FreeRTOS-Kernel/portable/MemMang/heap_4.c

/*
 * FreeRTOS Kernel <DEVELOPMENT BRANCH>
 * Copyright (C) 2021 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * SPDX-License-Identifier: MIT
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of
 * this software and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
 * the Software, and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
 * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
 * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
 * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 * https://www.FreeRTOS.org
 * https://github.com/FreeRTOS
 *
 */

/*
 * A sample implementation of pvPortMalloc() and vPortFree() that combines
 * (coalescences) adjacent memory blocks as they are freed, and in so doing
 * limits memory fragmentation.
 *
 * See heap_1.c, heap_2.c and heap_3.c for alternative implementations, and the
 * memory management pages of https://www.FreeRTOS.org for more information.
 */
#include <stdlib.h>
#include <string.h>

/* Defining MPU_WRAPPERS_INCLUDED_FROM_API_FILE prevents task.h from redefining
 * all the API functions to use the MPU wrappers.  That should only be done when
 * task.h is included from an application file. */
#define MPU_WRAPPERS_INCLUDED_FROM_API_FILE

#include "FreeRTOS.h"
#include "task.h"

#undef MPU_WRAPPERS_INCLUDED_FROM_API_FILE

#if ( configSUPPORT_DYNAMIC_ALLOCATION == 0 )
    #error This file must not be used if configSUPPORT_DYNAMIC_ALLOCATION is 0
#endif

#ifndef configHEAP_CLEAR_MEMORY_ON_FREE
    #define configHEAP_CLEAR_MEMORY_ON_FREE    0
#endif

/* Block sizes must not get too small. */
#define heapMINIMUM_BLOCK_SIZE    ( ( size_t ) ( xHeapStructSize << 1 ) )

/* Assumes 8bit bytes! */
#define heapBITS_PER_BYTE         ( ( size_t ) 8 )

/* Max value that fits in a size_t type. */
#define heapSIZE_MAX              ( ~( ( size_t ) 0 ) )

/* Check if multiplying a and b will result in overflow. */
#define heapMULTIPLY_WILL_OVERFLOW( a, b )     ( ( ( a ) > 0 ) && ( ( b ) > ( heapSIZE_MAX / ( a ) ) ) )

/* Check if adding a and b will result in overflow. */
#define heapADD_WILL_OVERFLOW( a, b )          ( ( a ) > ( heapSIZE_MAX - ( b ) ) )

/* Check if the subtraction operation ( a - b ) will result in underflow. */
#define heapSUBTRACT_WILL_UNDERFLOW( a, b )    ( ( a ) < ( b ) )

/* MSB of the xBlockSize member of an BlockLink_t structure is used to track
 * the allocation status of a block.  When MSB of the xBlockSize member of
 * an BlockLink_t structure is set then the block belongs to the application.
 * When the bit is free the block is still part of the free heap space. */
#define heapBLOCK_ALLOCATED_BITMASK    ( ( ( size_t ) 1 ) << ( ( sizeof( size_t ) * heapBITS_PER_BYTE ) - 1 ) )
#define heapBLOCK_SIZE_IS_VALID( xBlockSize )    ( ( ( xBlockSize ) & heapBLOCK_ALLOCATED_BITMASK ) == 0 )
#define heapBLOCK_IS_ALLOCATED( pxBlock )        ( ( ( pxBlock->xBlockSize ) & heapBLOCK_ALLOCATED_BITMASK ) != 0 )
#define heapALLOCATE_BLOCK( pxBlock )            ( ( pxBlock->xBlockSize ) |= heapBLOCK_ALLOCATED_BITMASK )
#define heapFREE_BLOCK( pxBlock )                ( ( pxBlock->xBlockSize ) &= ~heapBLOCK_ALLOCATED_BITMASK )

/*-----------------------------------------------------------*/

/* Allocate the memory for the heap. */
#if ( configAPPLICATION_ALLOCATED_HEAP == 1 )

/* The application writer has already defined the array used for the RTOS
 * heap - probably so it can be placed in a special segment or address. */
    extern uint8_t ucHeap[ configTOTAL_HEAP_SIZE ];
#else
    PRIVILEGED_DATA static uint8_t ucHeap[ configTOTAL_HEAP_SIZE ];
#endif /* configAPPLICATION_ALLOCATED_HEAP */

/* Define the linked list structure.  This is used to link free blocks in order
 * of their memory address. */
typedef struct A_BLOCK_LINK
{
    struct A_BLOCK_LINK * pxNextFreeBlock; /**< The next free block in the list. */
    size_t xBlockSize;                     /**< The size of the free block. */
} BlockLink_t;

/* Setting configENABLE_HEAP_PROTECTOR to 1 enables heap block pointers
 * protection using an application supplied canary value to catch heap
 * corruption should a heap buffer overflow occur.
 */
#if ( configENABLE_HEAP_PROTECTOR == 1 )

/**
 * @brief Application provided function to get a random value to be used as canary.
 *
 * @param pxHeapCanary [out] Output parameter to return the canary value.
 */
    extern void vApplicationGetRandomHeapCanary( portPOINTER_SIZE_TYPE * pxHeapCanary );

/* Canary value for protecting internal heap pointers. */
    PRIVILEGED_DATA static portPOINTER_SIZE_TYPE xHeapCanary;

