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Handle stepping through ObjC vtable trampoline code. 

llvm-svn: 118270
This commit is contained in:
Jim Ingham 2010-11-05 00:18:21 +00:00
parent 7da7cc568f
commit 5822173bc8
5 changed files with 567 additions and 45 deletions
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414
lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCTrampolineHandler.cpp
View File

@ -15,7 +15,9 @@
// Project includes
#include "AppleThreadPlanStepThroughObjCTrampoline.h"
#include "lldb/Breakpoint/StoppointCallbackContext.h"
#include "lldb/Core/ConstString.h"
#include "lldb/Core/Debugger.h"
#include "lldb/Core/FileSpec.h"
#include "lldb/Core/Log.h"
#include "lldb/Core/Module.h"
@ -33,6 +35,351 @@
using namespace lldb;
using namespace lldb_private;
AppleObjCTrampolineHandler::AppleObjCVTables::VTableRegion::VTableRegion(AppleObjCVTables *owner, lldb::addr_t header_addr) :
m_valid (true),
m_owner(owner),
m_header_addr (header_addr),
m_code_start_addr(0),
m_code_end_addr (0),
m_next_region (0)
{
SetUpRegion ();
}
void
AppleObjCTrampolineHandler::AppleObjCVTables::VTableRegion::SetUpRegion()
{
// The header looks like:
//
// uint16_t headerSize
// uint16_t descSize
// uint32_t descCount
// void * next
//
// First read in the header:
char memory_buffer[16];
Process *process = m_owner->GetProcess();
DataExtractor data(memory_buffer, sizeof(memory_buffer),
process->GetByteOrder(),
process->GetAddressByteSize());
size_t actual_size = 8 + process->GetAddressByteSize();
Error error;
size_t bytes_read = process->ReadMemory (m_header_addr, memory_buffer, actual_size, error);
if (bytes_read != actual_size)
{
m_valid = false;
return;
}
uint32_t offset_ptr = 0;
uint16_t header_size = data.GetU16(&offset_ptr);
uint16_t descriptor_size = data.GetU16(&offset_ptr);
size_t num_descriptors = data.GetU32(&offset_ptr);
m_next_region = data.GetPointer(&offset_ptr);
// If the header size is 0, that means we've come in too early before this data is set up.
// Set ourselves as not valid, and continue.
if (header_size == 0)
{
m_valid = false;
return;
}
// Now read in all the descriptors:
// The descriptor looks like:
//
// uint32_t offset
// uint32_t flags
//
// Where offset is either 0 - in which case it is unused, or
// it is the offset of the vtable code from the beginning of the descriptor record.
// Below, we'll convert that into an absolute code address, since I don't want to have
// to compute it over and over.
// Ingest the whole descriptor array:
lldb::addr_t desc_ptr = m_header_addr + header_size;
size_t desc_array_size = num_descriptors * descriptor_size;
DataBufferSP data_sp(new DataBufferHeap (desc_array_size, '\0'));
uint8_t* dst = (uint8_t*)data_sp->GetBytes();
DataExtractor desc_extractor (dst, desc_array_size,
process->GetByteOrder(),
process->GetAddressByteSize());
bytes_read = process->ReadMemory(desc_ptr, dst, desc_array_size, error);
if (bytes_read != desc_array_size)
{
m_valid = false;
return;
}
// The actual code for the vtables will be laid out consecutively, so I also
// compute the start and end of the whole code block.
offset_ptr = 0;
m_code_start_addr = 0;
m_code_end_addr = 0;
for (int i = 0; i < num_descriptors; i++)
{
lldb::addr_t start_offset = offset_ptr;
uint32_t offset = desc_extractor.GetU32 (&offset_ptr);
uint32_t flags = desc_extractor.GetU32 (&offset_ptr);
lldb:addr_t code_addr = desc_ptr + start_offset + offset;
m_descriptors.push_back (VTableDescriptor(flags, code_addr));
if (m_code_start_addr == 0 || code_addr < m_code_start_addr)
m_code_start_addr = code_addr;
if (code_addr > m_code_end_addr)
m_code_end_addr = code_addr;
offset_ptr = start_offset + descriptor_size;
}
// Finally, a little bird told me that all the vtable code blocks are the same size.
// Let's compute the blocks and if they are all the same add the size to the code end address:
lldb::addr_t code_size = 0;
bool all_the_same = true;
for (int i = 0; i < num_descriptors - 1; i++)
{
lldb::addr_t this_size = m_descriptors[i + 1].code_start - m_descriptors[i].code_start;
if (code_size == 0)
code_size = this_size;
else
{
if (this_size != code_size)
all_the_same = false;
if (this_size > code_size)
code_size = this_size;
}
}
if (all_the_same)
m_code_end_addr += code_size;
}
bool
AppleObjCTrampolineHandler::AppleObjCVTables::VTableRegion::AddressInRegion (lldb::addr_t addr, uint32_t &flags)
{
if (!IsValid())
return false;
if (addr < m_code_start_addr || addr > m_code_end_addr)
return false;
std::vector<VTableDescriptor>::iterator pos, end = m_descriptors.end();
for (pos = m_descriptors.begin(); pos != end; pos++)
{
if (addr <= (*pos).code_start)
{
flags = (*pos).flags;
return true;
}
}
return false;
}
void
AppleObjCTrampolineHandler::AppleObjCVTables::VTableRegion::Dump (Stream &s)
{
s.Printf ("Header addr: 0x%llx Code start: 0x%llx Code End: 0x%llx Next: 0x%llx\n",
m_header_addr, m_code_start_addr, m_code_end_addr, m_next_region);
size_t num_elements = m_descriptors.size();
for (size_t i = 0; i < num_elements; i++)
{
s.Indent();
s.Printf ("Code start: 0x%llx Flags: %d\n", m_descriptors[i].code_start, m_descriptors[i].flags);
}
}
AppleObjCTrampolineHandler::AppleObjCVTables::AppleObjCVTables (ProcessSP &process_sp, ModuleSP &objc_module_sp) :
m_process_sp(process_sp),
m_trampoline_header(LLDB_INVALID_ADDRESS),
m_trampolines_changed_bp_id(LLDB_INVALID_BREAK_ID),
m_objc_module_sp(objc_module_sp)
{
}
AppleObjCTrampolineHandler::AppleObjCVTables::~AppleObjCVTables()
{
if (m_trampolines_changed_bp_id != LLDB_INVALID_BREAK_ID)
m_process_sp->GetTarget().RemoveBreakpointByID (m_trampolines_changed_bp_id);
}
bool
AppleObjCTrampolineHandler::AppleObjCVTables::InitializeVTableSymbols ()
{
if (m_trampoline_header != LLDB_INVALID_ADDRESS)
return true;
Target &target = m_process_sp->GetTarget();
ModuleList &modules = target.GetImages();
size_t num_modules = modules.GetSize();
if (!m_objc_module_sp)
{
for (size_t i = 0; i < num_modules; i++)
{
if (m_process_sp->GetObjCLanguageRuntime()->IsModuleObjCLibrary (modules.GetModuleAtIndex(i)))
{
m_objc_module_sp = modules.GetModuleAtIndex(i);
break;
}
}
}
if (m_objc_module_sp)
{
ConstString trampoline_name ("gdb_objc_trampolines");
const Symbol *trampoline_symbol = m_objc_module_sp->FindFirstSymbolWithNameAndType(trampoline_name,
eSymbolTypeData);
if (trampoline_symbol != NULL)
{
const Address &temp_address = trampoline_symbol->GetValue();
if (!temp_address.IsValid())
return false;
m_trampoline_header = temp_address.GetLoadAddress(&target);
if (m_trampoline_header == LLDB_INVALID_ADDRESS)
return false;
// Next look up the "changed" symbol and set a breakpoint on that...
ConstString changed_name ("gdb_objc_trampolines_changed");
const Symbol *changed_symbol = m_objc_module_sp->FindFirstSymbolWithNameAndType(changed_name,
eSymbolTypeCode);
if (changed_symbol != NULL)
{
const Address &temp_address = changed_symbol->GetValue();
if (!temp_address.IsValid())
return false;
lldb::addr_t changed_addr = temp_address.GetLoadAddress(&target);
if (changed_addr != LLDB_INVALID_ADDRESS)
{
BreakpointSP trampolines_changed_bp_sp = target.CreateBreakpoint (changed_addr,
true);
if (trampolines_changed_bp_sp != NULL)
{
m_trampolines_changed_bp_id = trampolines_changed_bp_sp->GetID();
trampolines_changed_bp_sp->SetCallback (RefreshTrampolines, this, true);
return true;
}
}
}
}
}
return false;
}
bool
AppleObjCTrampolineHandler::AppleObjCVTables::RefreshTrampolines (void *baton,
StoppointCallbackContext *context,
lldb::user_id_t break_id,
lldb::user_id_t break_loc_id)
{
AppleObjCVTables *vtable_handler = (AppleObjCVTables *) baton;
if (vtable_handler->InitializeVTableSymbols())
{
// The Update function is called with the address of an added region. So we grab that address, and
// feed it into ReadRegions. Of course, our friend the ABI will get the values for us.
