[ruby-dev:52183] [Ruby Bug#21673] Segmentation Fault in IRB when refining `Kernel#puts` using `Module#refine` (Regression since Ruby 3.4)

8 Nov 2025

      Issue #21673 has been updated by tompng (tomoya ishida).

It can be reproduced without IRB
~~~ruby
module Foo
  refine Kernel do
    def puts; end
  end
end
method(:puts)
~~~

----------------------------------------
Bug #21673: Segmentation Fault in IRB when refining `Kernel#puts` using `Module#refine` (Regression since Ruby 3.4)
https://bugs.ruby-lang.org/issues/21673#change-115122

* Author: yokomaru (Yoko Suzuki)
* Status: Open
* ruby -v: ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +PRISM [arm64-darwin24]
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
In the IRB environment running Ruby 3.4 and later, the VM crashes with a Segmentation Fault when a module refining `Kernel#puts` is defined and `puts` is subsequently executed. The crash does not occur when the exact same code is executed as a regular Ruby script.

**Environment**

Reproduced on multiple environments:

```
macOS 15.5 (Apple Silicon M1, MacBook Pro)
- ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +PRISM [arm64-darwin24] 
- ruby 3.5.0dev (2025-11-06 master cf4a034d59) +PRISM [arm64-darwin24]
- irb 1.15.3 (also reproduced with 1.13.1)
- Installed via rbenv
```

```
Omarhy 3.1.3(Linux 6.17.5-arch1-1)
- ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +PRISM [x86_64-linux]
- irb 1.15.3
- Installed via mise
```

This does not occur on: Ruby 3.3.10 + IRB 1.13.1

**Steps to Reproduce (Reproduction Script)**

The crash reproduces with these steps (on Ruby 3.4+):

1.  Start irb.
    ```bash
    $ irb
    ```
2.  Define the refinement module for `Kernel#puts`.
    ```ruby
    module Foo
      refine Kernel do
        def puts
        end
      end
    end
    # Explicit 'using Foo' is NOT required
    ```
3.  Execute `puts` at the IRB prompt.
    ```ruby
    puts # ← Segmentation Fault occurs here
    ```

