Programmatically cache line

[Konstantin Belousov]

On Mon, Jan 01, 2018 at 06:52:37AM +0000, David Chisnall wrote:
> On 1 Jan 2018, at 05:09, Adrian Chadd <adrian.chadd at gmail.com> wrote:
> > 
> > On 30 December 2017 at 00:28, Konstantin Belousov <kostikbel at gmail.com> wrote:
> >> On Sat, Dec 30, 2017 at 07:50:19AM +0000, blubee blubeeme wrote:
> >>> Is there some way to programmatically get the CPU cache line sizes on
> >>> FreeBSD?
> >> 
> >> There are, all of them are MD.
> >> 
> >> On x86, the CPUID instruction leaf 0x1 returns the information in
> >> %ebx register.
> > 
> > Hm, weird. Why don't we extend sysctl to include this info?
For the same reason we do not provide a sysctl to add two integers.

> 
> It would be nice to expose this kind of information via VDSO or similar.  There are a lot of similar bits of info that people want to use for ifunc and, SVE is going to have a bunch of similar requirements.
> 
Is VDSO a new trendy word ?

ifunc resolvers in usermode on FreeBSD/x86 get four arguments which
are essentially cpu_features / cpu_features2 / cpu_stdext_features /
cpu_stdext_features2.  I suspect that only FreeBSD/x86 arches have the
ifunc support, in rtld and coming shortly in kernel.

Recently HW_CAP/HW_CAP2 were added to the ELF auxv, and elf_aux_info(3)
interface exported from libc.

ARM* did not implemented yet the ifunc stubs in rtld. I believe this is
considered a low priority because there is no ready to use toolchain
which allow to utilize ifuncs on FreeBSD, except if you use recent bfd
ld externally.