Process *process = context->exe_ctx.process;
const ABI *abi = process->GetABI();
ClangASTContext *clang_ast_context = process->GetTarget().GetScratchClangASTContext();
ValueList argument_values;
Value input_value;
void *clang_void_ptr_type = clang_ast_context->GetVoidPtrType(false);
input_value.SetValueType (Value::eValueTypeScalar);
input_value.SetContext (Value::eContextTypeOpaqueClangQualType, clang_void_ptr_type);
argument_values.PushValue(input_value);
bool success = abi->GetArgumentValues (*(context->exe_ctx.thread), argument_values);
if (!success)
return false;
// Now get a pointer value from the zeroth argument.
Error error;
DataExtractor data;
error = argument_values.GetValueAtIndex(0)->GetValueAsData(&(context->exe_ctx), clang_ast_context->getASTContext(), data, 0);
uint32_t offset_ptr = 0;
lldb::addr_t region_addr = data.GetPointer(&offset_ptr);
if (region_addr != 0)
vtable_handler->ReadRegions(region_addr);
}
return false;
}
bool
AppleObjCTrampolineHandler::AppleObjCVTables::ReadRegions ()
{
// The no argument version reads the start region from the value of the gdb_regions_header, and
// gets started from there.
m_regions.clear();
if (!InitializeVTableSymbols())
return false;
char memory_buffer[8];
DataExtractor data(memory_buffer, sizeof(memory_buffer),
m_process_sp->GetByteOrder(),
m_process_sp->GetAddressByteSize());
Error error;
size_t bytes_read = m_process_sp->ReadMemory (m_trampoline_header, memory_buffer, m_process_sp->GetAddressByteSize(), error);
if (bytes_read != m_process_sp->GetAddressByteSize())
return false;
uint32_t offset_ptr = 0;
lldb::addr_t region_addr = data.GetPointer(&offset_ptr);
return ReadRegions (region_addr);
}
bool
AppleObjCTrampolineHandler::AppleObjCVTables::ReadRegions (lldb::addr_t region_addr)
{
if (!m_process_sp)
return false;
Log *log = lldb_private::GetLogIfAllCategoriesSet (LIBLLDB_LOG_STEP);
// We aren't starting at the trampoline symbol.
InitializeVTableSymbols ();
lldb::addr_t next_region = region_addr;
// Read in the sizes of the headers.
while (next_region != 0)
{
m_regions.push_back (VTableRegion(this, next_region));
if (!m_regions.back().IsValid())
{
m_regions.clear();
return false;
}
if (log)
{
StreamString s;
m_regions.back().Dump(s);
log->Printf("Read vtable region: \n%s", s.GetData());
}
next_region = m_regions.back().GetNextRegionAddr();
}
return true;
}
bool
AppleObjCTrampolineHandler::AppleObjCVTables::IsAddressInVTables (lldb::addr_t addr, uint32_t &flags)
{
region_collection::iterator pos, end = m_regions.end();
for (pos = m_regions.begin(); pos != end; pos++)
{
if ((*pos).AddressInRegion (addr, flags))
return true;
}
return false;
}
const AppleObjCTrampolineHandler::DispatchFunction
AppleObjCTrampolineHandler::g_dispatch_functions[] =
{
@ -60,24 +407,9 @@ AppleObjCTrampolineHandler::g_dispatch_functions[] =
{NULL}
};
bool
AppleObjCTrampolineHandler::ModuleIsObjCLibrary (const ModuleSP &module_sp)
{
const FileSpec &module_file_spec = module_sp->GetFileSpec();
static ConstString ObjCName ("libobjc.A.dylib");
if (module_file_spec)
{
if (module_file_spec.GetFilename() == ObjCName)
return true;
}
return false;
}
AppleObjCTrampolineHandler::AppleObjCTrampolineHandler (ProcessSP process_sp, ModuleSP objc_module) :
