Eliminate code for gs trick to track per-cpu state. We rely on lapiccpunum()
to find a per-cpu id with which we locate a cpu's cpu struct.

Read curproc from cpu structure, but be careful because after a schedule event
myproc() points to a different thread.

myproc();
sched();
myproc(); // this proc maybe different than the one

Read curproc from cpu structure, but be careful because after a schedule event
myproc() points to a different thread.

myproc();
sched();
myproc(); // this proc maybe different than the one before sched

Thus, in a function that operates on one thread better to retrieve the
current process once at the start of the function.

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Start of an experiment to remove the use of gs for cpu local variables.

APIC IDs may not be consecutive and start from zero, so we cannot really use it
as a direct index into cpus. Record apicid in struct cpu and have cpunum() look
for it. Replace cpu->id with cpunum()

APIC IDs may not be consecutive and start from zero, so we cannot really use it
as a direct index into cpus. Record apicid in struct cpu and have cpunum() look
for it. Replace cpu->id with cpunum() everywhere, and replace cpu->id with cpu->apicid.
Thanks to Xi Wang.

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Remove trailing white space with:
for f in *.{h,c}; do sed -i .sed 's/[[:blank:]]*$//' $f; done
(Thanks to Nicolás Wolovick)

tiny clarifications to some gdt code.

use acquire/release to force order for pid=np->pid;np->state=RUNNING
for bug reported by symingz@gmail.com and cs1100254@cse.iitd.ernet.in

junk

Avoid "boot" in xv6

One definition of several macros and constants

change some comments, maybe more informative
delete most comments from bootother.S (since copy of bootasm.S)
ksegment() -> seginit()
move more stuff from main() to mainc()

Rearrange proc.h and proc.c to get our action-packed spreads back (mostly). They also make sense in this order, so it's not just for page layout.

Oops, missed a comment about the stack guard

fix corner cases in exec of ELF
put an invalid page below the stack
have fork() handle invalid pages

add some comments
find out the hard way why user and kernel must have separate segment descriptors

Initial version of single-cpu xv6 with page tables

fine-tune comment

fine tune comment

another attempt at cpu-local variables.
this time do it ourselves instead of piggybacking on TLS.
add -fno-pic to Makefile; pic code breaks our fake TLS.

fix TLS again;
still not quite but a lot better.

Fix TLS for PIC systems

assorted fixes:
* rename c/cp to cpu/proc
* rename cpu.context to cpu.scheduler
* fix some comments
* formatting for printout

group locks into structs they protect.
few naming nits.

tab police

Some proc cleanup, moving some of copyproc into allocproc.

Also, an experiment: use "thread-local" storage for c and cp
instead of the #define macro for curproc[cpu()].