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[lldb] Add parent address to Task synthetic provider #10936

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Merged
merged 4 commits into from
Jul 3, 2025
Merged

[lldb] Add parent address to Task synthetic provider #10936

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d9d6986
[lldb] Add parent address to Task synthetic provider
kastiglione Jul 1, 2025
5b5fd2c
Use UnsafeRawPointer?; Fix num children
kastiglione Jul 1, 2025
5bb4cc6
Additional test updates
kastiglione Jul 2, 2025
5ef6378
[lldb] Avoid mangling empty opaque types
kastiglione Jul 2, 2025
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62 changes: 48 additions & 14 deletions lldb/source/Plugins/Language/Swift/SwiftFormatters.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -734,6 +734,13 @@ namespace lldb_private {
namespace formatters {
namespace swift {

namespace {
/// The size of Swift Tasks. Fragments are tail allocated.
static constexpr size_t AsyncTaskSize = sizeof(::swift::AsyncTask);
/// The offset of ChildFragment, which is the first fragment of an AsyncTask.
static constexpr offset_t ChildFragmentOffset = AsyncTaskSize;
} // namespace

class EnumSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
public:
EnumSyntheticFrontEnd(lldb::ValueObjectSP valobj_sp);
Expand Down Expand Up @@ -806,6 +813,7 @@ class TaskSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
"address",
"id",
"enqueuePriority",
"parent",
"children",

// Children below this point are hidden.
Expand Down Expand Up @@ -873,6 +881,33 @@ class TaskSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
RETURN_CHILD(m_enqueue_priority_sp, enqueuePriority, priority_type);
}
case 3: {
if (!m_parent_task_sp) {
// TypeMangling for "Swift.UnsafeRawPointer"
CompilerType raw_pointer_type =
m_ts->GetTypeFromMangledTypename(ConstString("$sSVD"));

addr_t parent_addr = 0;
if (m_task_info.isChildTask) {
if (auto process_sp = m_backend.GetProcessSP()) {
Status status;
// Read ChildFragment::Parent, the first field of the ChildFragment.
parent_addr = process_sp->ReadPointerFromMemory(
m_task_ptr + ChildFragmentOffset, status);
if (status.Fail() || parent_addr == LLDB_INVALID_ADDRESS)
parent_addr = 0;
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is this really what we want to do here? When the task has no parent, does the runtime write a 0 to its slot, or do we expect an error?

If the runtime is explicitly writing a 0 and we don't expect the memory read to fail, I think we can just return nullptr here.

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For the case of a parent-less task, should we try to customize the formatter output to say something "root task" or "no parent", instead of 0s?

I think 0s could give users the impression that the debugger failed to get the value

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When the task has no parent, does the runtime write a 0 to its slot

A swift Task can have tail allocated "fragments", including a ChildFragment. Child tasks have a ChildFragment, while root tasks do not.

One way to model that is to make the existence of a parent conditional. In other words, for a root task, no parent member will be shown at all. The reason I didn't do that is:

  1. Users might find it confusing (why is there a parent some times, but not other times)
  2. It makes the synthetic child provider more complex (which is fine if we have good reason)

For the case of a parent-less task, should we try to customize the formatter output to say something "root task" or "no parent", instead of 0s?

The parent member needs a data type, which currently is UnsafeRawPointer. To show a task-specific string like "root task", we'd need to use some other data type, one we invent ourselves. This adds complexity, and will be exposed to users who might wonder "what's a LLDBParentTaskPointer?".

We could put a string like "root task" into Task's summary formatter. In which case the parent = 0x0000... would be accompanied with "root task" in the summary string, which should explain the parent address.

On this subject, one of the questions I have for reviewers is the name of this member. I used parent, but felt like make it should be parent_addr. The main reason I didn't do that is the provider has an address field, and I didn't like the inconsistency of using address and addr, and I didn't like the verbose choice of parent_address. Maybe we can rename address to addr, and then use parent_addr. Thoughts? I think including addr in the name might make it more clear that a bunch of zeros means root task/no parent.

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A swift Task can have tail allocated "fragments", including a ChildFragment. Child tasks have a ChildFragment, while root tasks do not.

