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I don't believe they are allocating 128 bytes, or accessing out of bounds memory.

He explicitly states 128byte filename allocates 129 bytes. https://www.youtube.com/watch?v=kPR8h4-qZdk&t=1417s

In that case the bug he described simply does not exist.

This is well outside my expertise, but some discussion happened at the time https://www.reddit.com/r/programming/comments/56xxmb/the_str...

Some people suggest that maybe Facebook runs with MAP_UNINITIALIZED

Unfortunately this hypothesis is also wrong. MAP_UNINITIALIZED can only be enabled in the kernel when there is no MMU, and in that case the page will already be in physical memory, so the very first pointer dereference will read the correct byte, not a fake zero because it's "uninitialized".

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