False positive permanent breakpoints

Pedro Alves palves@redhat.com
Wed Oct 26 15:14:00 GMT 2016


On 10/26/2016 04:02 PM, Ofir Cohen wrote:
>> I'd rather that upstreaming that bit was done when the
>> rest of the port is submitted as well.
> Alright, will do.
> 
> As a temporary mitigation,
> Is it OK for the target to return NULL from gdbarch_breakpoint_from_pc
> to state that it doesn't support software breakpoints ?
> 

I think so.

> 
> There are some places that check that return value, like:
> /* Software breakpoints unsupported?  */
> if (bpoint == NULL)
>   return 0;
> 
> in bp_loc_is_permanent(), and others that don't, like breakpoint_xfer_memory().
> Furthermore, it performs pointer arithmetic based on the returned value.

If you don't have software breakpoints in the list, then
bp_location_has_shadow will return false for all breakpoints?
Sounds like we could skip most of the work, but that's an
optimization, not a correctness issue?

> 
> Currently the tests we have pass, but I'm concerned about other corner
> cases are not covered
> that might pop up as a result of this change.

I can't think of any offhand.  Mainly because it's not usual for me to
work with targets that don't support sofware breakpoints.  So I'd
say -- try it and see what breaks.  Which you already did.  :-)

Thanks,
Pedro Alves



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