[Lldb-commits] [PATCH] D85705: Add a "Trace" plug-in to LLDB to add process trace support in stages.

Vedant Kumar via Phabricator via lldb-commits lldb-commits at lists.llvm.org
Tue Aug 11 15:35:29 PDT 2020

vsk added a comment.

In D85705#2211607 <https://reviews.llvm.org/D85705#2211607>, @clayborg wrote:

> In D85705#2211073 <https://reviews.llvm.org/D85705#2211073>, @vsk wrote:
>> This looks very cool, thanks @clayborg! I think using JSON to describe the trace data (what kind of trace is this, what's in it, etc.) sounds reasonable.
>>> For "trace load", I get the plugin for the JSON file by matching it up with the "name" field in the JSON, but I don't store the "trace_sp" anywhere. We will need to store it with the target that we create, or for later commands add it to a target that is stopped when the trace data is loaded via the process interface (through lldb-server is the current thinking for this).
>> Have you considered what might happen if there are multiple targets covered by a single trace? Strawman proposal: would it make sense to register the trace with a Debugger instance? This can be a list of traces if it makes sense to support debugging more than one trace at a time.
> I hadn't thought of that but that does make sense!
> We can work this all into the JSON format. We should actually make a schema for the common parts of information that should be represented in the JSON and also allow each plug-in to supply a schema for the parts that is requires in the JSON.
> Some ideas that this information should contain:
> - array of process infos dictionaries
> - process info dictionary
>   - pid
>   - array of shared library dictionaries
> - shared library dictionary:
>   - original path
>   - UUID if available
>   - MD5 of file if no UUID
>   - load location
>   - optional URL to download
> And LLDB will easily be able to load up N targets with everything setup correctly.

I'm generally on board with this. On Darwin we tend not to have the original path to a DSO available, so I'd argue that that ought to be optional as well. Really the only mandatory stuff for debugging purposes is the load address and some kind of UUID.

>>> "trace dump" does nothing for now, but this is what we can use to test that "trace load" worked and was able to create a target.
>> It'd be great to have some test for this, even if all 'trace load' does at this point is print an error about bad JSON input.
> I agree! If we like this format, Walter Erquinigo can commandeer this revision and fill in actual Intel PT guts and have this work. The idea is I am going to get the infrastructure in place and once we work this out, I will let Walter take over the patch and actually fill it in with real Intel PT stuff and test it fully.

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