Characteristic write error on cli process stack guard page. Resetting log2_n_stack_bytes to 16 fixes the problem.

DBGvpp# ex /scratch/dbarach/janitor/build-root/setup.40g
PMD: i40e_set_tx_function(): Simple tx finally be used.
PMD: i40e_set_rx_function(): Port[0] doesn't meet Vector Rx preconditions
PMD: i40e_set_rx_function(): Rx Burst Bulk Alloc Preconditions are satisfied. Rx Burst Bulk Alloc function will be used on port=0.
PMD: i40e_dev_rx_queue_start(): >>
PMD: i40e_dev_tx_queue_start(): >>

Program received signal SIGSEGV, Segmentation fault.
0x00000000006b660e in i40e_asq_send_command (hw=0x7fff38bcde80, desc=0x7fffc4ef6540, buff=0x0, buff_size=0, cmd_details=0x0)
at /scratch/dbarach/janitor/build-root/build-vpp_debug-native/dpdk/dpdk-16.04/drivers/net/i40e/base/i40e_adminq.c:896
(gdb) x/i $pc
=> 0x6b660e <i40e_asq_send_command+22349>: mov %rax,-0x7048(%rbp)
(gdb) i r rbp
rbp 0x7fffc4ef6500 0x7fffc4ef6500
(gdb) p/x 0x7fffc4ef6500
$11 = 0x7fffc4ef6500
(gdb) p/x 0x7fffc4ef6500 - 0x7048
$12 = 0x7fffc4eef4b8 <--- in stack guard page
(gdb) p getpid()
$13 = 8429
(gdb) i r sp
sp 0x7fffc4eee830 0x7fffc4eee830

From /proc/maps:

7fff9ec45000-7fffc4eef000 rw-p 00000000 00:00 0 cli process stack
7fffc4eef000-7fffc4ef0000 r--p 00000000 00:00 0 stack guard page
$