From: bo@...
Date: 2017-02-01T20:32:14+00:00
Subject: [ruby-core:79382] [Ruby trunk Bug#13164] A second `SystemStackError` exception results in `Segmentation fault (core dumped)`

Issue #13164 has been updated by Boaz Segev.


What about flattening recursion in core types (Hash, Array and Set)?

I know this won't resolve the issue, but it will prevent `eql?` and `hash` from exploding the stack, so the issue is less likely to occur when there isn't an error in the code being executed.

----------------------------------------
Bug #13164: A second `SystemStackError` exception  results in `Segmentation fault (core dumped)`
https://bugs.ruby-lang.org/issues/13164#change-62809

* Author: Boaz Segev
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.4.0p0 (2016-12-24 revision 57164) [x86_64-darwin16]
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
----------------------------------------
This issue is was exposed by leveraging the fact that `Object#hash` is implemented recursively for core Ruby datatypes (i.e., Hash and Array). See the discussion here: https://github.com/boazsegev/combine_pdf/pull/91#issuecomment-275552131.

TO reproduce the issue, explode the stack **twice**.

Expected results: 

SystemStackError will be raised both times.

Actual results:

SystemStackError is raised once. The second time will cause a core dump.

Code to cause core dump:

~~~ ruby
def compute_nest_depth
  h = {nest: {}}
  nest = h[:nest]
  i = 0

  while true
    i += 1
    puts "nested #{i}" if ((i & 511) == 0)
    next_nest = { nest: {} }
    nest[:nest] = next_nest
    nest = next_nest[:nest]
    h.hash
  end

rescue SystemStackError
  puts "Stack exploded at nesting #{i}"
end

counter = 0;
while(true)
  begin
    counter +=1
    puts "starting test #{counter}"
    compute_nest_depth
  rescue SystemStackError => e
    nil
  ensure
    puts "test #{counter} complete"
  end
end

~~~

results:

~~~
starting test 1
nested 512
nested 1024
nested 1536
nested 2048
nested 2560
Stack exploded at nesting 2783
test 1 complete
starting test 2
nested 512
nested 1024
nested 1536
nested 2048
nested 2560
Segmentation fault (core dumped)
~~~



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