From 2d4e44a91a753648cbe8732781412a11aeeff7c5 Mon Sep 17 00:00:00 2001
From: Sergei Petrunia <sergey@mariadb.com>
Date: Wed, 4 Feb 2026 16:03:49 +0200
Subject: [PATCH 1/2] MDEV-38753: Debugging help: print which MEM_ROOT the
 object is on

Add two functions intended for use from debugger:
  bool dbug_is_mem_on_mem_root(MEM_ROOT *mem_root, void *ptr);
  const char *dbug_which_mem_root(THD *thd, void *ptr);

Also, collect declarations of all other functions intended for use
from debugger in sql/sql_test.h
---
 sql/item.h      |  6 ------
 sql/sql_test.cc | 44 ++++++++++++++++++++++++++++++++++++++++++++
 sql/sql_test.h  | 33 +++++++++++++++++++++++++++++++++
 3 files changed, 77 insertions(+), 6 deletions(-)

diff --git a/sql/item.h b/sql/item.h
index c74097739d389..6caf2f0dd4b63 100644
--- a/sql/item.h
+++ b/sql/item.h
@@ -100,12 +100,6 @@ class ValueBuffer: public Value
 };
 
 
-#ifdef DBUG_OFF
-static inline const char *dbug_print_item(Item *item) { return NULL; }
-#else
-const char *dbug_print_item(Item *item);
-#endif
-
 class Virtual_tmp_table;
 class sp_head;
 class Protocol;
diff --git a/sql/sql_test.cc b/sql/sql_test.cc
index 8afc6cad347c6..a5fc8a2c71a98 100644
--- a/sql/sql_test.cc
+++ b/sql/sql_test.cc
@@ -714,3 +714,47 @@ void print_keyuse_array_for_trace(THD *thd, DYNAMIC_ARRAY *keyuse_array)
     keyuse_elem.add("null_rejecting",keyuse->null_rejecting);
   }
 }
+
+
+#ifndef DBUG_OFF
+
+/* Check if ptr points to memory on the mem_root */
+
+bool dbug_is_mem_on_mem_root(const MEM_ROOT *mem_root, void *ptr)
+{
+  const USED_MEM *ptrs[]= {mem_root->free, mem_root->used};
+  for (const USED_MEM **p= ptrs; p!=ptrs + 2; p++)
+  {
+    for (const USED_MEM *block= *p; block; block= block->next)
+    {
+      const char *start= (const char*)block;
+      const char *end= start + block->size - block->left;
+      DBUG_ASSERT(end >= start);
+      if (ptr >= start && ptr < end)
+        return true;
+    }
+  }
+  return false;
+}
+
+
+/*
+  Check whether ptr has been allocated on a statement mem_root
+  or transient mem_root or somewhere else.
+*/
+const char *dbug_which_mem_root(THD *thd, void *ptr)
+{
+  if (dbug_is_mem_on_mem_root(thd->mem_root, ptr))
+  {
+    if (thd->mem_root == thd->stmt_arena->mem_root)
+      return "thd->mem_root, same as stmt_arena->mem_root";
+    return "thd->mem_root";
+  }
+
+  if (dbug_is_mem_on_mem_root(thd->stmt_arena->mem_root, ptr))
+    return "thd->stmt_arena->mem_root";
+
+  return "Unknown";
+}
+
+#endif
diff --git a/sql/sql_test.h b/sql/sql_test.h
index 2ab305acd6686..ce154ed9954f7 100644
--- a/sql/sql_test.h
+++ b/sql/sql_test.h
@@ -23,9 +23,42 @@ class JOIN;
 struct TABLE_LIST;
 typedef class Item COND;
 typedef class st_select_lex SELECT_LEX;
+typedef class st_select_lex_unit SELECT_LEX_UNIT;
 struct SORT_FIELD;
+class SEL_ARG;
+
+
+#ifndef DBUG_OFF
+/*
+  Functions intended for manual use in debugger. NOT thread-safe.
+*/
+
+/* Print various data structures */
+const char *dbug_print_item(Item *item);
+const char *dbug_print_select(SELECT_LEX *sl);
+const char *dbug_print_unit(SELECT_LEX_UNIT *un);
+const char *dbug_print_sel_arg(SEL_ARG *sel_arg);
+
+/* A single overloaded function (not inline so debugger sees them): */
+const char *dbug_print(Item *x);
+const char *dbug_print(SELECT_LEX *x);
+const char *dbug_print(SELECT_LEX_UNIT *x);
+
+/* Print current table row */
+const char* dbug_print_table_row(TABLE *table);
+const char *dbug_print_row(TABLE *table, const uchar *rec);
+
+/* Check which MEM_ROOT the data is on */
+bool dbug_is_mem_on_mem_root(const MEM_ROOT *mem_root, void *ptr);
+const char *dbug_which_mem_root(THD *thd, void *ptr);
+
+#else
+// A dummy implementation is used in release builds
+inline const char *dbug_print_item(Item *item) { return NULL; }
+#endif
 
 #ifndef DBUG_OFF
+/* Functions that print into DBUG_FILE (/tmp/mariadb.trace by default) */
 void print_where(COND *cond,const char *info, enum_query_type query_type);
 void TEST_filesort(SORT_FIELD *sortorder,uint s_length);
 void TEST_join(JOIN *join);

From 06322f5c3ed84a2a7bd67c8438614cc6204f63ac Mon Sep 17 00:00:00 2001
From: Sergei Petrunia <sergey@mariadb.com>
Date: Thu, 5 Feb 2026 14:41:24 +0200
Subject: [PATCH 2/2] Add comment about Debug_key.

---
 sql/sql_debug.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/sql/sql_debug.h b/sql/sql_debug.h
index 003caec54544f..fe2b15ae8ccd7 100644
--- a/sql/sql_debug.h
+++ b/sql/sql_debug.h
@@ -19,6 +19,9 @@
 */
 
 
+/*
+  Used in mtr tests to check index flags and key part flags and datatypes.
+*/
 class Debug_key: public String
 {
 public: