Re: [PING][PATCH,v5][AArch64] MTE corefile support

[John Baldwin <jhb@FreeBSD.org>]

On 7/28/21 7:26 PM, Simon Marchi via Gdb-patches wrote:
> On 2021-07-14 9:07 a.m., Catalin Marinas wrote:
>> On Sun, Jul 11, 2021 at 07:22:00AM -0700, Joel Brobecker wrote:
>>> Luis is trying to have this new feature ready for the GDB 11.1
>>> release. As I understand it, the AArch64-specific part has already
>>> been approved, so he's waiting for someone to review the rest of
>>> the changes. Is there a Global Maintainer who would feel comfortable
>>> doing so and who would have the time?
>>
>> I'm a Linux kernel maintainer, so not much for me to review on the gdb
>> front. But feedback from the gdb maintainers would be appreciated.
>>
>> W.r.t. upstreaming the feature in gdb, I'd wait until the Linux
>> counterpart is merged. We agreed in principle on the ABI but I wouldn't
>> consider it stable until the feature hits a kernel release.
> 
> I reviewed a few of the previous iterations, and there were only really
> some nits remaining, so I am confident that this version is OK, from a
> GDB point of view.
> 
> ABI-wise, I tend to agree with Catalin: as long as it's not in a
> released kernel, the format *could* change.  But is it a problem in
> practice?  Let's say this happens:
> 
>   - We merge support for MTE core files in GDB 11
>   - The format gets changed, merged and released in a kernel
>   - We fix GDB 12 based on the new format
> 
> Then GDB 11 users end up with a GDB that can't read MTE notes.  But had
> we not merged the support for it, they would also end up with a GDB that
> can't read MTE notes.  In both cases, we'll tell them "upgrade to GDB
> 12" (once it's released).
> 
> If we merge support for MTE in core files now and if the format
> doesn't change, everybody is happy.  I guess it depends on how likely it
> is that the format is going to change.

I think the format is suitable and probably won't need to change.  I have an
interest in using it for another type of memory tags (CHERI & Morello) and
this format will support those (and in fact it would even support an
architecture with multiple memory tags).

-- 
John Baldwin