[lld] [lld-macho] Category merger: handle addends when getting symbol at offset (PR #91238)

[via llvm-commits]

================
@@ -518,12 +519,32 @@ void ObjcCategoryMerger::collectSectionWriteInfoFromIsec(
 Symbol *
 ObjcCategoryMerger::tryGetSymbolAtIsecOffset(const ConcatInputSection *isec,
                                              uint32_t offset) {
+  if (!isec)
+    return nullptr;
   const Reloc *reloc = isec->getRelocAt(offset);
 
   if (!reloc)
     return nullptr;
 
-  return reloc->referent.get<Symbol *>();
+  Symbol *sym = reloc->referent.get<Symbol *>();
+
+  if (reloc->addend) {
+    assert(isa<Defined>(sym) && "Expected defined for non-zero addend");
+    Defined *definedSym = cast<Defined>(sym);
+    sym = tryFindDefinedOnIsec(definedSym->isec(),
+                               definedSym->value + reloc->addend);
+  }
+
+  return sym;
+}
+
+Defined *ObjcCategoryMerger::tryFindDefinedOnIsec(const InputSection *isec,
+                                                  uint32_t offset) {
+  for (Defined *sym : isec->symbols)
+    if ((sym->value <= offset) && (sym->value + sym->size > offset))
----------------
alx32 wrote:

In the test, the addend comes from:

```
__CATEGORY__TtC11SimpleClass11SimpleClass_$_SimpleClass:
	[...]
	.quad	_$s11SimpleClassAACMf+24    // <---- Addend = 24
```


https://github.com/llvm/llvm-project/pull/91238