[LLDB] Do not dereference promise pointer in `coroutine_handle` pretty printer

So far, the pretty printer for `std::coroutine_handle` internally
dereferenced the contained frame pointer displayed the `promise`
as a sub-value. As noticed in https://reviews.llvm.org/D132624
by @labath, this can lead to an endless loop in lldb during printing
if the coroutine frame pointers form a cycle.

This commit breaks the cycle by exposing the `promise` as a pointer
type instead of a value type. The depth to which the `frame variable`
and the `expression` commands dereference those pointers can be
controlled using the `--ptr-depth` argument.

Differential Revision: https://reviews.llvm.org/D132815

diff --git a/lldb/packages/Python/lldbsuite/test/lldbtest.py b/lldb/packages/Python/lldbsuite/test/lldbtest.py
index 97fe14e..e2c0761 100644 (file)
--- a/lldb/packages/Python/lldbsuite/test/lldbtest.py
+++ b/lldb/packages/Python/lldbsuite/test/lldbtest.py
@@ -247,7 +247,7 @@ def which(program):
 
 class ValueCheck:
     def __init__(self, name=None, value=None, type=None, summary=None,
-                 children=None):
+                 children=None, dereference=None):
         """
         :param name: The name that the SBValue should have. None if the summary
                      should not be checked.
@@ -262,12 +262,15 @@ class ValueCheck:
                          The order of checks is the order of the checks in the
                          list. The number of checks has to match the number of
                          children.
+        :param dereference: A ValueCheck for the SBValue returned by the
+                            `Dereference` function.
         """
         self.expect_name = name
         self.expect_value = value
         self.expect_type = type
         self.expect_summary = summary
         self.children = children
+        self.dereference = dereference
 
     def check_value(self, test_base, val, error_msg=None):
         """
@@ -309,6 +312,9 @@ class ValueCheck:
         if self.children is not None:
             self.check_value_children(test_base, val, error_msg)
 
+        if self.dereference is not None:
+            self.dereference.check_value(test_base, val.Dereference(), error_msg)
+
     def check_value_children(self, test_base, val, error_msg=None):
         """
         Checks that the children of a SBValue match a certain structure and

diff --git a/lldb/source/Plugins/Language/CPlusPlus/Coroutines.cpp b/lldb/source/Plugins/Language/CPlusPlus/Coroutines.cpp
index bd9ff99..bd428a8 100644 (file)
--- a/lldb/source/Plugins/Language/CPlusPlus/Coroutines.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/Coroutines.cpp
@@ -17,38 +17,37 @@ using namespace lldb;
 using namespace lldb_private;
 using namespace lldb_private::formatters;
 
-static ValueObjectSP GetCoroFramePtrFromHandle(ValueObject &valobj) {
-  ValueObjectSP valobj_sp(valobj.GetNonSyntheticValue());
+static lldb::addr_t GetCoroFramePtrFromHandle(ValueObjectSP valobj_sp) {
   if (!valobj_sp)
-    return nullptr;
+    return LLDB_INVALID_ADDRESS;
 
   // We expect a single pointer in the `coroutine_handle` class.
   // We don't care about its name.
   if (valobj_sp->GetNumChildren() != 1)
-    return nullptr;
+    return LLDB_INVALID_ADDRESS;
   ValueObjectSP ptr_sp(valobj_sp->GetChildAtIndex(0, true));
   if (!ptr_sp)
-    return nullptr;
+    return LLDB_INVALID_ADDRESS;
   if (!ptr_sp->GetCompilerType().IsPointerType())
-    return nullptr;
-
-  return ptr_sp;
-}
-
-static Function *ExtractDestroyFunction(ValueObjectSP &frame_ptr_sp) {
-  lldb::TargetSP target_sp = frame_ptr_sp->GetTargetSP();
-  lldb::ProcessSP process_sp = frame_ptr_sp->GetProcessSP();
-  auto ptr_size = process_sp->GetAddressByteSize();
+    return LLDB_INVALID_ADDRESS;
 
