Build kernel with option VERBOSE_SYSINIT, turn the knob debug.verbose_sysinit on and boot with pre-loaded kernel modules such zfs.ko.
```
# dmesg
...
subsystem 2000000
usb_dev_init(0)... done.
linker_init(0)... done.
module_init(0)... done.
dpcpu_startup(0)... done.
vnet_data_startup(0)... done.
link_elf_init(0)... done.
link_elf_init(0)... done.
linker_preload(0)... done.
subsystem 700000
tunable_int_init(&__tunable_int_293)... done.
tunable_int_init(&__tunable_int_299)... done.
tunable_int_init(&__tunable_int_461)... done.
tunable_int_init(&__tunable_int_467)... done.
opensolaris_utsname_init(0)... done.
subsystem 1800000
malloc_init(&M_CRYPTODEV)... done.
malloc_init(&M_CXGBE)... done.
malloc_init(&M_SOLARIS)... done.
malloc_init(&M_KSTAT)... done.
malloc_init(&M_TASKQ)... done.
malloc_init(&M_ZONES)... done.
malloc_init(&M_SFSNODES)... done.
kmem_size_init(0)... done.
subsystem 1b00000
sx_sysinit(&cxgbe_mlu_args)... done.
mtx_sysinit(&zfs_debug_mtx_args)... done.
subsystem 2000000
dbcmd_panic_add(0)... done.
dbshow_all_procs_add(0)... done.
dbshow_thread_add(0)... done.
dbshow_proc_add(0)... done.
dbshow_watches_add(0)... done.
acpi_pm_register(0)... done.
...
```