panic in ivy_rng_store() when compiled with -O0

[Navdeep Parhar]

I built my kernel + modules (head as of today) with -O0 and now it 
panics during boot.  I did bump up KSTACK_PAGES significantly so that's 
not the problem.  I'm going to take out the RNG device next and see if I 
can get past this.

Regards,
Navdeep

Fatal trap 9: general protection fault while in kernel mode
cpuid = 0; apic id = 00
instruction pointer	= 0x20:0xffffffff814ac661
stack pointer	        = 0x28:0xfffffe01ed6c6930
frame pointer	        = 0x28:0xfffffe01ed6c6960
code segment		= base 0x0, limit 0xfffff, type 0x1b
			= DPL 0, pres 1, long 1, def32 0, gran 1
processor eflags	= interrupt enabled, resume, IOPL = 0
current process		= 14 (rand_harvestq)
[ thread pid 14 tid 100017 ]
Stopped at      ivy_rng_store+0x31:     movq    %rdi,(%rdi)
db> bt
Tracing pid 14 tid 100017 td 0xfffff800042c84c0
ivy_rng_store() at ivy_rng_store+0x31/frame 0xfffffe01ed6c6960
random_ivy_read() at random_ivy_read+0x78/frame 0xfffffe01ed6c6990
live_entropy_sources_feed() at live_entropy_sources_feed+0x73/frame 
0xfffffe01ed6c69d0
random_kthread() at random_kthread+0x224/frame 0xfffffe01ed6c6a30
fork_exit() at fork_exit+0x14a/frame 0xfffffe01ed6c6ab0
fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe01ed6c6ab0
--- trap 0, rip = 0, rsp = 0xfffffe01ed6c6b70, rbp = 0 ---