mariadb/mariadb-10.5-fix-prevent-optimizing-out-buf-argument-in-ch.patch

From 35c277851972267d4d020126ab8f893c4b17dd36 Mon Sep 17 00:00:00 2001
From: Martin Liska <mliska@suse.cz>
Date: Sun, 8 Dec 2019 10:52:27 +0100
Subject: [PATCH] MDEV-21248: Prevent optimizing out buf argument in
 check_stack_overrun.

When using LTO, one can see optimization of stack variables that
are passed to check_stack_overrun as argument buf. That prevents
proper stack overrun detection.
---
 sql/sql_parse.cc | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/sql/sql_parse.cc b/sql/sql_parse.cc
index dc81e8a2b91..6f3c076709a 100644
--- a/sql/sql_parse.cc
+++ b/sql/sql_parse.cc
@@ -7392,8 +7392,17 @@ long max_stack_used;
     corresponding exec. (Thus we only have to check in fix_fields.)
   - Passing to check_stack_overrun() prevents the compiler from removing it.
 */
-bool check_stack_overrun(THD *thd, long margin,
-			 uchar *buf __attribute__((unused)))
+
+bool
+#ifdef __GNUC__
+/*
+  Do not optimize the function in order to preserve a stack variable creation.
+  Otherwise, the variable pointed as "buf" can be removed due to a missing
+  usage.
+ */
+__attribute__((optimize("-O0")))
+#endif
+check_stack_overrun(THD *thd, long margin, uchar *buf __attribute__((unused)))
 {
   long stack_used;
   DBUG_ASSERT(thd == current_thd);
-- 
2.25.1