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    For what it's worth, your most recent code returns different addresses and (occasional) uninitialised (non-zero) data when run on OpenBSD. This obviously does not say anything about the behaviour that you are witnessing on Linux. Commented Mar 28, 2019 at 21:07
  • Please do not change the scope of your question, and do not try to edit it in order to make answers and comments redundant. In C, the "heap" is nothing else but the memory returned by malloc() and calloc(), and only the latter is zeroing out the memory; the new operator in C++ (also "heap") is on Linux just a wrapper for malloc(); the kernel doesn't know nor care what the "heap" is. Commented Mar 28, 2019 at 21:16
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    Your second example is simply exposing an artifact of the malloc implementation in glibc; if you do that repeated malloc/free with a buffer larger than 8 bytes, you will clearly see that only the first 8 bytes are zeroed. Commented Mar 28, 2019 at 21:16
  • @Kusalananda I see. That my result differs from the result on OpenBSD is indeed interesting. Apparently, you and Mosvy have shown that my experiments were discovering not a kernel (or linker) security protocol, as I had thought, but a mere implementational artifact. Commented Mar 28, 2019 at 22:05
  • @thb I believe that this may be a correct observation, yes. Commented Mar 28, 2019 at 22:07