Fix some bad syscall dispatching log. This change is not testable until these is a tested NuttX kernel build.

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@5713 42af7a65-404d-4744-a932-0658087f49c3

11 files changed, 345 insertions, 424 deletions

diff --git a/nuttx/arch/arm/include/armv6-m/irq.h b/nuttx/arch/arm/include/armv6-m/irq.h
index 68f8c75d4..f4bfea33f 100644
--- a/nuttx/arch/arm/include/armv6-m/irq.h
+++ b/nuttx/arch/arm/include/armv6-m/irq.h
@@ -147,11 +147,11 @@
 #ifndef __ASSEMBLY__
 struct xcptcontext
 {
+#ifndef CONFIG_DISABLE_SIGNALS
   /* The following function pointer is non-zero if there
    * are pending signals to be processed.
    */
 
-#ifndef CONFIG_DISABLE_SIGNALS
   void *sigdeliver; /* Actual type is sig_deliver_t */
 
   /* These are saved copies of LR, PRIMASK, and xPSR used during
@@ -163,6 +163,12 @@ struct xcptcontext
   uint32_t saved_xpsr;
 #endif
 
+#ifdef CONFIG_NUTTX_KERNEL
+  /* The following holds the return address from a system call */
+
+  uint32_t sysreturn;
+#endif
+
   /* Register save area */
 
   uint32_t regs[XCPTCONTEXT_REGS];
diff --git a/nuttx/arch/arm/include/armv7-m/irq.h b/nuttx/arch/arm/include/armv7-m/irq.h
index 8acec4c07..d815aba30 100644
--- a/nuttx/arch/arm/include/armv7-m/irq.h
+++ b/nuttx/arch/arm/include/armv7-m/irq.h
@@ -106,11 +106,11 @@
 #ifndef __ASSEMBLY__
 struct xcptcontext
 {
+#ifndef CONFIG_DISABLE_SIGNALS
   /* The following function pointer is non-zero if there
    * are pending signals to be processed.
    */
 
-#ifndef CONFIG_DISABLE_SIGNALS
   void *sigdeliver; /* Actual type is sig_deliver_t */
 
   /* These are saved copies of LR, PRIMASK, and xPSR used during
@@ -126,6 +126,12 @@ struct xcptcontext
   uint32_t saved_xpsr;
 #endif
 
+#ifdef CONFIG_NUTTX_KERNEL
+  /* The following holds the return address from a system call */
+
+  uint32_t sysreturn;
+#endif
+
   /* Register save area */
 
   uint32_t regs[XCPTCONTEXT_REGS];
diff --git a/nuttx/arch/arm/src/armv6-m/svcall.h b/nuttx/arch/arm/src/armv6-m/svcall.h
index 38c672ff6..46a385631 100644
--- a/nuttx/arch/arm/src/armv6-m/svcall.h
+++ b/nuttx/arch/arm/src/armv6-m/svcall.h
@@ -51,15 +51,15 @@
  ************************************************************************************/
 
 /* Configuration ********************************************************************/
-/* This logic uses three system calls {0,1,2} for context switching.  The first three
- * syscall values must be reserved.
+/* This logic uses three system calls {0,1,2} for context switching and one for the
+ * syscall return.  The first four syscall values must be reserved.
  */
 
 #ifdef CONFIG_NUTTX_KERNEL
 #  ifndef CONFIG_SYS_RESERVED
-#    error "CONFIG_SYS_RESERVED must be defined to the value 3"
-#  elif CONFIG_SYS_RESERVED != 3
-#    error "CONFIG_SYS_RESERVED must have the value 3"
+#    error "CONFIG_SYS_RESERVED must be defined to the value 4"
+#  elif CONFIG_SYS_RESERVED != 4
+#    error "CONFIG_SYS_RESERVED must have the value 4"
 #  endif
 #endif
 
@@ -86,6 +86,15 @@
 
 #define SYS_switch_context  (2)
 
+#ifdef CONFIG_NUTTX_KERNEL
+/* SYS call 3:
+ *
+ * void up_syscall_return(void);
+ */
+
+#define SYS_syscall_return  (3)
+#endif
+
 /************************************************************************************
  * Inline Functions
  ************************************************************************************/
diff --git a/nuttx/arch/arm/src/armv6-m/up_svcall.c b/nuttx/arch/arm/src/armv6-m/up_svcall.c
index 60dde4bf5..e8aa977bd 100644
--- a/nuttx/arch/arm/src/armv6-m/up_svcall.c
+++ b/nuttx/arch/arm/src/armv6-m/up_svcall.c
@@ -52,6 +52,8 @@
 #endif
 
 #include "svcall.h"
+#include "exc_return.h"
+#include "os_internal.h"
 #include "up_internal.h"
 
 /****************************************************************************
@@ -59,29 +61,15 @@
  ****************************************************************************/
 /* Configuration ************************************************************/
 