/* Macro to load/store BlockLink_t pointers to memory. By XORing the
 * pointers with a random canary value, heap overflows will result
 * in randomly unpredictable pointer values which will be caught by
 * heapVALIDATE_BLOCK_POINTER assert. */
    #define heapPROTECT_BLOCK_POINTER( pxBlock )    ( ( BlockLink_t * ) ( ( ( portPOINTER_SIZE_TYPE ) ( pxBlock ) ) ^ xHeapCanary ) )
#else

    #define heapPROTECT_BLOCK_POINTER( pxBlock )    ( pxBlock )

#endif /* configENABLE_HEAP_PROTECTOR */

/* Assert that a heap block pointer is within the heap bounds. */
#define heapVALIDATE_BLOCK_POINTER( pxBlock )                          \
    configASSERT( ( ( uint8_t * ) ( pxBlock ) >= &( ucHeap[ 0 ] ) ) && \
                  ( ( uint8_t * ) ( pxBlock ) <= &( ucHeap[ configTOTAL_HEAP_SIZE - 1 ] ) ) )

/*-----------------------------------------------------------*/

/*
 * Inserts a block of memory that is being freed into the correct position in
 * the list of free memory blocks.  The block being freed will be merged with
 * the block in front it and/or the block behind it if the memory blocks are
 * adjacent to each other.
 */
static void prvInsertBlockIntoFreeList( BlockLink_t * pxBlockToInsert ) PRIVILEGED_FUNCTION;

/*
 * Called automatically to setup the required heap structures the first time
 * pvPortMalloc() is called.
 */
static void prvHeapInit( void ) PRIVILEGED_FUNCTION;

/*-----------------------------------------------------------*/

/* The size of the structure placed at the beginning of each allocated memory
 * block must by correctly byte aligned. */
static const size_t xHeapStructSize = ( sizeof( BlockLink_t ) + ( ( size_t ) ( portBYTE_ALIGNMENT - 1 ) ) ) & ~( ( size_t ) portBYTE_ALIGNMENT_MASK );

/* Create a couple of list links to mark the start and end of the list. */
PRIVILEGED_DATA static BlockLink_t xStart;
PRIVILEGED_DATA static BlockLink_t * pxEnd = NULL;

/* Keeps track of the number of calls to allocate and free memory as well as the
 * number of free bytes remaining, but says nothing about fragmentation. */
PRIVILEGED_DATA static size_t xFreeBytesRemaining = ( size_t ) 0U;
PRIVILEGED_DATA static size_t xMinimumEverFreeBytesRemaining = ( size_t ) 0U;
PRIVILEGED_DATA static size_t xNumberOfSuccessfulAllocations = ( size_t ) 0U;
PRIVILEGED_DATA static size_t xNumberOfSuccessfulFrees = ( size_t ) 0U;

/*-----------------------------------------------------------*/

void * pvPortMalloc( size_t xWantedSize )
{
    BlockLink_t * pxBlock;
    BlockLink_t * pxPreviousBlock;
    BlockLink_t * pxNewBlockLink;
    void * pvReturn = NULL;
    size_t xAdditionalRequiredSize;
    size_t xAllocatedBlockSize = 0;

    if( xWantedSize > 0 )
    {
        /* The wanted size must be increased so it can contain a BlockLink_t
         * structure in addition to the requested amount of bytes. */
        if( heapADD_WILL_OVERFLOW( xWantedSize, xHeapStructSize ) == 0 )
        {
            xWantedSize += xHeapStructSize;

            /* Ensure that blocks are always aligned to the required number
             * of bytes. */
            if( ( xWantedSize & portBYTE_ALIGNMENT_MASK ) != 0x00 )
            {
                /* Byte alignment required. */
                xAdditionalRequiredSize = portBYTE_ALIGNMENT - ( xWantedSize & portBYTE_ALIGNMENT_MASK );

                if( heapADD_WILL_OVERFLOW( xWantedSize, xAdditionalRequiredSize ) == 0 )
                {
                    xWantedSize += xAdditionalRequiredSize;
                }
                else
                {
                    xWantedSize = 0;
                }
            }
            else
            {
                mtCOVERAGE_TEST_MARKER();
            }
        }
        else
        {
            xWantedSize = 0;
        }
    }
    else
    {
        mtCOVERAGE_TEST_MARKER();
    }

    vTaskSuspendAll();
    {
        /* If this is the first call to malloc then the heap will require
         * initialisation to setup the list of free blocks. */
        if( pxEnd == NULL )
        {
            prvHeapInit();
        }
        else
        {
            mtCOVERAGE_TEST_MARKER();
        }

        /* Check the block size we are trying to allocate is not so large that the
         * top bit is set.  The top bit of the block size member of the BlockLink_t
         * structure is used to determine who owns the block - the application or
         * the kernel, so it must be free. */
        if( heapBLOCK_SIZE_IS_VALID( xWantedSize ) != 0 )
        {
            if( ( xWantedSize > 0 ) && ( xWantedSize <= xFreeBytesRemaining ) )
            {
                /* Traverse the list from the start (lowest address) block until
                 * one of adequate size is found. */
                pxPreviousBlock = &xStart;
                pxBlock = heapPROTECT_BLOCK_POINTER( xStart.pxNextFreeBlock );
                heapVALIDATE_BLOCK_POINTER( pxBlock );

                while( ( pxBlock->xBlockSize < xWantedSize ) && ( pxBlock->pxNextFreeBlock != heapPROTECT_BLOCK_POINTER( NULL ) ) )
                {
                    pxPreviousBlock = pxBlock;
                    pxBlock = heapPROTECT_BLOCK_POINTER( pxBlock->pxNextFreeBlock );
                    heapVALIDATE_BLOCK_POINTER( pxBlock );
                }

