[lld] [lld-macho] Implement support for ObjC relative method lists (PR #86231)

[Kyungwoo Lee via llvm-commits]

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@@ -1974,6 +1975,234 @@ void InitOffsetsSection::setUp() {
   }
 }
 
+ObjCMethListSection::ObjCMethListSection()
+    : SyntheticSection(segment_names::text, section_names::objcMethList) {
+  flags = S_ATTR_NO_DEAD_STRIP;
+  align = m_align;
+}
+
+// Go through all input method lists and ensure that we have selrefs for all
+// their method names. The selrefs will be needed later by ::writeTo. We need to
+// create them early on here to ensure they are processed correctly by the lld
+// pipeline.
+void ObjCMethListSection::setUp() {
+  for (const ConcatInputSection *isec : inputs) {
+    uint32_t structSizeAndFlags = 0, structCount = 0;
+    readMethodListHeader(isec->data.data(), structSizeAndFlags, structCount);
+    uint32_t structSize = structSizeAndFlags & m_structSizeMask;
+
+    // Method name is immediately after header
+    uint32_t methodNameOff = m_methodListHeaderSize;
+
+    // Loop through all methods, and ensure a selref for each of them exists.
+    while (methodNameOff < isec->data.size()) {
+      const Reloc *reloc = isec->getRelocAt(methodNameOff);
+      assert(reloc && "Relocation expected at method list name slot");
+      auto *def = dyn_cast_or_null<Defined>(reloc->referent.get<Symbol *>());
+      assert(def && "Expected valid Defined at method list name slot");
+      auto *cisec = cast<CStringInputSection>(def->isec);
+      assert(cisec && "Expected method name to be in a CStringInputSection");
+      auto methname = cisec->getStringRefAtOffset(def->value);
+      if (!in.objcSelRefs->getSelRef(methname))
+        in.objcSelRefs->makeSelRef(methname);
----------------
kyulee-com wrote:

Looks like this conflicts with https://github.com/llvm/llvm-project/pull/86456

https://github.com/llvm/llvm-project/pull/86231