Add Thread Local Storage (TLS) support using Picolibc functions

This patch provides definitions of the general TLS support macros in
terms of the Picolibc TLS support functions.

Picolibc is normally configured to use TLS internally for all
variables that are intended to be task-local, so these changes are
necessary for picolibc to work correctly with FreeRTOS.

The picolibc helper functions rely on elements within the linker
script to arrange the TLS data in memory and define some symbols.
Applications wanting to use this mechanism will need changes in their
linker script when migrating to picolibc.

Signed-off-by: Keith Packard <[email protected]>

Author: Keith Packard

.github/lexicon.txt

@@ -1061,6 +1061,7 @@ mclk
 mconfigintcoresw
 mcr
 mcu
+md
 mddr
 mder
 mdh
@@ -1342,6 +1343,7 @@ phy
 phya
 pic
 picnt
+picolibc
 pien
 piir
 pimr

include/FreeRTOS.h

@@ -76,6 +76,17 @@
 
 #endif /* if ( configUSE_NEWLIB_REENTRANT == 1 ) */
 
+/* Must be defaulted before configUSE_PICOLIBC_TLS is used below. */
+#ifndef configUSE_PICOLIBC_TLS
+    #define configUSE_PICOLIBC_TLS    0
+#endif
+
+#if ( configUSE_PICOLIBC_TLS == 1 )
+
+    #include "picolibc-freertos.h"
+
+#endif /* if ( configUSE_PICOLIBC_TLS == 1 ) */
+
 #ifndef configUSE_C_RUNTIME_TLS_SUPPORT
     #define configUSE_C_RUNTIME_TLS_SUPPORT    0
 #endif

include/picolibc-freertos.h

@@ -0,0 +1,69 @@
+/*
+ * FreeRTOS Kernel <DEVELOPMENT BRANCH>
+ * Copyright (C) 2021 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
+ *
+ * SPDX-License-Identifier: MIT
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ * https://www.FreeRTOS.org
+ * https://github.com/FreeRTOS
+ *
+ */
+
+#ifndef INC_PICOLIBC_FREERTOS_H
+#define INC_PICOLIBC_FREERTOS_H
+
+/* Use picolibc TLS support to allocate space for __thread variables,
+ * initialize them at thread creation and set the TLS context at
+ * thread switch time.
+ *
+ * See the picolibc TLS docs:
+ * https://github.com/picolibc/picolibc/blob/main/doc/tls.md
+ * for additional information. */
+
+#include <picotls.h>
+
+#define configUSE_C_RUNTIME_TLS_SUPPORT    1
+
+#define configTLS_BLOCK_TYPE               void *
+
+/* Allocate thread local storage block off the end of the
+* stack. The _tls_size() function returns the size (in
+* bytes) of the total TLS area used by the application */
+#if ( portSTACK_GROWTH < 0 )
+    #define configINIT_TLS_BLOCK( xTLSBlock, pxTopOfStack )                                            \
+    do {                                                                                               \
+        pxTopOfStack = ( StackType_t * ) ( ( ( portPOINTER_SIZE_TYPE ) pxTopOfStack ) - _tls_size() ); \
+        xTLSBlock = pxTopOfStack;                                                                      \
+        _init_tls( xTLSBlock );                                                                        \
+    } while( 0 )
+#else /* portSTACK_GROWTH */
+    #define configINIT_TLS_BLOCK( xTLSBlock, pxTopOfStack )                                            \
+    do {                                                                                               \
+        xTLSBlock = pxTopOfStack;                                                                      \
+        pxTopOfStack = ( StackType_t * ) ( ( ( portPOINTER_SIZE_TYPE ) pxTopOfStack ) + _tls_size() ); \
+        _init_tls( xTLSBlock );                                                                        \
+    } while( 0 )
+#endif /* portSTACK_GROWTH */
+
+#define configSET_TLS_BLOCK( xTLSBlock )    _set_tls( xTLSBlock )
+
+#define configDEINIT_TLS_BLOCK( xTLSBlock )
+
+#endif /* INC_PICOLIBC_FREERTOS_H */