[ruby-core:124638] [Ruby Bug#21854] ruby-prof breaks on 4.0.1

29 Jan 2026

      Issue #21854 has been reported by cfis (Charlie Savage).

----------------------------------------
Bug #21854: ruby-prof breaks on 4.0.1
https://bugs.ruby-lang.org/issues/21854

* Author: cfis (Charlie Savage)
* Status: Open
* ruby -v: ruby 4.0.1 (2026-01-13 revision e04267a14b) +PRISM [x64-mswin64_140]
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
----------------------------------------
ruby-prof breaks on 4.0.1 with segmentation faults when measuring memory. See:

https://github.com/ruby-prof/ruby-prof/actions/runs/21465420365/job/61826466...

(note failures for ruby 3.x are some test that fail, not segementation faults).

Tracking this down, one test that fails measure memory (see traceback below). That way that works:

* Get a tracearg event (https://github.com/ruby-prof/ruby-prof/blob/master/ext/ruby_prof/rp_profile....)
* Get a measurement - time, memory, etc. - https://github.com/ruby-prof/ruby-prof/blob/master/ext/ruby_prof/rp_measurem...
* Get the tracearg object - https://github.com/ruby-prof/ruby-prof/blob/master/ext/ruby_prof/rp_measure_...
* Call rb_obj_memsize_of - https://github.com/ruby-prof/ruby-prof/blob/master/ext/ruby_prof/rp_measure_...
* For a T_DATA object in gc.c
...
case T_DATA:
  size += rb_objspace_data_type_memsize(obj);
  break;
Then segmentation fault.

Running in debugger:

```
RTYPEDDATA_TYPE(obj)
0x332d747365676964 {wrap_struct_name=??? function={dmark=??? dfree=??? dsize=??? ...} parent=??? ...}
    wrap_struct_name: <Unable to read memory>
    function: {dmark=??? dfree=??? dsize=??? ...}
    parent: <Unable to read memory>
    data: <Unable to read memory>
    flags: <Unable to read memory>
```

It sure seems like the object that was provide by tracearg has been garbage collected and is no longer valid.

