[cfe-dev] [RFC] New ClangDebuggerSupport Library

[Chris Bieneman via cfe-dev]

David, the two approaches address very different problems.

The YAML tools are focused on a bit-for-bit identical round trip path for DWARF into and out of YAML. The goal with that work is to be able to generate a test suite from the output of many different versions of many different compilers. This is specifically with the goal of creating LIT-style tests that read DWARF and operate on it.

-Chris

> On Dec 12, 2016, at 3:57 PM, David Blaikie via cfe-dev <cfe-dev at lists.llvm.org> wrote:
> 
> I realize work is already underway/being committed here, but figured discussing the following in this thread rather than on some random commit email might be better.
> 
> We now have two ways of generating DWARF, both committed in relation to a similar effort to integrate LLDB better with teh rest of the LLVM project.
> 
> There's this YAML effort, to help test the library that will allow the generation of Clang ASTs from DWARF. (currently such code resides in LLDB, and it's proposing to be rolled up into Clang here)
> 
> Then there's Greg's effort to provide a unit test API for generating DWARF for unit testing LLVM's DWARF parsing APIs for use in LLDB (currently what LLVM has was a fork of LLDB's, and Greg's working on reconciling that, rolling in LLDB's post-fork features, then migrating LLDB to use the fully featured LLVM version)
> 
> Why are these done in two different ways? They seem like really similar use cases - generating DWARF for the purpose of testing some (LLVM or Clang) API that consumes DWARF bytes.
> 
> Could we resolve this in favor of one approach or the other - I'm somewhat partial to the API approach & writing unit tests against the ClangDebuggerSupport library, myself.
> 
> - David
> 
> On Wed, Nov 9, 2016 at 2:26 PM Chris Bieneman via cfe-dev <cfe-dev at lists.llvm.org <mailto:cfe-dev at lists.llvm.org>> wrote:
> Hello cfe-dev,
> 
> I would like to propose a new Clang library for implementing functionality that is used by LLDB. I see this as the first step in a long process of refactoring the language interfaces for LLDB.
> 
> The short-term goal is for this library is to be a place for us to rebuild functionality that exists in LLDB today and relies heavily on the implementation of Clang. As we rebuild the functionality we will build a suite of testing tools in Clang that exercise this library and more general Clang functionality in the same ways that LLDB will.
> 
> As bits of functionality become fully implemented and tested, we will migrate LLDB to using the Clang implementations, allowing LLDB to remove its own copies. This will provide the Clang community with a higher confidence that changes in Clang do not break LLDB, and it will provide LLDB with better test coverage of the Clang functionality.
> 
> The long-term goal of this library is to provide the implementation for what could some day become a defined debugger<->frontend interface for providing modularized (maybe even plugin-based) language debugging support in LLDB. In the distant future I could see us being able to tell people building new frontends that we have a defined interface they need to implement for the debugger, and once implemented the debugger should “Just Work”.
> 
> The first bit of functionality that I would like to build up into the ClangDebuggerSupport library is materialization of Clang AST types from DWARF. To support this development I intend to add a new tool in Clang that reads DWARF types, generates a Clang AST, and prints the AST. I will also add DWARF support to obj2yaml and yaml2obj, so we will be able to write YAML LIT tests for the functionality.
> 
> If people are in favor of this general approach I’ll begin working in this direction, and I’ll probably add the new library sometime next month.
> 
> Thoughts?
> -Chris
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