savectx() is only used for panic dump (dumppcb) and kdb (stoppcbs). Thus,
saving additional information does not hurt and it may be even beneficial.
Unfortunately, struct pcb has grown larger to accommodate more data.
Move 512-byte long pcb_user_save to the end of struct pcb while I am here.
- savectx() now saves FPU state unconditionally and copy it to the PCB of
FPU thread if necessary. This gives panic dump and kdb a chance to take
a look at the current FPU state even if the FPU is "supposedly" not used.
- Resuming CPU now unconditionally reinitializes FPU. If the saved FPU
state was irrelevant, it could be in an unknown state.
Suggested by: bde [1]
the kernel on amd64. Fill and read segment registers for mcontext and
signals. Handle traps caused by restoration of the
invalidated selectors.
Implement user-mode creation and manipulation of the process-specific
LDT descriptors for amd64, see sysarch(2).
Implement support for TSS i/o port access permission bitmap for amd64.
Context-switch LDT and TSS. Do not save and restore segment registers on
the context switch, that is handled by kernel enter/leave trampolines
now. Remove segment restore code from the signal trampolines for
freebsd/amd64, freebsd/ia32 and linux/i386 for the same reason.
Implement amd64-specific compat shims for sysarch.
Linuxolator (temporary ?) switched to use gsbase for thread_area pointer.
TODO:
Currently, gdb is not adapted to show segment registers from struct reg.
Also, no machine-depended ptrace command is added to set segment
registers for debugged process.
In collaboration with: pho
Discussed with: peter
Reviewed by: jhb
Linuxolator tested by: dchagin
This code is heavily inspired by Takanori Watanabe's experimental SMP patch
for i386 and large portion was shamelessly cut and pasted from Peter Wemm's
AP boot code.