Here is the traceback. This is from a MSVC build, but you can see in the gitlab pipelines the same happens on Ubuntu.

```bash
-- C level backtrace information -------------------------------------------
C:\WINDOWS\SYSTEM32\ntdll.dll(NtWaitForSingleObject+0x14) [0x00007FF817DA1C44]
C:\WINDOWS\System32\KERNELBASE.dll(WaitForSingleObjectEx+0xaf) [0x00007FF814F2BC5F]
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_print_backtrace+0x3e) [0x00007FFEEBB01F92] C:\Source\ruby-4.0.1-mswin\vm_dump.c:1129
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_vm_bugreport+0x223) [0x00007FFEEBB021BB] C:\Source\ruby-4.0.1-mswin\vm_dump.c:1453
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_bug_for_fatal_signal+0x75) [0x00007FFEEB9BE779] C:\Source\ruby-4.0.1-mswin\error.c:1131
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(sigsegv+0x3d) [0x00007FFEEBAFAF91] C:\Source\ruby-4.0.1-mswin\signal.c:948
C:\WINDOWS\System32\ucrtbase.dll(seh_filter_exe+0x84) [0x00007FF81591E8A4]
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\ruby.exe(`__scrt_common_main_seh'::`1'::filt$0+0x16) [0x00007FF7B95D1B4C] D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:304
C:\WINDOWS\SYSTEM32\VCRUNTIME140.dll(_C_specific_handler+0x9d) [0x00007FFFF400F55D]
C:\WINDOWS\SYSTEM32\ntdll.dll(_chkstk+0x9f) [0x00007FF817DA62FF]
C:\WINDOWS\SYSTEM32\ntdll.dll(RtlLocateExtendedFeature+0x597) [0x00007FF817C52327]
C:\WINDOWS\SYSTEM32\ntdll.dll(KiUserExceptionDispatcher+0x2e) [0x00007FF817DA5C3E]
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_obj_memsize_of+0x1dc) [0x00007FFEEB9A2C8C] C:\Source\ruby-4.0.1-mswin\gc.c:2351
C:\Source\ruby-prof\ext\ruby_prof\ruby_prof.so(measure_memory+0x51) [0x00007FFFA8427161] C:\Source\ruby-prof\ext\ruby_prof\rp_measure_memory.c:23
C:\Source\ruby-prof\ext\ruby_prof\ruby_prof.so(prof_measure+0x1a) [0x00007FFFA8425D8A] C:\Source\ruby-prof\ext\ruby_prof\rp_measurement.c:38
C:\Source\ruby-prof\ext\ruby_prof\ruby_prof.so(prof_event_hook+0x43) [0x00007FFFA842AC23] C:\Source\ruby-prof\ext\ruby_prof\rp_profile.c:200
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(tp_call_trace+0x26) [0x00007FFEEBA41E12] C:\Source\ruby-4.0.1-mswin\vm_trace.c:1300
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(exec_hooks_body+0x74) [0x00007FFEEBA3FCA4] C:\Source\ruby-4.0.1-mswin\vm_trace.c:457
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_exec_event_hooks+0x4a) [0x00007FFEEBA40326] C:\Source\ruby-4.0.1-mswin\vm_trace.c:543
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_gc_event_hook+0xc1) [0x00007FFEEB99DE35] C:\Source\ruby-4.0.1-mswin\gc.c:241
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(newobj_of+0x17c) [0x00007FFEEB99C348] C:\Source\ruby-4.0.1-mswin\gc.c:1014
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(typed_data_alloc+0xb6) [0x00007FFEEB9A565A] C:\Source\ruby-4.0.1-mswin\gc.c:1102
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_data_typed_object_zalloc+0x3b) [0x00007FFEEB99D877] C:\Source\ruby-4.0.1-mswin\gc.c:1125
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_managed_id_table_create+0x21) [0x00007FFEEBA2AF2D] C:\Source\ruby-4.0.1-mswin\id_table.c:375
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(callable_method_entry_or_negative+0x299) [0x00007FFEEB9C434D] C:\Source\ruby-4.0.1-mswin\vm_method.c:1918
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(callable_method_entry+0x9) [0x00007FFEEB9C4081] C:\Source\ruby-4.0.1-mswin\vm_method.c:1937
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_populate_cc+0x2a) [0x00007FFEEB9E1CF2] C:\Source\ruby-4.0.1-mswin\vm_insnhelper.c:2155
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_vm_search_method_slowpath+0x7d) [0x00007FFEEB9D0D21] C:\Source\ruby-4.0.1-mswin\vm_insnhelper.c:2299
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_search_method_slowpath0+0x20) [0x00007FFEEB9E261C] C:\Source\ruby-4.0.1-mswin\vm_insnhelper.c:2321
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_sendish+0x14e) [0x00007FFEEB9E2B2E] C:\Source\ruby-4.0.1-mswin\vm_insnhelper.c:6123
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_exec_core+0x1f41) [0x00007FFEEB9DCA85] C:\Source\ruby-4.0.1-mswin\vm_exec.c:101
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_vm_exec+0x101) [0x00007FFEEB9CF7C9] C:\Source\ruby-4.0.1-mswin\vm.c:2801
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(invoke_block_from_c_bh+0x2eb) [0x00007FFEEB9C688B] C:\Source\ruby-4.0.1-mswin\vm.c:1834
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_yield_with_cref+0x93) [0x00007FFEEB9E41BF] C:\Source\ruby-4.0.1-mswin\vm.c:1874
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_yield+0x55) [0x00007FFEEB9D1125] C:\Source\ruby-4.0.1-mswin\vm_eval.c:1380
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_protect+0x14a) [0x00007FFEEB9B8DFA] C:\Source\ruby-4.0.1-mswin\eval.c:1127
C:\Source\ruby-prof\ext\ruby_prof\ruby_prof.so(prof_profile_instance+0x58) [0x00007FFFA842C128] C:\Source\ruby-prof\ext\ruby_prof\rp_profile.c:820
C:\Source\ruby-prof\ext\ruby_prof\ruby_prof.so(prof_profile_class+0x2f) [0x00007FFFA842C19F] C:\Source\ruby-prof\ext\ruby_prof\rp_profile.c:845
