Hi D community!

I'm here again, to describe what I've done during the fourteenth week of
Symmetry Autumn of Code. Updates on my COVID situation: I successfully
recovered from it, just feel some tiredness and lack of energy sometimes, but
other than that, dry cough is now occasional and I already recovered from the
other symptoms such as lack of smell and taste, and fever. Nothing to worry,
from now on :)

Milestone 4 rough task list

Since the route of the project changed a bit and I had no concrete plans for
the 4th milestone on my previous milestone list, I wrote some rough list of
tasks to tick off during development. This list can be quite extensive, since
there is a lot to integrate with LLDB. The general idea would be to adapt Clang
logic and decouple it as much as possible to make that logic more language
agnostic and therefore fit D or other future languages:

• Implement DWARF basic type parsing and integration with the TypeSystem:
  To implement this, it is required to support the majority of the basic types
  not including type modifiers (only DWARF base type, DW_TAG_base_type). It
  is required to have a map between DType wrapper and the following LLDB
  enumerations:

  • lldb::Format
  • lldb::Encoding
  • lldb::BasicType

  It is also required to have some knowledge of the bit size of each basic
  type. Other built-in types like vectors may be skipped, if complicated to
  integrate at this stage.

  This enumeration mapping is responsible of formatting the output value with
  the right encoding, according to a certain type. From what I'm aware of and
  according to my knowledge on the LLVM infrastructure, this is the only thing
  required to get value dumping done, but some additional step may be required,
  in practice. I still need to understand a bit more what Dump, DumpValue,
  DumpSummary and other dump related methods are for.

  After this, the next step is to support other types such as:

  • Support type modifiers: To fully support types it is required to read
    other considered type modifiers such as pointers, typedefs (aliases) and
    types associated with a type qualifier such as const, immutable, ...

  • Support aggregate types: Aggregate types such as structs, unions or
    classes need to be supported. Only simple support is desired, since stuff
    like inheritance can be a bit more complicated to handle. At least struct
    fields or base class members may be simple enough.

  • Support arrays: Not to be confused with D slices, which are technically
    interpreted as structs. D slices can be later recognized as native dynamic
    arrays, but synthetic formatters can handle it for now (work done on the
    Milestone 2). The idea here, at this stage, would be to support static
    stack allocated arrays.

  • Support other types: Other types like enumerations can be supported.

• Implement DWARF function parsing and integration with the TypeSystem: To
  implement this, it is required to support
  DW_TAG_subprogram/DW_TAG_subroutine_type tags which is dependent of a
  special type for functions called subroutine types. Support D linkage is
  blocked due to inconsistent calling convention on both DMD/LDC
  implementations (see my attempt to fix it
  here), so C linkage should be a
  simple way to support it or rely on GDC implementation.

  After having support for this special type, we should implement the
  ParseFunctionFromDWARF DWARFASTParser override, which is responsible of
  parsing all the function child tags, such as formal parameters including
  normal parameters and variadic parameters, and inner functions (functions
  with the context of the parent outer function).

  I haven't explored much about function features on LLDB, so there might be
  some hidden dependency I don't know about.

LLVM upstream updates

During the development of DType mapping to lldb::BasicType, I found out that
UTF-8 char basic type was missing, so I wrote two patches to implement it on
the upstream:

• https://reviews.llvm.org/D116136
• https://reviews.llvm.org/D116138

With that in mind, I also got the missing part to make unicode8 formatting
working on Clang-based TypeSystem, completing the D language plugin as well.
I've done a partial patch to fix that in the past
(D112564), so I amended it and added the
requested tests to be ready to merge.

Helpers in DType wrapper for LLDB enumerations

I implemented some helpers required in the DType wrapper to make the type kind
with:

• lldb::Format
• lldb::Encoding
• lldb::BasicType

With that done, I started tinkering with LLDB dumping system, although, some
unknown dependency is still missing (Dump functions are not being called with
those helpers implemented). My guess is that some missing type information is
required in order to LLDB recognize a type as, e.g. scalar type.

Type name dumping

Value dumping is not yet working, but I already got a way to dump the type
name. For now it is only dumping type name for bool. The output looks
something like this:

(lldb) ta v
Global variables for app.d in app:
(bool) app.bar = <No TLS data currently exists for this thread.>

app.ptr = <could not resolve type>
(bool) app.foobar =

You can consult the source code for those changes
here.

What is next?

I plan to extend type name dumping to the rest of the built-in type kinds by
mapping constant names to the kind enumeration. I also plan to hopefully have
some output about app.foobar value. For that, I'm going to investigate the
missing dependency and implement the missing logic. If that is successful, I
will extend it to the rest of the built-in types.

You can also read this on my blog,
here.

Glad to hear that you recovered from COVID!

And thanks a lot for continuing the work on LLDB integration, having great debugging capabilities is very important, the work is insane, thanks!

On Thursday, 23 December 2021 at 21:32:56 UTC, Luís Ferreira wrote:

Glad you're feeling better!

Great work! And your reports are excellent, they really communicate well what you're doing and why.