From ea520ca9273699fc1c77a71bbeba4b6e06ccfc6c Mon Sep 17 00:00:00 2001
From: Aaron Patterson <tenderlove@ruby-lang.org>
Date: Mon, 22 Apr 2019 17:14:36 -0700
Subject: [PATCH] Prevent rb_define_(class|module) classes from moving

Before this commit, classes and modules would be registered with the
VM's `defined_module_hash`.  The key was the ID of the class, but that
meant that it was possible for hash collisions to occur.  The compactor
doesn't allow classes in the `defined_module_hash` to move, but if there
is a conflict, then it's possible a class would be removed from the hash
and not get pined.

This commit changes the key / value of the hash just to be the class
itself, thus preventing movement.
---
 class.c   |  3 +++
 gc.c      |  2 +-
 vm.c      | 10 ++++++----
 vm_core.h |  2 +-
 4 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/class.c b/class.c
index d0ff92b6eb..0cee5caae2 100644
--- a/class.c
+++ b/class.c
@@ -659,6 +659,9 @@ rb_define_class(const char *name, VALUE super)
 	if (rb_class_real(RCLASS_SUPER(klass)) != super) {
 	    rb_raise(rb_eTypeError, "superclass mismatch for class %s", name);
 	}
+
+        /* Class may have been defined in Ruby and not pin-rooted */
+        rb_vm_add_root_module(id, klass);
 	return klass;
     }
     if (!super) {
diff --git a/gc.c b/gc.c
index f90bdd99bf..9529b2d4a4 100644
--- a/gc.c
+++ b/gc.c
@@ -8159,7 +8159,7 @@ gc_verify_compaction_references(VALUE mod)
     heap_eden->using_page = NULL;
 
     gc_verify_internal_consistency(mod);
-    rb_gc_enable();
+
     /* GC after compaction to eliminate T_MOVED */
     rb_gc();
 
diff --git a/vm.c b/vm.c
index c4144b5b99..41064f07c3 100644
--- a/vm.c
+++ b/vm.c
@@ -2251,9 +2251,8 @@ rb_vm_mark(void *ptr)
 	rb_gc_mark(vm->loaded_features_snapshot);
 	rb_gc_mark(vm->top_self);
 	RUBY_MARK_UNLESS_NULL(vm->coverages);
-	rb_gc_mark(vm->defined_module_hash);
         /* Prevent classes from moving */
-        rb_mark_tbl(rb_hash_tbl(vm->defined_module_hash, __FILE__, __LINE__));
+        rb_mark_tbl(vm->defined_module_hash);
 
 	if (vm->loading_table) {
 	    rb_mark_tbl(vm->loading_table);
@@ -2286,7 +2285,7 @@ rb_vm_add_root_module(ID id, VALUE module)
 {
     rb_vm_t *vm = GET_VM();
 
-    rb_hash_aset(vm->defined_module_hash, ID2SYM(id), module);
+    st_insert(vm->defined_module_hash, (st_data_t)module, (st_data_t)module);
 
     return TRUE;
 }
@@ -2561,6 +2560,9 @@ thread_mark(void *ptr)
     RUBY_MARK_UNLESS_NULL(th->top_self);
     RUBY_MARK_UNLESS_NULL(th->top_wrapper);
     if (th->root_fiber) rb_fiber_mark_self(th->root_fiber);
+
+    /* Ensure EC stack objects are pinned */
+    rb_execution_context_mark(th->ec);
     RUBY_MARK_UNLESS_NULL(th->stat_insn_usage);
     RUBY_MARK_UNLESS_NULL(th->last_status);
     RUBY_MARK_UNLESS_NULL(th->locking_mutex);
@@ -3230,7 +3232,7 @@ Init_vm_objects(void)
 {
     rb_vm_t *vm = GET_VM();
 
-    vm->defined_module_hash = rb_hash_new();
+    vm->defined_module_hash = st_init_numtable();
 
     /* initialize mark object array, hash */
     vm->mark_object_ary = rb_ary_tmp_new(128);
diff --git a/vm_core.h b/vm_core.h
index 2e8ddfe37f..2c38911d58 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -660,7 +660,7 @@ typedef struct rb_vm_struct {
     VALUE coverages;
     int coverage_mode;
 
-    VALUE defined_module_hash;
+    st_table * defined_module_hash;
 
     struct rb_objspace *objspace;