Tested by:	Timothy Pearson (tpearson_raptorengineering.com)
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D53801

There is no need to support pre-12.0 (and thus pre-ino64) kernels in a
15.x libc.

Continue to check if the CPU supports these features before using them
and fall back as required.

Reviewed by:	kib
Differential Revision:	https://reviews.freebsd.org/D50732

When this code was first written we didn't have even a struct tcb, so to
make it MI a pointer to the DTV pointer in the TCB was passed around.
Now that we have a struct tcb we can simplify the code by instead
passing around a pointer to that, and the MI code can access the tcb_dtv
member wherever it happens to be in the layout. This reduces boilerplate
in all the various callers of tls_get_addr_common/slow and makes it
clearer that tls_get_addr_common/slow are operating on the TCB, rather
than obfuscating it slightly through the double pointer.

Whilst here, clarify the comments in aarch64's TLSDESC dynamic resolver,
which were using tp without clarifying what this was for (previously a
pointer to the DTV pointer, now a pointer to the TCB, which happen to be
the same thing for Variant I TLS, and in the case of AArch64 are what
TPIDR_EL0 point to directly, with no offset/bias).

Reviewed by:	kib
Differential Revision:	https://reviews.freebsd.org/D50591

Reported and tested:    Alex S <iwtcex@gmail.com>
Tested by:	pho
Reviewed by:	olce
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D50482

Rather than treating the DTV as a raw array of uintptr_t, use proper
struct types and gain the benefit of having different types for
different members. In particular, the module slots now have real pointer
types so less casting is generally needed.

Note that, whilst struct dtv_slot may seem a little unnecessary, this
will help downstream in CheriBSD where we wish to be able to easily
alter the layout of a module's slot, which this helps abstract.

Reviewed by:	kib
Differential Revision:	https://reviews.freebsd.org/D50231

Discussed with:	emaste, imp
Sponsored by:   The FreeBSD Foundation
Differential revision:	https://reviews.freebsd.org/D48509

Discussed with:	emaste, imp
Sponsored by:	The FreeBSD Foundation
MFC after:	3 days
Differential revision:	https://reviews.freebsd.org/D48509

Currently we pass the raw pointer to the on-stack auxargs. This can
legitimately have fewer than AT_COUNT entries, so the use of
__min_size(AT_COUNT), i.e. static AT_COUNT, is inaccurate, and also
needlessly forces the callee to iterate over the elements to find the
entry for a given type. Instead we can just pass aux_info like we use
for everything else.

Note that the argument has been left unused by every callee since its
introduction in 4352999e0e6c ("Pass CPUID[1] %edx (cpu_feature), %ecx
(cpu_feature2) and CPUID[7].%ebx (cpu_stdext_feature), %ecx
(cpu_stdext_feature2) to the ifunc resolvers on x86.")

Reviewed by:	kib
MFC after:	1 month
Differential Revision:	https://reviews.freebsd.org/D46276

This is a residual of the $FreeBSD$ removal.

MFC After: 3 days (though I'll just run the command on the branches)
Sponsored by: Netflix

This will be used to handle the DT_AARCH64_VARIANT_PCS tag.

Reviewed by:	kib
Sponsored by:	Arm Ltd
Differential Revision:	https://reviews.freebsd.org/D45117