-#undef SYSCALL_INTERRUPTIBLE
-#if defined(CONFIG_NUTTX_KERNEL)
-#  if CONFIG_ARCH_INTERRUPTSTACK > 3
-#    warning "CONFIG_ARCH_INTERRUPTSTACK and CONFIG_NUTTX_KERNEL are incompatible"
-#    warning "options as currently implemented.  Interrupts will have to be disabled"
-#    warning "during SYScall processing to avoid un-handled nested interrupts"
-#  else
-#    define SYSCALL_INTERRUPTIBLE 1
-#  endif
-#endif
-
 /* Debug ********************************************************************/
 /* Debug output from this file may interfere with context switching!  To get
  * debug output you must enabled the following in your NuttX configuration:
  *
- * CONFIG_DEBUG and CONFIG_DEBUG_SCHED
- *
- * And you must explicitly define DEBUG_SVCALL below:
+ * CONFIG_DEBUG and CONFIG_DEBUG_SYSCALL
  */
 
-#undef DEBUG_SVCALL         /* Define to debug SVCall */
-#ifdef DEBUG_SVCALL
-# define svcdbg(format, arg...) slldbg(format, ##arg)
+#ifdef CONFIG_DEBUG_SYSCALL
+# define svcdbg(format, arg...) lldbg(format, ##arg)
 #else
 # define svcdbg(x...)
 #endif
@@ -102,121 +90,29 @@
  * Name: dispatch_syscall
  *
  * Description:
- *   Dispatch a system call to the appropriate handling logic.
+ *   Call the stub function corresponding to the system call.
  *
  ****************************************************************************/
 
 #ifdef CONFIG_NUTTX_KERNEL
-static inline void dispatch_syscall(uint32_t *regs)
+static void dispatch_syscall(void) naked_function;
+static void dispatch_syscall(void)
 {
-  uint32_t  cmd = regs[REG_R0];
-  FAR struct tcb_s *rtcb = sched_self();
-  uintptr_t ret = (uintptr_t)ERROR;
-
-  /* Verify the the SYS call number is within range */
-
-  if (cmd < SYS_maxsyscall)
-    {
-      /* Report error and return ERROR */
-
-      slldbg("ERROR: Bad SYS call: %d\n", cmd);
-    }
-  else
-    {
-      /* The index into the syscall table is offset by the number of architecture-
-       * specific reserved entries at the beginning of the SYS call number space.
-       */
-
-      int index = cmd - CONFIG_SYS_RESERVED;
-
-      /* Enable interrupts while the SYSCALL executes */
-
-#ifdef SYSCALL_INTERRUPTIBLE
-      irqenable();
-#endif
-
-      /* Call the correct stub for each SYS call, based on the number of parameters */
-
-      svcdbg("Calling stub%d at %p\n", index, g_stubloopkup[index].stub0);
-
-      switch (g_stubnparms[index])
-        {
-        /* No parameters */
-
-        case 0:
-          ret = g_stublookup[index].stub0();
-          break;
-
-        /* Number of parameters: 1 */
-
-        case 1:
-          ret = g_stublookup[index].stub1(regs[REG_R1]);
-          break;
-
-        /* Number of parameters: 2 */
-
-        case 2:
-          ret = g_stublookup[index].stub2(regs[REG_R1], regs[REG_R2]);
-          break;
-
-         /* Number of parameters: 3 */
-
-       case 3:
-          ret = g_stublookup[index].stub3(regs[REG_R1], regs[REG_R2],
-                                          regs[REG_R3]);
-          break;
-
-         /* Number of parameters: 4 */
-
-       case 4:
-          ret = g_stublookup[index].stub4(regs[REG_R1], regs[REG_R2],
-                                          regs[REG_R3], regs[REG_R4]);
-          break;
-
-        /* Number of parameters: 5 */
-
-        case 5:
-          ret = g_stublookup[index].stub5(regs[REG_R1], regs[REG_R2],
-                                          regs[REG_R3], regs[REG_R4],
-                                          regs[REG_R5]);
-          break;
-
-        /* Number of parameters: 6 */
-
-        case 6:
-          ret = g_stublookup[index].stub6(regs[REG_R1], regs[REG_R2],
-                                          regs[REG_R3], regs[REG_R4],
-                                          regs[REG_R5], regs[REG_R6]);
-          break;
-
-        /* Unsupported number of paramters. Report error and return ERROR */
-
-        default:
-          slldbg("ERROR: Bad SYS call %d number parameters %d\n",
-                 cmd, g_stubnparms[index]);
-          break;
-        }
-
-#ifdef SYSCALL_INTERRUPTIBLE
-      irqdisable();
-#endif
-    }
-
-  /* Set up the return value.  First, check if a context switch occurred. 
-   * In this case, regs will no longer be the same as current_regs.  In
-   * the case of a context switch, we will have to save the return value
-   * in the TCB where it can be returned later when the task is restarted.
-   */
-
-  if (regs != current_regs)
-    {
-      regs = rtcb->xcp.regs;
-    }
-
-  /* Then return the result in R0 */
-
-  svcdbg("Return value regs: %p value: %d\n", regs, ret);
-  regs[REG_R0] = (uint32_t)ret;
+  __asm__ __volatile__
+  (
+    " push {r4-r6}\n"             /* Save R4, R5 and R6 */
+    " mov r6, r14\n"              /* Save LR in R6 */
+    " ldr r4, =g_stublookup\n"    /* Get the base of the stub lookup table */
+    " lsl r3, r0, #2\n"           /* Get the offset of the stub for this syscall */
+    " ldr r3, [r4, r3]\n"         /* Load the entry of the stub for this syscall */
+    " blx r3\n"                   /* Call the stub */
+    " mov r14, r6\n"              /* Restore R14 */
+    " pop {r4-r6}\n"              /* Restore R4, R5, and R6 */
+    " mov r2, r0\n"               /* Save the return value in R0 in R2 for now */
+    " mov r0, #3\n"               /* R0=SYS_syscall_return */
+    " svc 0"                      /* Return from the syscall */
+    :::
+  );
 }
 #endif
 
