test/MachO/objc-category-merging-minimal.s

@@ -9,15 +9,15 @@
 ## Create our main testing dylib - linking against the fake dylib above
 # RUN: llvm-mc -filetype=obj -triple=arm64-apple-macos -o merge_cat_minimal.o merge_cat_minimal.s
 # RUN: %lld -arch arm64 -dylib -o merge_cat_minimal_no_merge.dylib a64_fakedylib.dylib merge_cat_minimal.o
-# RUN: %lld -arch arm64 -dylib -o merge_cat_minimal_merge.dylib -objc_category_merging a64_fakedylib.dylib merge_cat_minimal.o
+# RUN: %lld -objc_relative_method_lists -arch arm64 -dylib -o merge_cat_minimal_merge.dylib -objc_category_merging a64_fakedylib.dylib merge_cat_minimal.o
 
 ## Now verify that the flag caused category merging to happen appropriatelly
 # RUN: llvm-objdump --objc-meta-data --macho merge_cat_minimal_no_merge.dylib | FileCheck %s --check-prefixes=NO_MERGE_CATS
 # RUN: llvm-objdump --objc-meta-data --macho merge_cat_minimal_merge.dylib | FileCheck %s --check-prefixes=MERGE_CATS
 
 ############ Test merging multiple categories into the base class ############
 # RUN: llvm-mc -filetype=obj -triple=arm64-apple-macos -o merge_base_class_minimal.o merge_base_class_minimal.s
-# RUN: %lld -arch arm64 -dylib -o merge_base_class_minimal_yes_merge.dylib -objc_category_merging merge_base_class_minimal.o merge_cat_minimal.o
+# RUN: %lld -arch arm64 -dylib -objc_relative_method_lists -o merge_base_class_minimal_yes_merge.dylib -objc_category_merging merge_base_class_minimal.o merge_cat_minimal.o
 # RUN: %lld -arch arm64 -dylib -o merge_base_class_minimal_no_merge.dylib merge_base_class_minimal.o merge_cat_minimal.o
 
 # RUN: llvm-objdump --objc-meta-data --macho merge_base_class_minimal_no_merge.dylib  | FileCheck %s --check-prefixes=NO_MERGE_INTO_BASE
@@ -37,14 +37,14 @@ MERGE_CATS-NOT: __OBJC_$_CATEGORY_MyBaseClass_$_Category02
 MERGE_CATS: __OBJC_$_CATEGORY_MyBaseClass(Category01|Category02)
 MERGE_CATS-NEXT:   name {{.*}} Category01|Category02
 MERGE_CATS:       instanceMethods
-MERGE_CATS-NEXT:  24
-MERGE_CATS-NEXT:  2
+MERGE_CATS-NEXT:  entsize 12 (relative)
+MERGE_CATS-NEXT:  count 2
 MERGE_CATS-NEXT:   name {{.*}} cat01_InstanceMethod
 MERGE_CATS-NEXT:  types {{.*}} v16@0:8
-MERGE_CATS-NEXT:    imp -[MyBaseClass(Category01) cat01_InstanceMethod]
+MERGE_CATS-NEXT:    imp {{.*}} -[MyBaseClass(Category01) cat01_InstanceMethod]
 MERGE_CATS-NEXT:   name {{.*}} cat02_InstanceMethod
 MERGE_CATS-NEXT:  types {{.*}} v16@0:8
-MERGE_CATS-NEXT:    imp -[MyBaseClass(Category02) cat02_InstanceMethod]
+MERGE_CATS-NEXT:    imp {{.*}} -[MyBaseClass(Category02) cat02_InstanceMethod]
 MERGE_CATS-NEXT:         classMethods 0x0
 MERGE_CATS-NEXT:            protocols 0x0
 MERGE_CATS-NEXT:   instanceProperties 0x0
@@ -69,17 +69,17 @@ YES_MERGE_INTO_BASE-NOT: __OBJC_$_CATEGORY_MyBaseClass_$_Category02
 YES_MERGE_INTO_BASE: _OBJC_CLASS_$_MyBaseClass
 YES_MERGE_INTO_BASE-NEXT: _OBJC_METACLASS_$_MyBaseClass
 YES_MERGE_INTO_BASE: baseMethods
-YES_MERGE_INTO_BASE-NEXT: entsize 24
+YES_MERGE_INTO_BASE-NEXT: entsize 12 (relative)
 YES_MERGE_INTO_BASE-NEXT: count 3
 YES_MERGE_INTO_BASE-NEXT: name {{.*}} cat01_InstanceMethod
 YES_MERGE_INTO_BASE-NEXT: types {{.*}} v16@0:8
-YES_MERGE_INTO_BASE-NEXT: imp -[MyBaseClass(Category01) cat01_InstanceMethod]
+YES_MERGE_INTO_BASE-NEXT: imp {{.*}} -[MyBaseClass(Category01) cat01_InstanceMethod]
 YES_MERGE_INTO_BASE-NEXT: name {{.*}} cat02_InstanceMethod
 YES_MERGE_INTO_BASE-NEXT: types {{.*}} v16@0:8
-YES_MERGE_INTO_BASE-NEXT: imp -[MyBaseClass(Category02) cat02_InstanceMethod]
+YES_MERGE_INTO_BASE-NEXT: imp {{.*}} -[MyBaseClass(Category02) cat02_InstanceMethod]
 YES_MERGE_INTO_BASE-NEXT: name {{.*}} baseInstanceMethod
 YES_MERGE_INTO_BASE-NEXT: types {{.*}} v16@0:8
-YES_MERGE_INTO_BASE-NEXT: imp -[MyBaseClass baseInstanceMethod]
+YES_MERGE_INTO_BASE-NEXT: imp {{.*}} -[MyBaseClass baseInstanceMethod]
 
 
 #### Check merge swift category into base class ###