Bug#215448: di_mem_chunk_alloc() should return sizeof(long) or better alignment

[Richard Hirst <rhirst@linuxcare.com>]

package: libdebian-installer
version: cvs
tags: d-i

di_mem_chunk_alloc() returns 4 byte aligned areas, even on 64 bit
platforms.  This is bad, when the caller is going to lay some struct
containing longs or pointers over the alloc-ed memory.  On ia64 it
results in loads of unaligned access exceptions flooding dmesg.

Alloc-ed memory comes from the mem[] array in the following struct
(from src/mem.c):

struct di_mem_area
{
  di_mem_area *next;           /**< the next mem area */
  di_mem_area *prev;           /**< the previous mem area */
  di_ksize_t index;            /**< the current index into the "mem" array */
  di_ksize_t free;             /**< the number of free bytes in this mem area */
  di_ksize_t allocated;        /**< the number of atoms allocated from this area */
  char mem[MEM_AREA_SIZE];     /**< the mem array from which atoms get allocated
                                *   the actual size of this array is determined by
                                *   the mem chunk "area_size". ANSI says that it
                                *   must be declared to be the maximum size it
                                *   can possibly be (even though the actual size
                                *   may be less).
                                */
};


given:

include/debian-installer/types.h:typedef uint32_t di_ksize_t

the above array comes out at 4 byte alignment.

We need to make mem[] aligned(MEM_ALIGN).

I also wonder about MEM_AREA_SIZE being hardwired at 4, although I
didn't dig in to the code far enough to see if it should be 8 on 64 bit
platforms.