@@ -309,7 +205,7 @@ int up_svcall(int irq, FAR void *context)
        *
        * At this point, the following values are saved in context:
        *
-       *   R0 = 1
+       *   R0 = SYS_switch_context
        *   R1 = saveregs
        *   R2 = restoreregs
        *
@@ -327,17 +223,81 @@ int up_svcall(int irq, FAR void *context)
         }
         break;
 
+      /* R0=SYS_syscall_return: This a switch context command:
+       *
+       *   void up_sycall_return(void);
+       *
+       * At this point, the following values are saved in context:
+       *
+       *   R0 = SYS_syscall_return
+       *
+       * We need to restore the saved return address and return in
+       * unprivileged thread mode.
+       */
+
+#ifdef CONFIG_NUTTX_KERNEL
+      case SYS_syscall_return:
+        {
+          struct tcb_s *rtcb = sched_self();
+
+          /* Make sure that we got here from a privileged thread and
+           * that there is a saved syscall return address.
+           */
+
+          DEBUGASSERT(rtcb->xcp.sysreturn != NULL &&
+                      regs[REG_EXC_RETURN] == EXC_RETURN_PRIVTHR);
+
+          /* Setup to return to the saved syscall return address in
+           * unprivileged mode.
+           */
+
+          current_regs[REG_PC]         = rtcb->xcp.sysreturn;
+          current_regs[REG_EXC_RETURN] = EXC_RETURN_UNPRIVTHR;
+          rtcb->sysreturn              = NULL;
+
+          /* The return value must be in R0-R1.  dispatch_syscall() temporarily
+           * moved the value to R2.
+           */
+
+          current_regs[REG_R0]         = current_regs[REG_R2];
+        }
+        break;
+#endif
+
       /* This is not an architecture-specific system call.  If NuttX is built
        * as a standalone kernel with a system call interface, then all of the
        * additional system calls must be handled as in the default case.
        */
 
       default:
+        {
 #ifdef CONFIG_NUTTX_KERNEL
-        dispatch_syscall(regs);
+          FAR struct tcb_s *rtcb = sched_self();
+
+          /* Verify the the SYS call number is within range */
+
+          DEBUGASSERT(current_regs[REG_R0] < SYS_maxsyscall);
+
+          /* Make sure that we got here from an unprivileged thread and that
+           * there is a no saved syscall return address.
+           */
+
+          DEBUGASSERT(rtcb->xcp.sysreturn == NULL &&
+                      regs[REG_EXC_RETURN] == EXC_RETURN_UNPRIVTHR);
+
+          /* Setup to return to dispatch_syscall in privileged mode. */
+
+          rtcb->sysreturn              = regs[REG_PC]
+          regs[REG_PC]                 = (uint32_t)dispatch_syscall;
+          current_regs[REG_EXC_RETURN] = EXC_RETURN_PRIVTHR;
+
+          /* Offset R0 to account for the reserved values */
+
+          current_regs[REG_R0]        -= CONFIG_SYS_RESERVED;
 #else
-        slldbg("ERROR: Bad SYS call: %d\n", regs[REG_R0]);
+          slldbg("ERROR: Bad SYS call: %d\n", regs[REG_R0]);
 #endif
+        }
         break;
     }
 
diff --git a/nuttx/arch/arm/src/armv7-m/svcall.h b/nuttx/arch/arm/src/armv7-m/svcall.h
index 675829799..13b9935a0 100644
--- a/nuttx/arch/arm/src/armv7-m/svcall.h
+++ b/nuttx/arch/arm/src/armv7-m/svcall.h
@@ -1,7 +1,7 @@
 /************************************************************************************
  * arch/arm/src/armv7-m/svcall.h
  *
- *   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
@@ -51,15 +51,15 @@
  ************************************************************************************/
 
 /* Configuration ********************************************************************/
-/* This logic uses three system calls {0,1,2} for context switching.  The first three
- * syscall values must be reserved.
+/* This logic uses three system calls {0,1,2} for context switching and one for the
+ * syscall return.  The first four syscall values must be reserved.
  */
 
 #ifdef CONFIG_NUTTX_KERNEL
 #  ifndef CONFIG_SYS_RESERVED
-#    error "CONFIG_SYS_RESERVED must be defined to the value 3"
-#  elif CONFIG_SYS_RESERVED != 3
-#    error "CONFIG_SYS_RESERVED must have the value 3"
+#    error "CONFIG_SYS_RESERVED must be defined to the value 4"
+#  elif CONFIG_SYS_RESERVED != 4
+#    error "CONFIG_SYS_RESERVED must have the value 4"
 #  endif
 #endif
 
@@ -86,6 +86,15 @@
 
 #define SYS_switch_context  (2)
 