   AddressType addr_type;
-  lldb::addr_t frame_ptr_addr = frame_ptr_sp->GetPointerValue(&addr_type);
+  lldb::addr_t frame_ptr_addr = ptr_sp->GetPointerValue(&addr_type);
   if (!frame_ptr_addr || frame_ptr_addr == LLDB_INVALID_ADDRESS)
-    return nullptr;
+    return LLDB_INVALID_ADDRESS;
   lldbassert(addr_type == AddressType::eAddressTypeLoad);
+  if (addr_type != AddressType::eAddressTypeLoad)
+    return LLDB_INVALID_ADDRESS;
+
+  return frame_ptr_addr;
+}
+
+static Function *ExtractDestroyFunction(lldb::TargetSP target_sp,
+                                        lldb::addr_t frame_ptr_addr) {
+  lldb::ProcessSP process_sp = target_sp->GetProcessSP();
+  auto ptr_size = process_sp->GetAddressByteSize();
 
   Status error;
-  // The destroy pointer is the 2nd pointer inside the compiler-generated
-  // `pair<resumePtr,destroyPtr>`.
   auto destroy_func_ptr_addr = frame_ptr_addr + ptr_size;
   lldb::addr_t destroy_func_addr =
       process_sp->ReadPointerFromMemory(destroy_func_ptr_addr, error);
@@ -59,12 +58,7 @@ static Function *ExtractDestroyFunction(ValueObjectSP &frame_ptr_sp) {
   if (!target_sp->ResolveLoadAddress(destroy_func_addr, destroy_func_address))
     return nullptr;
 
-  Function *destroy_func =
-      destroy_func_address.CalculateSymbolContextFunction();
-  if (!destroy_func)
-    return nullptr;
-
-  return destroy_func;
+  return destroy_func_address.CalculateSymbolContextFunction();
 }
 
 static CompilerType InferPromiseType(Function &destroy_func) {
@@ -85,37 +79,19 @@ static CompilerType InferPromiseType(Function &destroy_func) {
   return promise_type->GetForwardCompilerType();
 }
 
-static CompilerType GetCoroutineFrameType(TypeSystemClang &ast_ctx,
-                                          CompilerType promise_type) {
-  CompilerType void_type = ast_ctx.GetBasicType(lldb::eBasicTypeVoid);
-  CompilerType coro_func_type = ast_ctx.CreateFunctionType(
-      /*result_type=*/void_type, /*args=*/&void_type, /*num_args=*/1,
-      /*is_variadic=*/false, /*qualifiers=*/0);
-  CompilerType coro_abi_type;
-  if (promise_type.IsVoidType()) {
-    coro_abi_type = ast_ctx.CreateStructForIdentifier(
-        ConstString(), {{"resume", coro_func_type.GetPointerType()},
-                        {"destroy", coro_func_type.GetPointerType()}});
-  } else {
-    coro_abi_type = ast_ctx.CreateStructForIdentifier(
-        ConstString(), {{"resume", coro_func_type.GetPointerType()},
-                        {"destroy", coro_func_type.GetPointerType()},
-                        {"promise", promise_type}});
-  }
-  return coro_abi_type;
-}
-
 bool lldb_private::formatters::StdlibCoroutineHandleSummaryProvider(
     ValueObject &valobj, Stream &stream, const TypeSummaryOptions &options) {
-  ValueObjectSP ptr_sp(GetCoroFramePtrFromHandle(valobj));
-  if (!ptr_sp)
+  lldb::addr_t frame_ptr_addr =
+      GetCoroFramePtrFromHandle(valobj.GetNonSyntheticValue());
+  if (frame_ptr_addr == LLDB_INVALID_ADDRESS)
     return false;
 
-  if (!ptr_sp->GetValueAsUnsigned(0)) {
+  if (frame_ptr_addr == 0) {
     stream << "nullptr";
   } else {
-    stream.Printf("coro frame = 0x%" PRIx64, ptr_sp->GetValueAsUnsigned(0));
+    stream.Printf("coro frame = 0x%" PRIx64, frame_ptr_addr);
   }
+
   return true;
 }
 
