memorymanager.h

//===----- memorymanager.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.
//
//===----------------------------------------------------------------------===//

#pragma once

// Force default visibility of the llvm::ErrorInfoBase class. The conda
// compilers use the -fvisibility-inlines-hidden flag, which seems to
// erroneously result in ErrorInfoBase::isA() being hidden (and not exported) on
// PowerPC. The reason for this is not conclusively known, but the circumstances
// appear similar to those reported in GCC Bug 45065
// (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=45066) - ErrorInfoBase has
// both a template and non-template version, and the non-template version is
// overridden by the derived class ErrorInfo; the template vs. non-template
// versions may have different inlining decisions applied, and this could create
// a similar circumstance to that described in the bug.
//
// The workaround here adds the default visiblity attribute to ErrorInfoBase
// before its definition, which precludes it from being inferred to be hidden
// later on.
#if not defined(_MSC_VER)
namespace llvm {
class __attribute__((visibility("default"))) ErrorInfoBase;
}
#endif

#include "core.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ExecutionEngine/RTDyldMemoryManager.h"
#include "llvm/Support/Alignment.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 LlvmliteMemoryManager::finalizeMemory
/// directly.  Clients of MCJIT should call MCJIT::finalizeObject.
class API_EXPORT(LlvmliteMemoryManager : 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 LlvmliteMemoryManager 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 LlvmliteMemoryManager 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.
    LlvmliteMemoryManager(MemoryMapper *MM = nullptr);
    LlvmliteMemoryManager(const LlvmliteMemoryManager &) = delete;
    void operator=(const LlvmliteMemoryManager &) = delete;
    ~LlvmliteMemoryManager() 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();

    virtual bool needsToReserveAllocationSpace() override { return true; }

    virtual void reserveAllocationSpace(uintptr_t CodeSize, Align CodeAlign,
                                        uintptr_t RODataSize, Align RODataAlign,
                                        uintptr_t RWDataSize,
                                        Align RWDataAlign) override;

  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);

    bool hasSpace(const MemoryGroup &MemGroup, uintptr_t Size) const;

    void anchor() override;

    MemoryGroup CodeMem;
    MemoryGroup RWDataMem;
    MemoryGroup RODataMem;
    MemoryMapper &MMapper;
};

} // end namespace llvm