MFC: r306318

Allocate a zeroed LDT.

Failing to do this might result in the LDT appearing to run out of free
descriptors because of random junk in the descriptor's 'sd_type' field.

http://lists.freebsd.org/pipermail/freebsd-amd64/2014-May/016088.html

PR: 212639
Submitted by: wheelcomplex@gmail.com

MFC r300305, r300332:
Check for overflow and return EINVAL if detected. Use unsigned index.

MFC 291947:
Set %esp correctly in the extended TSS.

The pcb is saved at the top of the kernel stack on x86 platforms.
The initial kenrel stack pointer is set in the TSS so that the trapframe
from user -> kernel transitions begins directly below the pcb and grows
down.

The XSAVE changes moved the FPU save area out of the pcb and into a
variable-sized area after the pcb. This required updating the expressions
to calculate the initial stack pointer from 'stacktop - sizeof(pcb)' to
'stacktop - sizeof(pcb) + FPU save area size'.

The i386_set_ioperm() system call allows user applications to access
individual I/O ports via the I/O port permission bitmap in the TSS.
On FreeBSD this requires allocating a custom per-process TSS instead of
using the shared per-CPU TSS.

The expression to initialize the initial kernel stack pointer in the
per-process TSS created for i386_set_ioperm() was not properly updated
after the XSAVE changes. Processes that used i386_set_ioperm() would
trash the trapframe during subsequent context switches resulting in
panics from memory corruption.

This changes fixes the kernel stack pointer calculation for the per-process
TSS.

Implement x86 ptrace(2) requests PT_{GET,SET}{FS,GS}BASE.

MFC r284918:
Add helper fill_based_sd(9).

MFC r284919:
Add x86 PT_GETFSBASE, PT_GETGSBASE machine-depended ptrace requests to
obtain the thread %fs and %gs bases. Add x86 PT_SETFSBASE and
PT_SETGSBASE requests to set the bases from debuggers. The set
requests, similarly to the sysarch({I386,AMD64}_SET_FSBASE), override
the corresponding segment registers.

MFC r284965:
Document x86 machine-specific ptrace(2) requests.

MFC r285011:
Disallow a debugger on 64bit system to set fs/gs bases of the 32bit
process beyond the end of the process address space.

MFC r285104:
Grammar and language fixes.

Merge r263233 from HEAD to stable/10:

Update kernel inclusions of capability.h to use capsicum.h instead; some
further refinement is required as some device drivers intended to be
portable over FreeBSD versions rely on __FreeBSD_version to decide whether
to include capability.h.

Sponsored by: Google, Inc.

MFC 273988,273989,273995,274057:
MFamd64: Add support for extended FPU states on i386. This includes
support for AVX on i386.

MFC r267492:
Fix some cosmetic issues with the use of kmem_malloc() in the i386 LDT
sysarch(2) code.

Implement x86 ptrace(2) requests PT_{GET,SET}{FS,GS}BASE.

MFC r284918:
Add helper fill_based_sd(9).

MFC r284919:
Add x86 PT_GETFSBASE, PT_GETGSBASE machine-depended ptrace requests to
obtain the thread %fs and %gs bases. Add x86 PT_SETFSBASE and
PT_SETGSBASE requests to set the bases from debuggers. The set
requests, similarly to the sysarch({I386,AMD64}_SET_FSBASE), override
the corresponding segment registers.

MFC r284965:
Document x86 machine-specific ptrace(2) requests.

MFC r285011:
Disallow a debugger on 64bit system to set fs/gs bases of the 32bit
process beyond the end of the process address space.

MFC r285104:
Grammar and language fixes.

Merge r263233 from HEAD to stable/10:

Update kernel inclusions of capability.h to use capsicum.h instead; some
further refinement is required as some device drivers intended to be
portable over FreeBSD versions rely on __FreeBSD_version to decide whether
to include capability.h.

Sponsored by: Google, Inc.

MFC 273988,273989,273995,274057:
MFamd64: Add support for extended FPU states on i386. This includes
support for AVX on i386.

MFC r267492:
Fix some cosmetic issues with the use of kmem_malloc() in the i386 LDT
sysarch(2) code.