**Expected Result**
As observed in Ruby 3.3.10, the IRB session should continue to operate normally.

**Actual Result (Execution Log Excerpt)**
The full crash logs (for macOS and Arch Linux) and the macOS crash report are provided in the attached files.

```
$ irb
irb(main):001* module Foo
irb(main):002*   refine Kernel do
irb(main):003*     def puts
irb(main):004*     end
irb(main):005*   end
irb(main):006> end
=> #<refinement:Kernel@Foo>
irb(main):007> put/Users/USER/.rbenv/versions/3.4.7/lib/ruby/gems/3.4.0/gems/irb-1.15.3/lib/irb/context.rb:636: [BUG] Segmentation fault at 0x0000000000000030
ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +PRISM [arm64-darwin24]
               puts
-- Crash Report log information --------------------------------------------
   See Crash Report log file in one of the following locations:
     * ~/Library/Logs/DiagnosticReports
     * /Library/Logs/DiagnosticReports
   for more details.
Don't forget to include the above Crash Report log file in bug reports.

-- Control frame information -----------------------------------------------
c:0049 p:---- s:0274 e:000273 CFUNC :public_method
c:0048 p:---- s:0271 e:000270 CFUNC :bind_call
c:0047 p:0221 s:0265 e:000264 METHOD /Users/USER/.rbenv/versions/3.4.7/lib/ruby/gems/3.4.0/gems/irb-1.15.3/lib/irb/context.rb:636
c:0046 p:0034 s:0251 e:000250 METHOD /Users/USER/.rbenv/versions/3.4.7/lib/ruby/gems/3.4.0/gems/irb-1.15.3/lib/irb/context.rb:648
c:0045 p:0010 s:0239 e:000238 BLOCK /Users/USER/.rbenv/versions/3.4.7/lib/ruby/gems/3.4.0/gems/irb-1.15.3/lib/irb/input-method.rb:277
c:0044 p:0024 s:0233 e:000232 METHOD /Users/USER/.rbenv/versions/3.4.7/lib/ruby/gems/3.4.0/gems/reline-0.6.2/lib/reline/line_editor.rb:787

<...snip...>

-- Ruby level backtrace information ----------------------------------------
/Users/USER/.rbenv/versions/3.4.7/bin/irb:25:in '<main>'
/Users/USER/.rbenv/versions/3.4.7/bin/irb:25:in 'load'
/Users/USER/.rbenv/versions/3.4.7/lib/ruby/gems/3.4.0/gems/irb-1.15.3/exe/irb:9:in '<top (required)>'
/Users/USER/.rbenv/versions/3.4.7/lib/ruby/gems/3.4.0/gems/irb-1.15.3/lib/irb.rb:54:in 'start'
/Users/USER/.rbenv/versions/3.4.7/lib/ruby/gems/3.4.0/gems/irb-1.15.3/lib/irb.rb:173:in 'run'
/Users/USER/.rbenv/versions/3.4.7/lib/ruby/gems/3.4.0/gems/irb-1.15.3/lib/irb.rb:173:in 'catch'
/Users/USER/.rbenv/versions/3.4.7/lib/ruby/gems/3.4.0/gems/irb-1.15.3/lib/irb.rb:174:in 'block in run'
/Users/USER/.rbenv/versions/3.4.7/lib/ruby/gems/3.4.0/gems/irb-1.15.3/lib/irb.rb:193:in 'eval_input'
/Users/USER/.rbenv/versions/3.4.7/lib/ruby/gems/3.4.0/gems/irb-1.15.3/lib/irb.rb:278:in 'each_top_level_statement'
<internal:kernel>:168:in 'loop'

<...snip...>

-- C level backtrace information -------------------------------------------
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_vm_bugreport+0xb6c) [0x102ccdaa8]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_bug_for_fatal_signal+0x100) [0x102b07bfc]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(sigsegv+0x84) [0x102c2e2f4]
/usr/lib/system/libsystem_platform.dylib(_sigtramp+0x38) [0x19e60c624]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_callable_method_entry_with_refinements+0xd8) [0x102caabb4]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_callable_method_entry_with_refinements+0xd8) [0x102caabb4]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(obj_method+0x160) [0x102bcbf74]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(vm_call0_body+0x35c) [0x102cc4b50]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_vm_call_kw+0xc4) [0x102cae300]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(vm_call_cfunc_with_frame_+0xf0) [0x102cbf798]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(vm_exec_core+0x46c8) [0x102ca77f0]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_vm_exec+0x1b4) [0x102ca1fa4]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(invoke_block_from_c_bh+0x36c) [0x102cc7614]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_yield+0xa8) [0x102cafa54]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_ary_each+0x40) [0x102a5b7f8]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(vm_call_cfunc_with_frame_+0xf0) [0x102cbf798]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(vm_exec_core+0x2620) [0x102ca5748]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_vm_exec+0x1b4) [0x102ca1fa4]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(invoke_block_from_c_bh+0x36c) [0x102cc7614]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_yield+0xa8) [0x102cafa54]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_protect+0xb0) [0x102b13918]
/Users/USER/.rbenv/versions/3.4.7/lib/ruby/3.4.0/arm64-darwin24/io/console.bundle(ttymode+0x1e0) [0x102462ab4]
/Users/USER/.rbenv/versions/3.4.7/lib/ruby/3.4.0/arm64-darwin24/io/console.bundle(ttymode) (null):0
/Users/USER/.rbenv/versions/3.4.7/lib/ruby/3.4.0/arm64-darwin24/io/console.bundle(console_raw+0x40) [0x102460ca0]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(vm_call_cfunc_with_frame_+0xf0) [0x102cbf798]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(vm_exec_core+0x2620) [0x102ca5748]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_vm_exec+0x134) [0x102ca1f24]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(invoke_block_from_c_bh+0x36c) [0x102cc7614]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_yield+0xa8) [0x102cafa54]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_ensure+0xac) [0x102b13a70]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(vm_call_cfunc_with_frame_+0xf0) [0x102cbf798]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(vm_exec_core+0x2620) [0x102ca5748]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_vm_exec+0x134) [0x102ca1f24]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(invoke_block_from_c_bh+0x36c) [0x102cc7614]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(catch_i+0x6c) [0x102cc6d50]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(vm_catch_protect+0xbc) [0x102cb1b70]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_f_catch+0x70) [0x102cb2560]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(vm_call_cfunc_with_frame_+0xf0) [0x102cbf798]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(vm_exec_core+0x2620) [0x102ca5748]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_vm_exec+0x1b4) [0x102ca1fa4]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(load_iseq_eval+0x224) [0x102b73b50]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_load_internal+0x84) [0x102b70e8c]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_f_load+0x8c) [0x102b72aa0]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(vm_call_cfunc_with_frame_+0xf0) [0x102cbf798]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(vm_exec_core+0x46c8) [0x102ca77f0]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_vm_exec+0x134) [0x102ca1f24]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(rb_ec_exec_node+0x8c) [0x102b12c14]
/Users/USER/.rbenv/versions/3.4.7/lib/libruby.3.4.dylib(ruby_run_node+0x40) [0x102b12b3c]
/Users/USER/.rbenv/versions/3.4.7/bin/ruby(main+0x68) [0x1022c0618]
```

---Files--------------------------------
backtrace_ruby-3.4.7_macos.txt (111 KB)
macos_crash_report_ruby-3.4.7.ips.txt (31.4 KB)
backtrace_ruby-3.4.7_omarchy(archlinux).txt (90.4 KB)

-- 
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