                /* If the end marker was reached then a block of adequate size
                 * was not found. */
                if( pxBlock != pxEnd )
                {
                    /* Return the memory space pointed to - jumping over the
                     * BlockLink_t structure at its start. */
                    pvReturn = ( void * ) ( ( ( uint8_t * ) heapPROTECT_BLOCK_POINTER( pxPreviousBlock->pxNextFreeBlock ) ) + xHeapStructSize );
                    heapVALIDATE_BLOCK_POINTER( pvReturn );

                    /* This block is being returned for use so must be taken out
                     * of the list of free blocks. */
                    pxPreviousBlock->pxNextFreeBlock = pxBlock->pxNextFreeBlock;

                    /* If the block is larger than required it can be split into
                     * two. */
                    configASSERT( heapSUBTRACT_WILL_UNDERFLOW( pxBlock->xBlockSize, xWantedSize ) == 0 );

                    if( ( pxBlock->xBlockSize - xWantedSize ) > heapMINIMUM_BLOCK_SIZE )
                    {
                        /* This block is to be split into two.  Create a new
                         * block following the number of bytes requested. The void
                         * cast is used to prevent byte alignment warnings from the
                         * compiler. */
                        pxNewBlockLink = ( void * ) ( ( ( uint8_t * ) pxBlock ) + xWantedSize );
                        configASSERT( ( ( ( size_t ) pxNewBlockLink ) & portBYTE_ALIGNMENT_MASK ) == 0 );

                        /* Calculate the sizes of two blocks split from the
                         * single block. */
                        pxNewBlockLink->xBlockSize = pxBlock->xBlockSize - xWantedSize;
                        pxBlock->xBlockSize = xWantedSize;

                        /* Insert the new block into the list of free blocks. */
                        pxNewBlockLink->pxNextFreeBlock = pxPreviousBlock->pxNextFreeBlock;
                        pxPreviousBlock->pxNextFreeBlock = heapPROTECT_BLOCK_POINTER( pxNewBlockLink );
                    }
                    else
                    {
                        mtCOVERAGE_TEST_MARKER();
                    }

                    xFreeBytesRemaining -= pxBlock->xBlockSize;

                    if( xFreeBytesRemaining < xMinimumEverFreeBytesRemaining )
                    {
                        xMinimumEverFreeBytesRemaining = xFreeBytesRemaining;
                    }
                    else
                    {
                        mtCOVERAGE_TEST_MARKER();
                    }

                    xAllocatedBlockSize = pxBlock->xBlockSize;

                    /* The block is being returned - it is allocated and owned
                     * by the application and has no "next" block. */
                    heapALLOCATE_BLOCK( pxBlock );
                    pxBlock->pxNextFreeBlock = heapPROTECT_BLOCK_POINTER( NULL );
                    xNumberOfSuccessfulAllocations++;
                }
                else
                {
                    mtCOVERAGE_TEST_MARKER();
                }
            }
            else
            {
                mtCOVERAGE_TEST_MARKER();
            }
        }
        else
        {
            mtCOVERAGE_TEST_MARKER();
        }

        traceMALLOC( pvReturn, xAllocatedBlockSize );

        /* Prevent compiler warnings when trace macros are not used. */
        ( void ) xAllocatedBlockSize;
    }
    ( void ) xTaskResumeAll();

    #if ( configUSE_MALLOC_FAILED_HOOK == 1 )
    {
        if( pvReturn == NULL )
        {
            vApplicationMallocFailedHook();
        }
        else
        {
            mtCOVERAGE_TEST_MARKER();
        }
    }
    #endif /* if ( configUSE_MALLOC_FAILED_HOOK == 1 ) */

    configASSERT( ( ( ( size_t ) pvReturn ) & ( size_t ) portBYTE_ALIGNMENT_MASK ) == 0 );
    return pvReturn;
}
/*-----------------------------------------------------------*/

void vPortFree( void * pv )
{
    uint8_t * puc = ( uint8_t * ) pv;
    BlockLink_t * pxLink;

    if( pv != NULL )
    {
        /* The memory being freed will have an BlockLink_t structure immediately
         * before it. */
        puc -= xHeapStructSize;

        /* This casting is to keep the compiler from issuing warnings. */
        pxLink = ( void * ) puc;

        heapVALIDATE_BLOCK_POINTER( pxLink );
        configASSERT( heapBLOCK_IS_ALLOCATED( pxLink ) != 0 );
        configASSERT( pxLink->pxNextFreeBlock == heapPROTECT_BLOCK_POINTER( NULL ) );

        if( heapBLOCK_IS_ALLOCATED( pxLink ) != 0 )
        {
            if( pxLink->pxNextFreeBlock == heapPROTECT_BLOCK_POINTER( NULL ) )
            {
                /* The block is being returned to the heap - it is no longer
                 * allocated. */
                heapFREE_BLOCK( pxLink );
                #if ( configHEAP_CLEAR_MEMORY_ON_FREE == 1 )
                {
                    /* Check for underflow as this can occur if xBlockSize is
                     * overwritten in a heap block. */
                    if( heapSUBTRACT_WILL_UNDERFLOW( pxLink->xBlockSize, xHeapStructSize ) == 0 )
                    {
                        ( void ) memset( puc + xHeapStructSize, 0, pxLink->xBlockSize - xHeapStructSize );
                    }
                }
                #endif