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_call_cfunc_with_frame_+0x14a) [0x00007FFEEB9D52DA] C:\Source\ruby-4.0.1-mswin\vm_insnhelper.c:3904
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_call_cfunc_with_frame+0x29) [0x00007FFEEB9D5189] C:\Source\ruby-4.0.1-mswin\vm_insnhelper.c:3949
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_call_cfunc_other+0xbc) [0x00007FFEEB9D5154] C:\Source\ruby-4.0.1-mswin\vm_insnhelper.c:3976
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_call_cfunc+0x103) [0x00007FFEEB9D4E67] C:\Source\ruby-4.0.1-mswin\vm_insnhelper.c:4057
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_call_method_each_type+0x67b) [0x00007FFEEB9D7503] C:\Source\ruby-4.0.1-mswin\vm_insnhelper.c:4888
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_call_method+0x14c) [0x00007FFEEB9D6E68] C:\Source\ruby-4.0.1-mswin\vm_insnhelper.c:5052
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_sendish+0x163) [0x00007FFEEB9E2B43] C:\Source\ruby-4.0.1-mswin\vm_insnhelper.c:6134
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_exec_core+0x1f41) [0x00007FFEEB9DCA85] C:\Source\ruby-4.0.1-mswin\vm_exec.c:101
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_vm_exec+0x101) [0x00007FFEEB9CF7C9] C:\Source\ruby-4.0.1-mswin\vm.c:2801
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(invoke_block_from_c_bh+0x2eb) [0x00007FFEEB9C688B] C:\Source\ruby-4.0.1-mswin\vm.c:1834
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_yield_with_cref+0x93) [0x00007FFEEB9E41BF] C:\Source\ruby-4.0.1-mswin\vm.c:1874
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_yield+0x55) [0x00007FFEEB9D1125] C:\Source\ruby-4.0.1-mswin\vm_eval.c:1380
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_ary_each+0x7f) [0x00007FFEEBA1A083] C:\Source\ruby-4.0.1-mswin\array.c:2754
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_call_cfunc_with_frame_+0x14a) [0x00007FFEEB9D52DA] C:\Source\ruby-4.0.1-mswin\vm_insnhelper.c:3904
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_call_cfunc_with_frame+0x29) [0x00007FFEEB9D5189] C:\Source\ruby-4.0.1-mswin\vm_insnhelper.c:3949
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_sendish+0x163) [0x00007FFEEB9E2B43] C:\Source\ruby-4.0.1-mswin\vm_insnhelper.c:6134
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_exec_core+0x1f41) [0x00007FFEEB9DCA85] C:\Source\ruby-4.0.1-mswin\vm_exec.c:101
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_vm_exec+0x101) [0x00007FFEEB9CF7C9] C:\Source\ruby-4.0.1-mswin\vm.c:2801
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(invoke_block_from_c_bh+0x2eb) [0x00007FFEEB9C688B] C:\Source\ruby-4.0.1-mswin\vm.c:1834
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_yield_with_cref+0x93) [0x00007FFEEB9E41BF] C:\Source\ruby-4.0.1-mswin\vm.c:1874
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_yield+0x55) [0x00007FFEEB9D1125] C:\Source\ruby-4.0.1-mswin\vm_eval.c:1380
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_ary_collect+0xa4) [0x00007FFEEBA18F38] C:\Source\ruby-4.0.1-mswin\array.c:3767
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_call_cfunc_with_frame_+0x14a) [0x00007FFEEB9D52DA] C:\Source\ruby-4.0.1-mswin\vm_insnhelper.c:3904
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_call_cfunc_with_frame+0x29) [0x00007FFEEB9D5189] C:\Source\ruby-4.0.1-mswin\vm_insnhelper.c:3949
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_sendish+0x163) [0x00007FFEEB9E2B43] C:\Source\ruby-4.0.1-mswin\vm_insnhelper.c:6134
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_exec_core+0x1f41) [0x00007FFEEB9DCA85] C:\Source\ruby-4.0.1-mswin\vm_exec.c:101
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_vm_exec+0x101) [0x00007FFEEB9CF7C9] C:\Source\ruby-4.0.1-mswin\vm.c:2801
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(vm_invoke_proc+0x304) [0x00007FFEEB9DF6D8] C:\Source\ruby-4.0.1-mswin\vm.c:1944
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_vm_invoke_proc+0x95) [0x00007FFEEB9CFCE9] C:\Source\ruby-4.0.1-mswin\vm.c:1967
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_proc_call_kw+0x70) [0x00007FFEEBAADD6C] C:\Source\ruby-4.0.1-mswin\proc.c:1134
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(exec_end_procs_chain+0x3d) [0x00007FFEEB9B5B4D] C:\Source\ruby-4.0.1-mswin\eval_jump.c:106
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_ec_exec_end_proc+0x13b) [0x00007FFEEB9B73AF] C:\Source\ruby-4.0.1-mswin\eval_jump.c:122
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_ec_teardown+0x11e) [0x00007FFEEB9B789A] C:\Source\ruby-4.0.1-mswin\eval.c:158
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(rb_ec_cleanup+0x260) [0x00007FFEEB9B6C68] C:\Source\ruby-4.0.1-mswin\eval.c:211
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\x64-vcruntime140-ruby400.dll(ruby_run_node+0x4d) [0x00007FFEEB9B998D] C:\Source\ruby-4.0.1-mswin\eval.c:321
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\ruby.exe(wmain+0x52) [0x00007FF7B95D1052] C:\Source\ruby-4.0.1-mswin\main.c:48
C:\msys64\usr\local\ruby-4.0.1-mswin\bin\ruby.exe(__scrt_common_main_seh+0x10c) [0x00007FF7B95D126C] D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288
C:\WINDOWS\System32\KERNEL32.DLL(BaseThreadInitThunk+0x17) [0x00007FF816AEE8D7]
```

-- 
https://bugs.ruby-lang.org/