[ruby-core:91185] [Ruby trunk Bug#15346] Core dump during GC if covering a special require

Issue #15346 has been updated by nagachika (Tomoyuki Chikanaga).

Backport changed from 2.4: UNKNOWN, 2.5: REQUIRED to 2.4: DONTNEED, 2.5: DONTNEED

I misunderstood this could be reproducible in 2.5 but it isn't.

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Bug #15346: Core dump during GC if covering a special require
https://bugs.ruby-lang.org/issues/15346#change-76416

* Author: MaxLap (Maxime Lapointe)
* Status: Closed
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.6.0dev (2018-11-27 trunk 66002) [x86_64-linux]
* Backport: 2.4: DONTNEED, 2.5: DONTNEED
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On my environment, (ruby-head, updated today) the following script generates a core dump almost all the time. (I join a core dump to this report)

I am running on Ubuntu 16.04, I first saw the problem on Travis-CI and managed to make this much simpler reproduction code.

~~~ ruby
# Just setting up a file to require, this could be in a regular file and be required.
require 'tempfile'
f = Tempfile.new(['ruby', '.rb'])
f.write(<<-RUBY)
  a = 123
  begin
  ensure
    a
  end
RUBY
f.close

# Now the actual code to trigger the problem
require 'coverage'
Coverage.start
load f.path # require can do the same thing, but less frequently

# The problem is during GC, so we trigger it ourself
puts 'gc time!'
GC.start

# When it doesn't crash the first time, doing the load/require again seems to take care of it
puts '2nd gc'
load f.path
GC.start

puts 'gc done, try again!'
~~~

The problem seems related to the content of the ensure, if it's too simple, things break? It's weird.
If the content of the ensure is:
  a
  puts 'something'
  #=> All good

  puts 'something'
  a
  #=> Core dump

  puts 'something'; a
  #=> All good

  a + 1
  #=> All good

My personal guess is, if the last line of the ensure is useless, ruby optimizes it away, but that causes a problem with Coverage.


---Files--------------------------------
cov-require_core_dump.txt (10.4 KB)


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