llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT--> @llvm/pr-subscribers-lldb Author: Michael Buch (Michael137) <details> <summary>Changes</summary> Depends on: * https://github.com/llvm/llvm-project/pull/97544 * https://github.com/llvm/llvm-project/pull/97549 * https://github.com/llvm/llvm-project/pull/97551 This patch tries to simplify the way in which the `std::map` formatter goes from the root `__tree` pointer to a specific key/value pair. Previously we would synthesize a structure that mimicked what `__iter_pointer` looked like in memory, then called `GetChildCompilerTypeAtIndex` on it to find the byte offset into that structure at which the pair was located at, and finally use that offset through a call to `GetSyntheticChildAtOffset` to retrieve that pair. Not only was this logic hard to follow, and encoded the libc++ layout in non-obvious ways, it was also fragile to alignment miscalculations (https://github.com/llvm/llvm-project/pull/97443); this would break after the new layout of std::map landed as part of inhttps://github.com/https://github.com/llvm/llvm-project/issues/93069. Instead, this patch simply casts the `__iter_pointer` to the `__node_pointer` and uses a straightforward `GetChildMemberWithName("__value_")` to get to the key/value we care about. This allows us to get rid of some support infrastructure/class state. Ideally we would fix the underlying alignment issue, but this unblocks the libc++ refactor in the interim, while also benefitting the formatter in terms of readability (in my opinion). --- Full diff: https://github.com/llvm/llvm-project/pull/97579.diff 1 Files Affected: - (modified) lldb/source/Plugins/Language/CPlusPlus/LibCxxMap.cpp (+93-140) ``````````diff diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibCxxMap.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibCxxMap.cpp index 44fe294ced722..120f3ac131b34 100644 --- a/lldb/source/Plugins/Language/CPlusPlus/LibCxxMap.cpp +++ b/lldb/source/Plugins/Language/CPlusPlus/LibCxxMap.cpp @@ -17,11 +17,32 @@ #include "lldb/Utility/Endian.h" #include "lldb/Utility/Status.h" #include "lldb/Utility/Stream.h" +#include "lldb/lldb-forward.h" +#include <cstdint> +#include <locale> +#include <optional> using namespace lldb; using namespace lldb_private; using namespace lldb_private::formatters; +// The flattened layout of the std::__tree_iterator::__ptr_ looks +// as follows: +// +// The following shows the contiguous block of memory: +// +// +-----------------------------+ class __tree_end_node +// __ptr_ | pointer __left_; | +// +-----------------------------+ class __tree_node_base +// | pointer __right_; | +// | __parent_pointer __parent_; | +// | bool __is_black_; | +// +-----------------------------+ class __tree_node +// | __node_value_type __value_; | <<< our key/value pair +// +-----------------------------+ +// +// where __ptr_ has type __iter_pointer. + class MapEntry { public: MapEntry() = default; @@ -180,14 +201,25 @@ class LibcxxStdMapSyntheticFrontEnd : public SyntheticChildrenFrontEnd { size_t GetIndexOfChildWithName(ConstString name) override; private: - bool GetDataType(); - - void GetValueOffset(const lldb::ValueObjectSP &node); + /// Returns the ValueObject for the __tree_node type that + /// holds the key/value pair of the node at index \ref idx. + /// + /// \param[in] idx The child index that we're looking to get + /// the key/value pair for. + /// + /// \param[in] max_depth The maximum search depth after which + /// we stop trying to find the key/value + /// pair for. + /// + /// \returns On success, returns the ValueObjectSP corresponding + /// to the __tree_node's __value_ member (which holds + /// the key/value pair the formatter wants to display). + /// On failure, will return nullptr. + ValueObjectSP GetKeyValuePair(size_t idx, size_t max_depth); ValueObject *m_tree = nullptr; ValueObject *m_root_node = nullptr; - CompilerType m_element_type; - uint32_t m_skip_size = UINT32_MAX; + CompilerType m_node_ptr_type; size_t