elf: Implement __rtld_malloc_is_complete

In some cases, it is difficult to determine the kind of malloc
based on the execution context, so a function to determine that
is helpful.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

elf/dl-minimal.c

@@ -59,6 +59,14 @@ __rtld_malloc_init_stubs (void)
   __rtld_realloc = &rtld_realloc;
 }
 
+bool
+__rtld_malloc_is_complete (void)
+{
+  /* The caller assumes that there is an active malloc.  */
+  assert (__rtld_malloc != NULL);
+  return __rtld_malloc != &rtld_malloc;
+}
+
 /* Lookup NAME at VERSION in the scope of MATCH.  */
 static void *
 lookup_malloc_symbol (struct link_map *main_map, const char *name,

include/rtld-malloc.h

@@ -66,6 +66,10 @@ realloc (void *ptr, size_t size)
    implementation.  */
 void __rtld_malloc_init_stubs (void) attribute_hidden;
 
+/* Return false if the active malloc is the ld.so minimal malloc, true
+   if it is the full implementation from libc.so.  */
+_Bool __rtld_malloc_is_complete (void) attribute_hidden;
+
 /* Called shortly before the final self-relocation (when RELRO
    variables are still writable) to activate the real malloc
    implementation.  MAIN_MAP is the link map of the executable.  */