Re: Does the page boundary check still necessary?

[Richard Henderson]

On 2/14/23 22:39, Kenneth Lee wrote:
> Hello,
>
> I hope I send this mail to the right place.
>
> I'm porting a new guest arch. It jumps of out of physical page
> constantly. So many TBs cannot be chained with goto_tb. I'm wondering
> if the following check is still necessary?
>
>         bool translator_use_goto_tb(DisasContextBase *db, target_ulong dest)
>         {
>             /* Suppress goto_tb if requested. */
>             if (tb_cflags(db->tb) & CF_NO_GOTO_TB) {
>                 return false;
>             }
>
>             /* Check for the dest on the same page as the start of the TB.  */
>             return ((db->pc_first ^ dest) & TARGET_PAGE_MASK) == 0;    <--- Is 
> this check really necessary?
>         }
>
> Now the chained TBs have been link with tb_link_page(), the chain will
> be rebuilt if it is invalidate on page. So why is this check still there?

Even for a guest which doesn't use paging, and therefore does not need to worry about 
memory maps changing, we still enable breakpoints and watchpoints on a per-page basis.


r~