Fix complex transi compact #547
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casperisfine
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It's crashing on: case VM_METHOD_TYPE_ISEQ:
if (def->body.iseq.iseqptr) gc_mark(objspace, (VALUE)def->body.iseq.iseqptr); |
due to a failure on a CI http://ci.rvm.jp/results/trunk-iseq_binary@ruby-sp2-docker/4779277 ``` expected: == disasm: #<ISeq:prism_test_forwarding_arguments_node1@<compiled>:2 (2,8)-(4,11)> local table (size: 1, argc: 0 [opts: 0, rest: -1, post: 0, block: -1, kw: -1@-1, kwrest: 1]) [ 1] "..."@0 0000 putself ( 3) 0001 getlocal_WC_0 ?@-2 0003 splatarray false 0005 getblockparamproxy ?@-1, 0 0008 send <calldata!mid:prism_test_forwarding_arguments_node, argc:1, ARGS_SPLAT|ARGS_BLOCKARG|FCALL>, nil 0011 leave ( 2) actual: == disasm: #<ISeq:prism_test_forwarding_arguments_node1@<compiled>:2 (2,8)-(4,11)> local table (size: 1, argc: 0 [opts: 0, rest: -1, post: 0, block: -1, kw: -1@-1, kwrest: 1]) [ 1] "..."@0 0000 putself ( 3) 0001 getlocal_WC_0 ?@-2 0003 splatarray false 0005 getblockparamproxy "!"@-1, 0 0008 send <calldata!mid:prism_test_forwarding_arguments_node, argc:1, ARGS_SPLAT|ARGS_BLOCKARG|FCALL>, nil 0011 leave ( 2) /tmp/ruby/src/trunk-iseq_binary/tool/lib/iseq_loader_checker.rb:36:in `exit': exit (SystemExit) ```
That function is a bit too low level to called from multiple
places. It's always used in tandem with `rb_shape_set_too_complex`
and both have to know how the object is laid out to update the
`iv_ptr`.
So instead we can provide two higher level function:
- `rb_obj_copy_ivs_to_hash_table` to prepare a `st_table` from an
arbitrary oject.
- `rb_obj_convert_to_too_complex` to assign the new `st_table`
to the old object, and safely free the old `iv_ptr`.
Unfortunately both can't be combined into one, because `rb_obj_copy_ivar`
need `rb_obj_copy_ivs_to_hash_table` to copy from one object
to another.
We ran into that case on our CI, including some sizes would help debug it much easier.
Reproduction script:
```
o = Object.new
10.times { |i| o.instance_variable_set(:"@A#{i}", i) }
i = 0
a = Object.new
while RubyVM::Shape.shapes_available > 2
a.instance_variable_set(:"@i#{i}", 1)
i += 1
end
o.remove_instance_variable(:@a0)
puts o.instance_variable_get(:@A1)
```
Before this patch, it would incorrectly output `2` and now it correctly
outputs `1`.
Now the documentation that was already in the codebase for `File::Stat#directory?` shows up.
Found through GC.stress + GC.auto_compact crashes in rubyGH-8932. Previously, the compaction run within `rb_method_entry_alloc()` could move the `def->body.iseq.cref` and `iseqptr` set up before the call and leave the `def` pointing to moved addresses. Nothing was marking `def` during that GC run. Low probability reproducer: GC.stress = true GC.auto_compact = true arr = [] alloc = 1000.times.map { [] } alloc = nil a = arr.first GC.start
When transitioning an object to TOO_COMPLEX we copy all its ivar in a table, but if GC (and compaction) trigger in the middle of the transition, the old `iv_ptr` might still be the canonical ivar list and will be updated by the GC, but the reference we copied in the table will be outdated. So we must pin these reference until they are all copied and the object `iv_ptr` is pointing to the table. To do this we allocate a temporary TOO_COMPLEX object which we use as the host for the copy. TOO_COMPLEX objects are marked with `mark_tbl` which does pin references. Co-Authored-By: Alan Wu <[email protected]>
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I think this PR fixes the compaction issue, but now I run into the bug I was looking to in the first place: