The previous implementation had several subtle issues.  It's not
clear if any of these could actually be causing the flakiness
problems on openbsd/386, but fixing them should only help.

1. thrsleep() is implemented internally as unlock, then test *abort
(if abort != nil), then tsleep().  Under the current code, that makes
it theoretically possible that semasleep()/thrsleep() could release
waitsemalock, then a racing semawakeup() could acquire the lock,
increment waitsemacount, and call thrwakeup()/wakeup() before
thrsleep() reaches tsleep().  (In practice, OpenBSD's big kernel lock
seems unlikely to let this actually happen.)

The proper way to avoid this is to pass &waitsemacount as the abort
pointer to thrsleep so thrsleep knows to re-check it before going to
sleep, and to wakeup if it's non-zero.  Then we avoid any races.
(I actually suspect openbsd's sema{sleep,wakeup}() could be further
simplified using cas/xadd instead of locks, but I don't want to be
more intrusive than necessary so late in the 1.4 release cycle.)

2. semasleep() takes a relative sleep duration, but thrsleep() needs
an absolute sleep deadline.  Instead of recomputing the deadline each
iteration, compute it once up front and use (*Timespec)(nil) to signify
no deadline.  Ensures we retry properly if there's a spurious wakeup.

3. Instead of assuming if thrsleep() woke up and waitsemacount wasn't
available that we must have hit the deadline, check that the system
call returned EWOULDBLOCK.

4. Instead of assuming that 64-bit systems are little-endian, compute
timediv() using a temporary int32 nsec and then assign it to tv_nsec.

LGTM=iant
R=jsing, iant
CC=golang-codereviews
https://golang.org/cl/137960043

A race exists between the parent and child processes after a fork.
The child needs to access the new M pointer passed as an argument
but the parent may have already returned and clobbered it.

Previously, we avoided this by saving the necessary data into
registers before the rfork system call but this isn't guaranteed
to work because Plan 9 makes no promises about the register state
after a system call. Only the 386 kernel seems to save them.
For amd64 and arm, this method won't work.

We eliminate the race by allocating stack space for the scheduler
goroutines (g0) in the per-process copy-on-write stack segment and
by only calling rfork on the scheduler stack.

LGTM=aram, 0intro, rsc
R=aram, 0intro, mischief, rsc
CC=golang-codereviews
https://golang.org/cl/110680044

Move timenow thunk into time.s
Move declarations for generic c/asm services into stubs.go

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/137360043

Fixes #8688

LGTM=rsc
R=golang-codereviews, bradfitz, rsc, khr
CC=golang-codereviews
https://golang.org/cl/135660043

The only thing I can see that is really Plan 9-specific
is that the stack pointer used for signal handling used
to have more mapped memory above it.
Specifically it used to have at most 88 bytes (StackTop),
so change the allocation of a 40-byte frame to a 128-byte frame.

No idea if this will work, but worth a try.

Note that "fix" here means get it back to timing out
instead of crashing.

TBR=iant
CC=golang-codereviews
https://golang.org/cl/142840043

The difference between the old and the new (from earlier) code
is that we set stackguard = stack.lo + StackGuard, while the old
code set stackguard = stack.lo. That 512 bytes appears to be
the difference between the profileloop function running and not running.

We don't know how big the system stack is, but it is likely MUCH bigger than 4k.
Give Go/C 8k.

TBR=iant
CC=golang-codereviews
https://golang.org/cl/140440044

Start the stack a few words below the actual top, so that
if something tries to read goexit's caller PC from the stack,
it won't fault on a bad memory address.
Today, heapdump does that.
Maybe tomorrow, traceback or something else will do that.
Make it not a bug.

TBR=khr
R=khr
CC=golang-codereviews
https://golang.org/cl/136450043

For -mode=atomic, we need to read the counters
using an atomic load to avoid a race. Not worth worrying
about when -mode=atomic is set during generation
of the profile, so we use atomic loads always.

Fixes #8630.

LGTM=rsc
R=dvyukov, rsc
CC=golang-codereviews
https://golang.org/cl/141800043

With new interface allocation rules, the old counts were wrong and
so was the commentary.

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/142760044

Space is not a control character.

Fixes #8571.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/137380043

No promise about correctness, but they do build.

TBR=khr
CC=golang-codereviews
https://golang.org/cl/143720043

Commit to stack copying for stack growth.

We're carrying around a surprising amount of cruft from older schemes.
I am confident that precise stack scans and stack copying are here to stay.

Delete fallback code for when precise stack info is disabled.
Delete fallback code for when copying stacks is disabled.
Delete fallback code for when StackCopyAlways is disabled.
Delete Stktop chain - there is only one stack segment now.
Delete M.moreargp, M.moreargsize, M.moreframesize, M.cret.
Delete G.writenbuf (unrelated, just dead).
Delete runtime.lessstack, runtime.oldstack.
Delete many amd64 morestack variants.
Delete initialization of morestack frame/arg sizes (shortens split prologue!).

Replace G's stackguard/stackbase/stack0/stacksize/
syscallstack/syscallguard/forkstackguard with simple stack
bounds (lo, hi).

Update liblink, runtime/cgo for adjustments to G.

LGTM=khr
R=khr, bradfitz
CC=golang-codereviews, iant, r
https://golang.org/cl/137410043

I have found better approach, then longer wait.
See CL 134360043 for details.

««« original CL description
runtime/pprof: adjust cpuHogger so that tests pass on windows builders

LGTM=rsc
R=dvyukov, rsc
CC=golang-codereviews
https://golang.org/cl/140110043

»»»

LGTM=dave
R=golang-codereviews, dave, dvyukov
CC=golang-codereviews
https://golang.org/cl/133500043

I assumed they were the same when I wrote
cgocallback.go earlier today. Merge them
to eliminate confusion.

I can't tell what gomallocgc did before with
a nil type but without FlagNoScan.
I created a call like that in cgocallback.go
this morning, translating from a C file.
It was supposed to do what the C version did,
namely treat the block conservatively.
Now it will.

LGTM=khr
R=khr
CC=golang-codereviews
https://golang.org/cl/141810043

It already is updating parts of them; we're just getting lucky
retraversing them and not finding much to do.
Change argp to a pointer so that it will be updated too.
Existing tests break if you apply the change to adjustpanics
without also updating the type of argp.

LGTM=khr
R=khr
CC=golang-codereviews
https://golang.org/cl/139380043

Like https://golang.org/cl/139360044

LGTM=rsc, alex.brainman
R=alex.brainman, rsc
CC=golang-codereviews
https://golang.org/cl/138250043

This change brings the iter/delete pattern down to O(n lgn) from O(n^2).

Fixes #8412.

before:
BenchmarkMapPop100	   50000	     32498 ns/op
BenchmarkMapPop1000	     500	   3244851 ns/op
BenchmarkMapPop10000	       5	 270276855 ns/op

after:
BenchmarkMapPop100	  100000	     16169 ns/op
BenchmarkMapPop1000	    5000	    300416 ns/op
BenchmarkMapPop10000	     300	   5990814 ns/op

LGTM=iant
R=golang-codereviews, iant, khr
CC=golang-codereviews
https://golang.org/cl/141270043

src/pkg -> src

LGTM=alex.brainman
R=alex.brainman
CC=golang-codereviews
https://golang.org/cl/139400043

It worked at CL 134660043 on the builders,
so I believe it will stick this time.

LGTM=bradfitz
R=khr, bradfitz
CC=golang-codereviews
https://golang.org/cl/141280043

Generated by a+c.

LGTM=jtolds, jbd
R=gobot, jbd, jtolds
CC=golang-codereviews
https://golang.org/cl/137300043

LGTM=bradfitz
R=dave, bradfitz
CC=golang-codereviews
https://golang.org/cl/136390043

Fixes #8679.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/141730043

windows/amd64 failure:
http://build.golang.org/log/1ded5e3ef4bd1226f976e3180772f87e6c918255

# ..\misc\cgo\testso
runtime: copystack: locals size info only for syscall.Syscall
fatal error: split stack not allowed

runtime stack:
runtime.throw(0xa64cc7)
        c:/go/src/runtime/panic.go:395 +0xad fp=0x6fde0 sp=0x6fdb0
runtime.newstack()
        c:/go/src/runtime/stack.c:1001 +0x750 fp=0x6ff20 sp=0x6fde0
runtime.morestack()
        c:/go/src/runtime/asm_amd64.s:306 +0x73 fp=0x6ff28 sp=0x6ff20

goroutine 1 [stack growth, locked to thread]:
runtime.freedefer(0xc0820ce120)
        c:/go/src/runtime/panic.go:162 fp=0xc08201b1a0 sp=0xc08201b198
runtime.deferreturn(0xa69420)
        c:/go/src/runtime/panic.go:211 +0xa8 fp=0xc08201b1e8 sp=0xc08201b1a0
runtime.cgocall_errno(0x498c00, 0xc08201b228, 0x0)
        c:/go/src/runtime/cgocall.go:134 +0x10e fp=0xc08201b210 sp=0xc08201b1e8
syscall.Syscall(0x7786b1d0, 0x2, 0xc0820c85b0, 0xc08201b2d8, 0x0, 0x0, 0x0, 0x0)
        c:/go/src/runtime/syscall_windows.c:74 +0x3c fp=0xc08201b260 sp=0xc08201b210
syscall.findFirstFile1(0xc0820c85b0, 0xc08201b2d8, 0x500000000000000, 0x0, 0x0)
        c:/go/src/syscall/zsyscall_windows.go:340 +0x76 fp=0xc08201b2b0 sp=0xc08201b260
syscall.FindFirstFile(0xc0820c85b0, 0xc08210c500, 0xc0820c85b0, 0x0, 0x0)
        c:/go/src/syscall/syscall_windows.go:907 +0x6a fp=0xc08201b530 sp=0xc08201b2b0
os.openDir(0xc0820b2e40, 0x33, 0x0, 0x0, 0x0)
        c:/go/src/os/file_windows.go:96 +0x110 fp=0xc08201b5e0 sp=0xc08201b530
os.OpenFile(0xc0820b2e40, 0x33, 0x0, 0x0, 0x41, 0x0, 0x0)
        c:/go/src/os/file_windows.go:143 +0x1e9 fp=0xc08201b650 sp=0xc08201b5e0

TBR=khr
CC=golang-codereviews
https://golang.org/cl/138230043

Should help windows/amd64.

TBR=khr
CC=golang-codereviews
https://golang.org/cl/134660043

Inside a control clause (if ... {}), composite
literals starting with a type name must be parenthesized.
A composite literal used in the array length expression
of an array composite literal is already parenthesized.
Not a valid program, but syntactically is should
be accepted.

LGTM=adonovan
R=adonovan
CC=golang-codereviews
https://golang.org/cl/142760043

This should make deferreturn nosplit all the way down,
which should fix the current windows/amd64 failure.
If not, I will change StackCopyAlways back to 0.

TBR=khr
CC=golang-codereviews
https://golang.org/cl/135600043

Fixes #8674.

LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/139320044

Let's see how close we are to this being ready.
Will roll back if it breaks any builds in non-trivial ways.

LGTM=r, khr
R=iant, khr, r
CC=golang-codereviews
https://golang.org/cl/138200043

Was having serious editor problems on Windows.

TBR=brainman, iant
CC=golang-codereviews
https://golang.org/cl/137370043

Given:

        p := alloc()
        fn_taking_ptr(p)

p is NOT recorded as live at the call to fn_taking_ptr:
it's not needed by the code following the call.
p was passed to fn_taking_ptr, and fn_taking_ptr must keep
it alive as long as it needs it.
In practice, fn_taking_ptr will keep its own arguments live
for as long as the function is executing.

