Issue #21352 has been updated by byroot (Jean Boussier). I suspect it's caused by either a T_NONE or a T_IMEMO. I have a feature branch that ran into that issue I think and I haven't merged yet, but I could just cherry-pick that fix. ---------------------------------------- Bug #21352: Invalid read in shape lookup code https://bugs.ruby-lang.org/issues/21352#change-113340 * Author: Earlopain (Earlopain _) * Status: Open * ruby -v: ruby 3.5.0dev (2025-05-19T04:27:50Z master 40c957ba21) +PRISM [x86_64-linux] * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- Prism runs tests with valgrind and it recently started to report an invalid read in `rb_shape_lookup`. Example workflow: https://github.com/ruby/prism/actions/runs/15111527208/job/42471945845?pr=35... ``` Invalid read of size 8 rb_shape_lookup (shape.c:347) rb_obj_shape (shape.h:184) rb_shape_obj_too_complex_p (shape.c:1098) rb_free_generic_ivar (variable.c:1274) rb_gc_obj_free_vm_weak_references (gc.c:2061) rb_gc_impl_shutdown_free_objects (default.c:2965) rb_objspace_free_objects (gc.c:1759) ruby_vm_destruct (vm.c:3209) rb_ec_cleanup (eval.c:263) ruby_run_node (eval.c:319) rb_main (main.c:42) main (main.c:62) ``` cc @byroot since you did recent changes around the shape code. I'm lacking knowledge to dig into this, so it may be a false positive (it uses https://github.com/Shopify/ruby_memcheck which does some heuristics). I confirmed that this happens locally on current ruby-dev when running `bundle exec rake test:valgrind` from `ruby/prism`. -- https://bugs.ruby-lang.org/