Re: [RFC PATCH v2 1/4] rseq: Add sched_state field to struct rseq

[Florian Weimer]

* Dmitry Vyukov:

> In reality it's a bit more involved since the field is actually 8
> bytes and only partially overlaps with rseq.cpu_id_start (it's an
> 8-byte pointer with high 4 bytes overlap rseq.cpu_id_start):
>
> https://github.com/google/tcmalloc/blob/229908285e216cca8b844c1781bf16b838128d1b/tcmalloc/internal/percpu.h#L101-L165

This does not compose with other rseq users, as noted in the sources:

  // Note: this makes __rseq_abi.cpu_id_start unusable for its original purpose.

For a core library such a malloc replacement, that is a very bad trap.

Thanks,
Florian