Squashed commit of the following:

include/nuttx/arch.h:  Add prototype for an architecture-specific up_trigger_irq function
    arch/, include/nuttx, sched/sched:  Add the garbage collection hook so each architecture can do custom memory cleanup if necesary.
    arch/Kconfig:  Add configureation CONFIG_ARCH_GNU_NO_WEAKFUNCTIONS to suppress use of weak functions.  Some gnu derived toolchains do not support weak symbols

arch/Kconfig

@@ -139,6 +139,13 @@ config ARCH_TOOLCHAIN_GNU
 	bool
 	default n
 
+config ARCH_GNU_NO_WEAKFUNCTIONS
+	bool
+	depends on ARCH_TOOLCHAIN_GNU
+	default n
+	---help---
+		Disable support for weak functions.
+
 comment "Architecture Options"
 
 config ARCH_NOINTC
@@ -222,6 +229,10 @@ config ARCH_HAVE_RTC_SUBSECONDS
 	bool
 	default n
 
+config ARCH_HAVE_GARBAGE
+	bool
+	default n
+
 config ARCH_GLOBAL_IRQDISABLE
 	bool
 	default n

include/nuttx/arch.h

@@ -1,7 +1,7 @@
 /****************************************************************************
  * include/nuttx/arch.h
  *
- *   Copyright (C) 2007-2017 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2018 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -732,7 +732,26 @@ uintptr_t pgalloc(uintptr_t brkaddr, unsigned int npages);
 #endif
 
 /****************************************************************************
- * Name: up_setpicbase, up_getpicbase
+ * Name: up_sched_have_garbage and up_sched_garbage_collection
+ *
+ * Description:
+ *   Some architectures may soft unique memory allocators.  If
+ *   CONFIG_ARCH_HAVE_GARBAGE is defined, those architectures must provide
+ *   both up_sched_have_garbage and up_sched_garbage_collection.  These will
+ *   be tied into the NuttX memory garbage collection logic.
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_ARCH_HAVE_GARBAGE
+bool up_sched_have_garbage(void);
+void up_sched_garbage_collection(void);
+#else
+#  define up_sched_have_garbage() false
+#  define up_sched_garbage_collection()
+#endif
+
+/****************************************************************************
+ * Name: up_setpicbase and up_getpicbase
  *
  * Description:
  *   It NXFLAT external modules (or any other binary format that requires)

include/nuttx/compiler.h

@@ -93,7 +93,7 @@
  * unnecessary "weak" functions can be excluded from the link.
  */
 
-# ifndef __CYGWIN__
+# if !defined(__CYGWIN__) && !defined(CONFIG_ARCH_GNU_NO_WEAKFUNCTIONS)
 #  define CONFIG_HAVE_WEAKFUNCTIONS 1
 #  define weak_alias(name, aliasname) \
    extern __typeof (name) aliasname __attribute__ ((weak, alias (#name)));

include/nuttx/kmalloc.h

@@ -1,7 +1,8 @@
 /****************************************************************************
  * include/nuttx/kmalloc.h
  *
- *   Copyright (C) 2007-2008, 2011, 2013, 2016 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2008, 2011, 2013, 2016, 2018 Gregory Nutt. All
+ *     rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -203,6 +204,10 @@ void sched_kfree(FAR void *address);
 #  define sched_kfree(a) sched_ufree(a)
 #endif
 
+/* Signal the worker thread that is has some clean up to do */
+
+void sched_signal_free(void);
+
 /* Functions defined in sched/sched_garbage *********************************/
 
 /* Must be called periodically to clean up deallocations delayed by

sched/sched/sched_free.c

@@ -1,7 +1,8 @@
 /****************************************************************************
  * sched/sched/sched_free.c
  *
- *   Copyright (C) 2007, 2009, 2012-2013, 2015-2016 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007, 2009, 2012-2013, 2015-2016, 2018 Gregory Nutt. All
+ *     rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -105,9 +106,7 @@ void sched_ufree(FAR void *address)
 
       /* Signal the worker thread that is has some clean up to do */
 
-#ifdef CONFIG_SCHED_WORKQUEUE
+      sched_signal_free();
-      work_signal(LPWORK);
-#endif
       leave_critical_section(flags);
     }
   else
@@ -146,9 +145,7 @@ void sched_kfree(FAR void *address)
 
       /* Signal the worker thread that is has some clean up to do */
 
-#ifdef CONFIG_SCHED_WORKQUEUE
+      sched_signal_free();
-      work_signal(LPWORK);
-#endif
       leave_critical_section(flags);
     }
   else
@@ -160,3 +157,20 @@ void sched_kfree(FAR void *address)
     }
 }
 #endif
+
+/****************************************************************************
+ * Name: sched_signal_free
+ *
+ * Description:
+ *   Signal the worker thread that is has some clean up to do.
+ *
+ ****************************************************************************/
+
+void sched_signal_free(void)
+{
+#ifdef CONFIG_SCHED_WORKQUEUE
+  /* Signal the worker thread that is has some clean up to do */
+
+  work_signal(LPWORK);
+#endif
+}

sched/sched/sched_garbage.c

@@ -237,6 +237,10 @@ void sched_garbage_collection(void)
   /* Handle deferred deallocations for the user heap */
 
   sched_kucleanup();
+
+  /* Handle the architecure-specific garbage collection */
+
+  up_sched_garbage_collection();
 }
 
 /****************************************************************************
@@ -264,5 +268,6 @@ void sched_garbage_collection(void)
 
 bool sched_have_garbage(void)
 {
-  return (sched_have_kgarbage() || sched_have_kugarbage());
+  return (sched_have_kgarbage() || sched_have_kugarbage() ||
+          up_sched_have_garbage());
 }