| //===- Core/UndefinedAtom.h - An Undefined Atom ---------------------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef LLD_CORE_UNDEFINED_ATOM_H |
| #define LLD_CORE_UNDEFINED_ATOM_H |
| |
| #include "lld/Core/Atom.h" |
| |
| namespace lld { |
| |
| /// An UndefinedAtom has no content. |
| /// It exists as a placeholder for a future atom. |
| class UndefinedAtom : public Atom { |
| public: |
| /// Whether this undefined symbol needs to be resolved, |
| /// or whether it can just evaluate to nullptr. |
| /// This concept is often called "weak", but that term |
| /// is overloaded to mean other things too. |
| enum CanBeNull { |
| /// Normal symbols must be resolved at build time |
| canBeNullNever, |
| |
| /// This symbol can be missing at runtime and will evaluate to nullptr. |
| /// That is, the static linker still must find a definition (usually |
| /// is some shared library), but at runtime, the dynamic loader |
| /// will allow the symbol to be missing and resolved to nullptr. |
| /// |
| /// On Darwin this is generated using a function prototype with |
| /// __attribute__((weak_import)). |
| /// On linux this is generated using a function prototype with |
| /// __attribute__((weak)). |
| /// On Windows this feature is not supported. |
| canBeNullAtRuntime, |
| |
| /// This symbol can be missing at build time. |
| /// That is, the static linker will not error if a definition for |
| /// this symbol is not found at build time. Instead, the linker |
| /// will build an executable that lets the dynamic loader find the |
| /// symbol at runtime. |
| /// This feature is not supported on Darwin nor Windows. |
| /// On linux this is generated using a function prototype with |
| /// __attribute__((weak)). |
| canBeNullAtBuildtime |
| }; |
| |
| virtual CanBeNull canBeNull() const = 0; |
| |
| static bool classof(const Atom *a) { |
| return a->definition() == definitionUndefined; |
| } |
| |
| static bool classof(const UndefinedAtom *) { return true; } |
| |
| protected: |
| UndefinedAtom() : Atom(definitionUndefined) {} |
| |
| ~UndefinedAtom() override = default; |
| }; |
| |
| } // namespace lld |
| |
| #endif // LLD_CORE_UNDEFINED_ATOM_H |