+#ifdef CONFIG_NUTTX_KERNEL
+/* SYS call 3:
+ *
+ * void up_syscall_return(void);
+ */
+
+#define SYS_syscall_return  (3)
+#endif
+
 /************************************************************************************
  * Inline Functions
  ************************************************************************************/
diff --git a/nuttx/arch/arm/src/armv7-m/up_svcall.c b/nuttx/arch/arm/src/armv7-m/up_svcall.c
index 9fa5a0b82..48ab00eba 100644
--- a/nuttx/arch/arm/src/armv7-m/up_svcall.c
+++ b/nuttx/arch/arm/src/armv7-m/up_svcall.c
@@ -52,6 +52,8 @@
 #endif
 
 #include "svcall.h"
+#include "exc_return.h"
+#include "os_internal.h"
 #include "up_internal.h"
 
 /****************************************************************************
@@ -59,29 +61,15 @@
  ****************************************************************************/
 /* Configuration ************************************************************/
 
-#undef SYSCALL_INTERRUPTIBLE
-#if defined(CONFIG_NUTTX_KERNEL)
-#  if CONFIG_ARCH_INTERRUPTSTACK > 3
-#    warning "CONFIG_ARCH_INTERRUPTSTACK and CONFIG_NUTTX_KERNEL are incompatible"
-#    warning "options as currently implemented.  Interrupts will have to be disabled"
-#    warning "during SYScall processing to avoid un-handled nested interrupts"
-#  else
-#    define SYSCALL_INTERRUPTIBLE 1
-#  endif
-#endif
-
 /* Debug ********************************************************************/
 /* Debug output from this file may interfere with context switching!  To get
  * debug output you must enabled the following in your NuttX configuration:
  *
- * CONFIG_DEBUG and CONFIG_DEBUG_SCHED
- *
- * And you must explicitly define DEBUG_SVCALL below:
+ * CONFIG_DEBUG and CONFIG_DEBUG_SYSCALL
  */
 
-#undef DEBUG_SVCALL         /* Define to debug SVCall */
-#ifdef DEBUG_SVCALL
-# define svcdbg(format, arg...) slldbg(format, ##arg)
+#ifdef CONFIG_DEBUG_SYSCALL
+# define svcdbg(format, arg...) lldbg(format, ##arg)
 #else
 # define svcdbg(x...)
 #endif
@@ -102,121 +90,28 @@
  * Name: dispatch_syscall
  *
  * Description:
- *   Dispatch a system call to the appropriate handling logic.
+ *   Call the stub function corresponding to the system call.
  *
  ****************************************************************************/
 
 #ifdef CONFIG_NUTTX_KERNEL
-static inline void dispatch_syscall(uint32_t *regs)
+static void dispatch_syscall(void) naked_function;
+static void dispatch_syscall(void)
 {
-  uint32_t  cmd = regs[REG_R0];
-  FAR struct tcb_s *rtcb = sched_self();
-  uintptr_t ret = (uintptr_t)ERROR;
-
-  /* Verify the the SYS call number is within range */
-
-  if (cmd < SYS_maxsyscall)
-    {
-      /* Report error and return ERROR */
-
-      slldbg("ERROR: Bad SYS call: %d\n", cmd);
-    }
-  else
-    {
-      /* The index into the syscall table is offset by the number of architecture-
-       * specific reserved entries at the beginning of the SYS call number space.
-       */
-
-      int index = cmd - CONFIG_SYS_RESERVED;
-
-      /* Enable interrupts while the SYSCALL executes */
-
-#ifdef SYSCALL_INTERRUPTIBLE
-      irqenable();
-#endif
-
-      /* Call the correct stub for each SYS call, based on the number of parameters */
-
-      svcdbg("Calling stub%d at %p\n", index, g_stubloopkup[index].stub0);
-
-      switch (g_stubnparms[index])
-        {
-        /* No parameters */
-
-        case 0:
-          ret = g_stublookup[index].stub0();
-          break;
-
-        /* Number of parameters: 1 */
-
-        case 1:
-          ret = g_stublookup[index].stub1(regs[REG_R1]);
-          break;
-
-        /* Number of parameters: 2 */
-
-        case 2:
-          ret = g_stublookup[index].stub2(regs[REG_R1], regs[REG_R2]);
-          break;
-
-         /* Number of parameters: 3 */
-
-       case 3:
-          ret = g_stublookup[index].stub3(regs[REG_R1], regs[REG_R2],
-                                          regs[REG_R3]);
-          break;
-
-         /* Number of parameters: 4 */
-
-       case 4:
-          ret = g_stublookup[index].stub4(regs[REG_R1], regs[REG_R2],
-                                          regs[REG_R3], regs[REG_R4]);
-          break;
-
-        /* Number of parameters: 5 */
-
-        case 5:
-          ret = g_stublookup[index].stub5(regs[REG_R1], regs[REG_R2],
-                                          regs[REG_R3], regs[REG_R4],
-                                          regs[REG_R5]);
-          break;
-
-        /* Number of parameters: 6 */
-
-        case 6:
-          ret = g_stublookup[index].stub6(regs[REG_R1], regs[REG_R2],
-                                          regs[REG_R3], regs[REG_R4],
-                                          regs[REG_R5], regs[REG_R6]);
-          break;
-
-        /* Unsupported number of paramters. Report error and return ERROR */
-
-        default:
-          slldbg("ERROR: Bad SYS call %d number parameters %d\n",
-                 cmd, g_stubnparms[index]);
-          break;
-        }
-
-#ifdef SYSCALL_INTERRUPTIBLE
-      irqdisable();
-#endif
-    }
-
-  /* Set up the return value.  First, check if a context switch occurred. 
-   * In this case, regs will no longer be the same as current_regs.  In
-   * the case of a context switch, we will have to save the return value
-   * in the TCB where it can be returned later when the task is restarted.
-   */
-
-  if (regs != current_regs)
-    {
-      regs = rtcb->xcp.regs;
-    }
-
-  /* Then return the result in R0 */
-
-  svcdbg("Return value regs: %p value: %d\n", regs, ret);
-  regs[REG_R0] = (uint32_t)ret;
+  __asm__ __volatile__
+  (
+    " push {r4, r5}\n"             /* Save R4 and R5 */
+    " mov r5, r14\n"               /* Save LR in R5 */
+    " ldr r4, =g_stublookup\n"     /* Get the base of the stub lookup table */
+    " ldr r4, [r4, r0, lsl #2]\n"  /* Load the entry of the stub for this syscall */
+    " blx r4\n"                    /* Call the stub */
+    " mov r14, r5\n"               /* Restore R14 */
+    " pop {r4, r5}\n"              /* Restore R4 and R5 */
+    " mov r2, r0\n"                /* Save the return value in R0 in R2 for now */
+    " mov r0, #3\n"                /* R0=SYS_syscall_return */
+    " svc 0"                       /* Return from the syscall */
+    :::
+  );
 }
 #endif
 
