#7039 Indeo3 unaligned accesses

[Willem Jan Palenstijn]

The indeo3 codec reads from the unaligned pointer 'ref_frm_pos' without using the appropriate memory access macros (READ_UINT16, READ_UINT32).

This causes crashes at least for BBVS on MIPS. Reported and tracked down by joostp.

[Willem Jan Palenstijn]

NB: There are also derived pointers such as 'ref_lp' that need attention.

[Joost Peters]

Attached is a patch that enables alignment checking in Indeo3Decoder::decodeChunk() on x86/x86_64, so that the issue can be reproduced more easily.

After applying the patch, make sure to compile ScummVM with SCUMM_NEED_ALIGNMENT defined:

CXXFLAGS="-DSCUMM_NEED_ALIGNMENT" ./configure ...

[Willem Jan Palenstijn]

I don't think that patch will work, since it won't force the compiler to generate unaligned read instructions.

I have an attempt at a fix at https://github.com/wjp/scummvm/commits/indeo3_align .
Could you test if it works for you?

[Willem Jan Palenstijn]

If I disable optimizations, and force common/endian.h to fall back to the block of single-byte reads, I can use this patch to test it on x86 it seems, and with my patch to indeo3 it then no longer crashes.

[Joost Peters]

Your patch fixes the crashes for me as well, nice. :)

[Johannes Schickel]

Sounds good. Did we convince ourselves that the writes really are no issue and are always aligned?

[Joost Peters]

I didn't check extensively, but the pointers that were written to that I looked at seemed to be aligned (don't know if that was due to luck or 'design', though).