Ruby crashing and emitting 'Illegal instruction' - c

Question

On a client's legacy Rails 2.1.1 app, I'm encountering an error where ruby crashes and emits 'Illegal instruction.' The crash is triggered by calls to methods on Digest::SHA2.
>> Digest::SHA2
=> Digest::SHA2
>> Digest::SHA2.new()
Illegal instruction
The Rails app is running on two servers behind a load balancer. The stacks on the two servers are very close to being identical and only one triggers the crash. They're both REE 1.8.7, Rails 2.1 and Debian 6. One is running the Linux kernel version 3.9.3 and one is running version 3.9.2—but I'm unsure how to determine if that's even relevant.
Digest::SHA2 seems to be mostly implemented in C. I know very little C and diagnosing this one is over my head. Any help / pointers in the right direction would be greatly appreciated!
Thanks a bunch!!
Environment Info
Here's the REE source for Digest::SHA2:
https://github.com/FooBarWidget/rubyenterpriseedition187-330/tree/master/ext/digest/sha2
On the server that's encountering the crash:
hostname#node1:~/appname$ cat /etc/issue
Debian GNU/Linux 6.0 \n \l
hostname#node1:~/appname$ uname -a
Linux node1.hostname.org 3.9.2-x86_64-[redacted] #1 SMP Tue May 14 17:16:34 EDT 2013 x86_64 GNU/Linux
hostname#node1:~/appname$ which ruby
/opt/ruby-enterprise-1.8.7-2012.02/bin/ruby
hostname#node1:~/appname$ irb
irb(main):001:0> require 'digest'
=> true
irb(main):002:0> Digest::SHA2.hexdigest('foo')
=> "2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae"
irb(main):003:0> exit
hostname#node1:~/appname$ ./script/console
Loading development environment (Rails 2.1.1)
>> Digest::SHA2.hexdigest('foo')
Illegal instruction
On the server that is not crashing:
hostname#node2:~/appname$ cat /etc/issue
Debian GNU/Linux 6.0 \n \l
hostname#node2:~/appname$ uname -a
Linux node2.hostname.org 3.9.3-x86_64-[redacted] #1 SMP Mon May 20 10:22:57 EDT 2013 x86_64 GNU/Linux
hostname#node2:~/appname$ which ruby
/opt/ruby-enterprise-1.8.7-2012.02/bin/ruby
hostname#node2:~/appname$ irb
irb(main):001:0> require 'digest'
=> true
irb(main):002:0> Digest::SHA2.hexdigest('foo')
=> "2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae"
irb(main):003:0> exit
hostname#node2:~/appname$ ./script/console
Loading development environment (Rails 2.1.1)
>> Digest::SHA2.hexdigest('foo')
=> "2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae"