LazyReexports.h

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//===------ LazyReexports.h -- Utilities for lazy reexports -----*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Lazy re-exports are similar to normal re-exports, except that for callable
// symbols the definitions are replaced with trampolines that will look up and
// call through to the re-exported symbol at runtime. This can be used to
// enable lazy compilation.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_EXECUTIONENGINE_ORC_LAZYREEXPORTS_H
#define LLVM_EXECUTIONENGINE_ORC_LAZYREEXPORTS_H
 
#include "llvm/ADT/STLExtras.h"
#include "llvm/ExecutionEngine/Orc/Core.h"
#include "llvm/ExecutionEngine/Orc/IndirectionUtils.h"
#include "llvm/ExecutionEngine/Orc/Speculation.h"
 
namespace llvm {
 
class Triple;
 
namespace orc {
 
/// Manages a set of 'lazy call-through' trampolines. These are compiler
/// re-entry trampolines that are pre-bound to look up a given symbol in a given
/// JITDylib, then jump to that address. Since compilation of symbols is
/// triggered on first lookup, these call-through trampolines can be used to
/// implement lazy compilation.
///
/// The easiest way to construct these call-throughs is using the lazyReexport
/// function.
class LazyCallThroughManager {
public:
  using NotifyResolvedFunction =
      unique_function<Error(ExecutorAddr ResolvedAddr)>;
 
  LazyCallThroughManager(ExecutionSession &ES, ExecutorAddr ErrorHandlerAddr,
                         TrampolinePool *TP);
 
  // Return a free call-through trampoline and bind it to look up and call
  // through to the given symbol.
  Expected<ExecutorAddr>
  getCallThroughTrampoline(JITDylib &SourceJD, SymbolStringPtr SymbolName,
                           NotifyResolvedFunction NotifyResolved);
 
  void resolveTrampolineLandingAddress(
      ExecutorAddr TrampolineAddr,
      TrampolinePool::NotifyLandingResolvedFunction NotifyLandingResolved);
 
  virtual ~LazyCallThroughManager() = default;
 
protected:
  using NotifyLandingResolvedFunction =
      TrampolinePool::NotifyLandingResolvedFunction;
 
  struct ReexportsEntry {
    JITDylib *SourceJD;
    SymbolStringPtr SymbolName;
  };
 
  ExecutorAddr reportCallThroughError(Error Err);
  Expected<ReexportsEntry> findReexport(ExecutorAddr TrampolineAddr);
  Error notifyResolved(ExecutorAddr TrampolineAddr, ExecutorAddr ResolvedAddr);
  void setTrampolinePool(TrampolinePool &TP) { this->TP = &TP; }
 
private:
  using ReexportsMap = std::map<ExecutorAddr, ReexportsEntry>;
 
  using NotifiersMap = std::map<ExecutorAddr, NotifyResolvedFunction>;
 
  std::mutex LCTMMutex;
  ExecutionSession &ES;
  ExecutorAddr ErrorHandlerAddr;
  TrampolinePool *TP = nullptr;
  ReexportsMap Reexports;
  NotifiersMap Notifiers;
};
 
/// A lazy call-through manager that builds trampolines in the current process.
class LocalLazyCallThroughManager : public LazyCallThroughManager {
private:
  using NotifyTargetResolved = unique_function<void(ExecutorAddr)>;
 
  LocalLazyCallThroughManager(ExecutionSession &ES,
                              ExecutorAddr ErrorHandlerAddr)
      : LazyCallThroughManager(ES, ErrorHandlerAddr, nullptr) {}
 
  template <typename ORCABI> Error init() {
    auto TP = LocalTrampolinePool<ORCABI>::Create(
        [this](ExecutorAddr TrampolineAddr,
               TrampolinePool::NotifyLandingResolvedFunction
                   NotifyLandingResolved) {
          resolveTrampolineLandingAddress(TrampolineAddr,
                                          std::move(NotifyLandingResolved));
        });
 
    if (!TP)
      return TP.takeError();
 
    this->TP = std::move(*TP);
    setTrampolinePool(*this->TP);
    return Error::success();
  }
 
  std::unique_ptr<TrampolinePool> TP;
 
public:
  /// Create a LocalLazyCallThroughManager using the given ABI. See
  /// createLocalLazyCallThroughManager.
  template <typename ORCABI>
  static Expected<std::unique_ptr<LocalLazyCallThroughManager>>
  Create(ExecutionSession &ES, ExecutorAddr ErrorHandlerAddr) {
    auto LLCTM = std::unique_ptr<LocalLazyCallThroughManager>(
        new LocalLazyCallThroughManager(ES, ErrorHandlerAddr));
 
    if (auto Err = LLCTM->init<ORCABI>())
      return std::move(Err);
 
    return std::move(LLCTM);
  }
};
 
/// Create a LocalLazyCallThroughManager from the given triple and execution
/// session.
Expected<std::unique_ptr<LazyCallThroughManager>>
createLocalLazyCallThroughManager(const Triple &T, ExecutionSession &ES,
                                  ExecutorAddr ErrorHandlerAddr);
 
/// A materialization unit that builds lazy re-exports. These are callable
/// entry points that call through to the given symbols.
/// Unlike a 'true' re-export, the address of the lazy re-export will not
/// match the address of the re-exported symbol, but calling it will behave
/// the same as calling the re-exported symbol.
class LazyReexportsMaterializationUnit : public MaterializationUnit {
public:
  LazyReexportsMaterializationUnit(LazyCallThroughManager &LCTManager,
                                   IndirectStubsManager &ISManager,
                                   JITDylib &SourceJD,
                                   SymbolAliasMap CallableAliases,
                                   ImplSymbolMap *SrcJDLoc);
 
  StringRef getName() const override;
 
private:
  void materialize(std::unique_ptr<MaterializationResponsibility> R) override;
  void discard(const JITDylib &JD, const SymbolStringPtr &Name) override;
  static MaterializationUnit::Interface
  extractFlags(const SymbolAliasMap &Aliases);
 
  LazyCallThroughManager &LCTManager;
  IndirectStubsManager &ISManager;
  JITDylib &SourceJD;
  SymbolAliasMap CallableAliases;
  ImplSymbolMap *AliaseeTable;
};
 
/// Define lazy-reexports based on the given SymbolAliasMap. Each lazy re-export
/// is a callable symbol that will look up and dispatch to the given aliasee on
/// first call. All subsequent calls will go directly to the aliasee.
inline std::unique_ptr<LazyReexportsMaterializationUnit>
lazyReexports(LazyCallThroughManager &LCTManager,
              IndirectStubsManager &ISManager, JITDylib &SourceJD,
              SymbolAliasMap CallableAliases,
              ImplSymbolMap *SrcJDLoc = nullptr) {
  return std::make_unique<LazyReexportsMaterializationUnit>(
      LCTManager, ISManager, SourceJD, std::move(CallableAliases), SrcJDLoc);
}
 
} // End namespace orc
} // End namespace llvm
 
#endif // LLVM_EXECUTIONENGINE_ORC_LAZYREEXPORTS_H