[ruby-core:117288] [Ruby master Misc#20387] Meta-ticket for ASAN support

["kjtsanaktsidis (KJ Tsanaktsidis) via ruby-core" <ruby-core@ml.ruby-lang.org>]

Issue #20387 has been reported by kjtsanaktsidis (KJ Tsanaktsidis).

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Misc #20387: Meta-ticket for ASAN support
https://bugs.ruby-lang.org/issues/20387

* Author: kjtsanaktsidis (KJ Tsanaktsidis)
* Status: Open
* Assignee: kjtsanaktsidis (KJ Tsanaktsidis)
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I was asked to provide a bit of information about the current status of ASAN in CRuby, so I thought I'd open this meta-ticket to track all of the work I've been performing on fixing up address sanitizer support.

So far, I have fixed the following issues related to ASAN support:

* https://bugs.ruby-lang.org/issues/20001 + https://github.com/ruby/ruby/pull/9505, which dealt with two main themes:
  - Pushing the logic for capturing the start of the machine stack much closer to the top of the call stack, so that VALUEs stored close to the top of the machine stack get marked properly
  - Marking VALUEs stored on ASAN fake stacks during machine stack marking
* https://bugs.ruby-lang.org/issues/20220 + https://github.com/ruby/ruby/pull/9734, which made M:N threading notify ASAN about stack switches in the same way that fibers do
  - Note: ASAN still doesn't work with M:N threading, but that actually has nothing to do with ASAN; it's because the most recent versions of Clang which are needed for ASAN just don't work with M:N threading either. See https://bugs.ruby-lang.org/issues/20243 for more info about that.
* https://bugs.ruby-lang.org/issues/20273 + https://github.com/ruby/ruby/pull/10012, which disables `callcc` (and the associated tests) when ASAN is enabled
  - callcc is very rarely used in real code and the way it works is just fundamentally incompatible with ASAN (it performs longjmp's which I think are technically undefined behaviour)
* https://bugs.ruby-lang.org/issues/20221 + https://github.com/ruby/ruby/pull/9865, which ignore some global symbols that ASAN defines from the global symbol leak checker
* https://bugs.ruby-lang.org/issues/20274 + https://github.com/ruby/ruby/pull/10087, which ignores some false positive tests about memory leaks when ASAN is enabl
* I updated the ASAN docs in https://github.com/ruby/ruby/pull/9922 to more closely reflect current reality

The current state of things is that, by following the instructions in https://github.com/ruby/ruby/blob/master/doc/contributing/building_ruby.md, you can successfully build Ruby with ASAN enabled, however, the test suite has several failures. I'm currently working on addressing these:

The next step is to merge https://github.com/ruby/ruby/pull/10122 (https://bugs.ruby-lang.org/issues/20310) which I plan to do next week (I'm currently away on a work trip). That makes sure that VALUEs stored in ASAN fake stacks from threads other than the currently running thread get marked during GC.

After that, I need to push up patches for the remaining few issues. I mostly have these patches ready to go already; in fact, last week I got the full `make check` suite passing all tests with ASAN enabled!

Once that's working, I'd like to investigate how ASAN can fit into CRuby's CI matrix somewhere so that it _stays_ working, although I have not thought too deeply about this yet.

I will provide further updates on this ticket so anybody interested can stay in the loop.



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