228d13f6ed (master): gc.c: Pass shape_id to `newobj_init`

[Jean Boussier]

Jean Boussier 2025-12-03 17:08:14 +0000 (Wed, 03 Dec 2025)

New Revision: 228d13f6ed

https://github.com/ruby/ruby/commit/228d13f6ed

Log:
gc.c: Pass shape_id to `newobj_init`

Attempt to fix the following SEGV:

```
ruby(gc_mark) ../src/gc/default/default.c:4429
ruby(gc_mark_children+0x45) [0x560b380bf8b5] ../src/gc/default/default.c:4625
ruby(gc_mark_stacked_objects) ../src/gc/default/default.c:4647
ruby(gc_mark_stacked_objects_all) ../src/gc/default/default.c:4685
ruby(gc_marks_rest) ../src/gc/default/default.c:5707
ruby(gc_marks+0x4e7) [0x560b380c41c1] ../src/gc/default/default.c:5821
ruby(gc_start) ../src/gc/default/default.c:6502
ruby(heap_prepare+0xa4) [0x560b380c4efc] ../src/gc/default/default.c:2074
ruby(heap_next_free_page) ../src/gc/default/default.c:2289
ruby(newobj_cache_miss) ../src/gc/default/default.c:2396
ruby(RB_SPECIAL_CONST_P+0x0) [0x560b380c5df4] ../src/gc/default/default.c:2420
ruby(RB_BUILTIN_TYPE) ../src/include/ruby/internal/value_type.h:184
ruby(newobj_init) ../src/gc/default/default.c:2136
ruby(rb_gc_impl_new_obj) ../src/gc/default/default.c:2500
ruby(newobj_of) ../src/gc.c:996
ruby(rb_imemo_new+0x37) [0x560b380d8bed] ../src/imemo.c:46
ruby(imemo_fields_new) ../src/imemo.c:105
ruby(rb_imemo_fields_new) ../src/imemo.c:120
```

I have no reproduction, but my understanding based on the backtrace
and error is that GC is triggered inside `newobj_init` causing the
new object to be marked while in a incomplete state.

I believe the fix is to pass the `shape_id` down to `newobj_init`
so it can be set before the GC has a chance to trigger.

Modified files:
gc.c
gc/default/default.c
gc/gc_impl.h
gc/mmtk/mmtk.c
shape.h