3 days ago

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:

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

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 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
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:

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
)
but dwarf->ResolveTypeUID got removed.

You can consult the source code
here.

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, so I created two posts there to
describe my problems:

The first one already got some attention and
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 branch,
although.