Re: [Qemu-devel] Question regarding self-modifying code.

[farmdve]

Sorry about that. Somehow Google decided it should reply to you, rather than the mailing list. It was an honest mistake.

Original question is below

I am unable to get this part here if (!(tb_end <= start || tb_start >= end)) in tb_invalidate_phys_page_range

What would happen if code forward modifies itself, but that condition evaluates to true? 

Then this piece here won't get executed

> #ifdef TARGET_HAS_PRECISE_SMC

>             if (current_tb_not_found) {

>                 current_tb_not_found = 0;

>                 current_tb = NULL;

>                 if (cpu->mem_io_pc) {

>                     /* now we have a real cpu fault */

>                     current_tb = tb_find_pc(uc, cpu->mem_io_pc);

>                 }

>             }

>            if (current_tb == tb &&

>                 (current_tb->cflags & CF_COUNT_MASK) != 1) {

>                 /* If we are modifying the current TB, we must stop

>                 its execution. We could be more precise by checking

>                 that the modification is after the current PC, but it

>                 would require a specialized function to partially

>                 restore the CPU state */

> 

>                current_tb_modified = 1;

>                 // self-modifying code will restore state from TB

>                 cpu_restore_state_from_tb(cpu, current_tb, cpu->mem_io_pc);

>                 cpu_get_tb_cpu_state(env, &current_pc, &current_cs_base,

>                                      &current_flags);

>            }

> #endif /* TARGET_HAS_PRECISE_SMC */

> It just so happens I am experiencing such a case.

On 14 January 2016 at 11:58, Peter Maydell <address@hidden> wrote:

On 14 January 2016 at 00:37, farmdve <address@hidden> wrote:
> I am unable to get this part here if (!(tb_end <= start || tb_start >= end))
> in tb_invalidate_phys_page_range
>
> What would happen if code forward modifies itself, but that condition
> evaluates to true?

Please can you send questions to the mailing list, not to
me personally. That way anybody who knows and has time to
answer can do so.

thanks
-- PMM