@@ -327,17 +222,81 @@ int up_svcall(int irq, FAR void *context)
         }
         break;
 
+      /* R0=SYS_syscall_return: This a switch context command:
+       *
+       *   void up_sycall_return(void);
+       *
+       * At this point, the following values are saved in context:
+       *
+       *   R0 = SYS_syscall_return
+       *
+       * We need to restore the saved return address and return in
+       * unprivileged thread mode.
+       */
+
+#ifdef CONFIG_NUTTX_KERNEL
+      case SYS_syscall_return:
+        {
+          struct tcb_s *rtcb = sched_self();
+
+          /* Make sure that we got here from a privileged thread and
+           * that there is a saved syscall return address.
+           */
+
+          DEBUGASSERT(rtcb->xcp.sysreturn != NULL &&
+                      regs[REG_EXC_RETURN] == EXC_RETURN_PRIVTHR);
+
+          /* Setup to return to the saved syscall return address in
+           * unprivileged mode.
+           */
+
+          current_regs[REG_PC]         = rtcb->xcp.sysreturn;
+          current_regs[REG_EXC_RETURN] = EXC_RETURN_UNPRIVTHR;
+          rtcb->sysreturn              = NULL;
+
+          /* The return value must be in R0-R1.  dispatch_syscall() temporarily
+           * moved the value to R2.
+           */
+
+          current_regs[REG_R0]         = current_regs[REG_R2];
+        }
+        break;
+#endif
+
       /* This is not an architecture-specific system call.  If NuttX is built
        * as a standalone kernel with a system call interface, then all of the
        * additional system calls must be handled as in the default case.
        */
 
       default:
+        {
 #ifdef CONFIG_NUTTX_KERNEL
-        dispatch_syscall(regs);
+          FAR struct tcb_s *rtcb = sched_self();
+
+          /* Verify the the SYS call number is within range */
+
+          DEBUGASSERT(current_regs[REG_R0] < SYS_maxsyscall);
+
+          /* Make sure that we got here from a unprivileged thread and that
+           * there is a no saved syscall return address.
+           */
+
+          DEBUGASSERT(rtcb->xcp.sysreturn == NULL &&
+                      regs[REG_EXC_RETURN] == EXC_RETURN_UNPRIVTHR);
+
+          /* Setup to return to dispatch_syscall in privileged mode. */
+
+          rtcb->sysreturn              = regs[REG_PC]
+          regs[REG_PC]                 = (uint32_t)dispatch_syscall;
+          current_regs[REG_EXC_RETURN] = EXC_RETURN_PRIVTHR;
+
+          /* Offset R0 to account for the reserved values */
+
+          current_regs[REG_R0]        -= CONFIG_SYS_RESERVED;
 #else
-        slldbg("ERROR: Bad SYS call: %d\n", regs[REG_R0]);
+          slldbg("ERROR: Bad SYS call: %d\n", regs[REG_R0]);
 #endif
+        }
         break;
     }
 
diff --git a/nuttx/arch/arm/src/sam3u/sam3u_userspace.c b/nuttx/arch/arm/src/sam3u/sam3u_userspace.c
index e59cc5619..28f45afce 100644
--- a/nuttx/arch/arm/src/sam3u/sam3u_userspace.c
+++ b/nuttx/arch/arm/src/sam3u/sam3u_userspace.c
@@ -38,6 +38,10 @@
  ****************************************************************************/
 
 #include <nuttx/config.h>
+
+#include <stdint.h>
+#include <assert.h>
+
 #include <arch/board/user_map.h>
 
