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/*-------------------------------------------------------------------------
*
* alignedalloc.c
* Allocator functions to implement palloc_aligned
*
* This is not a fully-fledged MemoryContext type as there is no means to
* create a MemoryContext of this type. The code here only serves to allow
* operations such as pfree() and repalloc() to work correctly on a memory
* chunk that was allocated by palloc_aligned().
*
* Portions Copyright (c) 2022-2023, PostgreSQL Global Development Group
*
* IDENTIFICATION
* src/backend/utils/mmgr/alignedalloc.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "utils/memdebug.h"
#include "utils/memutils_memorychunk.h"
/*
* AlignedAllocFree
* Frees allocated memory; memory is removed from its owning context.
*/
void
AlignedAllocFree(void *pointer)
{
MemoryChunk *chunk = PointerGetMemoryChunk(pointer);
void *unaligned;
VALGRIND_MAKE_MEM_DEFINED(chunk, sizeof(MemoryChunk));
Assert(!MemoryChunkIsExternal(chunk));
/* obtain the original (unaligned) allocated pointer */
unaligned = MemoryChunkGetBlock(chunk);
#ifdef MEMORY_CONTEXT_CHECKING
/* Test for someone scribbling on unused space in chunk */
if (!sentinel_ok(pointer, chunk->requested_size))
elog(WARNING, "detected write past chunk end in %s %p",
GetMemoryChunkContext(unaligned)->name, chunk);
#endif
pfree(unaligned);
}
/*
* AlignedAllocRealloc
* Change the allocated size of a chunk and return possibly a different
* pointer to a memory address aligned to the same boundary as the
* originally requested alignment. The contents of 'pointer' will be
* copied into the returned pointer up until 'size'. Any additional
* memory will be uninitialized.
*/
void *
AlignedAllocRealloc(void *pointer, Size size)
{
MemoryChunk *redirchunk = PointerGetMemoryChunk(pointer);
Size alignto;
void *unaligned;
MemoryContext ctx;
Size old_size;
void *newptr;
VALGRIND_MAKE_MEM_DEFINED(redirchunk, sizeof(MemoryChunk));
alignto = MemoryChunkGetValue(redirchunk);
unaligned = MemoryChunkGetBlock(redirchunk);
/* sanity check this is a power of 2 value */
Assert((alignto & (alignto - 1)) == 0);
/*
* Determine the size of the original allocation. We can't determine this
* exactly as GetMemoryChunkSpace() returns the total space used for the
* allocation, which for contexts like aset includes rounding up to the
* next power of 2. However, this value is just used to memcpy() the old
* data into the new allocation, so we only need to concern ourselves with
* not reading beyond the end of the original allocation's memory. The
* drawback here is that we may copy more bytes than we need to, which
* only amounts to wasted effort. We can safely subtract the extra bytes
* that we requested to allow us to align the pointer. We must also
* subtract the space for the unaligned pointer's MemoryChunk since
* GetMemoryChunkSpace should have included that. This does assume that
* all context types use MemoryChunk as a chunk header.
*/
old_size = GetMemoryChunkSpace(unaligned) -
PallocAlignedExtraBytes(alignto) - sizeof(MemoryChunk);
#ifdef MEMORY_CONTEXT_CHECKING
/* check that GetMemoryChunkSpace returned something realistic */
Assert(old_size >= redirchunk->requested_size);
#endif
ctx = GetMemoryChunkContext(unaligned);
newptr = MemoryContextAllocAligned(ctx, size, alignto, 0);
/*
* We may memcpy beyond the end of the original allocation request size,
* so we must mark the entire allocation as defined.
*/
VALGRIND_MAKE_MEM_DEFINED(pointer, old_size);
memcpy(newptr, pointer, Min(size, old_size));
pfree(unaligned);
return newptr;
}
/*
* AlignedAllocGetChunkContext
* Return the MemoryContext that 'pointer' belongs to.
*/
MemoryContext
AlignedAllocGetChunkContext(void *pointer)
{
MemoryChunk *redirchunk = PointerGetMemoryChunk(pointer);
MemoryContext cxt;
VALGRIND_MAKE_MEM_DEFINED(redirchunk, sizeof(MemoryChunk));
Assert(!MemoryChunkIsExternal(redirchunk));
cxt = GetMemoryChunkContext(MemoryChunkGetBlock(redirchunk));
VALGRIND_MAKE_MEM_NOACCESS(redirchunk, sizeof(MemoryChunk));
return cxt;
}
/*
* AlignedAllocGetChunkSpace
* Given a currently-allocated chunk, determine the total space
* it occupies (including all memory-allocation overhead).
*/
Size
AlignedAllocGetChunkSpace(void *pointer)
{
MemoryChunk *redirchunk = PointerGetMemoryChunk(pointer);
void *unaligned;
Size space;
VALGRIND_MAKE_MEM_DEFINED(redirchunk, sizeof(MemoryChunk));
unaligned = MemoryChunkGetBlock(redirchunk);
space = GetMemoryChunkSpace(unaligned);
VALGRIND_MAKE_MEM_NOACCESS(redirchunk, sizeof(MemoryChunk));
return space;
}
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