                vTaskSuspendAll();
                {
                    /* Add this block to the list of free blocks. */
                    xFreeBytesRemaining += pxLink->xBlockSize;
                    traceFREE( pv, pxLink->xBlockSize );
                    prvInsertBlockIntoFreeList( ( ( BlockLink_t * ) pxLink ) );
                    xNumberOfSuccessfulFrees++;
                }
                ( void ) xTaskResumeAll();
            }
            else
            {
                mtCOVERAGE_TEST_MARKER();
            }
        }
        else
        {
            mtCOVERAGE_TEST_MARKER();
        }
    }
}
/*-----------------------------------------------------------*/

#if ( configSUPPORT_HEAP_REALLOC == 1 )
/*
 * pvPortRealloc - Reallocate memory block size
 *
 * Description: Resize an allocated memory block, attempting to expand or shrink
 * the block in place. If in-place resize is not possible, allocate a new block
 * and copy the data.
 *
 * Parameters:
 *   pv          - Pointer to the previously allocated memory block
 *   xWantedSize - New requested size of user data (in bytes)
 *
 * Return Value:
 *   On success: Pointer to the new memory block (may be the same as original)
 *   On failure: NULL
 *
 * Behavior:
 *   1) If pv == NULL, behaves like pvPortMalloc(xWantedSize).
 *   2) If xWantedSize == 0, behaves like vPortFree(pv) and returns NULL.
 *   3) Align the requested size and include the block header size; if the aligned
 *      size is invalid, return NULL.
 *   4) If the aligned requested size is <= current block size, shrink in place and
 *      insert any sufficiently large remainder as a free block.
 *   5) If expansion is required and there are enough free bytes in the heap, try to
 *      expand into adjacent free blocks in this order:
 *        - Merge with next free block if it is immediately after the current block.
 *        - Merge with previous free block if it is immediately before the current block.
 *        - Merge with both previous and next if combined they provide enough space.
 *      If none of the above succeed, fall back to allocating a new block, memcpy'ing
 *      the payload and freeing the old block.
 */
void * pvPortRealloc( void * pv,
                      size_t xWantedSize )
{
    BlockLink_t * pxBlock;
    BlockLink_t * pxNewBlockLink;
    BlockLink_t * pxNextFreeBlock;
    BlockLink_t * pxPreviousFreeBlock;
    BlockLink_t * pxBeforePreviousFreeBlock;
    uint8_t * puc;
    void * pvReturn = NULL;
    size_t xAlignedWantedSize;
    size_t xAdditionalRequiredSize;
    size_t xCurrentBlockSize;
    size_t xRemainingBlockSize;
    size_t xNextBlockSize;
    size_t xPreviousBlockSize;
    BaseType_t xHasNextBlock;
    BaseType_t xHasPreviousBlock;

    /* Ensure the end marker has been set up. */
    configASSERT( pxEnd );

    /* If pv is NULL behave like malloc. */
    if( pv == NULL )
    {
        pvReturn = pvPortMalloc( xWantedSize );
        goto realloc_exit;
    }

    /* If requested size is zero behave like free. */
    if( xWantedSize == 0 )
    {
        vPortFree( pv );
        pvReturn = NULL;
        goto realloc_exit;
    }

    /* Calculate the internal aligned size including the header. */
    xAlignedWantedSize = xWantedSize;

    /* Add the header size and check for overflow. */
    if( heapADD_WILL_OVERFLOW( xAlignedWantedSize, xHeapStructSize ) == 0 )
    {
        xAlignedWantedSize += xHeapStructSize;

        /* Ensure byte alignment. */
        if( ( xAlignedWantedSize & portBYTE_ALIGNMENT_MASK ) != 0x00 )
        {
            xAdditionalRequiredSize = portBYTE_ALIGNMENT - ( xAlignedWantedSize & portBYTE_ALIGNMENT_MASK );

            if( heapADD_WILL_OVERFLOW( xAlignedWantedSize, xAdditionalRequiredSize ) == 0 )
            {
                xAlignedWantedSize += xAdditionalRequiredSize;
            }
            else
            {
                /* Overflow -> invalid request. */
                xAlignedWantedSize = 0;
            }
        }
        else
        {
            mtCOVERAGE_TEST_MARKER();
        }
    }
    else
    {
        xAlignedWantedSize = 0;
    }

    /* Validate the aligned size. */
    if( ( xAlignedWantedSize == 0 ) || ( heapBLOCK_SIZE_IS_VALID( xAlignedWantedSize ) == 0 ) )
    {
        pvReturn = NULL;
        goto realloc_exit;
    }

    /* Get the block header for the allocated block. */
    puc = ( uint8_t * ) pv;
    puc -= xHeapStructSize;
    pxBlock = ( BlockLink_t * ) puc;

    heapVALIDATE_BLOCK_POINTER( pxBlock );
    configASSERT( heapBLOCK_IS_ALLOCATED( pxBlock ) );

    /* Current block size without the allocated bit. */
    xCurrentBlockSize = pxBlock->xBlockSize & ~heapBLOCK_ALLOCATED_BITMASK;

