From f66158648b978a1049340378bf6a76a32436f7cb Mon Sep 17 00:00:00 2001
From: Jonas Devlieghere <jonas@devlieghere.com>
Date: Mon, 8 Dec 2025 14:00:16 -0800
Subject: [PATCH] [lldb] Don't read firstSubclass and nextSiblingClass from
 class_rw_t

We're considering modifying the ObjC runtime's class_rw_t structure to
remove the firstSubclass and nextSiblingClass fields in some cases. LLDB
is currently reading those but not actually using them. Stop doing that
to avoid issues if they are removed by the runtime.

rdar://166084122
---
 .../ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.cpp     | 5 +----
 .../ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.h       | 3 ---
 2 files changed, 1 insertion(+), 7 deletions(-)

diff --git a/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.cpp b/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.cpp
index 954f269f8860b..ebde8892d8f62 100644
--- a/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.cpp
+++ b/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.cpp
@@ -111,7 +111,6 @@ bool ClassDescriptorV2::class_rw_t::Read(Process *process, lldb::addr_t addr) {
                           process->GetAddressByteSize());
 
   lldb::offset_t cursor = 0;
-
   m_flags = extractor.GetU32_unchecked(&cursor);
   m_version = extractor.GetU32_unchecked(&cursor);
   m_ro_ptr = extractor.GetAddress_unchecked(&cursor);
@@ -119,18 +118,16 @@ bool ClassDescriptorV2::class_rw_t::Read(Process *process, lldb::addr_t addr) {
     m_ro_ptr = abi_sp->FixCodeAddress(m_ro_ptr);
   m_method_list_ptr = extractor.GetAddress_unchecked(&cursor);
   m_properties_ptr = extractor.GetAddress_unchecked(&cursor);
-  m_firstSubclass = extractor.GetAddress_unchecked(&cursor);
-  m_nextSiblingClass = extractor.GetAddress_unchecked(&cursor);
 
   if (m_ro_ptr & 1) {
     DataBufferHeap buffer(ptr_size, '\0');
     process->ReadMemory(m_ro_ptr ^ 1, buffer.GetBytes(), ptr_size, error);
     if (error.Fail())
       return false;
-    cursor = 0;
     DataExtractor extractor(buffer.GetBytes(), ptr_size,
                             process->GetByteOrder(),
                             process->GetAddressByteSize());
+    lldb::offset_t cursor = 0;
     m_ro_ptr = extractor.GetAddress_unchecked(&cursor);
     if (ABISP abi_sp = process->GetABI())
       m_ro_ptr = abi_sp->FixCodeAddress(m_ro_ptr);
diff --git a/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.h b/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.h
index 0fff9af438367..8d19b00f1551f 100644
--- a/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.h
+++ b/lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.h
@@ -133,9 +133,6 @@ class ClassDescriptorV2 : public ObjCLanguageRuntime::ClassDescriptor {
     lldb::addr_t m_properties_ptr;
     lldb::addr_t m_protocols_ptr;
 
-    ObjCLanguageRuntime::ObjCISA m_firstSubclass;
-    ObjCLanguageRuntime::ObjCISA m_nextSiblingClass;
-
     bool Read(Process *process, lldb::addr_t addr);
   };