 #ifdef CONFIG_NUTTX_KERNEL
diff --git a/nuttx/arch/mips/include/mips32/irq.h b/nuttx/arch/mips/include/mips32/irq.h
index 01a50029f..22fa6c75e 100644
--- a/nuttx/arch/mips/include/mips32/irq.h
+++ b/nuttx/arch/mips/include/mips32/irq.h
@@ -1,7 +1,7 @@
 /****************************************************************************
  * arch/mips/include/mips32/irq.h
  *
- *   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
@@ -310,11 +310,11 @@
 
 struct xcptcontext
 {
+#ifndef CONFIG_DISABLE_SIGNALS
   /* The following function pointer is non-NULL if there are pending signals
    * to be processed.
    */
 
-#ifndef CONFIG_DISABLE_SIGNALS
   void *sigdeliver; /* Actual type is sig_deliver_t */
 
   /* These additional register save locations are used to implement the
@@ -325,6 +325,12 @@ struct xcptcontext
   uint32_t saved_status; /* Status with interrupts disabled. */
 #endif
 
+#ifdef CONFIG_NUTTX_KERNEL
+  /* The following holds the return address from a system call */
+
+  uint32_t sysreturn;
+#endif
+
   /* Register save area */
 
   uint32_t regs[XCPTCONTEXT_REGS];
diff --git a/nuttx/arch/mips/include/mips32/syscall.h b/nuttx/arch/mips/include/mips32/syscall.h
index d91eed993..349fba9bd 100644
--- a/nuttx/arch/mips/include/mips32/syscall.h
+++ b/nuttx/arch/mips/include/mips32/syscall.h
@@ -1,7 +1,7 @@
 /****************************************************************************
  * arch/mips/include/mips32/syscall.h
  *
- *   Copyright (C) 2011-2012 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
@@ -57,15 +57,17 @@
 #define SYS_syscall 0x00
 
 /* Configuration ********************************************************************/
-/* This logic uses three system calls {0,1,2} for context switching.  The first three
- * syscall values must be reserved.
+/* SYS call 1 and 2 are defined for internal use by the PIC32MX port (see
+ * arch/mips/include/mips32/syscall.h).  In addition, SYS call 3 is the return from
+ * a SYS call in kernel mode.  The first four syscall values must, therefore, be
+ * reserved (0 is not used).
  */
-
+ 
 #ifdef CONFIG_NUTTX_KERNEL
 #  ifndef CONFIG_SYS_RESERVED
-#    error "CONFIG_SYS_RESERVED must be defined to the value 2"
-#  elif CONFIG_SYS_RESERVED != 2
-#    error "CONFIG_SYS_RESERVED must have the value 2"
+#    error "CONFIG_SYS_RESERVED must be defined to the value 4"
+#  elif CONFIG_SYS_RESERVED != 4
+#    error "CONFIG_SYS_RESERVED must have the value 4"
 #  endif
 #endif
 
@@ -148,6 +150,8 @@
 
 /* Context switching system calls ***************************************************/
 
+/* SYS call 0: (not used) */
+
 /* SYS call 1:
  *
  * void up_fullcontextrestore(uint32_t *restoreregs) noreturn_function;
@@ -166,6 +170,16 @@
 #define up_switchcontext(saveregs, restoreregs) \
   (void)sys_call2(SYS_switch_context, (uintptr_t)saveregs, (uintptr_t)restoreregs)
 
+#ifdef CONFIG_NUTTX_KERNEL
+/* SYS call 3:
+ *
+ * void up_syscall_return(void);
+ */
+
+#define SYS_syscall_return (3)
+#define up_syscall_return() (void)sys_call0(SYS_syscall_return)
+
+#endif
 #endif /* __ASSEMBLY__ */
 
 /****************************************************************************
diff --git a/nuttx/arch/mips/src/mips32/up_swint0.c b/nuttx/arch/mips/src/mips32/up_swint0.c
index fc03de58b..068bd45ab 100644
--- a/nuttx/arch/mips/src/mips32/up_swint0.c
+++ b/nuttx/arch/mips/src/mips32/up_swint0.c
@@ -57,29 +57,15 @@
  ****************************************************************************/
 /* Configuration ************************************************************/
 
-#undef SYSCALL_INTERRUPTIBLE
-#if defined(CONFIG_NUTTX_KERNEL)
-#  if CONFIG_ARCH_INTERRUPTSTACK > 3
-#    warning "CONFIG_ARCH_INTERRUPTSTACK and CONFIG_NUTTX_KERNEL are incompatible"
-#    warning "options as currently implemented.  Interrupts will have to be disabled"
-#    warning "during SYScall processing to avoid un-handled nested interrupts"
-#  else
-#    define SYSCALL_INTERRUPTIBLE 1
-#  endif
-#endif
-
 /* Debug ********************************************************************/
 /* Debug output from this file may interfere with context switching!  To get
  * debug output you must enabled the following in your NuttX configuration:
  *
- * CONFIG_DEBUG and CONFIG_DEBUG_SCHED
- *
- * And you must explicitly define DEBUG_SWINT0 below:
+ * CONFIG_DEBUG and CONFIG_DEBUG_SYSCALL
  */
 