    /* 1) Shrink in place if possible. */
    if( xAlignedWantedSize <= xCurrentBlockSize )
    {
        xRemainingBlockSize = xCurrentBlockSize - xAlignedWantedSize;

        /* Only split if the remaining space is large enough to form a free block. */
        if( xRemainingBlockSize > heapMINIMUM_BLOCK_SIZE )
        {
            vTaskSuspendAll();
            {
                /* Set the block to the new size and mark as allocated. */
                pxBlock->xBlockSize = xAlignedWantedSize;
                heapALLOCATE_BLOCK( pxBlock );

                /* Create a new free block from the remainder and insert it. */
                pxNewBlockLink = ( BlockLink_t * ) ( ( ( uint8_t * ) pxBlock ) + xAlignedWantedSize );
                configASSERT( ( ( ( size_t ) pxNewBlockLink ) & portBYTE_ALIGNMENT_MASK ) == 0 );

                pxNewBlockLink->xBlockSize = xRemainingBlockSize;
                xFreeBytesRemaining += xRemainingBlockSize;
                prvInsertBlockIntoFreeList( pxNewBlockLink );
            }
            ( void ) xTaskResumeAll();
        }
        else
        {
            /* Remainder too small to split. */
            mtCOVERAGE_TEST_MARKER();
        }
        pvReturn = pv;
        goto realloc_exit;
    }
    /* 2) Expansion path: try to use adjacent free blocks if overall free bytes suffice. */
    else if( ( xAlignedWantedSize - xCurrentBlockSize ) <= xFreeBytesRemaining )
    {
        vTaskSuspendAll();
        {
            /* Walk the free list to find the free blocks immediately before and after pxBlock. */
            pxBeforePreviousFreeBlock = &xStart;
            pxPreviousFreeBlock = &xStart;
            pxNextFreeBlock = heapPROTECT_BLOCK_POINTER( xStart.pxNextFreeBlock );
            heapVALIDATE_BLOCK_POINTER( pxNextFreeBlock );

            while( ( pxNextFreeBlock < pxBlock ) && ( pxNextFreeBlock->pxNextFreeBlock != heapPROTECT_BLOCK_POINTER( NULL ) ) )
            {
                pxBeforePreviousFreeBlock = pxPreviousFreeBlock;
                pxPreviousFreeBlock = pxNextFreeBlock;
                pxNextFreeBlock = heapPROTECT_BLOCK_POINTER( pxNextFreeBlock->pxNextFreeBlock );
                heapVALIDATE_BLOCK_POINTER( pxNextFreeBlock );
            }

            /* Check if next is immediately after current. */
            if( ( pxNextFreeBlock != pxEnd ) &&
                ( ( ( size_t ) pxBlock + xCurrentBlockSize ) == ( size_t ) pxNextFreeBlock ) )
            {
                xHasNextBlock = pdTRUE;
            }
            else
            {
                xHasNextBlock = pdFALSE;
            }

            /* Check if previous is immediately before current. */
            if( ( pxPreviousFreeBlock != &xStart ) &&
                ( ( ( size_t ) pxPreviousFreeBlock + pxPreviousFreeBlock->xBlockSize ) == ( size_t ) pxBlock ) )
            {
                xHasPreviousBlock = pdTRUE;
            }
            else
            {
                xHasPreviousBlock = pdFALSE;
            }

            /* Compute required extra size and neighbor sizes. */
            xRemainingBlockSize = xAlignedWantedSize - xCurrentBlockSize;
            xNextBlockSize = pxNextFreeBlock->xBlockSize;
            xPreviousBlockSize = pxPreviousFreeBlock->xBlockSize;
            configASSERT( heapBLOCK_SIZE_IS_VALID( xNextBlockSize ) != 0 );
            configASSERT( heapBLOCK_SIZE_IS_VALID( xPreviousBlockSize ) != 0 );

            /* a) If next exists and is large enough, merge with next. */
            if( ( xHasNextBlock == pdTRUE ) &&
                ( xNextBlockSize >= xRemainingBlockSize ) )
            {
                /* Remove next from free list and update free bytes. */
                pxPreviousFreeBlock->pxNextFreeBlock = pxNextFreeBlock->pxNextFreeBlock;
                pxNextFreeBlock->pxNextFreeBlock = heapPROTECT_BLOCK_POINTER( NULL );
                xFreeBytesRemaining -= xNextBlockSize;

                /* Temporarily free the current block for merging. */
                heapFREE_BLOCK( pxBlock );

                /* Remaining bytes after creating the requested size. */
                xRemainingBlockSize = xCurrentBlockSize + xNextBlockSize - xAlignedWantedSize;

                if( xRemainingBlockSize > heapMINIMUM_BLOCK_SIZE )
                {
                    /* Set block to requested size and insert leftover as a free block. */
                    pxBlock->xBlockSize = xAlignedWantedSize;

                    pxNewBlockLink = ( BlockLink_t * ) ( ( ( uint8_t * ) pxBlock ) + xAlignedWantedSize );
                    configASSERT( ( ( ( size_t ) pxNewBlockLink ) & portBYTE_ALIGNMENT_MASK ) == 0 );

                    pxNewBlockLink->xBlockSize = xRemainingBlockSize;
                    xFreeBytesRemaining += xRemainingBlockSize;
                    prvInsertBlockIntoFreeList( pxNewBlockLink );
                }
                else
                {
                    /* Leftover too small, keep as part of allocated block. */
                    pxBlock->xBlockSize = xCurrentBlockSize + xNextBlockSize;
                }

