Add a test to verify that FPU registers are properly saved and restored on context switches.

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@4421 42af7a65-404d-4744-a932-0658087f49c3

8 files changed, 475 insertions, 33 deletions

diff --git a/apps/ChangeLog.txt b/apps/ChangeLog.txt
index f79305d47..5a1174596 100755
--- a/apps/ChangeLog.txt
+++ b/apps/ChangeLog.txt
@@ -190,3 +190,5 @@
 6.16 2012-xx-xx Gregory Nutt <gnutt@nuttx.org>
 
 	* apps/examples/qencoder:  Add a quadrature driver test.
+	* apps/examples/ostest/fpu.c:  Add a test to verify that FPU registers
+	  are properly saved and restored on context switches.
diff --git a/apps/examples/ostest/Makefile b/apps/examples/ostest/Makefile
index 1405a2afb..45eef5ff6 100644
--- a/apps/examples/ostest/Makefile
+++ b/apps/examples/ostest/Makefile
@@ -1,8 +1,8 @@
 ############################################################################
 # apps/examples/ostest/Makefile
 #
-#   Copyright (C) 2007-2011 Gregory Nutt. All rights reserved.
-#   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
+#   Copyright (C) 2007-2012 Gregory Nutt. All rights reserved.
+#   Author: Gregory Nutt <gnutt@nuttx.org>
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions
@@ -42,6 +42,10 @@ include $(APPDIR)/Make.defs
 ASRCS		=
 CSRCS		= main.c dev_null.c
 
