x86emul: fix SYSCALL/SYSENTER/SYSEXIT emulation

SYSCALL:
- make sure SS selector has RPL 0
- only use 32 bits of RIP to fill RCX when target execution mode is 32-bit
- don't shadow function wide variable 'rc'
- consolidate CS attribute setting into single statements
- drop pointless initializers and casts
- drop redundant MSR_STAR read (as suggested by Andrew Cooper)

SYSENTER/SYSEXIT:
- #GP condition doesn't depend on guest mode
- only use 32 bits for setting RIP/RSP when target execution mode is 32-bit
- don't shadow function wide variable 'rc'
- consolidate CS attribute setting into single statements
- drop pointless (and inconsistently used) casts

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
x86: make dump_pageframe_info() slightly more verbose for dying domains

Allowing more than just 10 pages to be printed in this case gives a
better chance to fully understand eventual page reference leaks: Report
up to 16 "normal" (writable or untyped) pages, and an unlimited number
of special type (page or descriptor table) ones.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
x86/LAPIC: drop support for non-integrated APIC

We never really supported such, even in the 32-bit days.

As a minor extra thing move the APIC_SELF_IPI definition out of the
middle of Divider Configuration Register ones.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
misc/coverity: Model __builtin_unreachable()

This resolves 23 issues Coverity had identified by following the false path of
an ASSERT().

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
x86/hvm: Forced Emulation Prefix for debug builds of Xen

Analysis of XSAs 105 and 106 show that is possible to force a race condition
which causes any arbitrary instruction to be emulated.

To aid testing, explicitly introduce the Forced Emulation Prefix for debug
builds alone.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
x86: define e820 entries counter as unsigned int

e820 entries counter is inherently an unsigned quantity
so define it as unsigned int.

Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
x86: use constant as multiboot protocol identifier

... instead of plain number.

Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
Reviewed-by: Andrew Cooper <andrew.cooper@citrix.com>