1//===- SectionMemoryManager.h - Memory manager for MCJIT/RtDyld -*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file contains the declaration of a section-based memory manager used by
10// the MCJIT execution engine and RuntimeDyld.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_EXECUTIONENGINE_SECTIONMEMORYMANAGER_H
15#define LLVM_EXECUTIONENGINE_SECTIONMEMORYMANAGER_H
16
17#include "llvm/ADT/SmallVector.h"
18#include "llvm/ExecutionEngine/RTDyldMemoryManager.h"
19#include "llvm/Support/Memory.h"
20#include <cstdint>
21#include <string>
22#include <system_error>
23
24namespace llvm {
25
26/// This is a simple memory manager which implements the methods called by
27/// the RuntimeDyld class to allocate memory for section-based loading of
28/// objects, usually those generated by the MCJIT execution engine.
29///
30/// This memory manager allocates all section memory as read-write.  The
31/// RuntimeDyld will copy JITed section memory into these allocated blocks
32/// and perform any necessary linking and relocations.
33///
34/// Any client using this memory manager MUST ensure that section-specific
35/// page permissions have been applied before attempting to execute functions
36/// in the JITed object.  Permissions can be applied either by calling
37/// MCJIT::finalizeObject or by calling SectionMemoryManager::finalizeMemory
38/// directly.  Clients of MCJIT should call MCJIT::finalizeObject.
39class SectionMemoryManager : public RTDyldMemoryManager {
40public:
41  /// This enum describes the various reasons to allocate pages from
42  /// allocateMappedMemory.
43  enum class AllocationPurpose {
44    Code,
45    ROData,
46    RWData,
47  };
48
49  /// Implementations of this interface are used by SectionMemoryManager to
50  /// request pages from the operating system.
51  class MemoryMapper {
52  public:
53    /// This method attempts to allocate \p NumBytes bytes of virtual memory for
54    /// \p Purpose.  \p NearBlock may point to an existing allocation, in which
55    /// case an attempt is made to allocate more memory near the existing block.
56    /// The actual allocated address is not guaranteed to be near the requested
57    /// address.  \p Flags is used to set the initial protection flags for the
58    /// block of the memory.  \p EC [out] returns an object describing any error
59    /// that occurs.
60    ///
61    /// This method may allocate more than the number of bytes requested.  The
62    /// actual number of bytes allocated is indicated in the returned
63    /// MemoryBlock.
64    ///
65    /// The start of the allocated block must be aligned with the system
66    /// allocation granularity (64K on Windows, page size on Linux).  If the
67    /// address following \p NearBlock is not so aligned, it will be rounded up
68    /// to the next allocation granularity boundary.
69    ///
70    /// \r a non-null MemoryBlock if the function was successful, otherwise a
71    /// null MemoryBlock with \p EC describing the error.
72    virtual sys::MemoryBlock
73    allocateMappedMemory(AllocationPurpose Purpose, size_t NumBytes,
74                         const sys::MemoryBlock *const NearBlock,
75                         unsigned Flags, std::error_code &EC) = 0;
76
77    /// This method sets the protection flags for a block of memory to the state
78    /// specified by \p Flags.  The behavior is not specified if the memory was
79    /// not allocated using the allocateMappedMemory method.
80    /// \p Block describes the memory block to be protected.
81    /// \p Flags specifies the new protection state to be assigned to the block.
82    ///
83    /// If \p Flags is MF_WRITE, the actual behavior varies with the operating
84    /// system (i.e. MF_READ | MF_WRITE on Windows) and the target architecture
85    /// (i.e. MF_WRITE -> MF_READ | MF_WRITE on i386).
86    ///
87    /// \r error_success if the function was successful, or an error_code
88    /// describing the failure if an error occurred.
89    virtual std::error_code protectMappedMemory(const sys::MemoryBlock &Block,
90                                                unsigned Flags) = 0;
91
92    /// This method releases a block of memory that was allocated with the
93    /// allocateMappedMemory method. It should not be used to release any memory
94    /// block allocated any other way.
95    /// \p Block describes the memory to be released.
96    ///
97    /// \r error_success if the function was successful, or an error_code
98    /// describing the failure if an error occurred.
99    virtual std::error_code releaseMappedMemory(sys::MemoryBlock &M) = 0;
100
101    virtual ~MemoryMapper();
102  };
103
104  /// Creates a SectionMemoryManager instance with \p MM as the associated
105  /// memory mapper.  If \p MM is nullptr then a default memory mapper is used
106  /// that directly calls into the operating system.
107  SectionMemoryManager(MemoryMapper *MM = nullptr);
108  SectionMemoryManager(const SectionMemoryManager &) = delete;
109  void operator=(const SectionMemoryManager &) = delete;
110  ~SectionMemoryManager() override;
111
112  /// Allocates a memory block of (at least) the given size suitable for
113  /// executable code.
114  ///
115  /// The value of \p Alignment must be a power of two.  If \p Alignment is zero
116  /// a default alignment of 16 will be used.
117  uint8_t *allocateCodeSection(uintptr_t Size, unsigned Alignment,
118                               unsigned SectionID,
119                               StringRef SectionName) override;
120
121  /// Allocates a memory block of (at least) the given size suitable for
122  /// executable code.
123  ///
124  /// The value of \p Alignment must be a power of two.  If \p Alignment is zero
125  /// a default alignment of 16 will be used.
126  uint8_t *allocateDataSection(uintptr_t Size, unsigned Alignment,
127                               unsigned SectionID, StringRef SectionName,
128                               bool isReadOnly) override;
129
130  /// Update section-specific memory permissions and other attributes.
131  ///
132  /// This method is called when object loading is complete and section page
133  /// permissions can be applied.  It is up to the memory manager implementation
134  /// to decide whether or not to act on this method.  The memory manager will
135  /// typically allocate all sections as read-write and then apply specific
136  /// permissions when this method is called.  Code sections cannot be executed
137  /// until this function has been called.  In addition, any cache coherency
138  /// operations needed to reliably use the memory are also performed.
139  ///
140  /// \returns true if an error occurred, false otherwise.
141  bool finalizeMemory(std::string *ErrMsg = nullptr) override;
142
143  /// Invalidate instruction cache for code sections.
144  ///
145  /// Some platforms with separate data cache and instruction cache require
146  /// explicit cache flush, otherwise JIT code manipulations (like resolved
147  /// relocations) will get to the data cache but not to the instruction cache.
148  ///
149  /// This method is called from finalizeMemory.
150  virtual void invalidateInstructionCache();
151
152private:
153  struct FreeMemBlock {
154    // The actual block of free memory
155    sys::MemoryBlock Free;
156    // If there is a pending allocation from the same reservation right before
157    // this block, store it's index in PendingMem, to be able to update the
158    // pending region if part of this block is allocated, rather than having to
159    // create a new one
160    unsigned PendingPrefixIndex;
161  };
162
163  struct MemoryGroup {
164    // PendingMem contains all blocks of memory (subblocks of AllocatedMem)
165    // which have not yet had their permissions applied, but have been given
166    // out to the user. FreeMem contains all block of memory, which have
167    // neither had their permissions applied, nor been given out to the user.
168    SmallVector<sys::MemoryBlock, 16> PendingMem;
169    SmallVector<FreeMemBlock, 16> FreeMem;
170
171    // All memory blocks that have been requested from the system
172    SmallVector<sys::MemoryBlock, 16> AllocatedMem;
173
174    sys::MemoryBlock Near;
175  };
176
177  uint8_t *allocateSection(AllocationPurpose Purpose, uintptr_t Size,
178                           unsigned Alignment);
179
180  std::error_code applyMemoryGroupPermissions(MemoryGroup &MemGroup,
181                                              unsigned Permissions);
182
183  void anchor() override;
184
185  MemoryGroup CodeMem;
186  MemoryGroup RWDataMem;
187  MemoryGroup RODataMem;
188  MemoryMapper *MMapper;
189  std::unique_ptr<MemoryMapper> OwnedMMapper;
190};
191
192} // end namespace llvm
193
194#endif // LLVM_EXECUTIONENGINE_SECTIONMEMORYMANAGER_H
195