1 files changed, 132 insertions, 0 deletions
diff --git a/src/backend/utils/mmgr/alignedalloc.c b/src/backend/utils/mmgr/alignedalloc.c
new file mode 100644
index 00000000000..62f9dbfe89a
--- /dev/null
+++ b/src/backend/utils/mmgr/alignedalloc.c
@@ -0,0 +1,132 @@
+/*-------------------------------------------------------------------------
+ *
+ * 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, 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;
+
+	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 = MemoryChunkGetValue(redirchunk);
+	void	   *unaligned = MemoryChunkGetBlock(redirchunk);
+	MemoryContext ctx;
+	Size		old_size;
+	void	   *newptr;
+
+	/* 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 *chunk = PointerGetMemoryChunk(pointer);
+
+	Assert(!MemoryChunkIsExternal(chunk));
+
+	return GetMemoryChunkContext(MemoryChunkGetBlock(chunk));
+}
+
+/*
+ * 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 = MemoryChunkGetBlock(redirchunk);
+
+	return GetMemoryChunkSpace(unaligned);
+}