[cfe-dev] [RFC] New ClangDebuggerSupport Library

[David Blaikie via cfe-dev]

On Wed, Nov 9, 2016 at 2:26 PM Chris Bieneman via cfe-dev <
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?
>

My knee-jerk reaction is that this could just as well live in LLDB if there
are no other users - though Keno points out he could use it in Julia, so
that seems like potentially sufficient interest to demonstrate that it
might be a reasonable/reusable abstraction.

I'll leave it up to Richard or others to weigh in on whether the ongoing
cost to the Clang project would be worth the benefit to these users/use
cases.

Beyond that - as for testing infrastructure. I'd like to make sure we only
have one piece of code for generating DWARF, as we are trying to have one
piece of code for reading it (& perhaps in some far off future - we could
have one piece of code that does both, to some degree - at least some more
shared information about the size/representation of forms, etc) - so
however we're generating DWARF, it'd be good if that used the APIs in
llvm's lib/CodeGen/AsmPrinter (potentially refactored out to some more
general purpose location & generalized somewhat).

Not sure exactly what sort of syntax (how low level - presumably not raw
bytes written in hex or anything) you're thinking of for writing DWARF -
wonder if we could have a syntax that's nice enough to read that it's
either the standard form llvm-dwarfdump could use, or at least a flag to
enable it? (obviously dwarfdump wants to print things like byte offsets,
etc - but a higher level symbolic rendering would probably be nice for many
uses and be more likely what you'd want to write when writing a test case)

- Dave


> -Chris
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