I misspoke. A root task will of course have a ChildFragment if it has children.

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Adrian's suggestion is to have the parent's type be UnsafeRawPointer?, and will show nil when there's no parent. Works for me, what do you think Felipe?

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yup that sounds good to me!

}
}
addr_t value = parent_addr;
DataExtractor data{reinterpret_cast<const void *>(&value),
sizeof(value), endian::InlHostByteOrder(),
sizeof(void *)};
m_parent_task_sp = ValueObject::CreateValueObjectFromData(
"parent", data, m_backend.GetExecutionContextRef(),
raw_pointer_type);
}
return m_parent_task_sp;
}
case 4: {
if (!m_child_tasks_sp) {
using task_type = decltype(m_task_info.childTasks)::value_type;
std::vector<task_type> tasks = m_task_info.childTasks;
Expand Down Expand Up @@ -901,26 +936,26 @@ class TaskSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
}
return m_child_tasks_sp;
}
case 4:
RETURN_CHILD(m_is_child_task_sp, isChildTask, bool_type);
case 5:
RETURN_CHILD(m_is_future_sp, isFuture, bool_type);
RETURN_CHILD(m_is_child_task_sp, isChildTask, bool_type);
case 6:
RETURN_CHILD(m_is_group_child_task_sp, isGroupChildTask, bool_type);
RETURN_CHILD(m_is_future_sp, isFuture, bool_type);
case 7:
RETURN_CHILD(m_is_async_let_task_sp, isAsyncLetTask, bool_type);
RETURN_CHILD(m_is_group_child_task_sp, isGroupChildTask, bool_type);
case 8:
RETURN_CHILD(m_is_cancelled_sp, isCancelled, bool_type);
RETURN_CHILD(m_is_async_let_task_sp, isAsyncLetTask, bool_type);
case 9:
RETURN_CHILD(m_is_cancelled_sp, isCancelled, bool_type);
case 10:
RETURN_CHILD(m_is_status_record_locked_sp, isStatusRecordLocked,
bool_type);
case 10:
RETURN_CHILD(m_is_escalated_sp, isEscalated, bool_type);
case 11:
RETURN_CHILD(m_is_enqueued_sp, isEnqueued, bool_type);
RETURN_CHILD(m_is_escalated_sp, isEscalated, bool_type);
case 12:
RETURN_CHILD(m_is_enqueued_sp, isEnqueued, bool_type);
case 13:
RETURN_CHILD(m_is_complete_sp, isComplete, bool_type);
case 13: {
case 14: {
if (m_task_info.hasIsRunning)
RETURN_CHILD(m_is_running_sp, isRunning, bool_type);
return {};
Expand Down Expand Up @@ -953,8 +988,8 @@ class TaskSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
m_is_child_task_sp, m_is_future_sp, m_is_group_child_task_sp,
m_is_async_let_task_sp, m_is_cancelled_sp,
m_is_status_record_locked_sp, m_is_escalated_sp,
m_is_enqueued_sp, m_is_complete_sp, m_child_tasks_sp,
m_is_running_sp})
m_is_enqueued_sp, m_is_complete_sp, m_parent_task_sp,
m_child_tasks_sp, m_is_running_sp})
child.reset();
}
}
Expand Down Expand Up @@ -990,6 +1025,7 @@ class TaskSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
ValueObjectSP m_is_escalated_sp;
ValueObjectSP m_is_enqueued_sp;
ValueObjectSP m_is_complete_sp;
ValueObjectSP m_parent_task_sp;
ValueObjectSP m_child_tasks_sp;
ValueObjectSP m_is_running_sp;
};
Expand Down Expand Up @@ -1280,8 +1316,6 @@ class TaskGroupSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
bool operator==(const Task &other) const { return addr == other.addr; }
bool operator!=(const Task &other) const { return !(*this == other); }

static constexpr offset_t AsyncTaskSize = sizeof(::swift::AsyncTask);
static constexpr offset_t ChildFragmentOffset = AsyncTaskSize;
static constexpr offset_t NextChildOffset = ChildFragmentOffset + 0x8;

Task getNextChild(Status &status) {
Expand Down