@@ -132,32 +108,61 @@ lldb_private::formatters::StdlibCoroutineHandleSyntheticFrontEnd::
 
 size_t lldb_private::formatters::StdlibCoroutineHandleSyntheticFrontEnd::
     CalculateNumChildren() {
-  if (!m_frame_ptr_sp)
+  if (!m_resume_ptr_sp || !m_destroy_ptr_sp)
     return 0;
 
-  return m_frame_ptr_sp->GetNumChildren();
+  return m_promise_ptr_sp ? 3 : 2;
 }
 
 lldb::ValueObjectSP lldb_private::formatters::
     StdlibCoroutineHandleSyntheticFrontEnd::GetChildAtIndex(size_t idx) {
-  if (!m_frame_ptr_sp)
-    return lldb::ValueObjectSP();
-
-  return m_frame_ptr_sp->GetChildAtIndex(idx, true);
+  switch (idx) {
+  case 0:
+    return m_resume_ptr_sp;
+  case 1:
+    return m_destroy_ptr_sp;
+  case 2:
+    return m_promise_ptr_sp;
+  }
+  return lldb::ValueObjectSP();
 }
 
 bool lldb_private::formatters::StdlibCoroutineHandleSyntheticFrontEnd::
     Update() {
-  m_frame_ptr_sp.reset();
+  m_resume_ptr_sp.reset();
+  m_destroy_ptr_sp.reset();
+  m_promise_ptr_sp.reset();
 
-  ValueObjectSP valobj_sp = m_backend.GetSP();
+  ValueObjectSP valobj_sp = m_backend.GetNonSyntheticValue();
   if (!valobj_sp)
     return false;
 
-  ValueObjectSP ptr_sp(GetCoroFramePtrFromHandle(m_backend));
-  if (!ptr_sp)
+  lldb::addr_t frame_ptr_addr = GetCoroFramePtrFromHandle(valobj_sp);
+  if (frame_ptr_addr == 0 || frame_ptr_addr == LLDB_INVALID_ADDRESS)
+    return false;
+
+  auto ts = valobj_sp->GetCompilerType().GetTypeSystem();
+  auto ast_ctx = ts.dyn_cast_or_null<TypeSystemClang>();
+  if (!ast_ctx)
     return false;
 
+  // Create the `resume` and `destroy` children.
+  lldb::TargetSP target_sp = m_backend.GetTargetSP();
+  auto &exe_ctx = m_backend.GetExecutionContextRef();
+  lldb::ProcessSP process_sp = target_sp->GetProcessSP();
+  auto ptr_size = process_sp->GetAddressByteSize();
+  CompilerType void_type = ast_ctx->GetBasicType(lldb::eBasicTypeVoid);
+  CompilerType coro_func_type = ast_ctx->CreateFunctionType(
+      /*result_type=*/void_type, /*args=*/&void_type, /*num_args=*/1,
+      /*is_variadic=*/false, /*qualifiers=*/0);
+  CompilerType coro_func_ptr_type = coro_func_type.GetPointerType();
+  m_resume_ptr_sp = CreateValueObjectFromAddress(
+      "resume", frame_ptr_addr + 0 * ptr_size, exe_ctx, coro_func_ptr_type);
+  lldbassert(m_resume_ptr_sp);
+  m_destroy_ptr_sp = CreateValueObjectFromAddress(
+      "destroy", frame_ptr_addr + 1 * ptr_size, exe_ctx, coro_func_ptr_type);
+  lldbassert(m_destroy_ptr_sp);
+
   // Get the `promise_type` from the template argument
   CompilerType promise_type(
       valobj_sp->GetCompilerType().GetTypeTemplateArgument(0));
@@ -165,12 +170,9 @@ bool lldb_private::formatters::StdlibCoroutineHandleSyntheticFrontEnd::
     return false;
 
