Issue #19554 has been updated by peterzhu2118 (Peter Zhu).
It's unlikely that Valgrind will work with CRuby out of the box without Valgrind specific code e.g. for marking stacks, poisoning "freed" memory, etc.
Valgrind (without the memory leak detection feature, so only detecting invalid memory access) actually works very well with CRuby (excluding Fibers), which is why I opened this ticket. For most C extensions, they are able to use Valgrind with memory leak detection using [ruby_memcheck](https://github.com/Shopify/ruby_memcheck), which applies heuristics to remove false-positive memory leaks in Ruby. In fact, issues like #18264 and #18936 were found by Valgrind. ---------------------------------------- Bug #19554: Invalid memory access detected by Valgrind when using Fibers https://bugs.ruby-lang.org/issues/19554#change-102593 * 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 ``` -- https://bugs.ruby-lang.org/