But if instead you have:

        p := alloc()
        i := uintptr(unsafe.Pointer(p))
        fn_taking_int(i)

p is STILL NOT recorded as live at the call to fn_taking_int:
it's not needed by the code following the call.
fn_taking_int is responsible for keeping its own arguments
live, but fn_taking_int is written to take an integer, so even
though fn_taking_int does keep its argument live, that argument
does not keep the allocated memory live, because the garbage
collector does not dereference integers.

The shorter form:

        p := alloc()
        fn_taking_int(uintptr(unsafe.Pointer(p)))

and the even shorter form:

        fn_taking_int(uintptr(unsafe.Pointer(alloc())))

are both the same as the 3-line form above.

syscall.Syscall is like fn_taking_int: it is written to take a list
of integers, and yet those integers are sometimes pointers.
If there is no other copy of those pointers being kept live,
the memory they point at may be garbage collected during
the call to syscall.Syscall.

This is happening on Solaris: for whatever reason, the timing
is such that the garbage collector manages to free the string
argument to the open(2) system call before the system call
has been invoked.

Change the system call wrappers to insert explicit references
that will keep the allocations alive in the original frame
(and therefore preserve the memory) until after syscall.Syscall
has returned.

Should fix Solaris flakiness.

This is not a problem for cgo, because cgo wrappers have
correctly typed arguments.

LGTM=iant, khr, aram, rlh
R=iant, khr, bradfitz, aram, rlh
CC=dvyukov, golang-codereviews, r
https://golang.org/cl/139360044

The sighander has been run at the bottom of the
currently executing goroutine stack, but it's in C,
and we don't want C on our ordinary goroutine stacks.
Worse, it does a lot of stuff, and it might need more
stack space. There is scary code in traceback_windows.go
that talks about stack splits during sighandler.
Moving sighandler to g0 will eliminate the possibility
of stack splits and such, and then we can delete
traceback_windows.go entirely. Win win.

On the builder, all.bat passes with GOARCH=amd64
and all.bat gets most of the way with GOARCH=386
except for a DLL-loading test that I think is unrelated.

Fixes windows build.

TBR=brainman, iant
CC=golang-codereviews
https://golang.org/cl/140380043

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/139370043

This CL contains compiler+runtime changes that detect C code
running on Go (not g0, not gsignal) stacks, and it contains
corrections for what it detected.

The detection works by changing the C prologue to use a different
stack guard word in the G than Go prologue does. On the g0 and
gsignal stacks, that stack guard word is set to the usual
stack guard value. But on ordinary Go stacks, that stack
guard word is set to ^0, which will make any stack split
check fail. The C prologue then calls morestackc instead
of morestack, and morestackc aborts the program with
a message about running C code on a Go stack.

This check catches all C code running on the Go stack
except NOSPLIT code. The NOSPLIT code is allowed,
so the check is complete. Since it is a dynamic check,
the code must execute to be caught. But unlike the static
checks we've been using in cmd/ld, the dynamic check
works with function pointers and other indirect calls.
For example it caught sigpanic being pushed onto Go
stacks in the signal handlers.

Fixes #8667.

LGTM=khr, iant
R=golang-codereviews, khr, iant
CC=golang-codereviews, r
https://golang.org/cl/133700043

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/134630043

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/142740043

Fixes warning

# _/home/dfc/go/misc/cgo/test/backdoor
/home/dfc/go/src/cmd/cc/bv.c:43:11: runtime error: left shift of 1 by 31 places cannot be represented in type 'int'

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/136330043

Fixes warning

/home/dfc/go/src/cmd/gc/subr.c:3469:8: runtime error: negation of -9223372036854775808 cannot be represented in type 'int64' (aka 'long'); cast to an unsigned type to negate this value to itself

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/141220043

CC=golang-codereviews
https://golang.org/cl/139310043

These were missed in CL 134570043.

Fixes nacl, solaris builds.

TBR=r
CC=golang-codereviews
https://golang.org/cl/136320043

Preparation was in CL 134570043.
This CL contains only the effect of 'hg mv src/pkg/* src'.
For more about the move, see golang.org/s/go14nopkg.