Hi,

I can't figure out how this field is used. The comment says it's "Currently executing TB", but actually it's the first TB in a chain of TBs executed. Grep shows the only place it is really checked is tb_invalidate_phys_page_range(). That code seems to be introduced long ago in:

commit ea1c18022edd0e2c45552d6fc2da6e15a3486b33
Author: bellard <bellard@c046a42c-6fe2-441c-8c8c-71466251a162>
Date:   Mon Jun 14 18:56:36 2004 +0000

    fixed self modifying code in case of asynchronous interrupt

I suspect it's only related to user emulation. But I would appreciate if someone could give me an idea of how this really works :)

/* mask must never be zero, except for A20 change call */
void cpu_interrupt(CPUState *env, int mask)
{              
    TranslationBlock *tb;
    static int interrupt_lock;
                         
    env->interrupt_request |= mask;
    /* if the cpu is currently executing code, we must unlink it and
       all the potentially executing TB */
    tb = env->current_tb;
    if (tb && !testandset(&interrupt_lock)) {
        env->current_tb = NULL;
        tb_reset_jump_recursive(tb);
        interrupt_lock = 0;
    }
}

if (cpu->interrupt_request && cpu->current_tb) {
    cpu_interrupt(cpu, cpu->interrupt_request);
}