SAOC LLDB D integration: 17th Weekly Update

[Luís Ferreira]

Hi D community!

Sorry for being late. I'm here again, to describe what I've done 
during the
seventeenth week of Symmetry Autumn of Code.

## LLVM upstream updates

This week I finished working on the three patches I was working 
about
demangling and finally merged them in the LLVM upstream:

- https://reviews.llvm.org/D111416
- https://reviews.llvm.org/D111417
- https://reviews.llvm.org/D111419

I also added another trivial patch to pass values by reference 
instead of a
pointer, requested by dblaikie:

- https://reviews.llvm.org/D117046

### Bug on LLVM + Clang 13

Before merging, I always run the sanitizer on the whole test 
suite and the
fuzzer I integrated, although I found a regression on recent LLVM 
+ Clang
builds with the sanitizer arguments. You can read more about the 
issue in
[this](https://reviews.llvm.org/D102453) patch. Briefly, the 
problem was that
LLVM is compiled with `-fPIC -fno-semantic-interposition` on LLVM 
+ Clang
13.0.0, although, when combined with `-fsanitize` flags, the 
generated binary
has incorrect PC-relative relocation information on the generated 
calls making
it fails on linking. Thanks to 
[MaskRay](https://reviews.llvm.org/p/MaskRay/)
by helping me diving into this and fixing the problem!

I got surprised by the fact that this was not caught by the 
buildbots. When
comparing the LLVM released binaries and Arch Linux binaries the 
problem was
not reproducible. Probably the patched version Arch Linux 
distributes had
something to do with it but I didn't get a clear answer. This 
makes some sense
since Arch Linux compiles with SSP (strong stack protection) by 
default and
that adds extra calls that, when compiled with `-fPIC` seem to be 
also
PC-relative.

That regression made me creating two more trivial patches:

- https://reviews.llvm.org/D117144
- https://reviews.llvm.org/D117145

## Extending dumping for derived types

I started tinkering with derived types, more specifically with 
`alias`. The
same with built-in types the logic can be extended to other 
derived types
as well. In DWARF `DW_TAG_typedef_type` is generated whenever a 
variable is
typed with an `alias`. I did some basic logic to make it work, 
although I need
to do some decoupling from Clang due to type forwarding.

I still need to understand how types are forwarded in DWARF, 
because the types
are read sequentially and a `DW_TAG_typedef_type` can reference 
an address "in
the future" that points to a `DW_TAG_base_type` which need to be 
resolved
later. I tried to search how Go plugin did that ([see
diff](https://github.com/llvm/llvm-project/commit/77198bc79b54267f2ce981c3a6c9c0d6384cac01#diff-72ec6c46e57cb00bb94855699a3a5d8d268a73e8ec226404d5f9b175de7d1d19))
but `dwarf->ResolveTypeUID` got removed.

You can consult the source code
[here](https://github.com/devtty63/llvm-project/commits/lldb-d/implement-typesystem-d).

## More decoupling on the Clang DWARF Parser

I was about to decouple `GetContainingClangModuleDIE` and
`GetContainingClangModule` functions, although, my test suite is 
not running
correctly. LLDB test suite is a nightmare to me and I'm trying to 
push forward
on more clarity about which tests are marked as Unsupported or 
Expected to
Fail. I always had this problem since I started working on the 
LLDB tree
although I took the risk of ignoring them. I couldn't contact 
`lldb-dev` since
there is some restrictions on the mailing list due to spam and I 
got not answer
on my subscription request. Finally LLVM moved to
[discourse](https://llvm.discourse.group/), so I created two 
posts there to
describe my problems:

- https://llvm.discourse.group/t/lldb-buildbots-verbosity/5253
- 
https://llvm.discourse.group/t/lldb-test-suite-is-failing-on-linux-x86-64/5696

The first one already got some attention and
[JDevlieghere](https://reviews.llvm.org/p/JDevlieghere/) already 
submitted a
patch. I had no idea that the buildbot infrastructure was open 
source. I
already have some patches to submit about this topic, including 
activating Lua
tests, which is failing locally and not tested on the buildbots.

## What is next?

Well, I plan to continue working on the custom DWARF Parser for 
D, including
adding support for other basic stuff like functions. Even though 
this is the
last weekly update, I'm going to try to keep up with some changes 
on the LLVM
tree. My goal is to have some minimum support (roughly the same 
of GDB) on
LLDB 14. I will try to submit the bare minimum support which need 
to include
some workarounds on the Clang DWARF Parser. This may not be 
accepted due to
that, but if it does, we can have custom formatters officially on 
LLDB. I will
try to provide soon some builds for the community of
[this](https://github.com/devtty63/llvm-project/commits/lldb-d/main) branch,
although.