mm/umm_heap: sbrk() is only available in the KERNEL build.

arch/arm/src/armv7-m/up_signal_dispatch.c

@@ -54,7 +54,7 @@
  * Name: up_signal_dispatch
  *
  * Description:
- *   In this kernel mode build, this function will be called to execute a
+ *   In the kernel mode build, this function will be called to execute a
  *   a signal handler in user-space.  When the signal is delivered, a
  *   kernel-mode stub will first run to perform some housekeeping functions.
  *   This kernel-mode stub will then be called transfer control to the user

mm/umm_heap/umm_calloc.c

@@ -59,7 +59,7 @@
 
 FAR void *calloc(size_t n, size_t elem_size)
 {
-#ifdef CONFIG_ARCH_ADDRENV
+#if defined(CONFIG_ARCH_ADDRENV) && defined(CONFIG_BUILD_KERNEL)
   /* Use zalloc() because it implements the sbrk() logic */
 
   FAR void *ret = NULL;

mm/umm_heap/umm_memalign.c

@@ -65,7 +65,7 @@
 
 FAR void *memalign(size_t alignment, size_t size)
 {
-#ifdef CONFIG_ARCH_ADDRENV
+#if defined(CONFIG_ARCH_ADDRENV) && defined(CONFIG_BUILD_KERNEL)
   FAR void *brkaddr;
   FAR void *mem;
 

mm/umm_heap/umm_realloc.c

@@ -67,7 +67,7 @@
 
 FAR void *realloc(FAR void *oldmem, size_t size)
 {
-#ifdef CONFIG_ARCH_ADDRENV
+#if defined(CONFIG_ARCH_ADDRENV) && defined(CONFIG_BUILD_KERNEL)
   FAR void *brkaddr;
   FAR void *mem;
 

sched/signal/sig_kill.c

@@ -56,7 +56,8 @@
  * Name: nxsig_kill
  *
  * Description:
- *   The nxsig_kill() system call can be used to send any signal to any task.
+ *   The nxsig_kill() system call can be used to send any signal to any task
+ *   group.
  *
  *   This is an internal OS interface.  It is functionally equivalent to
  *   the POSIX standard kill() function but does not modify the application
@@ -135,7 +136,8 @@ int nxsig_kill(pid_t pid, int signo)
  * Name: kill
  *
  * Description:
- *   The kill() system call can be used to send any signal to any task.
+ *   The kill() system call can be used to send any signal to any task
+ *   group.
  *
  *   Limitation: Sending of signals to 'process groups' is not
  *   supported in NuttX