[Lldb-commits] [PATCH] D96458: [LLDB] Add support for Arm64/Linux dynamic register sets

[Muhammad Omair Javaid via Phabricator via lldb-commits]

omjavaid added a comment.

In D96458#2613244 <https://reviews.llvm.org/D96458#2613244>, @labath wrote:

> In D96458#2578760 <https://reviews.llvm.org/D96458#2578760>, @omjavaid wrote:
>
>> In D96458#2566347 <https://reviews.llvm.org/D96458#2566347>, @labath wrote:
>>
>>> I'm sorry, my response times are pretty slow these days.
>>>
>>> I'm thinking about this `ConfigureRegisterInfos` business. I get that the vector length is variable, and so we need to refresh it after every stop. However, the set of enabled extensions seems more static.
>>>
>>> Is it possible for that to change during the lifetime of the process? I'd guess not, because otherwise we'd have to also resend the register lists after every stop. And, if that's the case, I'm wondering if there's a way to reflect this static-ness in the code. For example, by doing this setup in the constructor, instead of a late `ConfigureRegisterInfos` call. IIRC, the register contexts are created when the thread is stopped, so it should be possible to fetch the information about supported registers quite early.
>>>
>>> What do you think?
>>
>> Yes that is doable. I ll move ConfigureRegisterInfos part into constructor.
>
> There's still one `ConfigureRegisterInfos` call in the `RegisterContextCorePOSIX_arm64::ConfigureRegisterContext` function. Is that an omission, or is it intentional (i.e., needed to support some arm feature)? Because, if that's intentional, then the moving the setup to the constructor does not achieve what I wanted, as the set of registers can be overridden afterwards. It also means we need to have a bigger discussion about how to communicate the changed registers between the client and server. OTOH, if it's not intentional, then I'd like to remove that call, to make it obvious that the set of registers cannot change (only their length, for sve registers and such).
>
> So, let me try to ask a direct question: Is there any situation in which the set of registers accessible to the inferior (and lldb-server) can change during the lifetime of a single process. If so, what is it?

ConfigureRegisterContext is called only once in the lifetime of a core from RegisterContextCorePOSIX_arm64 constructor. A process registers cannot change during execution which is what made basis of this change. for NativeRegisterContextLinux_arm64 I moved the ConfigureRegisterInfos logic out of configure register context because it will be called again and again during execution. But for RegisterContextCorePOSIX_arm64 we call it once in the constructor so its safe to keep the function.


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