                /* Mark merged block as allocated. */
                heapALLOCATE_BLOCK( pxBlock );
                pvReturn = pv;
            }
            /* b) If previous exists and is large enough, merge with previous (data must be moved). */
            else if( ( xHasPreviousBlock == pdTRUE ) &&
                     ( xPreviousBlockSize >= xRemainingBlockSize ) )
            {
                /* Remove previous from free list and update free bytes. */
                pxBeforePreviousFreeBlock->pxNextFreeBlock = pxPreviousFreeBlock->pxNextFreeBlock;
                pxPreviousFreeBlock->pxNextFreeBlock = heapPROTECT_BLOCK_POINTER( NULL );
                xFreeBytesRemaining -= xPreviousBlockSize;

                heapFREE_BLOCK( pxBlock );

                /* Move the payload forward into the previous block's payload area. */
                puc = ( uint8_t * ) pxPreviousFreeBlock;
                puc += xHeapStructSize;
                /* Ensure memmove length will not underflow. */
                configASSERT( heapSUBTRACT_WILL_UNDERFLOW( xCurrentBlockSize, xHeapStructSize ) == 0 );
                ( void ) memmove( puc, pv, xCurrentBlockSize - xHeapStructSize );

                /* Remaining bytes after creating the requested size. */
                xRemainingBlockSize = xCurrentBlockSize + xPreviousBlockSize - xAlignedWantedSize;

                if( xRemainingBlockSize > heapMINIMUM_BLOCK_SIZE )
                {
                    /* previous becomes the allocated block of requested size, insert leftover. */
                    pxPreviousFreeBlock->xBlockSize = xAlignedWantedSize;

                    pxNewBlockLink = ( BlockLink_t * ) ( ( ( uint8_t * ) pxPreviousFreeBlock ) + xAlignedWantedSize );
                    configASSERT( ( ( ( size_t ) pxNewBlockLink ) & portBYTE_ALIGNMENT_MASK ) == 0 );

                    pxNewBlockLink->xBlockSize = xRemainingBlockSize;
                    xFreeBytesRemaining += xRemainingBlockSize;
                    prvInsertBlockIntoFreeList( pxNewBlockLink );
                }
                else
                {
                    /* Leftover too small, treat entire previous+current as allocated. */
                    pxPreviousFreeBlock->xBlockSize = xCurrentBlockSize + xPreviousBlockSize;
                }

                heapALLOCATE_BLOCK( pxPreviousFreeBlock );
                /* Return the payload pointer in the previous block. */
                pvReturn = ( void * ) puc;
            }
            /* c) If both neighbors exist and combined are large enough, merge both sides (move data). */
            else if( ( xHasNextBlock == pdTRUE ) &&
                     ( xHasPreviousBlock == pdTRUE ) &&
                     ( ( xNextBlockSize + xPreviousBlockSize ) >= xRemainingBlockSize ) )
            {
                /* Remove both previous and next from the free list and update free bytes. */
                pxBeforePreviousFreeBlock->pxNextFreeBlock = pxNextFreeBlock->pxNextFreeBlock;
                pxNextFreeBlock->pxNextFreeBlock = heapPROTECT_BLOCK_POINTER( NULL );
                pxPreviousFreeBlock->pxNextFreeBlock = heapPROTECT_BLOCK_POINTER( NULL );
                xFreeBytesRemaining -= xNextBlockSize + xPreviousBlockSize;

                heapFREE_BLOCK( pxBlock );

                /* Move payload forward into previous block's payload area. */
                puc = ( uint8_t * ) pxPreviousFreeBlock;
                puc += xHeapStructSize;
                configASSERT( heapSUBTRACT_WILL_UNDERFLOW( xCurrentBlockSize, xHeapStructSize ) == 0 );
                ( void ) memmove( puc, pv, xCurrentBlockSize - xHeapStructSize );

                /* Remaining bytes after allocation. */
                xRemainingBlockSize = xCurrentBlockSize + xNextBlockSize + xPreviousBlockSize - xAlignedWantedSize;

                if( xRemainingBlockSize > heapMINIMUM_BLOCK_SIZE )
                {
                    pxPreviousFreeBlock->xBlockSize = xAlignedWantedSize;

                    pxNewBlockLink = ( BlockLink_t * ) ( ( ( uint8_t * ) pxPreviousFreeBlock ) + xAlignedWantedSize );
                    configASSERT( ( ( ( size_t ) pxNewBlockLink ) & portBYTE_ALIGNMENT_MASK ) == 0 );

                    pxNewBlockLink->xBlockSize = xRemainingBlockSize;
                    xFreeBytesRemaining += xRemainingBlockSize;
                    prvInsertBlockIntoFreeList( pxNewBlockLink );
                }
                else
                {
                    pxPreviousFreeBlock->xBlockSize = xCurrentBlockSize + xNextBlockSize + xPreviousBlockSize;
                }

                heapALLOCATE_BLOCK( pxPreviousFreeBlock );
                pvReturn = ( void * ) puc;
            }
            else
            {
                /* None of the merge strategies worked on this path. */
                mtCOVERAGE_TEST_MARKER();
            }

