Make zero size allocation result consistent

The zero size allocations had no consistent behaviour in RTEMS.  For
example, malloc( 0 ) returned NULL and posix_memalign( &p, align, 0 )
returned in p a unique pointer (or NULL if no memory is available).  In
POSIX, zero size memory allocations are implementation-defined
behaviour.  The implementation has two options:

https://pubs.opengroup.org/onlinepubs/9699919799/functions/malloc.html

https://pubs.opengroup.org/onlinepubs/9699919799/functions/posix_memalign.html

Linux and FreeBSD return a unique pointer for zero size memory
allocations.   Use this approach for RTEMS as well throughout the memory
allocation directives

Close #4390.

3 files changed, 4 insertions, 14 deletions

diff --git a/cpukit/libcsupport/src/malloc.c b/cpukit/libcsupport/src/malloc.c
index e61128bf8c..795254fbab 100644
--- a/cpukit/libcsupport/src/malloc.c
+++ b/cpukit/libcsupport/src/malloc.c
@@ -30,12 +30,6 @@ void *malloc(
 {
   void        *return_this;
 
-  /*
-   * Validate the parameters
-   */
-  if ( !size )
-    return (void *) 0;
-
   return_this = rtems_heap_allocate_aligned_with_boundary( size, 0, 0 );
   if ( !return_this ) {
     errno = ENOMEM;
diff --git a/cpukit/libcsupport/src/malloc_deferred.c b/cpukit/libcsupport/src/malloc_deferred.c
index b319d1213e..aab76406c7 100644
--- a/cpukit/libcsupport/src/malloc_deferred.c
+++ b/cpukit/libcsupport/src/malloc_deferred.c
@@ -106,10 +106,6 @@ void *rtems_heap_allocate_aligned_with_boundary(
 
 void *rtems_malloc( size_t size )
 {
-  if ( size == 0 ) {
-    return NULL;
-  }
-
   return rtems_heap_allocate_aligned_with_boundary( size, 0, 0 );
 }
 #endif
diff --git a/cpukit/libcsupport/src/realloc.c b/cpukit/libcsupport/src/realloc.c
index 1d9ae45c5d..e28e3fbc33 100644
--- a/cpukit/libcsupport/src/realloc.c
+++ b/cpukit/libcsupport/src/realloc.c
@@ -53,15 +53,15 @@ void *realloc( void *ptr, size_t size )
   uintptr_t           old_size;
   uintptr_t           avail_size;
 
+  if ( ptr == NULL ) {
+    return malloc( size );
+  }
+
   if ( size == 0 ) {
     free( ptr );
     return NULL;
   }
 
-  if ( ptr == NULL ) {
-    return malloc( size );
-  }
-
   heap = RTEMS_Malloc_Heap;
 
   switch ( _Malloc_System_state() ) {