+ifeq ($(CONFIG_ARCH_FPU),y)
+CSRCS		+= fpu.c
+endif
+
 ifneq ($(CONFIG_DISABLE_PTHREAD),y)
 CSRCS		+= cancel.c cond.c mutex.c sem.c barrier.c
 ifneq ($(CONFIG_RR_INTERVAL),0)
diff --git a/apps/examples/ostest/fpu.c b/apps/examples/ostest/fpu.c
new file mode 100644
index 000000000..ca61c0089
--- /dev/null
+++ b/apps/examples/ostest/fpu.c
@@ -0,0 +1,278 @@
+/***********************************************************************
+ * apps/examples/ostest/fpu.c
+ *
+ *   Copyright (C) 2012 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <gnutt@nuttx.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name NuttX nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ***********************************************************************/
+
+/***********************************************************************
+ * Included Files
+ ***********************************************************************/
+
+#include <nuttx/config.h>
+#include <sys/wait.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sched.h>
+
+#include "ostest.h"
+
+/***********************************************************************
+ * Pre-processor definitions
+ ***********************************************************************/
+/* Configuration *******************************************************/
+
+#undef HAVE_FPU
+#ifdef CONFIG_ARCH_FPU
+#  if defined(CONFIG_EXAMPLES_OSTEST_FPUSIZE) && defined(CONFIG_SCHED_WAITPID) && !defined(CONFIG_DISABLE_SIGNALS)
+#    define HAVE_FPU 1
+#  else
+#    ifndef CONFIG_EXAMPLES_OSTEST_FPUSIZE
+#      warning "FPU test not built; CONFIG_EXAMPLES_OSTEST_FPUSIZE not defined"
+#    endif
+#    ifndef CONFIG_SCHED_WAITPID
+#      warning "FPU test not built; CONFIG_SCHED_WAITPID not defined"
+#    endif
+#    ifdef CONFIG_DISABLE_SIGNALS
+#      warning "FPU test not built; CONFIG_DISABLE_SIGNALS defined"
+#    endif
+#  endif
+#endif
+
+#ifdef HAVE_FPU
+
+#ifndef CONFIG_EXAMPLES_OSTEST_FPULOOPS
+#  define CONFIG_EXAMPLES_OSTEST_FPULOOPS 16
+#endif
+
+#ifndef CONFIG_EXAMPLES_OSTEST_FPUMSDELAY
+#  define CONFIG_EXAMPLES_OSTEST_FPUMSDELAY 750
+#endif
+
+#ifndef CONFIG_EXAMPLES_OSTEST_FPUPRIORITY
+#  define CONFIG_EXAMPLES_OSTEST_FPUPRIORITY SCHED_PRIORITY_DEFAULT
+#endif
+
+#ifndef CONFIG_EXAMPLES_OSTEST_FPUSTACKSIZE
+#  define CONFIG_EXAMPLES_OSTEST_FPUSTACKSIZE 2048
+#endif
+
+/* Other defintions ****************************************************/
+
+#ifndef NULL
+# define NULL (void*)0
+#endif
+
+/***********************************************************************
+ * External Dependencies
+ ***********************************************************************/
+/* This test is very dependent on support provided by the chip/board-
+ * layer logic.  In particular, it expects the following functions
+ * to be provided:
+ */
+
+/* Given a uint8_t array of size CONFIG_EXAMPLES_OSTEST_FPUSIZE, this
+ * function will return the current FPU registers.
+ */
+
+extern void arch_getfpu(FAR uint8_t *fpusave);
+
+/* Given a uint8_t array of size CONFIG_EXAMPLES_OSTEST_FPUSIZE, this
+ * function will set the current FPU regisers to match the provided
+ * register save set.
+ */
+
+extern void arch_setfpu(FAR const uint8_t *fpusave);
+
+/* Given a uint8_t array of size CONFIG_EXAMPLES_OSTEST_FPUSIZE and a
+ * seed value, this function will set the FPU registers to a known
+ * values for testing purposes.  The contents of the FPU registers
+ * must be uniqe for each sed value.
+ */
+
+extern void arch_initfpu(FAR uint8_t *fpusave, int seed);
+
+/* Given two uint8_t arrays of size CONFIG_EXAMPLES_OSTEST_FPUSIZE this
+ * function will compare then an return true if they are identical.
+ */
+
+extern bool arch_cmpfpu(FAR const uint8_t *fpusave1, FAR const uint8_t *fpusave2);
+
+/***********************************************************************
+ * Private Data
+ ***********************************************************************/
+
+static uint8_t g_fpuno;
+
+/***********************************************************************
+ * Private Functions
+ ***********************************************************************/
+
