MIPS stack alignment fix for floating point from Helmut

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@5681 42af7a65-404d-4744-a932-0658087f49c3

1 files changed, 30 insertions, 10 deletions

diff --git a/nuttx/arch/mips/src/common/up_createstack.c b/nuttx/arch/mips/src/common/up_createstack.c
index 722c1a35e..f72701042 100644
--- a/nuttx/arch/mips/src/common/up_createstack.c
+++ b/nuttx/arch/mips/src/common/up_createstack.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  * arch/mips/src/common/up_createstack.c
  *
- *   Copyright (C) 2011 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2011, 2013 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -52,6 +52,26 @@
 #include "up_internal.h"
 
 /****************************************************************************
+ * Pre-processor Macros
+ ****************************************************************************/
+
+/* MIPS requires at least a 4-byte stack alignment.  For floating point use, 
+ * however, the stack must be aligned to 8-byte addresses.
+ */
+
+#ifdef CONFIG_LIBC_FLOATINGPOINT
+#  define CONFIG_STACK_ALIGNMENT 8
+#else
+#  define CONFIG_STACK_ALIGNMENT 4
+#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
  ****************************************************************************/
 
@@ -107,21 +127,21 @@ int up_create_stack(struct tcb_s *tcb, size_t stack_size)
        size_t top_of_stack;
        size_t size_of_stack;
 
-       /* MIPS uses a push-down stack:  the stack grows
-        * toward loweraddresses in memory.  The stack pointer
-        * register, points to the lowest, valid work address
-        * (the "top" of the stack).  Items on the stack are
-        * referenced as positive word offsets from sp.
+       /* MIPS uses a push-down stack:  the stack grows toward lower
+        * addresses in memory.  The stack pointer register points to the
+        * lowest, valid working address (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 MIPS stack must be aligned at word (4 byte)
-        * boundaries. If necessary top_of_stack must be rounded
-        * down to the next boundary
+       /* The MIPS stack must be aligned at word (4 byte) boundaries; for
+        * floating point use, the stack must be aligned to 8-byte addresses.
+        * If necessary top_of_stack must be rounded down to the next
+        * boundary to meet these alignment requirements. 
         */
 
-       top_of_stack &= ~3;
+       top_of_stack = STACK_ALIGN_DOWN(top_of_stack);
        size_of_stack = top_of_stack - (uint32_t)tcb->stack_alloc_ptr + 4;
 
        /* Save the adjusted stack values in the struct tcb_s */