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

@@ -102,6 +102,45 @@
     #endif
 #endif /* if ( configUSE_NEWLIB_REENTRANT == 1 ) */
 
+#if ( configUSE_PICOLIBC_TLS == 1 )
+
+    /* 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 )                                                      \
+    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 )                                                      \
+    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 /* if ( configUSE_PICOLIBC_TLS == 1 ) */
+
 #ifndef configUSE_C_RUNTIME_TLS_SUPPORT
     #define configUSE_C_RUNTIME_TLS_SUPPORT    0
 #endif