+static void fpu_dump(FAR uint8_t *buffer, FAR const char *msg)
+{
+  int i, j, k;
+
+  printf("%s (%p):\n", msg, buffer);
+  for (i = 0; i < CONFIG_EXAMPLES_OSTEST_FPUSIZE; i += 32)
+    {
+      printf("%04x: ", i);
+      for (j = 0; j < 32; j++)
+        {
+          k = i + j;
+
+          if (k < CONFIG_EXAMPLES_OSTEST_FPUSIZE)
+            {
+              printf("%02x ", buffer[k]);
+            }
+          else
+            {
+              break;
+            }
+        }
+      printf("\n");
+   }
+}
+
+static int fpu_task(int argc, char *argv[])
+{
+  uint8_t fpusave1[CONFIG_EXAMPLES_OSTEST_FPUSIZE];
+  uint8_t fpusave2[CONFIG_EXAMPLES_OSTEST_FPUSIZE];
+  int id;
+  int seed;
+  int incr;
+  int i;
+
+  /* Which are we? */
+
+  sched_lock();
+  id = (int)(++g_fpuno);
+  sched_unlock();
+
+  seed = id << 24 | id << 16 | id << 8 | id;
+  incr = seed;
+
+  for (i = 0; i < CONFIG_EXAMPLES_OSTEST_FPULOOPS; i++)
+    {
+      /* Initialize the FPU registers to a known value */
+
+      sched_lock();
+      arch_initfpu(fpusave1, seed);
+      arch_setfpu(fpusave1);
+
+      /* Check that the FPU registers were set as we expected */
+
+      arch_getfpu(fpusave2);
+      if (!arch_cmpfpu(fpusave1, fpusave2))
+        {
+          printf("ERROR FPU#%d: fpusave1 and fpusave2 do not match (BEFORE waiting)\n");
+          fpu_dump(fpusave1, "Values written:");
+          fpu_dump(fpusave2, "Values read:");
+          sched_unlock();
+          return EXIT_FAILURE;
+        }
+
+      /* Now unlock and sleep for a while */
+
+      sched_unlock();
+      usleep(CONFIG_EXAMPLES_OSTEST_FPUMSDELAY * 1000);
+
+      /* Several context switches should have occurred.  Now verify that the floating
+       * point registers are still correctly set.
+       */
+
+      sched_lock();
+      arch_getfpu(fpusave2);
+      if (!arch_cmpfpu(fpusave1, fpusave2))
+        {
+          printf("ERROR FPU#%d: fpusave1 and fpusave2 do not match (AFTER waiting)\n");
+          fpu_dump(fpusave1, "Values written:");
+          fpu_dump(fpusave2, "Values read:");
+          sched_unlock();
+          return EXIT_FAILURE;
+        }
+
+      seed += incr;
+    }
+
+  printf("FPU#%d: Succeeded\n");
+  return EXIT_SUCCESS;
+}
+#endif /* HAVE_FPU */
+
+/***********************************************************************
+ * Private Functions
+ ***********************************************************************/
+
+void fpu_test(void)
+{
+#ifdef HAVE_FPU
+  pid_t task1;
+  pid_t task2;
+  int statloc;
+
+  /* Start two two tasks */
+
+  g_fpuno = 0;
+  printf("Starting task FPU#1\n");
+  task1 = TASK_CREATE("FPU#1", CONFIG_EXAMPLES_OSTEST_FPUPRIORITY, CONFIG_EXAMPLES_OSTEST_FPUSTACKSIZE, fpu_task, NULL);
+  if (task1 < 0)
+    {
+      printf("fpu_test: ERROR Failed to start task FPU#1\n");
+    }
+  else
+    {
+      printf("fpu_test: Started task FPU#1 at PID=%d\n", task1);
+    }
+  usleep(250);
+
+  printf("Starting task FPU#2\n");
+  task2 = TASK_CREATE("FPU#2", CONFIG_EXAMPLES_OSTEST_FPUPRIORITY, CONFIG_EXAMPLES_OSTEST_FPUSTACKSIZE, fpu_task, NULL);
+  if (task2 < 0)
+    {
+      printf("fpu_test: ERROR Failed to start task FPU#1\n");
+    }
+  else
+    {
+      printf("fpu_test: Started task FPU#2 at PID=%d\n", task2);
+    }
+
+  /* Wait for each task to complete */
+
+  (void)waitpid(task1, &statloc, 0);
+  (void)waitpid(task2, &statloc, 0);
+
+#else
+  printf("fpu_test: ERROR: The FPU test is not properly configured\n");
+#endif
+  printf("fpu_test: Returning\n");
+}
diff --git a/apps/examples/ostest/main.c b/apps/examples/ostest/main.c
index 327ec60e1..f48bca377 100644
--- a/apps/examples/ostest/main.c
+++ b/apps/examples/ostest/main.c
@@ -1,8 +1,8 @@
 /****************************************************************************
- * examples/ostest/main.c
+ * apps/examples/ostest/main.c
  *
- *   Copyright (C) 2007-2009, 2011 Gregory Nutt. All rights reserved.
- *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
+ *   Copyright (C) 2007-2009, 2011-2012 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -293,6 +293,14 @@ static int user_main(int argc, char *argv[])
       check_test_memory_usage();
 #endif
 
