Fix stack alignment for EABI floating point

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@4089 42af7a65-404d-4744-a932-0658087f49c3

ChangeLog

@@ -2194,4 +2194,7 @@
 	  support a file system (such as NXFFS). (Contributed by Hal Glenn).
 	* include/nuttx/rgbcolors.h: More fixes to RGB color conversion
 	  macros.
+	* arch/arm/src/common/up_createstack.c and up_usestack.c:  For ARM EABI
+	  the stack must be aligned to 8-byte boundaries.  This is necessary for
+	  passing aligned floating point values under EABI.
 

Documentation/NuttxPortingGuide.html

@@ -5114,7 +5114,12 @@ build
     some functions into RAM, either for better performance or for errata workarounds.
   </li>
   <li>
-    <code>CONFIG_STACK_POINTER</code>: The initial stack pointer
+    <code>CONFIG_STACK_POINTER</code>: The initial stack pointer (may not be supported
+    in all architectures).
+  </li>
+  <li>
+    <code>CONFIG_STACK_ALIGNMENT</code>: Set if the your application has specific
+    stack alignment requirements (may not be supported in all architectures).
   </li>
   <li>
     <code>CONFIG_IDLETHREAD_STACKSIZE</code>: The size of the initial stack.

arch/arm/src/common/up_createstack.c

@@ -51,6 +51,33 @@
 #include "up_arch.h"
 #include "up_internal.h"
 
+/****************************************************************************
+ * Pre-processor Macros
+ ****************************************************************************/
+
+/* ARM requires at least a 4-byte stack alignment.  For use with EABI and
+ * floating point, the stack must be aligned to 8-byte addresses.
+ */
+
+#ifndef CONFIG_STACK_ALIGNMENT
+
+/* The symbol  __ARM_EABI__ is defined by GCC if EABI is being used.  If you
+ * are not using GCC, make sure that CONFIG_STACK_ALIGNMENT is set correctly!
+ */
+
+#  ifdef __ARM_EABI__
+#    define CONFIG_STACK_ALIGNMENT 8
+#  else
+#    define CONFIG_STACK_ALIGNMENT 4
+#  endif
+#endif
+
+/* Stack alignment macros */
+
+#define STACK_ALIGN_MASK    (CONFIG_STACK_ALIGNMENT-1)
+#define STACK_ALIGN_DOWN(a) ((a) & ~STACK_ALIGN_MASK)
+#define STACK_ALIGN_UP(a)   (((a) + STACK_ALIGN_MASK) & ~STACK_ALIGN_MASK)
+
 /****************************************************************************
  * Private Types
  ****************************************************************************/
@@ -124,21 +151,27 @@ int up_create_stack(_TCB *tcb, size_t stack_size)
       size_t top_of_stack;
       size_t size_of_stack;
 
-       /* The ARM uses a push-down stack:  the stack grows
+      /* The ARM uses a push-down stack:  the stack grows toward lower
-        * toward loweraddresses in memory.  The stack pointer
+       * addresses in memory.  The stack pointer register, points to
-        * register, points to the lowest, valid work address
+       * the lowest, valid work address (the "top" of the stack).  Items
-        * (the "top" of the stack).  Items on the stack are
+       * on the stack are referenced as positive word offsets from sp.
-        * referenced as positive word offsets from sp.
        */
 
       top_of_stack = (uint32_t)tcb->stack_alloc_ptr + stack_size - 4;
 
-       /* The ARM stack must be aligned at word (4 byte)
+      /* The ARM stack must be aligned; 4 byte alignment for OABI and
-        * boundaries. If necessary top_of_stack must be rounded
+       * 8-byte alignment for EABI. If necessary top_of_stack must be
-        * down to the next boundary
+       * rounded down to the next boundary
+       */
+
+      top_of_stack = STACK_ALIGN_DOWN(top_of_stack);
+
+      /* The size of the stack in bytes is then the difference between
+       * the top and the bottom of the stack (+4 because if the top
+       * is the same as the bottom, then the size is one 32-bit element).
+       * The size need not be aligned.
        */
 
