Add nano-malloc-clear-freed option

With this option enabled, all memory released
in free or realloc gets cleared to zero.

Signed-off-by: Keith Packard <[email protected]>

Author: keith-packard

meson.build

@@ -185,6 +185,7 @@ newlib_iconv_external_ccs = get_option('newlib-iconv-external-ccs')
 
 newlib_atexit_dynamic_alloc = get_option('newlib-atexit-dynamic-alloc')
 newlib_nano_malloc = get_option('newlib-nano-malloc')
+nano_malloc_clear_freed = get_option('nano-malloc-clear-freed')
 lite_exit = get_option('lite-exit')
 
 newlib_elix_level = get_option('newlib-elix-level')
@@ -1365,6 +1366,7 @@ conf_data.set('_FSEEK_OPTIMIZATION', newlib_fseek_optimization)
 conf_data.set('_WIDE_ORIENT', newlib_wide_orient)
 conf_data.set('_HAVE_FCNTL', newlib_have_fcntl)
 conf_data.set('_NANO_MALLOC', newlib_nano_malloc)
+conf_data.set('_NANO_MALLOC_CLEAR_FREED', nano_malloc_clear_freed and newlib_nano_malloc)
 conf_data.set('_UNBUF_STREAM_OPT', get_option('newlib-unbuf-stream-opt'))
 conf_data.set('_LITE_EXIT', lite_exit)
 conf_data.set('_PICO_EXIT', picoexit)

meson_options.txt

@@ -263,6 +263,8 @@ option('atomic-signal', type: 'boolean', value: true,
 #
 option('newlib-nano-malloc', type: 'boolean', value: true,
        description: 'use small-footprint nano-malloc implementation')
+option('nano-malloc-clear-freed', type: 'boolean', value: false,
+       description: 'nano version erases memory on free/realloc')
 
 #
 # Locking support

newlib/libc/stdlib/nano-free.c

@@ -46,7 +46,12 @@ free (void * free_p)
     if (free_p == NULL) return;
 
     p_to_free = ptr_to_chunk(free_p);
+
+#ifdef _NANO_MALLOC_CLEAR_FREED
+    memset(p_to_free, 0, chunk_usable(p_to_free));
+#else
     p_to_free->next = NULL;
+#endif
 
 #if MALLOC_DEBUG
     __malloc_validate_block(p_to_free);

newlib/libc/stdlib/nano-realloc.c

@@ -113,6 +113,10 @@ realloc(void * ptr, size_t size)
     {
 	size_t extra = old_size - new_size;
 
+#ifdef _NANO_MALLOC_CLEAR_FREED
+        if (extra > MALLOC_HEAD)
+            memset((char *) ptr + new_size, 0, extra - MALLOC_HEAD);
+#endif
 	/* If there's enough space left over, split it out
 	 * and free it
 	 */