Integer overflow in codegen

[clayton-shopify]

An integer overflow in the codegen (leading to a segfault) can be demonstrated as follows:

ruby -e 'puts "begin" ; puts "rescue" ; 16380.times { puts "a" } ; puts "end"' | bin/mruby -v

The generated code begins as follows:

irep 0x7fb97e500020 nregs=3 nlocals=1 pools=0 syms=3 reps=0
file: -
    2 000 OP_ONERR	003
    2 001 OP_LOADNIL	R1
    2 002 OP_JMP	-32765
    2 003 OP_RESCUE	R1

Clearly the generated OP_JMP is invalid.

I see that jumps are 16 bit, so I guess the codegen should either detect the problem and exit, or cope with it some other way.

This issue was reported by https://hackerone.com/ssarong