[GitHub] [incubator-nuttx] acassis commented on a change in pull request #4935: arch/arm: Implement TLS support

[GitBox <gi...@apache.org>]

acassis commented on a change in pull request #4935:
URL: https://github.com/apache/incubator-nuttx/pull/4935#discussion_r761946005



##########
File path: arch/arm/src/common/arm_tls.c
##########
@@ -0,0 +1,82 @@
+/****************************************************************************
+ * arch/arm/src/common/arm_tls.c
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+#include <nuttx/arch.h>
+#include <nuttx/tls.h>
+
+#include "arm_internal.h"
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: up_tls_size
+ *
+ * Description:
+ *   Get tls (tdata + tbss) section size
+ *
+ * Returned Value:
+ *   Size of (tdata + tbss)
+ *
+ ****************************************************************************/
+
+int up_tls_size(void)
+{
+  /* Extra 8 byte (2 pointer) according to GCC */

Review comment:
       8 bytes

##########
File path: sched/Kconfig
##########
@@ -600,6 +600,13 @@ config SCHED_USER_IDENTITY
 		Those can then be managed using the interfaces.  Child tasks will
 		inherit the UID and GID of its parent.
 
+config SCHED_THREAD_LOCAL
+	bool "Support __thread keyword"
+	default n
+	depends on ARCH_ARM
+	---help---
+		The keyword __thread can be used to declare thread local variables.

Review comment:
       Please tell more! I think it is important to explain the performance gain when using it. I wasn't aware of it until read here: https://stackoverflow.com/questions/32245103/how-does-the-gcc-thread-work




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