[Lldb-commits] [lldb] 0c0ed39 - [lldb] Don't read firstSubclass and nextSiblingClass from class_rw_t (#171213)

[via lldb-commits]

Author: Jonas Devlieghere
Date: 2025-12-09T08:50:37-08:00
New Revision: 0c0ed398ecef2d3840b4ebc11b41d638339d299b

URL: https://github.com/llvm/llvm-project/commit/0c0ed398ecef2d3840b4ebc11b41d638339d299b
DIFF: https://github.com/llvm/llvm-project/commit/0c0ed398ecef2d3840b4ebc11b41d638339d299b.diff

LOG: [lldb] Don't read firstSubclass and nextSiblingClass from class_rw_t (#171213)

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

Added: 
    

Modified: 
    lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.cpp
    lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.h

Removed: 
    


################################################################################
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);
   };