AppleObjCTrampolineHandler::AppleObjCTrampolineHandler (ProcessSP process_sp, ModuleSP objc_module_sp) :
m_process_sp (process_sp),
m_objc_module_sp (objc_module),
m_objc_module_sp (objc_module_sp),
m_impl_fn_addr (LLDB_INVALID_ADDRESS),
m_impl_stret_fn_addr (LLDB_INVALID_ADDRESS)
{
@ -119,6 +451,11 @@ AppleObjCTrampolineHandler::AppleObjCTrampolineHandler (ProcessSP process_sp, Mo
m_msgSend_map.insert(std::pair<lldb::addr_t, int>(sym_addr, i));
}
}
// Build our vtable dispatch handler here:
m_vtables_ap.reset(new AppleObjCVTables(process_sp, m_objc_module_sp));
if (m_vtables_ap.get())
m_vtables_ap->ReadRegions();
}
ThreadPlanSP
@ -127,13 +464,38 @@ AppleObjCTrampolineHandler::GetStepThroughDispatchPlan (Thread &thread, bool sto
ThreadPlanSP ret_plan_sp;
lldb::addr_t curr_pc = thread.GetRegisterContext()->GetPC();
DispatchFunction this_dispatch;
bool found_it = false;
MsgsendMap::iterator pos;
pos = m_msgSend_map.find (curr_pc);
if (pos != m_msgSend_map.end())
{
this_dispatch = g_dispatch_functions[(*pos).second];
found_it = true;
}
if (!found_it)
{
uint32_t flags;
if (m_vtables_ap.get())
{
found_it = m_vtables_ap->IsAddressInVTables (curr_pc, flags);
if (found_it)
{
this_dispatch.name = "vtable";
this_dispatch.stret_return
= (flags & AppleObjCVTables::eOBJC_TRAMPOLINE_STRET) == AppleObjCVTables::eOBJC_TRAMPOLINE_STRET;
this_dispatch.is_super = false;
this_dispatch.fixedup = DispatchFunction::eFixUpFixed;
}
}
}
if (found_it)
{
Log *log = lldb_private::GetLogIfAllCategoriesSet (LIBLLDB_LOG_STEP);
const DispatchFunction *this_dispatch = &g_dispatch_functions[(*pos).second];
lldb::StackFrameSP thread_cur_frame = thread.GetStackFrameAtIndex(0);
@ -161,7 +523,7 @@ AppleObjCTrampolineHandler::GetStepThroughDispatchPlan (Thread &thread, bool sto
// If this is a struct return dispatch, then the first argument is the
// return struct pointer, and the object is the second, and the selector is the third.
// Otherwise the object is the first and the selector the second.
if (this_dispatch->stret_return)
if (this_dispatch.stret_return)
{
obj_index = 1;
sel_index = 2;
@ -197,7 +559,7 @@ AppleObjCTrampolineHandler::GetStepThroughDispatchPlan (Thread &thread, bool sto
isa_value.SetValueType(Value::eValueTypeLoadAddress);
isa_value.ResolveValue(&exec_ctx, clang_ast_context->getASTContext());
if (this_dispatch->fixedup == DispatchFunction::eFixUpFixed)
if (this_dispatch.fixedup == DispatchFunction::eFixUpFixed)
{
// For the FixedUp method the Selector is actually a pointer to a
// structure, the second field of which is the selector number.
@ -206,7 +568,7 @@ AppleObjCTrampolineHandler::GetStepThroughDispatchPlan (Thread &thread, bool sto
sel_value->SetValueType(Value::eValueTypeLoadAddress);
sel_value->ResolveValue(&exec_ctx, clang_ast_context->getASTContext());
}
else if (this_dispatch->fixedup == DispatchFunction::eFixUpToFix)
else if (this_dispatch.fixedup == DispatchFunction::eFixUpToFix)
{
// FIXME: If the method dispatch is not "fixed up" then the selector is actually a
// pointer to the string name of the selector. We need to look that up...
@ -219,7 +581,7 @@ AppleObjCTrampolineHandler::GetStepThroughDispatchPlan (Thread &thread, bool sto
// FIXME: If this is a dispatch to the super-class, we need to get the super-class from
// the class, and disaptch to that instead.
// But for now I just punt and return no plan.
if (this_dispatch->is_super)
if (this_dispatch.is_super)
{
if (log)
log->Printf ("Punting on stepping into super method dispatch.");
@ -244,7 +606,7 @@ AppleObjCTrampolineHandler::GetStepThroughDispatchPlan (Thread &thread, bool sto
if (impl_addr == LLDB_INVALID_ADDRESS)
{
Address resolve_address(NULL, this_dispatch->stret_return ? m_impl_stret_fn_addr : m_impl_fn_addr);
Address resolve_address(NULL, this_dispatch.stret_return ? m_impl_stret_fn_addr : m_impl_fn_addr);
StreamString errors;
{
@ -289,6 +651,12 @@ AppleObjCTrampolineHandler::GetStepThroughDispatchPlan (Thread &thread, bool sto
dispatch_values.GetValueAtIndex(0)->GetScalar().ULongLong(),
dispatch_values.GetValueAtIndex(1)->GetScalar().ULongLong(),
stop_others));
if (log)
{
StreamString s;
ret_plan_sp->GetDescription(&s, eDescriptionLevelFull);
log->Printf("Using ObjC step plan: %s.\n", s.GetData());
}
}
else
{

124
lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCTrampolineHandler.h
View File

@ -32,8 +32,6 @@ public:
~AppleObjCTrampolineHandler() {}
static bool ModuleIsObjCLibrary (const ModuleSP &module_sp);
ThreadPlanSP
GetStepThroughDispatchPlan (Thread &thread, bool stop_others);
@ -57,6 +55,127 @@ public:
};
private:
class AppleObjCVTables
{
public:
// These come from objc-gdb.h.
enum VTableFlags
{
eOBJC_TRAMPOLINE_MESSAGE = (1<<0), // trampoline acts like objc_msgSend
eOBJC_TRAMPOLINE_STRET = (1<<1), // trampoline is struct-returning
eOBJC_TRAMPOLINE_VTABLE = (1<<2), // trampoline is vtable dispatcher
};
private:
struct VTableDescriptor
{
VTableDescriptor(uint32_t in_flags, addr_t in_code_start) :
flags(in_flags),
code_start(in_code_start) {}
uint32_t flags;
lldb::addr_t code_start;
};
class VTableRegion
{
public:
VTableRegion() :
m_valid (false),
m_owner (NULL),
m_header_addr (LLDB_INVALID_ADDRESS),
m_code_start_addr(0),
m_code_end_addr (0),
m_next_region (0)
{}
VTableRegion(AppleObjCVTables *owner, lldb::addr_t header_addr);
void SetUpRegion();
lldb::addr_t GetNextRegionAddr ()
{
return m_next_region;
}
lldb::addr_t
GetCodeStart ()
{
return m_code_start_addr;
}
lldb::addr_t
GetCodeEnd ()
{
return m_code_end_addr;
}
uint32_t
GetFlagsForVTableAtAddress (lldb::addr_t address)
{
return 0;
}
bool
IsValid ()
{
return m_valid;
}
bool
AddressInRegion (lldb::addr_t addr, uint32_t &flags);
void
Dump (Stream &s);
public:
bool m_valid;
AppleObjCVTables *m_owner;
lldb::addr_t m_header_addr;
lldb::addr_t m_code_start_addr;
lldb::addr_t m_code_end_addr;
std::vector<VTableDescriptor> m_descriptors;
lldb::addr_t m_next_region;
};
public:
AppleObjCVTables(ProcessSP &process_sp, ModuleSP &objc_module_sp);
~AppleObjCVTables();
bool
InitializeVTableSymbols ();
static bool RefreshTrampolines (void *baton,
StoppointCallbackContext *context,
lldb::user_id_t break_id,
lldb::user_id_t break_loc_id);
bool
ReadRegions ();
bool
ReadRegions (lldb::addr_t region_addr);
bool
IsAddressInVTables (lldb::addr_t addr, uint32_t &flags);
Process *GetProcess ()
{
return m_process_sp.get();
}
private:
ProcessSP m_process_sp;
typedef std::vector<VTableRegion> region_collection;
lldb::addr_t m_trampoline_header;
lldb::break_id_t m_trampolines_changed_bp_id;
region_collection m_regions;
lldb::ModuleSP m_objc_module_sp;
};
static const DispatchFunction g_dispatch_functions[];
typedef std::map<lldb::addr_t, int> MsgsendMap; // This table maps an dispatch fn address to the index in g_dispatch_functions
@ -68,6 +187,7 @@ private:
Mutex m_impl_function_mutex;
lldb::addr_t m_impl_fn_addr;
lldb::addr_t m_impl_stret_fn_addr;
std::auto_ptr<AppleObjCVTables> m_vtables_ap;
};

7
lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleThreadPlanStepThroughObjCTrampoline.cpp