            /* Update historical minimum free bytes. */
            if( xFreeBytesRemaining < xMinimumEverFreeBytesRemaining )
            {
                xMinimumEverFreeBytesRemaining = xFreeBytesRemaining;
            }
            else
            {
                mtCOVERAGE_TEST_MARKER();
            }
        }
        ( void ) xTaskResumeAll();
    }
    else
    {
        /* Not enough free bytes in the entire heap to satisfy expansion. */
        pvReturn = NULL;
        goto realloc_exit;
    }

    /* If still NULL, fall back to allocating a new block and copying the payload. */
    if( pvReturn == NULL )
    {
        puc = pvPortMalloc( xWantedSize );

        if( puc != NULL )
        {
            /* Copy the old payload (old payload size = xCurrentBlockSize - xHeapStructSize). */
            configASSERT( heapSUBTRACT_WILL_UNDERFLOW( xCurrentBlockSize, xHeapStructSize ) == 0 );
            ( void ) memcpy( puc, pv, xCurrentBlockSize - xHeapStructSize );
            vPortFree( pv );

            pvReturn = ( void * ) puc;
        }
        else
        {
            mtCOVERAGE_TEST_MARKER();
        }
    }

realloc_exit:
    /* Ensure returned pointer is properly aligned (NULL also satisfies this). */
    configASSERT( ( ( size_t ) pvReturn & ( size_t ) portBYTE_ALIGNMENT_MASK ) == 0 );
    return pvReturn;
}
#endif /* if ( configSUPPORT_HEAP_REALLOC == 1 ) */
/*-----------------------------------------------------------*/

size_t xPortGetFreeHeapSize( void )
{
    return xFreeBytesRemaining;
}
/*-----------------------------------------------------------*/

size_t xPortGetMinimumEverFreeHeapSize( void )
{
    return xMinimumEverFreeBytesRemaining;
}
/*-----------------------------------------------------------*/

void xPortResetHeapMinimumEverFreeHeapSize( void )
{
    xMinimumEverFreeBytesRemaining = xFreeBytesRemaining;
}
/*-----------------------------------------------------------*/

void vPortInitialiseBlocks( void )
{
    /* This just exists to keep the linker quiet. */
}
/*-----------------------------------------------------------*/

void * pvPortCalloc( size_t xNum,
                     size_t xSize )
{
    void * pv = NULL;

    if( heapMULTIPLY_WILL_OVERFLOW( xNum, xSize ) == 0 )
    {
        pv = pvPortMalloc( xNum * xSize );

        if( pv != NULL )
        {
            ( void ) memset( pv, 0, xNum * xSize );
        }
    }

    return pv;
}
/*-----------------------------------------------------------*/

static void prvHeapInit( void ) /* PRIVILEGED_FUNCTION */
{
    BlockLink_t * pxFirstFreeBlock;
    portPOINTER_SIZE_TYPE uxStartAddress, uxEndAddress;
    size_t xTotalHeapSize = configTOTAL_HEAP_SIZE;

    /* Ensure the heap starts on a correctly aligned boundary. */
    uxStartAddress = ( portPOINTER_SIZE_TYPE ) ucHeap;

    if( ( uxStartAddress & portBYTE_ALIGNMENT_MASK ) != 0 )
    {
        uxStartAddress += ( portBYTE_ALIGNMENT - 1 );
        uxStartAddress &= ~( ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK );
        xTotalHeapSize -= ( size_t ) ( uxStartAddress - ( portPOINTER_SIZE_TYPE ) ucHeap );
    }

    #if ( configENABLE_HEAP_PROTECTOR == 1 )
    {
        vApplicationGetRandomHeapCanary( &( xHeapCanary ) );
    }
    #endif

    /* xStart is used to hold a pointer to the first item in the list of free
     * blocks.  The void cast is used to prevent compiler warnings. */
    xStart.pxNextFreeBlock = ( void * ) heapPROTECT_BLOCK_POINTER( uxStartAddress );
    xStart.xBlockSize = ( size_t ) 0;

    /* pxEnd is used to mark the end of the list of free blocks and is inserted
     * at the end of the heap space. */
    uxEndAddress = uxStartAddress + ( portPOINTER_SIZE_TYPE ) xTotalHeapSize;
    uxEndAddress -= ( portPOINTER_SIZE_TYPE ) xHeapStructSize;
    uxEndAddress &= ~( ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK );
    pxEnd = ( BlockLink_t * ) uxEndAddress;
    pxEnd->xBlockSize = 0;
    pxEnd->pxNextFreeBlock = heapPROTECT_BLOCK_POINTER( NULL );

    /* To start with there is a single free block that is sized to take up the
     * entire heap space, minus the space taken by pxEnd. */
    pxFirstFreeBlock = ( BlockLink_t * ) uxStartAddress;
    pxFirstFreeBlock->xBlockSize = ( size_t ) ( uxEndAddress - ( portPOINTER_SIZE_TYPE ) pxFirstFreeBlock );
    pxFirstFreeBlock->pxNextFreeBlock = heapPROTECT_BLOCK_POINTER( pxEnd );

    /* Only one block exists - and it covers the entire usable heap space. */
    xMinimumEverFreeBytesRemaining = pxFirstFreeBlock->xBlockSize;
    xFreeBytesRemaining = pxFirstFreeBlock->xBlockSize;
}
/*-----------------------------------------------------------*/

static void prvInsertBlockIntoFreeList( BlockLink_t * pxBlockToInsert ) /* PRIVILEGED_FUNCTION */
{
    BlockLink_t * pxIterator;
    uint8_t * puc;

