Re: [PATCH 1/2] [gdb/tdep] Fix gdb.base/watchpoint-unaligned.exp on aarch64

[Luis Machado <luis.machado@arm.com>]

On 3/7/24 20:19, Thiago Jung Bauermann wrote:
> 
> Hello,
> 
> Luis Machado <luis.machado@arm.com> writes:
> 
>> Raising the alignment enforcement means we will cover a bigger range of addresses,
>> potentially covering our target watchpoint/trap address,
>> but I'm afraid it also means we will raise the potential for false positives, if
>> watchpoints are placed within the alignment range.
>>
>> Furthermore, we are not limited to 16-byte accesses. For SVE and SME we may be looking at
>> even bigger accesses. And, more generally, the memset/memcpy
>> instructions (not yet widely used) can potentially access arbitrary amounts of memory. So
>> tweaking the alignment is only a focused fix towards the most often
>> used instructions and access sizes at the moment.
>> The more general problem of not being able to tell which particular watchpoint caused the
>> trap remains.
>>
>> How does the above fix behave on the overall testsuite in terms of watchpoint tests?
> 
> According to the Linaro CI, there's no impact:
> 
> https://ci.linaro.org/job/tcwg_gdb_check--master-aarch64-precommit/1749/artifact/artifacts/artifacts.precommit/notify/mail-body.txt
> 
> I'm a bit surprised that there were no progressions from this patch. The
> job ran on a Mt. Jade machine.

My guess is we don't have any specific hardware watchpoint tests exercising bigger memory accesses (with SVE/SME/MOPS) with a variety
of unaligned accesses to trigger failures due to the small alignment we currently have.

> 
> --
> Thiago