This is damn ugly patch if you need to update it, see PHP_5_2 branch version to
understand what this patch is supposed to do as in 5.3 the ini section is
enabled only if mysqlnd driver is enabled which makes the contexts really
small.

diff -urNp -x '*.orig' php-5.6.40.org/ext/pdo_mysql/mysql_driver.c php-5.6.40/ext/pdo_mysql/mysql_driver.c
--- php-5.6.40.org/ext/pdo_mysql/mysql_driver.c	2019-01-09 10:54:13.000000000 +0100
+++ php-5.6.40/ext/pdo_mysql/mysql_driver.c	2021-08-23 23:19:43.115775250 +0200
@@ -539,6 +539,7 @@ static int pdo_mysql_handle_factory(pdo_
 	pdo_mysql_db_handle *H;
 	int i, ret = 0;
 	char *host = NULL, *unix_socket = NULL;
+	char *connect_charset = NULL;
 	unsigned int port = 3306;
 	char *dbname;
 	struct pdo_data_src_parser vars[] = {
@@ -764,6 +765,12 @@ static int pdo_mysql_handle_factory(pdo_
 		password_len = strlen(dbh->password);
 	}
 
+	connect_charset = PDO_MYSQL_G(connect_charset);
+
+	if (connect_charset != NULL) {
+		mysql_options(H->server, MYSQL_SET_CHARSET_NAME, connect_charset);
+	}
+
 	if (mysqlnd_connect(H->server, host, dbh->username, dbh->password, password_len, dbname, dbname_len,
 						port, unix_socket, connect_opts, MYSQLND_CLIENT_NO_FLAG TSRMLS_CC) == NULL) {
 #else
diff -urNp -x '*.orig' php-5.6.40.org/ext/pdo_mysql/pdo_mysql.c php-5.6.40/ext/pdo_mysql/pdo_mysql.c
--- php-5.6.40.org/ext/pdo_mysql/pdo_mysql.c	2019-01-09 10:54:13.000000000 +0100
+++ php-5.6.40/ext/pdo_mysql/pdo_mysql.c	2021-08-23 23:19:43.115775250 +0200
@@ -95,6 +95,7 @@ PHP_INI_BEGIN()
 #if PDO_DBG_ENABLED
 	STD_PHP_INI_ENTRY("pdo_mysql.debug",	NULL, PHP_INI_SYSTEM, OnUpdateString, debug, zend_pdo_mysql_globals, pdo_mysql_globals)
 #endif
+	STD_PHP_INI_ENTRY("pdo_mysql.connect_charset",	NULL,	PHP_INI_ALL,	OnUpdateString,	connect_charset,	zend_pdo_mysql_globals,	pdo_mysql_globals)
 PHP_INI_END()
 /* }}} */
 
@@ -141,9 +142,7 @@ static PHP_MINIT_FUNCTION(pdo_mysql)
 static PHP_MSHUTDOWN_FUNCTION(pdo_mysql)
 {
 	php_pdo_unregister_driver(&pdo_mysql_driver);
-#if PDO_USE_MYSQLND
 	UNREGISTER_INI_ENTRIES();
-#endif
 
 	return SUCCESS;
 }
@@ -213,6 +212,7 @@ static PHP_GINIT_FUNCTION(pdo_mysql)
 	pdo_mysql_globals->debug = NULL;	/* The actual string */
 	pdo_mysql_globals->dbg = NULL;	/* The DBG object*/
 #endif
+	pdo_mysql_globals->connect_charset = NULL;
 }
 /* }}} */
 
diff -urNp -x '*.orig' php-5.6.40.org/ext/pdo_mysql/php_pdo_mysql_int.h php-5.6.40/ext/pdo_mysql/php_pdo_mysql_int.h
--- php-5.6.40.org/ext/pdo_mysql/php_pdo_mysql_int.h	2019-01-09 10:54:13.000000000 +0100
+++ php-5.6.40/ext/pdo_mysql/php_pdo_mysql_int.h	2021-08-23 23:19:43.115775250 +0200
@@ -72,6 +72,7 @@ ZEND_BEGIN_MODULE_GLOBALS(pdo_mysql)
 	char          *debug; /* The actual string */
 	MYSQLND_DEBUG *dbg;	/* The DBG object */
 #endif
+	char          *connect_charset;
 #if defined(PHP_WIN32) && !PDO_DBG_ENABLED
 	/* dummy member so we get at least one member in the struct
 	 * and avoids build errors.