    /* Iterate through the list until a block is found that has a higher address
     * than the block being inserted. */
    for( pxIterator = &xStart; heapPROTECT_BLOCK_POINTER( pxIterator->pxNextFreeBlock ) < pxBlockToInsert; pxIterator = heapPROTECT_BLOCK_POINTER( pxIterator->pxNextFreeBlock ) )
    {
        /* Nothing to do here, just iterate to the right position. */
    }

    if( pxIterator != &xStart )
    {
        heapVALIDATE_BLOCK_POINTER( pxIterator );
    }

    /* Do the block being inserted, and the block it is being inserted after
     * make a contiguous block of memory? */
    puc = ( uint8_t * ) pxIterator;

    if( ( puc + pxIterator->xBlockSize ) == ( uint8_t * ) pxBlockToInsert )
    {
        pxIterator->xBlockSize += pxBlockToInsert->xBlockSize;
        pxBlockToInsert = pxIterator;
    }
    else
    {
        mtCOVERAGE_TEST_MARKER();
    }

    /* Do the block being inserted, and the block it is being inserted before
     * make a contiguous block of memory? */
    puc = ( uint8_t * ) pxBlockToInsert;

    if( ( puc + pxBlockToInsert->xBlockSize ) == ( uint8_t * ) heapPROTECT_BLOCK_POINTER( pxIterator->pxNextFreeBlock ) )
    {
        if( heapPROTECT_BLOCK_POINTER( pxIterator->pxNextFreeBlock ) != pxEnd )
        {
            /* Form one big block from the two blocks. */
            pxBlockToInsert->xBlockSize += heapPROTECT_BLOCK_POINTER( pxIterator->pxNextFreeBlock )->xBlockSize;
            pxBlockToInsert->pxNextFreeBlock = heapPROTECT_BLOCK_POINTER( pxIterator->pxNextFreeBlock )->pxNextFreeBlock;
        }
        else
        {
            pxBlockToInsert->pxNextFreeBlock = heapPROTECT_BLOCK_POINTER( pxEnd );
        }
    }
    else
    {
        pxBlockToInsert->pxNextFreeBlock = pxIterator->pxNextFreeBlock;
    }

    /* If the block being inserted plugged a gap, so was merged with the block
     * before and the block after, then it's pxNextFreeBlock pointer will have
     * already been set, and should not be set here as that would make it point
     * to itself. */
    if( pxIterator != pxBlockToInsert )
    {
        pxIterator->pxNextFreeBlock = heapPROTECT_BLOCK_POINTER( pxBlockToInsert );
    }
    else
    {
        mtCOVERAGE_TEST_MARKER();
    }
}
/*-----------------------------------------------------------*/

void vPortGetHeapStats( HeapStats_t * pxHeapStats )
{
    BlockLink_t * pxBlock;
    size_t xBlocks = 0, xMaxSize = 0, xMinSize = SIZE_MAX;

    vTaskSuspendAll();
    {
        pxBlock = heapPROTECT_BLOCK_POINTER( xStart.pxNextFreeBlock );

        /* pxBlock will be NULL if the heap has not been initialised.  The heap
         * is initialised automatically when the first allocation is made. */
        if( pxBlock != NULL )
        {
            while( pxBlock != pxEnd )
            {
                /* Increment the number of blocks and record the largest block seen
                 * so far. */
                xBlocks++;

                if( pxBlock->xBlockSize > xMaxSize )
                {
                    xMaxSize = pxBlock->xBlockSize;
                }

                if( pxBlock->xBlockSize < xMinSize )
                {
                    xMinSize = pxBlock->xBlockSize;
                }

                /* Move to the next block in the chain until the last block is
                 * reached. */
                pxBlock = heapPROTECT_BLOCK_POINTER( pxBlock->pxNextFreeBlock );
            }
        }
    }
    ( void ) xTaskResumeAll();

    pxHeapStats->xSizeOfLargestFreeBlockInBytes = xMaxSize;
    pxHeapStats->xSizeOfSmallestFreeBlockInBytes = xMinSize;
    pxHeapStats->xNumberOfFreeBlocks = xBlocks;

    taskENTER_CRITICAL();
    {
        pxHeapStats->xAvailableHeapSpaceInBytes = xFreeBytesRemaining;
        pxHeapStats->xNumberOfSuccessfulAllocations = xNumberOfSuccessfulAllocations;
        pxHeapStats->xNumberOfSuccessfulFrees = xNumberOfSuccessfulFrees;
        pxHeapStats->xMinimumEverFreeBytesRemaining = xMinimumEverFreeBytesRemaining;
    }
    taskEXIT_CRITICAL();
}
/*-----------------------------------------------------------*/

/*
 * Reset the state in this file. This state is normally initialized at start up.
 * This function must be called by the application before restarting the
 * scheduler.
 */
void vPortHeapResetState( void )
{
    pxEnd = NULL;

    xFreeBytesRemaining = ( size_t ) 0U;
    xMinimumEverFreeBytesRemaining = ( size_t ) 0U;
    xNumberOfSuccessfulAllocations = ( size_t ) 0U;
    xNumberOfSuccessfulFrees = ( size_t ) 0U;
}
/*-----------------------------------------------------------*/