Re: [PATCH v3 02/23] rseq: Introduce extensible rseq ABI

* Mathieu Desnoyers:

Introduce the extensible rseq ABI, where the feature size supported by
the kernel and the required alignment are communicated to user-space
through ELF auxiliary vectors.

This allows user-space to call rseq registration with a rseq_len of
either 32 bytes for the original struct rseq size (which includes
padding), or larger.

If rseq_len is larger than 32 bytes, then it must be large enough to
contain the feature size communicated to user-space through ELF
auxiliary vectors.

I don't think this works with the glibc extension mechanism because
__rseq_size does not change until the padding is exhausted.

I think you'll need to add the suggested flags to the auxiliary vector,
and then we can use that during registration and also communicate these
flags via __rseq_flags.

Size and alignment can be stored in a single auxiliary vector entry.

Thanks,
Florian