This is another attempt at
d4b604baeadbb2498e4f2c3e260260eed210f5d6 and #12438
Instead of blindly using the extra allocated space, let's do so only
after telling libc about it, via a second realloc(). The second
realloc() should be quick, since it never has to copy memory around.
/* SPDX-License-Identifier: LGPL-2.1+ */
+#include <malloc.h>
#include <stdint.h>
#include <string.h>
if (!q)
return NULL;
+ if (size > 0) {
+ size_t bn;
+
+ /* Adjust for the 64 byte minimum */
+ newalloc = a / size;
+
+ bn = malloc_usable_size(q) / size;
+ if (bn > newalloc) {
+ void *qq;
+
+ /* The actual size allocated is larger than what we asked for. Let's call realloc() again to
+ * take possession of the extra space. This should be cheap, since libc doesn't have to move
+ * the memory for this. */
+
+ qq = realloc(q, bn * size);
+ if (_likely_(qq)) {
+ *p = qq;
+ *allocated = bn;
+ return qq;
+ }
+ }
+ }
+
*p = q;
*allocated = newalloc;
return q;