-       top_of_stack &= ~3;
       size_of_stack = top_of_stack - (uint32_t)tcb->stack_alloc_ptr + 4;
 
       /* Save the adjusted stack values in the _TCB */

arch/arm/src/common/up_usestack.c

@@ -49,6 +49,33 @@
 
 #include "up_internal.h"
 
+/****************************************************************************
+ * Pre-processor Macros
+ ****************************************************************************/
+
+/* ARM requires at least a 4-byte stack alignment.  For use with EABI and
+ * floating point, the stack must be aligned to 8-byte addresses.
+ */
+
+#ifndef CONFIG_STACK_ALIGNMENT
+
+/* The symbol  __ARM_EABI__ is defined by GCC if EABI is being used.  If you
+ * are not using GCC, make sure that CONFIG_STACK_ALIGNMENT is set correctly!
+ */
+
+#  ifdef __ARM_EABI__
+#    define CONFIG_STACK_ALIGNMENT 8
+#  else
+#    define CONFIG_STACK_ALIGNMENT 4
+#  endif
+#endif
+
+/* Stack alignment macros */
+
+#define STACK_ALIGN_MASK    (CONFIG_STACK_ALIGNMENT-1)
+#define STACK_ALIGN_DOWN(a) ((a) & ~STACK_ALIGN_MASK)
+#define STACK_ALIGN_UP(a)   (((a) + STACK_ALIGN_MASK) & ~STACK_ALIGN_MASK)
+
 /****************************************************************************
  * Private Types
  ****************************************************************************/
@@ -96,21 +123,27 @@ int up_use_stack(_TCB *tcb, void *stack, size_t stack_size)
 
   tcb->stack_alloc_ptr = stack;
 
-  /* The ARM uses a push-down stack:  the stack grows
+  /* The ARM uses a push-down stack:  the stack grows toward lower addresses
-   * toward loweraddresses in memory.  The stack pointer
+   * in memory.  The stack pointer register, points to the lowest, valid
-   * register, points to the lowest, valid work address
+   * work address (the "top" of the stack).  Items on the stack are
-   * (the "top" of the stack).  Items on the stack are
    * referenced as positive word offsets from sp.
    */
 
   top_of_stack = (uint32_t)tcb->stack_alloc_ptr + stack_size - 4;
 
-  /* The ARM stack must be aligned at word (4 byte)
+  /* The ARM stack must be aligned; 4 byte alignment for OABI and 8-byte
-   * boundaries. If necessary top_of_stack must be rounded
+   * alignment for EABI. If necessary top_of_stack must be rounded down
-   * down to the next boundary
+   * to the next boundary
+   */
+
+  top_of_stack = STACK_ALIGN_DOWN(top_of_stack);
+
+  /* The size of the stack in bytes is then the difference between
+   * the top and the bottom of the stack (+4 because if the top
+   * is the same as the bottom, then the size is one 32-bit element).
+   * The size need not be aligned.
    */
 
-  top_of_stack &= ~3;
   size_of_stack = top_of_stack - (uint32_t)tcb->stack_alloc_ptr + 4;
 
   /* Save the adjusted stack values in the _TCB */

configs/README.txt

@@ -1148,7 +1148,11 @@ defconfig -- This is a configuration file similar to the Linux
 		  but copy themselves entirely into RAM for better performance.
 		CONFIG_BOOT_RAMFUNCS - Other configurations may copy just some functions
 		  into RAM, either for better performance or for errata workarounds.
-		CONFIG_STACK_POINTER - The initial stack pointer
+		CONFIG_STACK_POINTER - The initial stack pointer (may not be supported
+		  in all architectures).
+		CONFIG_STACK_ALIGNMENT - Set if the your application has specific
+		  stack alignment requirements (may not be supported
+		  in all architectures).
 		CONFIG_IDLETHREAD_STACKSIZE - The size of the initial stack.
 		  This is the thread that (1) performs the inital boot of the system up
 		  to the point where user_start() is spawned, and (2) there after is the