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 <peter.mayd...@linaro.org> wrote:

> On 14 January 2016 at 00:37, farmdve <farm...@gmail.com> 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
>