V4 [PATCH 04/12] x86/CET: Extend arch_prctl syscall for CET control

[Sergey Senozhatsky]

On (08/13/18 13:11), Carlos O'Donell wrote:
> > Oh, my bad. Sorry, I should have mentioned that it was my own kernel
> > modification just to see how often I get -EINVAL prctl syscalls.
> 
> You should only see them at startup when we query the kernel for support.

Right. I'm not arguing, one extra syscall per-process is not a big deal.

> Like *all* glibc features we query for support to see if we're running on
> a new enough kernel to enable the feature.
[..]
> Is it? You get a '-1' ENOENT return for every process when it starts and
> tries to look for /etc/ld.so.preload. This is similar.

These all are valid points, sure. But, somehow, testing for a feature
that no kernel or HW supports looks *a bit* different. /etc/ld.so.preload
at least exists on some hosts, while ARCH_CET does not. Maybe it's OK.
My only real problem with ARCH_CET was valgrind.

	-ss