View File

@ -115,6 +115,13 @@ AppleThreadPlanStepThroughObjCTrampoline::ShouldStop (Event *event_ptr)
lldb::addr_t target_addr = target_addr_value.GetScalar().ULongLong();
Address target_address(NULL, target_addr);
Log *log = lldb_private::GetLogIfAllCategoriesSet (LIBLLDB_LOG_STEP);
if (target_addr == 0)
{
if (log)
log->Printf("Got target implementation of 0x0, stopping.");
SetPlanComplete();
return true;
}
if (log)
log->Printf("Running to ObjC method implementation: 0x%llx", target_addr);

49
lldb/source/Target/ThreadPlanStepInRange.cpp
View File

@ -83,23 +83,6 @@ ThreadPlanStepInRange::ShouldStop (Event *event_ptr)
if (InRange())
return false;
// If we're in an older frame then we should stop.
if (FrameIsOlder())
return true;
// See if we are in a place we should step through (i.e. a trampoline of some sort):
// One tricky bit here is that some stubs don't push a frame, so we have to check
// both the case of a frame that is younger, or the same as this frame.
// However, if the frame is the same, and we are still in the symbol we started
// in, the we don't need to do this. This first check isn't strictly necessary,
// but it is more efficient.
if (!FrameIsYounger() && InSymbol())
{
SetPlanComplete();
return true;
}
ThreadPlan* new_plan = NULL;
// Stepping through should be done stopping other threads in general, since we're setting a breakpoint and
@ -111,6 +94,38 @@ ThreadPlanStepInRange::ShouldStop (Event *event_ptr)
else
stop_others = false;
if (FrameIsOlder())
{
// If we're in an older frame then we should stop.
//
// A caveat to this is if we think the frame is older but we're actually in a trampoline.
// I'm going to make the assumption that you wouldn't RETURN to a trampoline. So if we are
// in a trampoline we think the frame is older because the trampoline confused the backtracer.
new_plan = m_thread.QueueThreadPlanForStepThrough (false, stop_others);
if (new_plan == NULL)
return true;
else if (log)
{
log->Printf("Thought I stepped out, but in fact arrived at a trampoline.");
}
}
else if (!FrameIsYounger() && InSymbol())
{
// If we are not in a place we should step through, we're done.
// One tricky bit here is that some stubs don't push a frame, so we have to check
// both the case of a frame that is younger, or the same as this frame.
// However, if the frame is the same, and we are still in the symbol we started
// in, the we don't need to do this. This first check isn't strictly necessary,
// but it is more efficient.
SetPlanComplete();
return true;
}
// We may have set the plan up above in the FrameIsOlder section:
if (new_plan == NULL)
new_plan = m_thread.QueueThreadPlanForStepThrough (false, stop_others);
if (log)

14
lldb/source/Target/ThreadPlanStepOverRange.cpp
View File

@ -88,7 +88,19 @@ ThreadPlanStepOverRange::ShouldStop (Event *event_ptr)
ThreadPlan* new_plan = NULL;
if (FrameIsOlder())
return true;
{
// If we're in an older frame then we should stop.
//
// A caveat to this is if we think the frame is older but we're actually in a trampoline.
// I'm going to make the assumption that you wouldn't RETURN to a trampoline. So if we are
// in a trampoline we think the frame is older because the trampoline confused the backtracer.
// As below, we step through first, and then try to figure out how to get back out again.
new_plan = m_thread.QueueThreadPlanForStepThrough (false, stop_others);
if (new_plan != NULL && log)
log->Printf("Thought I stepped out, but in fact arrived at a trampoline.");
}
else if (FrameIsYounger())
{
new_plan = m_thread.QueueThreadPlanForStepOut (false, NULL, true, stop_others, lldb::eVoteNo, lldb::eVoteNoOpinion);