(1) Enable softmmu for userland. This is of course the highest overhead,
but will work for all combinations.
This option would solve a lot of problems and simplify a lot of code:
unaligned access on hosts requiring strict alignements, different page
size between host and guest, self-modifying code, 64-bit user land on
32-bit host, etc... That's what currently comes to my mind, but that
would solve a lot more problems.
It will clearly have a high overhead, but it might be interesting to
quantify it, to see if we should continue to add tons of code/workaround
to linux-user instead of switching to softmmu for userland. It could
also be optimized, for example by increasing the TLB size compared to
system mode, and doing TLB preallocation on mmap calls.