Get LIBC_MEM and LIBC_STDIO building with aarch64

libc/mem/malloc_usable_size.c

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+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2023 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/mem/hook.internal.h"
+#include "libc/mem/mem.h"
+#include "third_party/dlmalloc/dlmalloc.h"
+
+size_t (*hook_malloc_usable_size)(void *) = dlmalloc_usable_size;
+
+/**
+ * Returns the number of bytes you can actually use in
+ * an allocated chunk, which may be more than you requested
+ * (although often not) due to alignment and minimum size
+ * constraints.
+ *
+ * You can use this many bytes without worrying about overwriting
+ * other allocated objects. This is not a particularly great
+ * programming practice. malloc_usable_size can be more useful in
+ * debugging and assertions, for example:
+ *
+ *     p = malloc(n)
+ *     assert(malloc_usable_size(p) >= 256)
+ *
+ * @param p is address of allocation
+ * @return total number of bytes
+ * @see dlmalloc_usable_size()
+ * @threadsafe
+ */
+size_t malloc_usable_size(void *p) {
+  return hook_malloc_usable_size(p);
+}