-#undef DEBUG_SWINT0         /* Define to debug SWInt */
-#ifdef DEBUG_SWINT0
-# define swidbg(format, arg...) slldbg(format, ##arg)
+#ifdef CONFIG_DEBUG_SYSCALL
+# define swidbg(format, arg...) lldbg(format, ##arg)
 #else
 # define swidbg(x...)
 #endif
@@ -100,7 +86,7 @@
  * Name: up_registerdump
  ****************************************************************************/
 
-#ifdef DEBUG_SWINT0
+#ifdef CONFIG_DEBUG_SYSCALL
 static void up_registerdump(const uint32_t *regs)
 {
   swidbg("MFLO:%08x MFHI:%08x EPC:%08x STATUS:%08x\n",
@@ -132,125 +118,27 @@ static void up_registerdump(const uint32_t *regs)
  * Name: dispatch_syscall
  *
  * Description:
- *   Dispatch a system call to the appropriate handling logic.
+ *   Call the stub function corresponding to the system call.
  *
  ****************************************************************************/
 
 #ifdef CONFIG_NUTTX_KERNEL
-static inline void dispatch_syscall(uint32_t *regs)
+static void dispatch_syscall(void) naked_function;
+static void dispatch_syscall(void)
 {
-  uint32_t  cmd = regs[REG_A0];
-  FAR struct tcb_s *rtcb = sched_self();
-  uintptr_t ret = (uintptr_t)ERROR;
-
-  /* Verify the the SYS call number is within range */
-
-  if (cmd < SYS_maxsyscall)
-    {
-      /* Report error and return ERROR */
-
-      slldbg("ERROR: Bad SYS call: %d\n", cmd);
-    }
-  else
-    {
-      /* The index into the syscall table is offset by the number of
-       * architecture-specific reserved entries at the beginning of the
-       * SYS call number space.
-       */
-
-      int index = cmd - CONFIG_SYS_RESERVED;
-
-      /* Enable interrupts while the SYSCALL executes */
-
-#ifdef SYSCALL_INTERRUPTIBLE
-      irqenable();
-#endif
-
-      /* Call the correct stub for each SYS call, based on the number of
-       * parameters:  $5=parm1, $6=parm2, $7=parm3, $8=parm4, $9=parm5, and
-       * $10=parm6.
-       */
-
-      swidbg("Calling stub%d at %p\n", index, g_stubloopkup[index].stub0);
-
-      switch (g_stubnparms[index])
-        {
-        /* No parameters */
-
-        case 0:
-          ret = g_stublookup[index].stub0();
-          break;
-
-        /* Number of parameters: 1 */
-
-        case 1:
-          ret = g_stublookup[index].stub1(regs[REG_A1]);
-          break;
-
-        /* Number of parameters: 2 */
-
-        case 2:
-          ret = g_stublookup[index].stub2(regs[REG_A1], regs[REG_A2]);
-          break;
-
-         /* Number of parameters: 3 */
-
-       case 3:
-          ret = g_stublookup[index].stub3(regs[REG_A1], regs[REG_A2],
-                                          regs[REG_A3]);
-          break;
-
-         /* Number of parameters: 4 */
-
-       case 4:
-          ret = g_stublookup[index].stub4(regs[REG_A1], regs[REG_A2],
-                                          regs[REG_A3], regs[REG_T0]);
-          break;
-
-        /* Number of parameters: 5 */
-
-        case 5:
-          ret = g_stublookup[index].stub5(regs[REG_A1], regs[REG_A2],
-                                          regs[REG_A3], regs[REG_T0],
-                                          regs[REG_T1]);
-          break;
-
-        /* Number of parameters: 6 */
-
-        case 6:
-          ret = g_stublookup[index].stub6(regs[REG_A1], regs[REG_A2],
-                                          regs[REG_A3], regs[REG_T0],
-                                          regs[REG_T1], regs[REG_T2]);
-          break;
-
-        /* Unsupported number of paramters. Report error and return ERROR */
-
-        default:
-          slldbg("ERROR: Bad SYS call %d number parameters %d\n",
-                 cmd, g_stubnparms[index]);
-          break;
-        }
-
-#ifdef SYSCALL_INTERRUPTIBLE
-      irqdisable();
-#endif
-    }
-
-  /* Set up the return vaue.  First, check if a context switch occurred. 
-   * In this case, regs will no longer be the same as current_regs.  In
-   * the case of a context switch, we will have to save the return value
-   * in the TCB where it can be returned later when the task is restarted.
-   */
-
-  if (regs != current_regs)
-    {
-      regs = rtcb->xcp.regs;
-    }
-
-  /* Then return the result in v0 */
-
-  swidbg("Return value regs: %p value: %d\n", regs, ret);
-  regs[REG_v0] = (uint32_t)ret;
+#  error "Missing logic"
+
+/* Refer to arch/arm/src/armv7-m/up_svcall.h for how this is done for ARM */
+/*  __asm__ __volatile__ */
+/* (
+/*   Save registers */
+/*   Get the base of the stub lookup table */
+/*   Get the offset of the stub for this syscall */
+/*   Load the entry of the stub for this syscall */
+/*   Call the stub */
+/*   Restore regsisters */
+/*   Return from the syscall */
+/* ); */
 }
 #endif
 
