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//===- SectionMemoryManager.h - Memory manager for MCJIT/RtDyld -*- 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

//

//===----------------------------------------------------------------------===//

//

// This file contains the declaration of a section-based memory manager used by

// the MCJIT execution engine and RuntimeDyld.

//

//===----------------------------------------------------------------------===//

#ifndef LLVM_EXECUTIONENGINE_SECTIONMEMORYMANAGER_H

#define LLVM_EXECUTIONENGINE_SECTIONMEMORYMANAGER_H

#include "llvm/ADT/SmallVector.h"

#include "llvm/ExecutionEngine/RTDyldMemoryManager.h"

#include "llvm/Support/Memory.h"

#include <cstdint>

#include <string>

#include <system_error>

namespace llvm {

/// This is a simple memory manager which implements the methods called by

/// the RuntimeDyld class to allocate memory for section-based loading of

/// objects, usually those generated by the MCJIT execution engine.

///

/// This memory manager allocates all section memory as read-write.  The

/// RuntimeDyld will copy JITed section memory into these allocated blocks

/// and perform any necessary linking and relocations.

///

/// Any client using this memory manager MUST ensure that section-specific

/// page permissions have been applied before attempting to execute functions

/// in the JITed object.  Permissions can be applied either by calling

/// MCJIT::finalizeObject or by calling SectionMemoryManager::finalizeMemory

/// directly.  Clients of MCJIT should call MCJIT::finalizeObject.

class SectionMemoryManager : public RTDyldMemoryManager {

public:

  /// This enum describes the various reasons to allocate pages from

  /// allocateMappedMemory.

  enum class AllocationPurpose {

    Code,

    ROData,

    RWData,

  };

  /// Implementations of this interface are used by SectionMemoryManager to

  /// request pages from the operating system.

  class MemoryMapper {

  public:

    /// This method attempts to allocate \p NumBytes bytes of virtual memory for

    /// \p Purpose.  \p NearBlock may point to an existing allocation, in which

    /// case an attempt is made to allocate more memory near the existing block.

    /// The actual allocated address is not guaranteed to be near the requested

    /// address.  \p Flags is used to set the initial protection flags for the

    /// block of the memory.  \p EC [out] returns an object describing any error

    /// that occurs.

    ///

    /// This method may allocate more than the number of bytes requested.  The

    /// actual number of bytes allocated is indicated in the returned

    /// MemoryBlock.

    ///

    /// The start of the allocated block must be aligned with the system

    /// allocation granularity (64K on Windows, page size on Linux).  If the

    /// address following \p NearBlock is not so aligned, it will be rounded up

    /// to the next allocation granularity boundary.

    ///

    /// \r a non-null MemoryBlock if the function was successful, otherwise a

    /// null MemoryBlock with \p EC describing the error.

    virtual sys::MemoryBlock

    allocateMappedMemory(AllocationPurpose Purpose, size_t NumBytes,

                         const sys::MemoryBlock *const NearBlock,

                         unsigned Flags, std::error_code &EC) = 0;

    /// This method sets the protection flags for a block of memory to the state

    /// specified by \p Flags.  The behavior is not specified if the memory was

    /// not allocated using the allocateMappedMemory method.

    /// \p Block describes the memory block to be protected.

    /// \p Flags specifies the new protection state to be assigned to the block.

    ///

    /// If \p Flags is MF_WRITE, the actual behavior varies with the operating

    /// system (i.e. MF_READ | MF_WRITE on Windows) and the target architecture

    /// (i.e. MF_WRITE -> MF_READ | MF_WRITE on i386).

    ///

    /// \r error_success if the function was successful, or an error_code

    /// describing the failure if an error occurred.

    virtual std::error_code protectMappedMemory(const sys::MemoryBlock &Block,

                                                unsigned Flags) = 0;

    /// This method releases a block of memory that was allocated with the

    /// allocateMappedMemory method. It should not be used to release any memory

    /// block allocated any other way.

