SAOC LLDB D integration: 2nd Weekly Update

[Luís Ferreira]

Hi D community!

Sorry for being late this week.

I'm here again, to describe what I've done during the second week of
Symmetry
Autumn of Code.

## Finalizing the LLDB integration

Last week some missing pieces on the test suite and on the LLDB side
was
concluded at the beginning of this week and put everything together.

## Restructure the code to be more C++ish

After successfully integrating `libiberty` D demangler into LLVM and
before
sending the patches to LLVM, code style needed to be properly handled
to
conform with `clang-format` style of LLVM, so, I decided to transform
the code
to be more C++ like:

- Move functions with `struct dlang_info` context to a struct making
them
  member functions to implicitly pass the context
- Make string handling on the demangler a bit more C++ish (class
OutputString)
- Fix structural codestyle to conform with clang formatting such as
variables
  names, spaces between identifiers, etc...

I also ended up writing documentation for everything inside the string
and
demangler struct for future understanding.

## Send patches to the LLVM review platform

Right after having the codestyle finished, I submitted the patches into
the
LLVM review platform. In the meantime, I'm striving for acceptance and
proactively changing the patches to accomplish with the LLVM
maintainers
requests.

The first patch introduces the demangler codebase with the ported code,
available [here](https://reviews.llvm.org/D110578). The second patch
enables
support for `llvm-cxxfilt` tool, similar to `c++filt` from GNU
binutils,
available [here](https://reviews.llvm.org/D110576). Finally, the last
patch
enables the most important part for the users, the LLDB part. The patch
is
available [here](https://reviews.llvm.org/D110577).

## Reflected GCC changes

Meanwhile, I found some things to improve on the `libiberty` side that
I
changed on my patches to LLVM:

- Use appendc for single chars append:
 
[patch](https://gcc.gnu.org/pipermail/gcc-patches/2021-September/580512.html
).
- Remove parenthesis where it is not needed:
 
[patch](https://gcc.gnu.org/pipermail/gcc-patches/2021-September/580525.html
).
- Rename function symbols to be more consistent:
 
[patch](https://gcc.gnu.org/pipermail/gcc-patches/2021-September/580542.html
).
- Use switch instead of if-else:
 
[patch](https://gcc.gnu.org/pipermail/gcc-patches/2021-September/580545.html
).

I also made this patch which fixes the testsuite that I previously
broke on the
security patches.

- Add missing format on d-demangle-expected:
 
[patch](https://gcc.gnu.org/pipermail/gcc-patches/2021-September/580544.html
).

## About the security issues

I made a thread on the GCC mailing list to encourage more fuzzing.
Currently
the demangler is being fuzzed without any heuristics which makes it
inefficient
to search for real security vulnerabilities. Instead, AFL and libfuzzer
should
be taken to consideration. My idea is to also add support for
GCC/libiberty to
OSS Fuzz. You can check the thread
[here](https://gcc.gnu.org/pipermail/gcc/2021-September/237442.html)
and
participate if you have any questions or suggestions on that topic.

About the exponential time complexity issue, I don't have any news,
since I
still don't have the full picture of it. I'm probably not going to
dedicate
much time to that since it's kinda out of the scope of this project.
Although,
if anyone wants to have a look and discuss hints and suggestions to
improve the
current demangler, I appreciate it.
[Here](http://ipfs.io/ipfs/bafybeihw6bk46r7gnkp6estkwk7ucilxb2swlwzzi2izpytaclypxeu2wq/
)
are the blobs generated by the fuzzer for timeout and slow-unit
triggers.

## What's next?

For now, I'm going to proactively fix the requested changes in the LLVM
patches. They seem to require smaller patches and probably the next
week will
be dedicated to that.

You can see this also on my blog, since my email client doesn't like 80
line splitted text: https://lsferreira.net/posts/d-saoc-2021-02

-- 
Sincerely,
Luís Ferreira @ lsferreira.net

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