[llvm-dev] RFC: libtrace

Adrian Prantl via llvm-dev llvm-dev at lists.llvm.org
Tue Jun 26 13:28:41 PDT 2018

> On Jun 26, 2018, at 11:58 AM, Zachary Turner via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> Hi all,
> We have been thinking internally about a lightweight llvm-based ptracer.  To address one question up front: the primary way in which this differs from LLDB is that it targets a more narrow use case -- there is no scripting support, no clang integration, no dynamic extensibility, no support for running jitted code in the target, and no user interface.  We have several use cases internally that call for varying levels of functionality from such a utility, and being able to use as little as possible of the library as is necessary for the given task is important for the scale in which we wish to use it. 
> We are still in early discussions and planning, but I think this would be a good addition to the LLVM upstream.  Since we’re approaching this as a set of small isolated components, my thinking is to work on this completely upstream, directly under the llvm project (as opposed to making a separate subproject), but I’m open to discussion if anyone feels differently.
> LLDB has solved a lot of the difficult problems needed for such a tool.  So in the spirit of code reuse, we think it’s worth trying componentize LLDB by sinking pieces into LLVM and rebasing LLDB as well as these smaller tools on top of these components, so that smaller tools can reduce code duplication and contribute to the overall health of the code base.

Do you have a rough idea of what components specifically the new tool would need to function?

>  At the same time we think that in doing so we can break things up into more granular pieces, ultimately exposing a larger testing surface and enabling us to create exhaustive tests, giving LLDB more fine grained testing of important subsystems.

Are you thinking of the new utility as something that would naturally live in llvm/tools or as something that would live in the LLDB repository?

> A good example of this would be LLDB’s DWARF parsing code, which is more featureful than LLVM’s but has kind of evolved in parallel.  Sinking this into LLVM would be one early target of such an effort, although over time there would likely be more.

As you are undoubtedly aware we've been carefully rearchitecting LLVM's DWARF parser over the last few years to eventually become featureful enough so that LLDB could use it, so any help on that front would be most welcome. As long as we are careful to not regress in performance/lazyness, features and fault-tolerance, deduplicating the implementations can only be good for LLVM and LLDB.

-- adrian

> Anyone have any thoughts / strong opinions on this proposal, or where the code should live?  Also, does anyone have any suggestions on things they’d like to see come out of this?  Whether it’s a specific new tool, new functionality to an existing tool, an architectural or design change to some existing tool or library, or something else entirely, all feedback and ideas are welcome.
> Thanks,
> Zach
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