From: "peterzhu2118 (Peter Zhu) via ruby-core" <ruby-core@...>
Date: 2023-03-29T20:47:45+00:00
Subject: [ruby-core:113043] [Ruby master Bug#19554] Invalid memory access detected by Valgrind when using Fibers

Issue #19554 has been updated by peterzhu2118 (Peter Zhu).


Thanks for the reply @ioquatix!

I haven't looked too much into ASAN, I'll look into it further. My main concern with ASAN is the need for Ruby to be compiled with it turned on and that additional code may need to be added into native extensions to support it. Both of these are barriers to entry compared to Valgrind.

In the [Valgrind manual](https://valgrind.org/docs/manual/mc-manual.html#mc-manual.clientreqs), it looks like there's a `VALGRIND_MAKE_MEM_DEFINED` function. Maybe that can be used to mark the regions as valid.

----------------------------------------
Bug #19554: Invalid memory access detected by Valgrind when using Fibers
https://bugs.ruby-lang.org/issues/19554#change-102582

* Author: peterzhu2118 (Peter Zhu)
* Status: Open
* Priority: Normal
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
This issue was originally reported here: https://github.com/Shopify/ruby_memcheck/issues/14

Running the script shown below using `valgrind --trace-children=yes --num-callers=500 ruby test.rb` outputs a lot of invalid memory access errors. I've shown a few sample errors below.

I am able to reproduce this issue on the master branch (commit [1e9a218ade](https://github.com/ruby/ruby/commit/1e9a218ade3af90c18f42e3fea08e2fcea81222a)), 3.2, 3.1, 3.0.


```ruby
require "bundler/inline"
gemfile do
  source "https://rubygems.org"
  gem "graphql"
end

module Example
  class FooType < GraphQL::Schema::Object
    field :id, ID, null: false
  end

  class FooSource < GraphQL::Dataloader::Source
    def fetch(ids)
      ids
    end
  end

  class QueryType < GraphQL::Schema::Object
    field :foo, Example::FooType do
      argument :foo_id, GraphQL::Types::ID, required: false, loads: Example::FooType
    end

    def foo(foo: nil); end
  end

  class Schema < GraphQL::Schema
    query Example::QueryType
    use GraphQL::Dataloader

    def self.object_from_id(id, ctx)
      ctx.dataloader.with(Example::FooSource).request(id)
    end
  end
end

Example::Schema.execute(<<-GRAPHQL)
{
  foo(fooId: "Other") {
    id
  }
}
GRAPHQL
```

```
==203957== Use of uninitialised value of size 8
==203957==    at 0x3453FD: vm_exec_core (vm.inc:4411)
==203957==    by 0x357EFB: rb_vm_exec (vm.c:2366)
==203957==    by 0x354E44: invoke_block (vm.c:1384)
==203957==    by 0x355759: invoke_iseq_block_from_c (vm.c:1440)
==203957==    by 0x355759: invoke_block_from_c_proc (vm.c:1538)
==203957==    by 0x355759: vm_invoke_proc (vm.c:1568)
==203957==    by 0x355DF4: rb_vm_invoke_proc (vm.c:1589)
==203957==    by 0x48F695: rb_fiber_start (cont.c:2513)
==203957==    by 0x48CCF8: fiber_entry (cont.c:831)
==203957==
==203957== Invalid write of size 8
==203957==    at 0x48C407: fiber_pool_stack_reset (cont.c:325)
==203957==    by 0x48C4E9: fiber_pool_vacancy_reset (cont.c:364)
==203957==    by 0x48CBB0: fiber_pool_stack_release (cont.c:752)
==203957==    by 0x48CECF: fiber_stack_release (cont.c:874)
==203957==    by 0x48FC9F: fiber_switch (cont.c:2726)
==203957==    by 0x4901F9: fiber_resume_kw (cont.c:2906)
==203957==    by 0x490235: rb_fiber_resume_kw (cont.c:2912)
==203957==    by 0x4903B7: rb_fiber_m_resume (cont.c:2973)
==203957==    by 0x3337D6: ractor_safe_call_cfunc_m1 (vm_insnhelper.c:3166)
==203957==    by 0x33440A: vm_call_cfunc_with_frame_ (vm_insnhelper.c:3357)
==203957==    by 0x3345E1: vm_call_cfunc_with_frame (vm_insnhelper.c:3385)
==203957==    by 0x3398E5: vm_sendish (vm_insnhelper.c:5225)
==203957==    by 0x341203: vm_exec_core (insns.def:835)
==203957==    by 0x357EFB: rb_vm_exec (vm.c:2366)
==203957==    by 0x354E44: invoke_block (vm.c:1384)
==203957==    by 0x355759: invoke_iseq_block_from_c (vm.c:1440)
==203957==    by 0x355759: invoke_block_from_c_proc (vm.c:1538)
==203957==    by 0x355759: vm_invoke_proc (vm.c:1568)
==203957==    by 0x355DF4: rb_vm_invoke_proc (vm.c:1589)
==203957==    by 0x48F695: rb_fiber_start (cont.c:2513)
==203957==    by 0x48CCF8: fiber_entry (cont.c:831)
==203957==  Address 0x9bad008 is in a rw- anonymous segment
```




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