From 9fab2c1a1a5f5e429eb88eac29d250685dcc4354 Mon Sep 17 00:00:00 2001
From: Matt Valentine-House <matt@eightbitraptor.com>
Date: Tue, 1 Feb 2022 21:36:29 +0000
Subject: [PATCH] Add the size pool slot size to the output of
 ObjectSpace.dump/dump_all

---
 ext/objspace/objspace_dump.c   |  9 +++++++++
 gc.h                           |  2 ++
 test/objspace/test_objspace.rb | 28 ++++++++++++++++++++++++++++
 3 files changed, 39 insertions(+)

diff --git a/ext/objspace/objspace_dump.c b/ext/objspace/objspace_dump.c
index cf7acb5c6f9597..e958a831c56cc8 100644
--- a/ext/objspace/objspace_dump.c
+++ b/ext/objspace/objspace_dump.c
@@ -35,6 +35,7 @@ struct dump_config {
     const char *root_category;
     VALUE cur_obj;
     VALUE cur_obj_klass;
+    size_t cur_page_slot_size;
     size_t cur_obj_references;
     unsigned int roots: 1;
     unsigned int full_heap: 1;
@@ -360,6 +361,9 @@ dump_object(VALUE obj, struct dump_config *dc)
     dump_append(dc, obj_type(obj));
     dump_append(dc, "\"");
 
+    dump_append(dc, ", \"slot_size\":");
+    dump_append_sizet(dc, dc->cur_page_slot_size);
+
     if (dc->cur_obj_klass) {
         dump_append(dc, ", \"class\":");
         dump_append_ref(dc, dc->cur_obj_klass);
@@ -539,6 +543,7 @@ heap_i(void *vstart, void *vend, size_t stride, void *data)
     for (; v != (VALUE)vend; v += stride) {
         void *ptr = asan_poisoned_object_p(v);
         asan_unpoison_object(v, false);
+        dc->cur_page_slot_size = stride;
 
 	if (dc->full_heap || RBASIC(v)->flags)
 	    dump_object(v, dc);
@@ -616,6 +621,10 @@ static VALUE
 objspace_dump(VALUE os, VALUE obj, VALUE output)
 {
     struct dump_config dc = {0,};
+    if (!RB_SPECIAL_CONST_P(obj)) {
+        dc.cur_page_slot_size = rb_gc_obj_slot_size(obj);
+    }
+
     dump_output(&dc, output, Qnil, Qnil);
 
     dump_object(obj, &dc);
diff --git a/gc.h b/gc.h
index 91d6e5787df37c..84c8eade6368d8 100644
--- a/gc.h
+++ b/gc.h
@@ -136,6 +136,8 @@ void rb_objspace_each_objects_without_setup(
     int (*callback)(void *, void *, size_t, void *),
     void *data);
 
+size_t rb_gc_obj_slot_size(VALUE obj);
+
 RUBY_SYMBOL_EXPORT_END
 
 #endif /* RUBY_GC_H */
diff --git a/test/objspace/test_objspace.rb b/test/objspace/test_objspace.rb
index b7342e899bf027..34d9dd76ecdd8c 100644
--- a/test/objspace/test_objspace.rb
+++ b/test/objspace/test_objspace.rb
@@ -431,6 +431,27 @@ def dump_my_heap_please
     end
   end
 
+  def test_dump_objects_dumps_page_slot_sizes
+    assert_in_out_err(%w[-robjspace], "#{<<-"begin;"}\n#{<<-'end;'}") do |output, error|
+      begin;
+        def dump_my_heap_please
+          ObjectSpace.dump_all(output: $stdout)
+        end
+
+        p $stdout == dump_my_heap_please
+      end;
+      assert_equal 'true', output.pop
+      assert(output.count > 1)
+      output.each { |l|
+        obj = JSON.parse(l)
+        next if obj["type"] == "ROOT"
+
+        assert(obj["slot_size"] != nil)
+        assert(obj["slot_size"] % GC::INTERNAL_CONSTANTS[:BASE_SLOT_SIZE] == 0)
+      }
+    end
+  end
+
   def test_dump_escapes_method_name
     method_name = "foo\"bar"
     klass = Class.new do
@@ -449,6 +470,13 @@ def test_dump_escapes_method_name
     ObjectSpace.trace_object_allocations_stop
   end
 
+  def test_dump_includes_slot_size
+    str = "TEST"
+    dump = ObjectSpace.dump(str)
+
+    assert_includes dump, "\"slot_size\":#{GC::INTERNAL_CONSTANTS[:BASE_SLOT_SIZE]}"
+  end
+
   def test_dump_reference_addresses_match_dump_all_addresses
     assert_in_out_err(%w[-robjspace], "#{<<-"begin;"}\n#{<<-'end;'}") do |output, error|
       begin;