+#ifdef  CONFIG_ARCH_FPU
+  /* Check that the FPU is properly supported during context switching */
+
+      printf("\nuser_main: FPU test\n");
+      fpu_test();
+      check_test_memory_usage();
+#endif
+
 #ifndef CONFIG_DISABLE_PTHREAD
       /* Verify pthreads and pthread mutex */
 
diff --git a/apps/examples/ostest/ostest.h b/apps/examples/ostest/ostest.h
index 99290828e..a4af37f05 100644
--- a/apps/examples/ostest/ostest.h
+++ b/apps/examples/ostest/ostest.h
@@ -1,8 +1,8 @@
 /****************************************************************************
- * examples/ostest/ostest.h
+ * apps/examples/ostest/ostest.h
  *
- *   Copyright (C) 2007-2009, 2011 Gregory Nutt. All rights reserved.
- *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
+ *   Copyright (C) 2007-2009, 2011-2012 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -33,8 +33,8 @@
  *
  ****************************************************************************/
 
-#ifndef __OSTEST_H
-#define __OSTEST_H
+#ifndef __APPS_EXAMPLES_OSTEST_OSTEST_H
+#define __APPS_EXAMPLES_OSTEST_OSTEST_H
 
 /****************************************************************************
  * Included Files
@@ -107,6 +107,10 @@
 
 extern int dev_null(void);
 
+/* fpu.c ********************************************************************/
+
+extern void fpu_test(void);
+
 /* mutex.c ******************************************************************/
 
 extern void mutex_test(void);
@@ -171,4 +175,4 @@ extern int sem_nfreeholders(void);
 #  define sem_nfreeholders()
 #endif
 
-#endif /* __OSTEST_H */
+#endif /* __APPS_EXAMPLES_OSTEST_OSTEST_H */
diff --git a/nuttx/configs/stm3240g-eval/src/Makefile b/nuttx/configs/stm3240g-eval/src/Makefile
index cddc791c5..fc2758431 100644
--- a/nuttx/configs/stm3240g-eval/src/Makefile
+++ b/nuttx/configs/stm3240g-eval/src/Makefile
@@ -68,6 +68,10 @@ ifeq ($(CONFIG_NSH_ARCHINIT),y)
 CSRCS		+= up_nsh.c
 endif
 
+ifeq ($(CONFIG_ARCH_FPU),y)
+CSRCS		+= up_ostest.c
+endif
+
 COBJS		= $(CSRCS:.c=$(OBJEXT))
 
