Memory exhaustion on AIX 7.2 on Rubygems >= 4.0

Describe the problem as clearly as you can

The SafeMarshal feature of Rubygems >= 4.0.0 causes memory exhaustion on AIX 7.2 when adding sources.

With Rubygems 4.0.3 on Ruby 4.0.1:

[0] [AIX] root@aix72-2-pix:~ # /opt/puppetlabs/puppet/bin/gem source --add $internal_artifactory_repo
[FATAL] failed to allocate memory

Did you try upgrading RubyGems?

This issue also seems to affect RubyGems upgrades:

[0] [AIX] root@aix72-2-pix:~ # /opt/puppetlabs/puppet/bin/gem update --system
[FATAL] failed to allocate memory

Post steps to reproduce the problem

The simplest reproduction is to take an AIX 7.2 machine and attempt to gem source --add.

@joshcooper also created this reproduction script:

require 'rubygems'
require 'rubygems/safe_marshal'
require 'objspace'

def safe_marshal_element_classes
  result = []
  Gem::SafeMarshal::Elements.constants(false).each do |const|
    c = Gem::SafeMarshal::Elements.const_get(const)
    result << c if c.is_a?(Class)
  rescue NameError
    # ignore
  end
  result
end

def histogram_counts(limit: 50, min_count: 1)
  klasses = safe_marshal_element_classes
  counts  = klasses.map do |k|
    n = 0
    ObjectSpace.each_object(k) { n += 1 }
    [k, n]
  end

  counts.select! { |(_, n)| n >= min_count }
  counts.sort_by! { |(_, n)| -n }
  counts.first(limit)
end

io = Gem.read_binary(ARGV[0])
data = Gem::SafeMarshal.safe_load(io)
#tuples = Gem::NameTuple.from_list(rval)
histogram_counts(limit: 25).each do |klass, n|
  puts "#{klass}: #{n}"
end

Even when attempting to load specs from rubygems.org, we see the same issue:

[0] [AIX] root@aix72-2-pix:~ # curl -s --output rubygems-specs.4.8.gz https://rubygems.org/specs.4.8.gz
[0] [AIX] root@aix72-2-pix:~ # gunzip rubygems-specs.4.8.gz
[0] [AIX] root@aix72-2-pix:~ # /opt/puppetlabs/puppet/bin/ruby spec_histogram.rb rubygems-specs.4.8
[FATAL] failed to allocate memory

Which command did you run?

gem source --add

What were you expecting to happen?

Rubygems adds another source for gems.

What actually happened?

The command failed with [FATAL] failed to allocate memory.

Run gem env and paste the output below

[0] [AIX] root@aix72-2-pix:~ # /opt/puppetlabs/puppet/bin/gem env
RubyGems Environment:
  - RUBYGEMS VERSION: 4.0.3
  - RUBY VERSION: 4.0.1 (2026-01-13 patchlevel 0) [powerpc-aix7.2.0.0]
  - INSTALLATION DIRECTORY: /opt/puppetlabs/puppet/lib/ruby/gems/4.0.0
  - USER INSTALLATION DIRECTORY: /root/.local/share/gem/ruby/4.0.0
  - CREDENTIALS FILE: /root/.local/share/gem/credentials
  - RUBY EXECUTABLE: /opt/puppetlabs/puppet/bin/ruby
  - GIT EXECUTABLE:
  - EXECUTABLE DIRECTORY: /opt/puppetlabs/puppet/bin
  - SPEC CACHE DIRECTORY: /root/.cache/gem/specs
  - SYSTEM CONFIGURATION DIRECTORY: /opt/puppetlabs/puppet/etc
  - RUBYGEMS PLATFORMS:
     - ruby
     - powerpc-aix-7
  - GEM PATHS:
     - /opt/puppetlabs/puppet/lib/ruby/gems/4.0.0
     - /root/.local/share/gem/ruby/4.0.0
     - /opt/puppetlabs/puppet/lib/ruby/vendor_gems
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :backtrace => true
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - https://rubygems.org/
  - SHELL PATH:
     -
     -
     - /usr/bin
     - /etc
     - /usr/sbin

Start with the rubygems/safe_marshal entry point and reproduce the failure using gem source --add or the provided spec_histogram.rb script on AIX 7.2. Compare SafeMarshal.safe_load behavior and memory usage for the supplied specs; done means these operations no longer exhaust memory on the reported platform.