x86/xen: fill hypercall page with int3

Filling the hypercall page with nops is not helpful from a debugging point of
view, as for example attempting to execute an hypercall before the page is
initialized will result in the execution flow falling through into
xen_start32, making the mistake less obvious to spot.

Instead fill the page with int3 (0xcc) which will result in a #BP trap.

Sponsored by: Cloud Software Group
Reviewed by: markj
Differential revision: https://reviews.freebsd.org/D43930

sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

xen: switch to use headers in contrib

These headers originate with the Xen project and shouldn't be mixed with
the main portion of the FreeBSD kernel. Notably they shouldn't be the
target of clean-up commits.

Switch to use the headers in sys/contrib/xen.

Reviewed by: royger

xen: remove support for PVHv1 bootpath

PVHv1 is a legacy interface supported only by Xen versions 4.4 through
4.9.

Reviewed by: royger

x86: remove gcov kernel support

Reviewed by: jhb
Sponsored by: The FreeBSD Foundation
Differential revision: https://reviews.freebsd.org/D29529

xen-locore: fix size in GDT descriptor

There was an off-by-one in the GDT descriptor size field used by the
early Xen boot code. The GDT descriptor size should be the size of the
GDT minus one. No functional change expected as a result of this
change.

Sponsored by: Citrix Systems R&D

xen: implement early init helper for PVHv2

In order to setup an initial environment and jump into the generic
hammer_time initialization function. Some of the code is shared with
PVHv1, while other code is PVHv2 specific.

This allows booting FreeBSD as a PVHv2 DomU and Dom0.

Sponsored by: Citrix Systems R&D

xen: add PVHv2 entry point

The PVHv2 entry point is fairly similar to the multiboot1 one. The
kernel is started in protected mode with paging disabled. More
information about the exact BSP state can be found in the pvh.markdown
document on the Xen tree.

This entry point is going to be joined with the native entry point at
hammer_time, and in order to do so the BSP needs to be bootstrapped
into long mode with the same set of page tables as used on bare metal.

Sponsored by: Citrix Systems R&D

Rename assym.s to assym.inc

assym is only to be included by other .s files, and should never
actually be assembled by itself.

Reviewed by: imp, bdrewery (earlier)
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D14180

amd64: set the correct LMA values

The current linker script generates program headers with VMA == LMA:

Entry point 0xffffffff802e7000
There are 6 program headers, starting at offset 64

Program Headers:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
PHDR 0x0000000000000040 0xffffffff80200040 0xffffffff80200040
0x0000000000000150 0x0000000000000150 R E 8
INTERP 0x0000000000000190 0xffffffff80200190 0xffffffff80200190
0x000000000000000d 0x000000000000000d R 1
[Requesting program interpreter: /red/herring]
LOAD 0x0000000000000000 0xffffffff80200000 0xffffffff80200000
0x00000000010559b0 0x00000000010559b0 R E 200000
LOAD 0x0000000001056000 0xffffffff81456000 0xffffffff81456000
0x0000000000132638 0x000000000052ecf8 RW 200000
DYNAMIC 0x0000000001056000 0xffffffff81456000 0xffffffff81456000
0x00000000000000d0 0x00000000000000d0 RW 8
GNU_STACK 0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 RWE 8

This is fine for the FreeBSD loader, because it completely ignores p_paddr
and instead uses p_vaddr with a hardcoded offset. Other loaders however
acknowledge p_paddr (like the Xen ELF loader), in which case they will try
to load the kernel at the wrong place. Fix this by adding an AT keyword to
the first section specifying the physical address, other sections will
follow suit, so it ends up looking like:

Entry point 0xffffffff802e7000
There are 6 program headers, starting at offset 64

Program Headers:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
PHDR 0x0000000000000040 0xffffffff80200040 0x0000000000200040
0x0000000000000150 0x0000000000000150 R E 8
INTERP 0x0000000000000190 0xffffffff80200190 0x0000000000200190
0x000000000000000d 0x000000000000000d R 1
[Requesting program interpreter: /red/herring]
LOAD 0x0000000000000000 0xffffffff80200000 0x0000000000200000
0x00000000010559b0 0x00000000010559b0 R E 200000
LOAD 0x0000000001056000 0xffffffff81456000 0x0000000001456000
0x0000000000132638 0x000000000052ecf8 RW 200000
DYNAMIC 0x0000000001056000 0xffffffff81456000 0x0000000001456000
0x00000000000000d0 0x00000000000000d0 RW 8
GNU_STACK 0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 RWE 8

Tested on bare metal using the native FreeBSD loader and grub2 from TRUEOS.

Sponsored by: Citrix Systems R&D
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D2783

xen: fix copyright header

Some of the code in xen-locore.S was picked from Cherry G. Mathew
amd64 Xen PV branch, but I've failed to set the proper copyright, so
do it now.

Approved by: gibbs

xen: add PV/PVH kernel entry point

Add the PV/PVH entry point and the low level functions for PVH
early initialization.

Approved by: gibbs
Sponsored by: Citrix Systems R&D

amd64/amd64/genassym.c:
- Add __FreeBSD_version define to assym.s so it can be used for the
Xen notes.

amd64/amd64/locore.S:
- Make bootstack global so it can be used from Xen kernel entry
point.

amd64/amd64/xen-locore.S:
- Add Xen notes to the kernel.
- Add the Xen PV entry point, that is going to call hammer_time_xen.

amd64/include/asmacros.h:
- Add ELFNOTE macros.

i386/xen/xen_machdep.c:
- Define HYPERVISOR_start_info for the XEN i386 PV port, which is
going to be used in some shared code between PV and PVH.

x86/xen/hvm.c:
- Define HYPERVISOR_start_info for the PVH port.

x86/xen/pv.c:
- Introduce hammer_time_xen which is going to perform early setup for
Xen PVH:
- Setup shared Xen variables start_info, shared_info and
xen_store.
- Set guest type.
- Create initial page tables as FreeBSD expects to find them.
- Call into native init function (hammer_time).

xen/xen-os.h:
- Declare HYPERVISOR_start_info.

conf/files.amd64:
- Add amd64/amd64/locore.S and x86/xen/pv.c to the list of files.