   // Try to infer the promise_type if it was type-erased
-  auto ts = valobj_sp->GetCompilerType().GetTypeSystem();
-  auto ast_ctx = ts.dyn_cast_or_null<TypeSystemClang>();
-  if (!ast_ctx)
-    return false;
   if (promise_type.IsVoidType()) {
-    if (Function *destroy_func = ExtractDestroyFunction(ptr_sp)) {
+    if (Function *destroy_func =
+            ExtractDestroyFunction(target_sp, frame_ptr_addr)) {
       if (CompilerType inferred_type = InferPromiseType(*destroy_func)) {
         // Copy the type over to the correct `TypeSystemClang` instance
         promise_type = m_ast_importer->CopyType(*ast_ctx, inferred_type);
@@ -178,10 +180,22 @@ bool lldb_private::formatters::StdlibCoroutineHandleSyntheticFrontEnd::
     }
   }
 
-  // Build the coroutine frame type
-  CompilerType coro_frame_type = GetCoroutineFrameType(*ast_ctx, promise_type);
+  // If we don't know the promise type, we don't display the `promise` member.
+  // `CreateValueObjectFromAddress` below would fail for `void` types.
+  if (promise_type.IsVoidType()) {
+    return false;
+  }
 
-  m_frame_ptr_sp = ptr_sp->Cast(coro_frame_type.GetPointerType());
+  // Add the `promise` member. We intentionally add `promise` as a pointer type
+  // instead of a value type, and don't automatically dereference this pointer.
+  // We do so to avoid potential very deep recursion in case there is a cycle
+  // formed between `std::coroutine_handle`s and their promises.
+  lldb::ValueObjectSP promise = CreateValueObjectFromAddress(
+      "promise", frame_ptr_addr + 2 * ptr_size, exe_ctx, promise_type);
+  Status error;
+  lldb::ValueObjectSP promisePtr = promise->AddressOf(error);
+  if (error.Success())
+    m_promise_ptr_sp = promisePtr->Clone(ConstString("promise"));
 
   return false;
 }
@@ -193,10 +207,17 @@ bool lldb_private::formatters::StdlibCoroutineHandleSyntheticFrontEnd::
 
 size_t StdlibCoroutineHandleSyntheticFrontEnd::GetIndexOfChildWithName(
     ConstString name) {
-  if (!m_frame_ptr_sp)
+  if (!m_resume_ptr_sp || !m_destroy_ptr_sp)
     return UINT32_MAX;
 
-  return m_frame_ptr_sp->GetIndexOfChildWithName(name);
+  if (name == ConstString("resume"))
+    return 0;
+  if (name == ConstString("destroy"))
+    return 1;
+  if (name == ConstString("promise_ptr") && m_promise_ptr_sp)
+    return 2;
+
+  return UINT32_MAX;
 }
 
 SyntheticChildrenFrontEnd *

diff --git a/lldb/source/Plugins/Language/CPlusPlus/Coroutines.h b/lldb/source/Plugins/Language/CPlusPlus/Coroutines.h
index c052bd2..e2e640a 100644 (file)
--- a/lldb/source/Plugins/Language/CPlusPlus/Coroutines.h
+++ b/lldb/source/Plugins/Language/CPlusPlus/Coroutines.h
@@ -47,7 +47,9 @@ public:
   size_t GetIndexOfChildWithName(ConstString name) override;
 
 private:
-  lldb::ValueObjectSP m_frame_ptr_sp;
+  lldb::ValueObjectSP m_resume_ptr_sp;
+  lldb::ValueObjectSP m_destroy_ptr_sp;
+  lldb::ValueObjectSP m_promise_ptr_sp;
   std::unique_ptr<lldb_private::ClangASTImporter> m_ast_importer;
 };
 

diff --git a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/coroutine_handle/TestCoroutineHandle.py b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/coroutine_handle/TestCoroutineHandle.py
index 44e5e64..4edf3eb 100644 (file)
--- a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/coroutine_handle/TestCoroutineHandle.py
+++ b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/coroutine_handle/TestCoroutineHandle.py
@@ -61,7 +61,7 @@ class TestCoroutineHandle(TestBase):
                 result_children=[
                     ValueCheck(name="resume", summary = test_generator_func_ptr_re),
                     ValueCheck(name="destroy", summary = test_generator_func_ptr_re),
-                    ValueCheck(name="promise", value="-1")
+                    ValueCheck(name="promise", dereference=ValueCheck(value="-1"))
                 ])
 
         # Run until after the `co_yield`