.gdbinit

define zephyr_show_thread
    printf "State=%d; ", ((struct k_thread *)$arg0)->base.thread_state
    printf "Prio=%d; ", ((struct k_thread *)$arg0)->base.prio
    printf "Entry=%p; ", ((struct k_thread *)$arg0)->entry.pEntry
    printf "PC=%p; ", *(((struct k_thread *)$arg0)->callee_saved.psp + 20)
    printf "LR=%p; ", *(((struct k_thread *)$arg0)->callee_saved.psp + 24)
    printf "PSP=%p; ", ((struct k_thread *)$arg0)->callee_saved.psp + 32

    set $stack_start = ((struct k_thread *)$arg0)->stack_info.start
    set $stack_size = ((struct k_thread *)$arg0)->stack_info.size
    printf "Stack: %p <- %p (%u bytes)", $stack_start, $stack_start + $stack_size, $stack_size
end

define zephyr_list_threads
    set $current_thread = _kernel.threads
    set $idx = 0

    while ($current_thread != 0)
        printf "Thread %02d (%p) ", $idx, $current_thread

        zephyr_show_thread $current_thread

        if ($current_thread == _kernel->current)
            printf " <- RUNNING"
        end
        printf "\n"

        set $PC = *(((struct k_thread *)$current_thread)->callee_saved.psp + 20)
        printf "\t"
        info line *$PC

        set $idx = $idx + 1
        set $current_thread = $current_thread->next_thread
    end
end

Enable CONFIG_THREAD_MONITOR and CONFIG_THREAD_STACK_INFO
Then run "zephyr_list_threads"