@@ -279,7 +167,7 @@ int up_swint0(int irq, FAR void *context)
    * arguments depending on the system call.
    */
 
-#ifdef DEBUG_SWINT0
+#ifdef CONFIG_DEBUG_SYSCALL
   swidbg("Entry: regs: %p cmd: %d\n", regs, regs[REG_R4]);
   up_registerdump(regs);
 #endif
@@ -334,23 +222,81 @@ int up_swint0(int irq, FAR void *context)
         }
         break;
 
+      /* R0=SYS_syscall_return: This a switch context command:
+       *
+       *   void up_sycall_return(void);
+       *
+       * At this point, the following values are saved in context:
+       *
+       *   R0 = SYS_syscall_return
+       *
+       * We need to restore the saved return address and return in
+       * unprivileged thread mode.
+       */
+
+#ifdef CONFIG_NUTTX_KERNEL
+      case SYS_syscall_return:
+        {
+          struct tcb_s *rtcb = sched_self();
+
+          /* Make sure that we got here from a privileged thread and
+           * that there is a saved syscall return address.
+           */
+
+#error "Missing logic -- need to test for privileged mode"
+          DEBUGASSERT(rtcb->xcp.sysreturn != NULL && ???);
+
+          /* Setup to return to the saved syscall return address in
+           * unprivileged mode.
+           */
+
+          current_regs[REG_EPC] = rtcb->xcp.sysreturn;
+#error "Missing logic -- need to set for unprivileged mode"
+          rtcb->sysreturn       = NULL;
+        }
+        break;
+#endif
+
       /* This is not an architecture-specify system call.  If NuttX is built
        * as a standalone kernel with a system call interface, then all of the
        * additional system calls must be handled as in the default case.
        */
 
       default:
+        {
 #ifdef CONFIG_NUTTX_KERNEL
-        dispatch_syscall(regs);
+          FAR struct tcb_s *rtcb = sched_self();
+
+          /* Verify the the SYS call number is within range */
+
+          DEBUGASSERT(current_regs[REG_A0] < SYS_maxsyscall);
+
+          /* Make sure that we got here from an unprivileged thread and that
+           * there is a no saved syscall return address.
+           */
+
+#error "Missing logic -- Need to set unprivileged mode"
+          DEBUGASSERT(rtcb->xcp.sysreturn == NULL && ???);
+
+          /* Setup to return to dispatch_syscall in privileged mode. */
+
+          rtcb->sysreturn              = regs[REG_EPC]
+          regs[REG_EPC]                = (uint32_t)dispatch_syscall;
+#error "Missing logic -- Need to set privileged mode"
+
+          /* Offset R0 to account for the reserved values */
+
+          current_regs[REG_R0]        -= CONFIG_SYS_RESERVED;
 #else
-        slldbg("ERROR: Bad SYS call: %d\n", regs[REG_A0]);
+          slldbg("ERROR: Bad SYS call: %d\n", regs[REG_A0]);
 #endif
+        }
         break;
     }
 
   /* Report what happened.  That might difficult in the case of a context switch */
 
-#ifdef DEBUG_SWINT0
+#ifdef CONFIG_DEBUG_SYSCALL
   if (regs != current_regs)
     {
       swidbg("SWInt Return: Context switch!\n");
diff --git a/nuttx/arch/mips/src/pic32mx/pic32mx-config.h b/nuttx/arch/mips/src/pic32mx/pic32mx-config.h
index 4dd0a150e..d64caf5fb 100644
--- a/nuttx/arch/mips/src/pic32mx/pic32mx-config.h
+++ b/nuttx/arch/mips/src/pic32mx/pic32mx-config.h
@@ -1,7 +1,7 @@
 /************************************************************************************
  * arch/mips/src/pic32mx/pic32mx-config.h
  *
- *   Copyright (C) 2011-2012 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
@@ -485,15 +485,17 @@
 #endif
 
 /* SYS calls ************************************************************************/
-/* SYS call 0 and 1 are defined for internal use by the PIC32MX port (see
- * arch/mips/include/mips32/syscall.h
+/* SYS call 1 and 2 are defined for internal use by the PIC32MX port (see
+ * arch/mips/include/mips32/syscall.h).  In addition, SYS call 3 is the return from
+ * a SYS call in kernel mode.  The first four syscall values must, therefore, be
+ * reserved (0 is not used).
  */
 
 #ifdef CONFIG_NUTTX_KERNEL
-#  if !defined(CONFIG_SYS_RESERVED) || CONFIG_SYS_RESERVED < 2
-#    error "CONFIG_SYS_RESERVED must be defined to be 2 for a kernel build"
-#  elif CONFIG_SYS_RESERVED > 2
-#    warning "CONFIG_SYS_RESERVED should be defined to be 2 for a kernel build"
+#  if !defined(CONFIG_SYS_RESERVED) || CONFIG_SYS_RESERVED < 4
+#    error "CONFIG_SYS_RESERVED must be defined to be 4 for a kernel build"
+#  elif CONFIG_SYS_RESERVED > 4
+#    warning "CONFIG_SYS_RESERVED should be defined to be 4 for a kernel build"
 #  endif
 #endif