| // Copyright 2019 The Fuchsia Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #include "src/developer/debug/zxdb/expr/resolve_base.h" |
| |
| #include "src/developer/debug/zxdb/common/string_util.h" |
| #include "src/developer/debug/zxdb/expr/cast.h" |
| #include "src/developer/debug/zxdb/expr/eval_context.h" |
| #include "src/developer/debug/zxdb/expr/expr_parser.h" |
| #include "src/developer/debug/zxdb/expr/find_name.h" |
| #include "src/developer/debug/zxdb/expr/resolve_collection.h" |
| #include "src/developer/debug/zxdb/expr/resolve_ptr_ref.h" |
| #include "src/developer/debug/zxdb/expr/resolve_type.h" |
| #include "src/developer/debug/zxdb/symbols/collection.h" |
| #include "src/developer/debug/zxdb/symbols/data_member.h" |
| #include "src/developer/debug/zxdb/symbols/elf_symbol.h" |
| #include "src/developer/debug/zxdb/symbols/location.h" |
| #include "src/developer/debug/zxdb/symbols/modified_type.h" |
| #include "src/developer/debug/zxdb/symbols/symbol_utils.h" |
| |
| namespace zxdb { |
| |
| namespace { |
| |
| // When a class has a vtable, the pointer to the vtable is generated as a member of the class' data. |
| // This member is marked with DW_AT_artificial and named "_vptr.MyClass" by GCC and "_vptr$MyClass" |
| // by Clang, where "MyClass" is the name of the class. There is no scoping information on the name |
| // (namespaces, etc.). |
| const char kVtableMemberPrefix[] = "_vptr"; |
| |
| // The Clang demangler produces this prefix for vtable symbols. |
| const char kVtableSymbolNamePrefix[] = "vtable for "; |
| |
| } // namespace |
| |
| // The code would be a little simpler if we just tried to dereference the pointer/reference and |
| // then check for the vtable member. But this will be called a lot when evaluating collections, |
| // usually won't match, and the dereference will require a slow memory fetch. By checking the |
| // pointed-to/referenced type first, we avoid this overhead. |
| void PromotePtrRefToDerived(const fxl::RefPtr<EvalContext>& context, PromoteToDerived what, |
| ExprValue value, EvalCallback cb) { |
| // Errors in this function should issue the callback with the original value. Errors mean that |
| // promotion has failed, but we can still handle the original base class pointer. |
| if (!value.type()) |
| return cb(std::move(value)); |
| |
| // Type must be the right match pointer or a reference. |
| fxl::RefPtr<ModifiedType> mod_type = context->GetConcreteTypeAs<ModifiedType>(value.type()); |
| if (!mod_type) |
| return cb(std::move(value)); |
| |
| bool tag_match = false; |
| switch (what) { |
| case PromoteToDerived::kPtrOnly: |
| tag_match = (mod_type->tag() == DwarfTag::kPointerType); |
| break; |
| case PromoteToDerived::kRefOnly: |
| tag_match = DwarfTagIsEitherReference(mod_type->tag()); |
| break; |
| case PromoteToDerived::kPtrOrRef: |
| tag_match = DwarfTagIsPointerOrReference(mod_type->tag()); |
| break; |
| } |
| if (!tag_match) |
| return cb(std::move(value)); |
| |
| // Referenced type must be a collection. Save the original non-concrete type for below. |
| const Type* original_type = mod_type->modified().Get()->As<Type>(); |
| if (!original_type) |
| return cb(std::move(value)); |
| fxl::RefPtr<Collection> modified_collection = |
| context->GetConcreteTypeAs<Collection>(original_type); |
| if (!modified_collection) |
| return cb(std::move(value)); |
| |
| // Referenced collection must have a vtable pointer. |
| fxl::RefPtr<DataMember> vtable_member = GetVtableMember(modified_collection.get()); |
| if (!vtable_member) |
| return cb(std::move(value)); |
| |
| // Type is a pointer or reference to a virtual type. Get the vtable pointer value to see where it |
| // goes. |
| TargetPointer object_loc = 0; |
