My personal website source code
Log | Files | Refs | Submodules | README | LICENSE (6617B)

      1 ---
      2 title: 'SAOC LLDB D integration: 14th Weekly Update'
      3 date: '2021-12-23T19:18:00+01:00'
      4 tags: ['saoc', 'saoc2021', 'dlang', 'llvm', 'lldb', 'debug', 'debugging', 'dwarf']
      5 description: "This post describes what I've done on the 14th week of the
      6 Symmetry Autumn of Code 2021, including milestone 4 tasks list, some patches on
      7 the upstream about unicode char support, add support for type name dumping and
      8 implementation of LLDB helpers for DType wrapper."
      9 ---
     11 Hi D community!
     13 I'm here again, to describe what I've done during the fourteenth week of
     14 Symmetry Autumn of Code. Updates on my COVID situation: I successfully
     15 recovered from it, just feel some tiredness and lack of energy sometimes, but
     16 other than that, dry cough is now occasional and I already recovered from the
     17 other symptoms such as lack of smell and taste, and fever. Nothing to worry,
     18 from now on :)
     20 ## Milestone 4 rough task list
     22 Since the route of the project changed a bit and I had no concrete plans for
     23 the 4th milestone on my previous milestone list, I wrote some rough list of
     24 tasks to tick off during development. This list can be quite extensive, since
     25 there is a lot to integrate with LLDB. The general idea would be to adapt Clang
     26 logic and decouple it as much as possible to make that logic more language
     27 agnostic and therefore fit D or other future languages:
     29 - **Implement DWARF basic type parsing and integration with the TypeSystem:**
     30   To implement this, it is required to support the majority of the basic types
     31   not including type modifiers (only DWARF base type, `DW_TAG_base_type`). It
     32   is required to have a map between DType wrapper and the following LLDB
     33   enumerations:
     35   * `lldb::Format`
     36   * `lldb::Encoding`
     37   * `lldb::BasicType`
     39   It is also required to have some knowledge of the bit size of each basic
     40   type. Other built-in types like vectors may be skipped, if complicated to
     41   integrate at this stage.
     43   This enumeration mapping is responsible of formatting the output value with
     44   the right encoding, according to a certain type. From what I'm aware of and
     45   according to my knowledge on the LLVM infrastructure, this is the only thing
     46   required to get value dumping done, but some additional step may be required,
     47   in practice. I still need to understand a bit more what `Dump`, `DumpValue`,
     48   `DumpSummary` and other dump related methods are for.
     50   After this, the next step is to support other types such as:
     52   - **Support type modifiers:** To fully support types it is required to read
     53     other considered type modifiers such as pointers, _typedefs_ (aliases) and
     54     types associated with a type qualifier such as const, immutable, ...
     56   - **Support aggregate types:** Aggregate types such as structs, unions or
     57     classes need to be supported. Only simple support is desired, since stuff
     58     like inheritance can be a bit more complicated to handle. At least struct
     59     fields or base class members may be simple enough.
     61   - **Support arrays:** Not to be confused with D slices, which are technically
     62     interpreted as structs. D slices can be later recognized as native dynamic
     63     arrays, but synthetic formatters can handle it for now (work done on the
     64     Milestone 2). The idea here, at this stage, would be to support static
     65     stack allocated arrays.
     67   - **Support other types:** Other types like enumerations can be supported.
     69 - **Implement DWARF function parsing and integration with the TypeSystem:** To
     70   implement this, it is required to support
     71   `DW_TAG_subprogram`/`DW_TAG_subroutine_type` tags which is dependent of a
     72   special type for functions called subroutine types. Support D linkage is
     73   blocked due to inconsistent calling convention on both DMD/LDC
     74   implementations (see my attempt to fix it
     75   [here](, so C linkage should be a
     76   simple way to support it or rely on GDC implementation.
     78   After having support for this special type, we should implement the
     79   `ParseFunctionFromDWARF` DWARFASTParser override, which is responsible of
     80   parsing all the function child tags, such as formal parameters including
     81   normal parameters and variadic parameters, and inner functions (functions
     82   with the context of the parent outer function).
     84   I haven't explored much about function features on LLDB, so there might be
     85   some hidden dependency I don't know about.
     88 ## LLVM upstream updates
     90 During the development of DType mapping to lldb::BasicType, I found out that
     91 UTF-8 char basic type was missing, so I wrote two patches to implement it on
     92 the upstream:
     94 -
     95 -
     97 With that in mind, I also got the missing part to make unicode8 formatting
     98 working on Clang-based TypeSystem, completing the D language plugin as well.
     99 I've done a partial patch to fix that in the past
    100 ([D112564](, so I amended it and added the
    101 requested tests to be ready to merge.
    103 ## Helpers in DType wrapper for LLDB enumerations
    105 I implemented some helpers required in the DType wrapper to make the type kind
    106 with:
    108   * `lldb::Format`
    109   * `lldb::Encoding`
    110   * `lldb::BasicType`
    112 With that done, I started tinkering with LLDB dumping system, although, some
    113 unknown dependency is still missing (`Dump` functions are not being called with
    114 those helpers implemented). My guess is that some missing type information is
    115 required in order to LLDB recognize a type as, e.g. scalar type.
    117 ## Type name dumping
    119 Value dumping is not yet working, but I already got a way to dump the type
    120 name. For now it is only dumping type name for `bool`. The output looks
    121 something like this:
    123 ```
    124 (lldb) ta v
    125 Global variables for app.d in app:
    126 (bool) = <No TLS data currently exists for this thread.>
    128 app.ptr = <could not resolve type>
    129 (bool) app.foobar =
    130 ```
    132 You can consult the source code for those changes
    133 [here](
    135 ## What is next?
    137 I plan to extend type name dumping to the rest of the built-in type kinds by
    138 mapping constant names to the kind enumeration. I also plan to hopefully have
    139 some output about `app.foobar` value. For that, I'm going to investigate the
    140 missing dependency and implement the missing logic. If that is successful, I
    141 will extend it to the rest of the built-in types.
    143 You can also read this on the D programming language forum,
    144 [here](,
    145 and discuss there!
    147 Read about the [previous week](../d-saoc-2021-13/) and the [next
    148 week](../d-saoc-2021-15/).