add support for watchpoint on kernel space address

[htbegin]

Description

Add support for watchpoint on absolute kernel space address, so the following command can run correctly:

# bpftrace -e "watchpoint::0x$(awk '$3 == "jiffies" {print $1}' /proc/kallsyms):8:w {@[kstack] = count();}"
Attaching 1 probe...   
^C
@[
    do_timer+12
    tick_do_update_jiffies64.part.22+89
    tick_sched_do_timer+103
    tick_sched_timer+39
    __hrtimer_run_queues+256
    hrtimer_interrupt+256
    smp_apic_timer_interrupt+106
    apic_timer_interrupt+15
    cpuidle_enter_state+188
    cpuidle_enter+41
    do_idle+536
    cpu_startup_entry+25
    start_secondary+355
    secondary_startup_64+164
]: 319

Checklist

• Language changes are updated in docs/reference_guide.md
• User-visible and non-trivial changes updated in CHANGELOG.md
• The new behaviour is covered by tests

[danobi]

Thanks for the patch!

Can you update the changelog as well? Other than that and a small nit, LGTM.

[danobi]

@fbs Do you think this should be a squash + rebase + merge or just rebase + merge?

[fbs]

@fbs Do you think this should be a squash + rebase + merge or just rebase + merge?

Looking at the individual commit messages an rebase+merge seems ok to me. But for cases where its a simple add test for a single change a squash sounds better to me