Line data    Source code

       1             : /*-------------------------------------------------------------------------
       2             :  *
       3             :  * alignedalloc.c
       4             :  *    Allocator functions to implement palloc_aligned
       5             :  *
       6             :  * This is not a fully-fledged MemoryContext type as there is no means to
       7             :  * create a MemoryContext of this type.  The code here only serves to allow
       8             :  * operations such as pfree() and repalloc() to work correctly on a memory
       9             :  * chunk that was allocated by palloc_aligned().
      10             :  *
      11             :  * Portions Copyright (c) 2022-2024, PostgreSQL Global Development Group
      12             :  *
      13             :  * IDENTIFICATION
      14             :  *    src/backend/utils/mmgr/alignedalloc.c
      15             :  *
      16             :  *-------------------------------------------------------------------------
      17             :  */
      18             : 
      19             : #include "postgres.h"
      20             : 
      21             : #include "utils/memdebug.h"
      22             : #include "utils/memutils_memorychunk.h"
      23             : 
      24             : /*
      25             :  * AlignedAllocFree
      26             : *       Frees allocated memory; memory is removed from its owning context.
      27             : */
      28             : void
      29      323324 : AlignedAllocFree(void *pointer)
      30             : {
      31      323324 :     MemoryChunk *chunk = PointerGetMemoryChunk(pointer);
      32             :     void       *unaligned;
      33             : 
      34             :     VALGRIND_MAKE_MEM_DEFINED(chunk, sizeof(MemoryChunk));
      35             : 
      36             :     Assert(!MemoryChunkIsExternal(chunk));
      37             : 
      38             :     /* obtain the original (unaligned) allocated pointer */
      39      323324 :     unaligned = MemoryChunkGetBlock(chunk);
      40             : 
      41             : #ifdef MEMORY_CONTEXT_CHECKING
      42             :     /* Test for someone scribbling on unused space in chunk */
      43             :     if (!sentinel_ok(pointer, chunk->requested_size))
      44             :         elog(WARNING, "detected write past chunk end in %s %p",
      45             :              GetMemoryChunkContext(unaligned)->name, chunk);
      46             : #endif
      47             : 
      48      323324 :     pfree(unaligned);
      49      323324 : }
      50             : 
      51             : /*
      52             :  * AlignedAllocRealloc
      53             :  *      Change the allocated size of a chunk and return possibly a different
      54             :  *      pointer to a memory address aligned to the same boundary as the
      55             :  *      originally requested alignment.  The contents of 'pointer' will be
      56             :  *      copied into the returned pointer up until 'size'.  Any additional
      57             :  *      memory will be uninitialized.
      58             :  */
      59             : void *
      60           0 : AlignedAllocRealloc(void *pointer, Size size, int flags)
      61             : {
      62           0 :     MemoryChunk *redirchunk = PointerGetMemoryChunk(pointer);
      63             :     Size        alignto;
      64             :     void       *unaligned;
      65             :     MemoryContext ctx;
      66             :     Size        old_size;
      67             :     void       *newptr;
      68             : 
      69             :     VALGRIND_MAKE_MEM_DEFINED(redirchunk, sizeof(MemoryChunk));
      70             : 
      71           0 :     alignto = MemoryChunkGetValue(redirchunk);
      72           0 :     unaligned = MemoryChunkGetBlock(redirchunk);
      73             : 
      74             :     /* sanity check this is a power of 2 value */
      75             :     Assert((alignto & (alignto - 1)) == 0);
      76             : 
      77             :     /*
      78             :      * Determine the size of the original allocation.  We can't determine this
      79             :      * exactly as GetMemoryChunkSpace() returns the total space used for the
      80             :      * allocation, which for contexts like aset includes rounding up to the
      81             :      * next power of 2.  However, this value is just used to memcpy() the old
      82             :      * data into the new allocation, so we only need to concern ourselves with
      83             :      * not reading beyond the end of the original allocation's memory.  The
      84             :      * drawback here is that we may copy more bytes than we need to, which
      85             :      * only amounts to wasted effort.  We can safely subtract the extra bytes
      86             :      * that we requested to allow us to align the pointer.  We must also
      87             :      * subtract the space for the unaligned pointer's MemoryChunk since
      88             :      * GetMemoryChunkSpace should have included that.  This does assume that
      89             :      * all context types use MemoryChunk as a chunk header.
      90             :      */
      91           0 :     old_size = GetMemoryChunkSpace(unaligned) -
      92             :         PallocAlignedExtraBytes(alignto) - sizeof(MemoryChunk);
      93             : 
      94             : #ifdef MEMORY_CONTEXT_CHECKING
      95             :     /* check that GetMemoryChunkSpace returned something realistic */
      96             :     Assert(old_size >= redirchunk->requested_size);
      97             : #endif
      98             : 
      99           0 :     ctx = GetMemoryChunkContext(unaligned);
     100           0 :     newptr = MemoryContextAllocAligned(ctx, size, alignto, flags);
     101             : 
     102             :     /*
     103             :      * We may memcpy beyond the end of the original allocation request size,
     104             :      * so we must mark the entire allocation as defined.
     105             :      */
     106           0 :     if (likely(newptr != NULL))
     107             :     {
     108             :         VALGRIND_MAKE_MEM_DEFINED(pointer, old_size);
     109           0 :         memcpy(newptr, pointer, Min(size, old_size));
     110             :     }
     111           0 :     pfree(unaligned);
     112             : 
     113           0 :     return newptr;
     114             : }
     115             : 
     116             : /*
     117             :  * AlignedAllocGetChunkContext
     118             :  *      Return the MemoryContext that 'pointer' belongs to.
     119             :  */
     120             : MemoryContext
     121           0 : AlignedAllocGetChunkContext(void *pointer)
     122             : {
     123           0 :     MemoryChunk *redirchunk = PointerGetMemoryChunk(pointer);
     124             :     MemoryContext cxt;
     125             : 
     126             :     VALGRIND_MAKE_MEM_DEFINED(redirchunk, sizeof(MemoryChunk));
     127             : 
     128             :     Assert(!MemoryChunkIsExternal(redirchunk));
     129             : 
     130           0 :     cxt = GetMemoryChunkContext(MemoryChunkGetBlock(redirchunk));
     131             : 
     132             :     VALGRIND_MAKE_MEM_NOACCESS(redirchunk, sizeof(MemoryChunk));
     133             : 
     134           0 :     return cxt;
     135             : }
     136             : 
     137             : /*
     138             :  * AlignedAllocGetChunkSpace
     139             :  *      Given a currently-allocated chunk, determine the total space
     140             :  *      it occupies (including all memory-allocation overhead).
     141             :  */
     142             : Size
     143           0 : AlignedAllocGetChunkSpace(void *pointer)
     144             : {
     145           0 :     MemoryChunk *redirchunk = PointerGetMemoryChunk(pointer);
     146             :     void       *unaligned;
     147             :     Size        space;
     148             : 
     149             :     VALGRIND_MAKE_MEM_DEFINED(redirchunk, sizeof(MemoryChunk));
     150             : 
     151           0 :     unaligned = MemoryChunkGetBlock(redirchunk);
     152           0 :     space = GetMemoryChunkSpace(unaligned);
     153             : 
     154             :     VALGRIND_MAKE_MEM_NOACCESS(redirchunk, sizeof(MemoryChunk));
     155             : 
     156           0 :     return space;
     157             : }