    /// \p Block describes the memory to be released.

    ///

    /// \r error_success if the function was successful, or an error_code

    /// describing the failure if an error occurred.

    virtual std::error_code releaseMappedMemory(sys::MemoryBlock &M) = 0;

    virtual ~MemoryMapper();

  };

  /// Creates a SectionMemoryManager instance with \p MM as the associated

  /// memory mapper.  If \p MM is nullptr then a default memory mapper is used

  /// that directly calls into the operating system.

  SectionMemoryManager(MemoryMapper *MM = nullptr);

  SectionMemoryManager(const SectionMemoryManager &) = delete;

  void operator=(const SectionMemoryManager &) = delete;

  ~SectionMemoryManager() override;

  /// Allocates a memory block of (at least) the given size suitable for

  /// executable code.

  ///

  /// The value of \p Alignment must be a power of two.  If \p Alignment is zero

  /// a default alignment of 16 will be used.

  uint8_t *allocateCodeSection(uintptr_t Size, unsigned Alignment,

                               unsigned SectionID,

                               StringRef SectionName) override;

  /// Allocates a memory block of (at least) the given size suitable for

  /// executable code.

  ///

  /// The value of \p Alignment must be a power of two.  If \p Alignment is zero

  /// a default alignment of 16 will be used.

  uint8_t *allocateDataSection(uintptr_t Size, unsigned Alignment,

                               unsigned SectionID, StringRef SectionName,

                               bool isReadOnly) override;

  /// Update section-specific memory permissions and other attributes.

  ///

  /// This method is called when object loading is complete and section page

  /// permissions can be applied.  It is up to the memory manager implementation

  /// to decide whether or not to act on this method.  The memory manager will

  /// typically allocate all sections as read-write and then apply specific

  /// permissions when this method is called.  Code sections cannot be executed

  /// until this function has been called.  In addition, any cache coherency

  /// operations needed to reliably use the memory are also performed.

  ///

  /// \returns true if an error occurred, false otherwise.

  bool finalizeMemory(std::string *ErrMsg = nullptr) override;

  /// Invalidate instruction cache for code sections.

  ///

  /// Some platforms with separate data cache and instruction cache require

  /// explicit cache flush, otherwise JIT code manipulations (like resolved

  /// relocations) will get to the data cache but not to the instruction cache.

  ///

  /// This method is called from finalizeMemory.

  virtual void invalidateInstructionCache();

private:

  struct FreeMemBlock {

    // The actual block of free memory

    sys::MemoryBlock Free;

    // If there is a pending allocation from the same reservation right before

    // this block, store it's index in PendingMem, to be able to update the

    // pending region if part of this block is allocated, rather than having to

    // create a new one

    unsigned PendingPrefixIndex;

  };

  struct MemoryGroup {

    // PendingMem contains all blocks of memory (subblocks of AllocatedMem)

    // which have not yet had their permissions applied, but have been given

    // out to the user. FreeMem contains all block of memory, which have

    // neither had their permissions applied, nor been given out to the user.

    SmallVector<sys::MemoryBlock, 16> PendingMem;

    SmallVector<FreeMemBlock, 16> FreeMem;

    // All memory blocks that have been requested from the system

    SmallVector<sys::MemoryBlock, 16> AllocatedMem;

    sys::MemoryBlock Near;

  };

  uint8_t *allocateSection(AllocationPurpose Purpose, uintptr_t Size,

                           unsigned Alignment);

  std::error_code applyMemoryGroupPermissions(MemoryGroup &MemGroup,

                                              unsigned Permissions);

  void anchor() override;

  MemoryGroup CodeMem;

  MemoryGroup RWDataMem;

  MemoryGroup RODataMem;

  MemoryMapper &MMapper;

};

} // end namespace llvm

#endif // LLVM_EXECUTIONENGINE_SECTIONMEMORYMANAGER_H