alloc.c:
#define ALIGN_CELL (sizeof(ScmCell))
/* 8-bytes alignment (not ScmCell alignment) is required by storage-compact. */
#define ALIGN_HEAP 8
[...]
/* heaps must be aligned to sizeof(ScmCell) */
SCM_ASSERT(!((uintptr_t)p % ALIGN_HEAP));
sizeof (ScmCell) の関連。直し方わからんから放置。