Instructions whose values rely on their size can cause the assembler to crash

[NewDefectus]

E.g. jmp end - 0x81; end: forces the assembler into an infinite loop, alternating between 2-byte and 5-byte encodings.
push $. - end + 0x81; end: crashes for the same reason, as well as push $end - . - 0x82; end:

Note that gcc assembles these correctly:

• jmp end - 0x81; end: becomes E9 7F FF FF FF
• push $. - end + 0x81; end: becomes 68 7C 00 00 00
• push $end - . - 0x82; end: becomes 68 83 FF FF FF

Because expressions can be fairly complicated, the solution should probably be all-encompassing, most likely involving enforcing larger sizes on instructions that fall into this loop.