#290 Fix crash caused by an unaligned memory access on arm64 machines

[f0rt]

The arm64 Linux kernel of the Debian distribution is configured to no longer handle unaligned memory accesses. An unalinged double word access can occur in line 375 within the generate_uninstall_icon_data function of the Source/icon.cpp file.

The size of the icon group is calculated as the following:

line 341-343:

  // calculate size
   size_t group_size = sizeof(IconGroupHeader) // header
     + order.size() * SIZEOF_RSRC_ICON_GROUP_ENTRY; // entries

sizeof(IconGroupHeader) = 6
SIZEOF_RSRC_ICON_GROUP_ENTRY = 14

group_size is a multiple of a double word for uneven numbers of order.size() but not if order.size() is an even number.

For illustration group_size for the order.size() values of 1 and 2:
group_size = 6 + 1 * 14 = 20 (double word aligned)
group_size = 6 + 2 * 14 = 34 (not double word aligned)

If group_size is not double world aligned then seeker will no longer be double word aligned from line 367 onwards.

line 366 and 367:

  memcpy(seeker, group, group_size);
  seeker += group_size;

The bug was originally submitted via the Debian Bug Tracking system as bug number #918376.

Instead of the proposed patch included in the e-mail thread of the Debian bug report I would rather go with the attached patch.

In the attached patch I use memcpy and memset to avoid the unaligned double word memory access. In addition the endian conversion for size is done only once in the for loop (line 370).

[Jason]

Does this not affect the uninstaller code in build.cpp? There is a duplicate there for icons too.