Re: [PATCH 1/2] This patch fixes GDBServer's run control for single stepping

[Yao Qi <qiyaoltc at gmail dot com>]

On Fri, Jan 27, 2017 at 4:06 PM, Antoine Tremblay
<antoine.tremblay@ericsson.com> wrote:
>> GDB/GDBserver has to emulate the instruction on how does it affect the
>> flag, and only insert the breakpoint on the "true" branch.  Since the
>> target instruction will be definitely executed, we can safely use
>> 16-bit breakpoint instruction.
>
> Ouch, reading the kernel thread it looks like this emulation would be
> complex to say the least.
>

There are some other ideas discussed in the kernel threads, but I didn't
go through them.  They may work.  If emulation is complex, probably
we can partially fix this problem by "always using 16-bit thumb instruction
if program is out of IT block".

> I think it would be better to get the current single stepping working
> with the stop all threads logic since GDBServer was working like that
> when GDB was doing the single stepping anyway. This would fix the current
> regression.
>
> Then work could be done to improve GDBServer to be better at
> non-stopping.
>
> WDYT ?
>

Sounds like we are applying the ARM linux limitation to a general place.
Other software single step targets may write breakpoint in atomic way,
so we don't need to stop all threads.  Even in -marm mode, we don't
have to stop all threads on inserting breakpoints.

-- 
Yao (齐尧)