On 08/05/2016 03:49 PM, H.Loom wrote:
On Friday, 5 August 2016 at 21:25:41 UTC, Ali Çehreli wrote:
malloc stores the allocation size and other information right before
the pointer that it returns.
TIL. Is it guaranteed for any malloc implementation ? I'm a bit surpised
to read that. I thought these kind of trick was only used for aligned
allocations !
Not guaranteed of course but it's a common technique. Here is an
implementation:
https://code.woboq.org/userspace/glibc/malloc/malloc.c.html#1116
As I had suspected, the imprecision in my test code comes from low order
bits being used as flags (P and M in that source code).
And I think malloc always returns memory properly aligned. After all,
the user should be able to put anything there.
Ali
