Issue #21373 has been updated by Ethan (Ethan -). Ah, I missed that one. Can close this duplicate, I think. ---------------------------------------- Bug #21373: "Illegal instruction: 4" when raising SystemStackError after rescuing https://bugs.ruby-lang.org/issues/21373#change-113445 * Author: Ethan (Ethan -) * Status: Open * ruby -v: ruby 3.4.2 (2025-02-15 revision d2930f8e7a) +PRISM [x86_64-darwin22] * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- I overflowed the stack in a test - this was rescued and tests continued, but when the next test also overflowed the stack, instead of handling the exception, ruby exited with "Illegal instruction: 4", exit code 132, and no other output (no stack trace or dump). A minimal reproduction follows. The C method JSON::Ext::Generator::GeneratorMethods::Hash#to_json alternates with X#to_json on the stack; this does not reproduce without the C method. This is on macos and does not reproduce on linux. ```ruby require 'json' class X def to_json(*args) {'data' => self}.to_json(*args) end end # raise and rescue once works fine begin JSON.dump(X.new) rescue SystemStackError end # upon overflowing stack a second time, ruby exits abnormally # with "Illegal instruction: 4" instead of SystemStackError JSON.dump(X.new) ``` -- https://bugs.ruby-lang.org/