[Bug 1999104] [NEW] libunwind causes crashes on arm64

[Ali Saidi]

Public bug reported:

There is a bug in libunwind in both 18.04 and 20.04 on arm64 where when
linked with libunwind instead of catching an exception, the program
crashes. This was first seen on mcrouter, but attached is a small
reproducer where `main_unwind` will crash. The libunwind shipping with
22.04 doesn't appear to have this problem, nor do unmodified upstream
versions (including the 1.2.1 which is the 18.04 and 20.04 version).

Attached is a small reproducer that demonstrates the problem.

Ubuntu 22.04:
```
$ ./main
int throws lib
int caught main
$ ./main_unwind
int throws lib
int caught main
```

Ubuntu 20.04:
```
$ ./main
int throws lib
int caught main
$ ./main_unwind
terminate called after throwing an instance of 'int'
terminate called recursively
Aborted (core dumped)
```

** Affects: libunwind (Ubuntu)
     Importance: Undecided
         Status: New

** Attachment added: "small reproducer"
   https://bugs.launchpad.net/bugs/1999104/+attachment/5635122/+files/libunwind.tar.gz

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https://bugs.launchpad.net/bugs/1999104

Title:
  libunwind causes crashes on arm64

Status in libunwind package in Ubuntu:
  New

Bug description:
  There is a bug in libunwind in both 18.04 and 20.04 on arm64 where
  when linked with libunwind instead of catching an exception, the
  program crashes. This was first seen on mcrouter, but attached is a
  small reproducer where `main_unwind` will crash. The libunwind
  shipping with 22.04 doesn't appear to have this problem, nor do
  unmodified upstream versions (including the 1.2.1 which is the 18.04
  and 20.04 version).

  Attached is a small reproducer that demonstrates the problem.

  Ubuntu 22.04:
  ```
  $ ./main
  int throws lib
  int caught main
  $ ./main_unwind
  int throws lib
  int caught main
  ```

  Ubuntu 20.04:
  ```
  $ ./main
  int throws lib
  int caught main
  $ ./main_unwind
  terminate called after throwing an instance of 'int'
  terminate called recursively
  Aborted (core dumped)
  ```

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