From 0ade5611df9f981005eed32b369d1e699e520221 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?V=C3=ADt=20Ondruch?= <vondruch@redhat.com>
Date: Thu, 10 Feb 2022 13:26:44 +0100
Subject: [PATCH] Don't query `RubyVM::FrozenCore` for class path.

The `RubyVM::FrozenCore` class path is corrupted during GC cycle and
returns random garbage, which might result in segfault.

But since it is easy to detect the `RubyVM::FrozenCore`, just provide
the class path explicitly as a workaround.

Other possibility would be to ignore `RubyVM::FrozenCore` simlarly as
TracePoint API does:

https://github.com/ruby/ruby/blob/46f6575157d4c2f6bbd5693896e26a65037e5552/vm_trace.c#L411
---
 vm.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/vm.c b/vm.c
index 8ce8b279d4..3d189fa63a 100644
--- a/vm.c
+++ b/vm.c
@@ -547,7 +547,15 @@ rb_dtrace_setup(rb_execution_context_t *ec, VALUE klass, ID id,
     }
     type = BUILTIN_TYPE(klass);
     if (type == T_CLASS || type == T_ICLASS || type == T_MODULE) {
-        VALUE name = rb_class_path(klass);
+        VALUE name = Qnil;
+        /*
+         * Special treatment for rb_mRubyVMFrozenCore wchi is broken by GC.
+         * https://bugs.ruby-lang.org/issues/18257
+         */
+        if (klass == rb_mRubyVMFrozenCore)
+            name = rb_str_new_cstr("RubyVM::FrozenCore");
+        else
+            name = rb_class_path(klass);
         const char *classname, *filename;
         const char *methodname = rb_id2name(id);
         if (methodname && (filename = rb_source_location_cstr(&args->line_no)) != 0) {