Re: [Qemu-devel] [PATCH] target-*: Advance pc after recognizing a breakpoint

[Sergey Fedorov <serge.fdrv@gmail.com>]

On 16.10.2015 19:36, Sergey Fedorov wrote:
> On 16.10.2015 17:08, Sergey Fedorov wrote:
>> On 16.10.2015 04:14, Richard Henderson wrote:
>>> On 10/16/2015 03:36 AM, Peter Maydell wrote:
>>>> On 14 October 2015 at 22:02, Richard Henderson <rth@twiddle.net> wrote:
>>>>> On 10/15/2015 06:34 AM, Peter Maydell wrote:
>>>>>> This is still the same cryptic comment we have in the
>>>>>> targets which do do this. Can we have something
>>>>>> that is a bit more explanatory about what is going on and
>>>>>> why we need to do this, please?
>>>>> Suggestions?
>>>> ...well, I don't entirely understand the problem it's
>>>> fixing, which is why I'm asking for a better comment :-)
>>> Heh.  Fair enough.  How about
>>>
>>>   /* The address covered by the breakpoint must be included in
>>>      [tb->pc, tb->pc + tb->size) in order to for it to be
>>>      properly cleared -- thus we increment the PC here so that
>>>      the logic setting tb->size below does the right thing.  */
>>>
>>> There are two edge cases that cause the problem with clearing that
>>> could be described, but I think that the comment becomes too bulky, as
>>> well as confuses the situation for someone cutting-and-pasting the
>>> logic to a new port.
>> Maybe we could rather fix that condition in
>> tb_invalidate_phys_page_range()? It seems weird that it can't handle a
>> zero-sized TB.
> I think extending "!(tb_end <= start || tb_start >= end)" condition to
> "!(tb_end <= start || tb_start >= end) || tb_start == start" would work
> fine. Thoughts? I could prepare a patch for that.

But there are at least two other places which doesn't seem to support a
zero-sized TB: build_page_bitmap(), and tb_gen_code() when checking if a
next page is needed.

Best,
Sergey