 SRCS		= $(ASRCS) $(CSRCS)
diff --git a/nuttx/configs/stm3240g-eval/src/up_ostest.c b/nuttx/configs/stm3240g-eval/src/up_ostest.c
new file mode 100644
index 000000000..477b67caf
--- /dev/null
+++ b/nuttx/configs/stm3240g-eval/src/up_ostest.c
@@ -0,0 +1,142 @@
+/************************************************************************************
+ * configs/stm3240g-eval/src/up_ostest.c
+ * arch/arm/src/board/up_ostest.c
+ *
+ *   Copyright (C) 2012 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <gnutt@nuttx.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name NuttX nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ************************************************************************************/
+
+/************************************************************************************
+ * Included Files
+ ************************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <string.h>
+#include <debug.h>
+
+#include <arch/irq.h>
+#include <arch/board/board.h>
+
+#include "up_arch.h"
+#include "up_internal.h"
+#include "stm3240g-internal.h"
+
+/************************************************************************************
+ * Definitions
+ ************************************************************************************/
+/* Configuration ********************************************************************/
+
+#undef HAVE_FPU
+#if defined(CONFIG_ARCH_FPU) && defined(CONFIG_EXAMPLES_OSTEST_FPUSIZE) && \
+    defined(CONFIG_SCHED_WAITPID) && !defined(CONFIG_DISABLE_SIGNALS) && \
+   !defined(CONFIG_ARMV7M_CMNVECTOR)
+#    define HAVE_FPU 1
+#endif
+
+#ifdef HAVE_FPU
+
+#if CONFIG_EXAMPLES_OSTEST_FPUSIZE != (4*SW_FPU_REGS)
+#  error "CONFIG_EXAMPLES_OSTEST_FPUSIZE has the wrong size"
+#endif
+
+/************************************************************************************
+ * Private Functions
+ ************************************************************************************/
+
+/************************************************************************************
+ * Public Functions
+ ************************************************************************************/
+/* Given a uint8_t array of size CONFIG_EXAMPLES_OSTEST_FPUSIZE, this
+ * function will return the current FPU registers.
+ */
+
+void arch_getfpu(FAR uint8_t *fpusave)
+{
+  irqstate_t flags;
+  uint32_t regs[XCPTCONTEXT_REGS];
+
+  flags = irqsave();
+  up_savefpu(regs);
+  irqrestore(flags);
+
+  memcpy(fpusave, &regs[REG_S0], (4*SW_FPU_REGS));
+}
+
+/* Given a uint8_t array of size CONFIG_EXAMPLES_OSTEST_FPUSIZE, this
+ * function will set the current FPU regisers to match the provided
+ * register save set.
+ */
+
+void arch_setfpu(FAR const uint8_t *fpusave)
+{
+  irqstate_t flags;
+  uint32_t regs[XCPTCONTEXT_REGS];
+
+  memcpy(&regs[REG_S0], fpusave, (4*SW_FPU_REGS));
+
+  flags = irqsave();
+  up_restorefpu(regs);
+  irqrestore(flags);
+}
+
+/* Given a uint8_t array of size CONFIG_EXAMPLES_OSTEST_FPUSIZE and a
+ * seed value, this function will set the FPU registers to a known
+ * values for testing purposes.  The contents of the FPU registers
+ * must be uniqe for each sed value.
+ */
+
+void arch_initfpu(FAR uint8_t *fpusave, int seed)
+{
+  FAR uint32_t *dest = (FAR uint32_t *)fpusave;
+  uint32_t mask = 0x01010101;
+  uint32_t incr = 0x01010101;
+  int i;
+
+  for (i = 0; i < 32; i++)
+    {
+      *dest = (uint32_t)seed ^ mask;
+      mask += incr;
+    }
+}
+
+/* Given two uint8_t arrays of size CONFIG_EXAMPLES_OSTEST_FPUSIZE this
+ * function will compare then an return true if they are identical.
+ */
+
+bool arch_cmpfpu(FAR const uint8_t *fpusave1, FAR const uint8_t *fpusave2)
+{
+  return memcmp(fpusave1, fpusave2, (4*32)) == 0;
+}
+
+#endif /* HAVE_FPU */
diff --git a/nuttx/sched/sched_waitpid.c b/nuttx/sched/sched_waitpid.c
index a1af343e1..5eefba371 100644
--- a/nuttx/sched/sched_waitpid.c
+++ b/nuttx/sched/sched_waitpid.c
@@ -1,8 +1,8 @@
 /*****************************************************************************
  * sched/sched_waitpid.c
  *
- *   Copyright (C) 2011 Gregory Nutt. All rights reserved.
- *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
+ *   Copyright (C) 2011-2012 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <gnutt@nuttx.org
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -188,18 +188,18 @@ pid_t waitpid(pid_t pid, int *stat_loc, int options)
   sched_lock();
   if (!tcb)
     {
-	  err = ECHILD;
-	  goto errout_with_errno;
-	}
+      err = ECHILD;
+      goto errout_with_errno;
+    }
 
   /* None of the options are supported */
 
 #ifdef CONFIG_DEBUG
   if (options != 0)
     {
-	  err = ENOSYS;
-	  goto errout_with_errno;
-	}
+      err = ENOSYS;
+      goto errout_with_errno;
+    }
 #endif
 
   /* "If more than one thread is suspended in waitpid() awaiting termination of
@@ -210,26 +210,26 @@ pid_t waitpid(pid_t pid, int *stat_loc, int options)
 
   if (stat_loc != NULL && tcb->stat_loc == NULL)
     {
-	  tcb->stat_loc = stat_loc;
-	  mystat        = true;
-	}
+      tcb->stat_loc = stat_loc;
+      mystat        = true;
+    }
 
   /* Then wait for the task to exit */
  
   ret = sem_wait(&tcb->exitsem);
   if (ret < 0)
     {
-	  /* Unlock pre-emption and return the ERROR (sem_wait has already set
-	   * the errno).  Handle the awkward case of whether or not we need to
-	   * nullify the stat_loc value.
-	   */
-
-	  if (mystat)
-	    {
-		  tcb->stat_loc = NULL;
-		}
-	  goto errout;
-	}
+      /* Unlock pre-emption and return the ERROR (sem_wait has already set
+       * the errno).  Handle the awkward case of whether or not we need to
+       * nullify the stat_loc value.
+       */
+
+      if (mystat)
+        {
+          tcb->stat_loc = NULL;
+        }
+      goto errout;
+    }
 
   /* On success, return the PID */