runtime: a few cleanups.

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/134630043
liblink, runtime: diagnose and fix C code running on Go stack

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 issue 8667.

LGTM=khr, iant
R=golang-codereviews, khr, iant
CC=golang-codereviews, r
https://codereview.appspot.com/133700043
runtime: merge panic1.go back into panic.go

LGTM=rsc
R=rsc
CC=golang-codereviews
https://codereview.appspot.com/139370043
runtime: run sighandler on g0 stack on windows

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://codereview.appspot.com/140380043
syscall: keep allocated C string live across call to Syscall

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://codereview.appspot.com/139360044
runtime: undo stray edit from CL 140380043

Was having serious editor problems on Windows.

TBR=brainman, iant
CC=golang-codereviews
https://codereview.appspot.com/137370043
runtime: enable StackCopyAlways

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://codereview.appspot.com/138200043
doc: amend installation instructions

Fixes issue 8674.

LGTM=r
R=r
CC=golang-codereviews
https://codereview.appspot.com/139320044
runtime: mark freedefer and deferclass go:nosplit

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://codereview.appspot.com/135600043
go/parser: fix (pathological) corner case

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://codereview.appspot.com/142760043
runtime: mark endcgo go:nosplit

Should help windows/amd64.

TBR=khr
CC=golang-codereviews
https://codereview.appspot.com/134660043
runtime: turn off StackCopyAlways

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://codereview.appspot.com/138230043
net: don't set wrong option for controlling tcp keepalive on openbsd

Fixes issue 8679.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://codereview.appspot.com/141730043
runtime: note the double-releasem isn't an error.

LGTM=bradfitz
R=dave, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/136390043
A+C: John Olds (individual CLA)

Generated by a+c.

LGTM=jtolds, jbd
R=gobot, jbd, jtolds
CC=golang-codereviews
https://codereview.appspot.com/137300043
runtime: enable StackCopyAlways

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://codereview.appspot.com/141280043
syscall: fix comment in mkall_windows.bat

src/pkg -> src

LGTM=alex.brainman
R=alex.brainman
CC=golang-codereviews
https://codereview.appspot.com/139400043
runtime: on bigger maps, start iterator at a random bucket.

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

Fixes issue 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://codereview.appspot.com/141270043
syscall: keep Windows syscall pointers live too

Like https://codereview.appspot.com/139360044

LGTM=rsc, alex.brainman
R=alex.brainman, rsc
CC=golang-codereviews
https://codereview.appspot.com/138250043
runtime: let stack copier update Panic structs for us

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://codereview.appspot.com/139380043