m_count = UINT32_MAX; std::map<size_t, MapIterator> m_iterators; }; @@ -196,7 +228,7 @@ class LibcxxStdMapSyntheticFrontEnd : public SyntheticChildrenFrontEnd { lldb_private::formatters::LibcxxStdMapSyntheticFrontEnd:: LibcxxStdMapSyntheticFrontEnd(lldb::ValueObjectSP valobj_sp) - : SyntheticChildrenFrontEnd(*valobj_sp), m_element_type(), m_iterators() { + : SyntheticChildrenFrontEnd(*valobj_sp) { if (valobj_sp) Update(); } @@ -222,81 +254,52 @@ llvm::Expected<uint32_t> lldb_private::formatters:: return m_count; } -bool lldb_private::formatters::LibcxxStdMapSyntheticFrontEnd::GetDataType() { - if (m_element_type.IsValid()) - return true; - m_element_type.Clear(); - ValueObjectSP deref; - Status error; - deref = m_root_node->Dereference(error); - if (!deref || error.Fail()) - return false; - deref = deref->GetChildMemberWithName("__value_"); - if (deref) { - m_element_type = deref->GetCompilerType(); - return true; - } - deref = m_backend.GetChildAtNamePath({"__tree_", "__pair3_"}); - if (!deref) - return false; - m_element_type = deref->GetCompilerType() - .GetTypeTemplateArgument(1) - .GetTypeTemplateArgument(1); - if (m_element_type) { - std::string name; - uint64_t bit_offset_ptr; - uint32_t bitfield_bit_size_ptr; - bool is_bitfield_ptr; - m_element_type = m_element_type.GetFieldAtIndex( - 0, name, &bit_offset_ptr, &bitfield_bit_size_ptr, &is_bitfield_ptr); - m_element_type = m_element_type.GetTypedefedType(); - return m_element_type.IsValid(); - } else { - m_element_type = m_backend.GetCompilerType().GetTypeTemplateArgument(0); - return m_element_type.IsValid(); - } -} +ValueObjectSP +lldb_private::formatters::LibcxxStdMapSyntheticFrontEnd::GetKeyValuePair( + size_t idx, size_t max_depth) { + MapIterator iterator(m_root_node, max_depth); -void lldb_private::formatters::LibcxxStdMapSyntheticFrontEnd::GetValueOffset( - const lldb::ValueObjectSP &node) { - if (m_skip_size != UINT32_MAX) - return; - if (!node) - return; - CompilerType node_type(node->GetCompilerType()); - uint64_t bit_offset; - if (node_type.GetIndexOfFieldWithName("__value_", nullptr, &bit_offset) != - UINT32_MAX) { - // Old layout (pre 089a7cc5dea) - m_skip_size = bit_offset / 8u; - } else { - auto ast_ctx = node_type.GetTypeSystem().dyn_cast_or_null<TypeSystemClang>(); - if (!ast_ctx) - return; - CompilerType tree_node_type = ast_ctx->CreateStructForIdentifier( - llvm::StringRef(), - {{"ptr0", ast_ctx->GetBasicType(lldb::eBasicTypeVoid).GetPointerType()}, - {"ptr1", ast_ctx->GetBasicType(lldb::eBasicTypeVoid).GetPointerType()}, - {"ptr2", ast_ctx->GetBasicType(lldb::eBasicTypeVoid).GetPointerType()}, - {"cw", ast_ctx->GetBasicType(lldb::eBasicTypeBool)}, - {"payload", (m_element_type.GetCompleteType(), m_element_type)}}); - std::string child_name; - uint32_t child_byte_size; - int32_t child_byte_offset = 0; - uint32_t child_bitfield_bit_size; - uint32_t child_bitfield_bit_offset; - bool child_is_base_class; - bool child_is_deref_of_parent; - uint64_t language_flags; - auto child_type = - llvm::expectedToStdOptional(tree_node_type.GetChildCompilerTypeAtIndex( - nullptr, 4, true, true, true, child_name, child_byte_size, - child_byte_offset, child_bitfield_bit_size, - child_bitfield_bit_offset, child_is_base_class, - child_is_deref_of_parent, nullptr, language_flags)); - if (child_type && child_type->IsValid()) - m_skip_size = (uint32_t)child_byte_offset; + size_t advance_by = idx; + if (idx > 0) { + // If we have already created the iterator for the previous + // index, we can start from there and advance by 1. + auto cached_iterator = m_iterators.find(idx - 1); + if (cached_iterator != m_iterators.end()) { + iterator = cached_iterator->second; + advance_by = 1; + } } + + ValueObjectSP iterated_sp(iterator.advance(advance_by)); + if (!iterated_sp) + // this tree is garbage - stop + return nullptr; + + if (!m_node_ptr_type.IsValid()) + return nullptr; + + // iterated_sp is a __iter_pointer at this point. + // We can cast it to a __node_pointer (which is what libc++ does). + auto value_type_sp = iterated_sp->Cast(m_node_ptr_type); + if (!value_type_sp) + return nullptr; + + // After dereferencing the __node_pointer, we will have a handle to + // a std::__1::__tree_node<void *>, which has the __value_ member + // we are looking for. + Status s; + value_type_sp = value_type_sp->Dereference(s); + if (!value_type_sp || s.Fail()) + return nullptr; + + // Finally, get the key/value pair. + value_type_sp = value_type_sp->GetChildMemberWithName("__value_"); + if (!value_type_sp) + return nullptr; + + m_iterators[idx] = iterator; + + return value_type_sp; } lldb::ValueObjectSP @@ -306,68 +309,16 @@ lldb_private::formatters::LibcxxStdMapSyntheticFrontEnd::GetChildAtIndex( static ConstString g_nc("__nc"); uint32_t num_children = CalculateNumChildrenIgnoringErrors(); if (idx >= num_children) - return lldb::ValueObjectSP(); - if (m_tree == nullptr || m_root_node == nullptr) - return lldb::ValueObjectSP(); + return nullptr; - MapIterator iterator(m_root_node, num_children); - - const bool need_to_skip = (idx > 0); - size_t actual_advancde = idx; - if (need_to_skip) { - auto cached_iterator = m_iterators.find(idx - 1); - if (cached_iterator != m_iterators.end()) { - iterator = cached_iterator->second; - actual_advancde = 1; - } - } - - ValueObjectSP iterated_sp(iterator.advance(actual_advancde)); - if (!iterated_sp) { - // this tree is garbage - stop - m_tree = - nullptr; // this will stop all future searches until an Update() happens - return iterated_sp; - } + if (m_tree == nullptr || m_root_node == nullptr) + return nullptr; - if (!GetDataType()) { + ValueObjectSP key_val_sp = GetKeyValuePair(idx, /*max_depth=*/num_children); + if (!key_val_sp) { + // this will stop all future searches until an Update() happens m_tree = nullptr; - return lldb::ValueObjectSP(); - } - - if (!need_to_skip) { - Status error; - iterated_sp = iterated_sp->Dereference(error); - if (!iterated_sp || error.Fail()) { - m_tree = nullptr; - return lldb::ValueObjectSP(); - } - GetValueOffset(iterated_sp); - auto child_sp = iterated_sp->GetChildMemberWithName("__value_"); - if (child_sp) - iterated_sp = child_sp; - else - iterated_sp = iterated_sp->GetSyntheticChildAtOffset( - m_skip_size, m_element_type, true); - if (!iterated_sp) { - m_tree = nullptr; - return lldb::ValueObjectSP(); - } - } else { - // because of the way our debug info is made, we need to read item 0 - // first so that we can cache information used to generate other elements - if (m_skip_size == UINT32_MAX) - GetChildAtIndex(0); - if (m_skip_size == UINT32_MAX) { - m_tree = nullptr; - return lldb::ValueObjectSP(); - } - iterated_sp = iterated_sp->GetSyntheticChildAtOffset(m_skip_size, - m_element_type, true); - if (!iterated_sp) { - m_tree = nullptr; - return lldb::ValueObjectSP(); - } + return nullptr; } // at this point we have a valid @@ -375,7 +326,7 @@ lldb_private::formatters::LibcxxStdMapSyntheticFrontEnd::GetChildAtIndex( // all items named __value_ StreamString name; name.Printf("[%" PRIu64 "]", (uint64_t)idx); - auto potential_child_sp = iterated_sp->Clone(ConstString(name.GetString())); + auto potential_child_sp = key_val_sp->Clone(ConstString(name.GetString())); if (potential_child_sp) { switch (potential_child_sp->GetNumChildrenIgnoringErrors()) { case 1: { @@ -396,7 +347,6 @@ lldb_private::formatters::LibcxxStdMapSyntheticFrontEnd::GetChildAtIndex( } } } - m_iterators[idx] = iterator; return potential_child_sp; } @@ -409,6 +359,9 @@ lldb_private::formatters::LibcxxStdMapSyntheticFrontEnd::Update() { if (!m_tree) return lldb::ChildCacheState::eRefetch; m_root_node = m_tree->GetChildMemberWithName("__begin_node_").get(); + m_node_ptr_type = + m_tree->GetCompilerType().GetDirectNestedTypeWithName("__node_pointer"); + return lldb::ChildCacheState::eRefetch; } `````````` </details> https://github.com/llvm/llvm-project/pull/97579 _______________________________________________ lldb-commits mailing list lldb-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
