Re: [PATCH 1/4] glibc: Perform rseq(2) registration at C startup and thread creation (v7)

[Florian Weimer]

* Michael Ellerman:

> I'm a bit vague on what we're trying to do here.
>
> But it seems like you want some sort of "eye catcher" prior to the branch?
>
> That value is a valid instruction on current CPUs (rlwimi.
> r5,r24,6,1,9), and even if it wasn't it could become one in future.
>
> If you change it to 0x8053530 that is both a valid instruction and is a
> nop (conditional trap immediate but with no conditions set).

I think we need something that is very unlikely to appear in the
instruction stream.  It's just a marker.  The instruction will never be
executed, and it does not have to be a trap, either (I believe that a
standard trap instruction would be a bad choice).

Thanks,
Florian