[GHC] #14675: GHC 8.4.1 regression: segfault when loading doctest on a module with ANNs on Ubuntu 16.04 or later

[GHC]

#14675: GHC 8.4.1 regression: segfault when loading doctest on a module with ANNs
on Ubuntu 16.04 or later
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  alpmestan
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.4.1
       Component:  GHC API           |              Version:  8.4.1-alpha1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Runtime crash     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #14603            |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by alpmestan):

 When work resumes after going back to the scheduler, we load the stack and
 jump to its top (`stg_enter_info`). This then leads us to execute a
 whoooooooole bunch of code. I saw many kinds of closure types along the
 way, among which a `Data.Data` related one (expected: we embed a `Data`
 dictionary in `AnnotationWrapper`), a ghci `BreakArray` related one,
 partial applications, `FUN_STATIC`, etc. The somewhat uninformative
 context in which the crash finally happens can be seen
 [https://gist.github.com/alpmestan/a029e46c9cb7beb6839c6ac6058a95f9#file-
 foo-asm-L1017 here], interleaved with my attempts to find out a bit of
 information about the addresses/closures/etc randomly in `rbx`, `rax`,
 printing the top of the stack, etc.

 I was honestly hoping that the context would be a little more informative.
 However, all hope is not lost. I'm going to use `rr` as suggested by Ben
 to record the run, and then I'll be able to go to the crash, look at the
 address we're trying to jump to, and use `reverse-cont` to see who wrote
 that address there. This however requires me to set up something else than
 VirtualBox as `rr` needs hardware performance counters that VirtualBox
 does not support. I got started with this today.

 In parallel, I might keep doing a few experiments in `gdb` in my existing
 (VirtualBox) VM. For instance, when looking at the `TcSplice` code
 yesterday, I saw a few `do` blocks with some important code (as far as
 annotation handling is concerned) that I haven't looked closely at yet. In
 particular, I'm not sure whether the code that produces
 `zonked_wrapped_expr'` could be the problem. I have a reason or two to
 believe that it's an interesting place to look at, like the fact that I
 did see some `Data.Data` related symbol _after_ `interpretBCO`, and these
 few lines of code are where we produce the `Data.Data` dictionary
 apparently.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14675#comment:17>
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