| if (value.PromoteTo64(&object_loc).has_error()) |
| return cb(std::move(value)); |
| |
| // Get the value of the vtable member. We user the original (non-concrete) type so the resulting |
| // type is correct, with all C-V qualifiers. |
| TargetPointer vtable_member_loc = object_loc + vtable_member->member_location(); |
| ResolvePointer( |
| context, vtable_member_loc, RefPtrTo(vtable_member->type().Get()->As<Type>()), |
| [context, original_value = std::move(value), modifier_tag = mod_type->tag(), |
| modified_type = RefPtrTo(original_type), cb = std::move(cb)](ErrOrValue result) mutable { |
| if (result.has_error()) |
| return cb(std::move(original_value)); |
| |
| TargetPointer vtable = 0; |
| if (result.value().PromoteTo64(&vtable).has_error()) |
| return cb(std::move(original_value)); |
| |
| fxl::RefPtr<Type> derived_type = DerivedTypeForVtable(context, vtable); |
| if (!derived_type) |
| return cb(std::move(original_value)); |
| |
| // Cast to the desired destination type. It should have the same type pattern as the |
| // original: [ <C-V qualifier> ] + <pointer or reference> + [ <C-V qualifier> ] We did two |
| // GetConcreteType() calls on each side of the ptr/ref and those stripped qualifiers need to |
| // be put back. |
| // |
| // This code isn't perfect and will get confused if there are typedefs. Copying the C-V |
| // qualifier will stop at typedefs, but the typedef could expand to something with a |
| // qualifier like "const Foo" and this code would miss it. This gets very complicated and |
| // the debugger doesn't actually follow qualifiers. This seems good enough for now. |
| auto dest_type = AddCVQualifiersToMatch(modified_type.get(), std::move(derived_type)); |
| dest_type = fxl::MakeRefCounted<ModifiedType>(modifier_tag, std::move(dest_type)); |
| dest_type = AddCVQualifiersToMatch(original_value.type(), std::move(dest_type)); |
| CastExprValue(context, CastType::kStatic, original_value, dest_type, ExprValueSource(), |
| [original_value, cb = std::move(cb)](ErrOrValue value) mutable { |
| // Discard casting errors to just use the original value. |
| if (value.has_error()) |
| cb(std::move(original_value)); |
| else |
| cb(value.value()); |
| }); |
| }); |
| } |
| |
| fxl::RefPtr<DataMember> GetVtableMember(const Collection* coll) { |
| for (const auto& lazy_member : coll->data_members()) { |
| const DataMember* member = lazy_member.Get()->As<DataMember>(); |
| if (!member) |
| continue; |
| |
| if (member->artificial() && StringStartsWith(member->GetAssignedName(), kVtableMemberPrefix)) |
| return RefPtrTo(member); |
| } |
| return fxl::RefPtr<DataMember>(); |
| } |
| |
| std::string TypeNameForVtableSymbolName(const std::string& sym_name) { |
| if (!StringStartsWith(sym_name, kVtableSymbolNamePrefix)) |
| return std::string(); |
| return sym_name.substr(std::size(kVtableSymbolNamePrefix) - 1); // Trim the prefix w/o the null. |
| } |
| |
| fxl::RefPtr<Type> DerivedTypeForVtable(const fxl::RefPtr<EvalContext>& context, TargetPointer ptr) { |
| Location loc = context->GetLocationForAddress(ptr); |
| if (!loc.symbol()) |
| return nullptr; |
| |
| // Expect vtable symbols to be ELF ones. There won't be DWARF entries since they don't appear in |
| // the program. |
| const ElfSymbol* elf_symbol = loc.symbol().Get()->As<ElfSymbol>(); |
| if (!elf_symbol) |
| return nullptr; |
| |
| std::string type_name = TypeNameForVtableSymbolName(elf_symbol->GetAssignedName()); |
| if (type_name.empty()) |
| return nullptr; // Not a vtable entry. |
| |
| ParsedIdentifier ident; |
| if (ExprParser::ParseIdentifier(type_name, &ident).has_error()) |
| return nullptr; // Type name not parseable. |
| |
| return FindTypeDefinition(context->GetFindNameContext(), std::move(ident)); |
| } |
| |
| } // namespace zxdb |