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.

This CL adjusts code referring to src/pkg to refer to src.

Immediately after submitting this CL, I will submit
a change doing 'hg mv src/pkg/* src'.
That change will be too large to review with Rietveld
but will contain only the 'hg mv'.

This CL will break the build.
The followup 'hg mv' will fix it.

For more about the move, see golang.org/s/go14nopkg.

LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/134570043

CC=golang-codereviews
https://golang.org/cl/132670045

Per discussions out of https://golang.org/cl/128930043/
and golang-nuts threads and with agl.

Fixes #8522

LGTM=agl, adg
R=agl, c, adg
CC=c, golang-codereviews
https://golang.org/cl/137940043

These all used a C implementation that contained 64-bit divide by 1000000000.
On 32-bit systems that ends up in the 64-bit C divide support, which makes
other calls and ends up using a fair amount of stack. We could convert them
to Go but then they'd still end up in software 64-bit divide code. That would
be okay, because Go code can split the stack, but it's still unnecessary.

Write time·now in assembly, just like on all the other systems, and use the
actual hardware support for 64/32 -> 64/32 division. This cuts the software
routines out entirely.

The actual code to do the division is copied and pasted from the sys_darwin_*.s files.

LGTM=alex.brainman
R=golang-codereviews, alex.brainman
CC=aram, golang-codereviews, iant, khr, r
https://golang.org/cl/136300043

Now it's failing on Windows:

panic: httptest: failed to listen on a port: listen tcp 127.0.0.1:0:
listen: An operation on a socket could not be performed because the
system lacked sufficient buffer space or because a queue was full.

Since we can't seem to understand what the test is trying to test,
and because it is causing problems on multiple systems,
delete it.

Fixes #7264.

TBR=bradfitz
CC=brainman, golang-codereviews
https://golang.org/cl/141210043

This is what broke the build at
http://build.golang.org/log/d9c6d334be16cbab85e99fddc6b4ba034319bd4e

LGTM=iant
R=golang-codereviews, iant
CC=dvyukov, golang-codereviews, khr, r
https://golang.org/cl/135580043

I am seeing deadlocks waiting on <-inHandler.
It seems to me that there is no guarantee that the
handler actually runs, if the client does

        write header
        close connection

fast enough. The server might see the EOF on the
connection before it manages to invoke the handler.

This change fixes the deadlock, but it may make
the test not actually test anything. Not sure.

LGTM=bradfitz
R=bradfitz, dvyukov
CC=golang-codereviews
https://golang.org/cl/140970043

This is one of those "how did this ever work?" bugs.
The current build failures are happening because
a fault comes up while executing on m->curg on a
system-created thread using an m obtained from needm,
but TLS is set to m->g0, not m->curg. On fault,
sigtramp starts executing, assumes r10 (g) might be
incorrect, reloads it from TLS, and gets m->g0, not
m->curg. Then sighandler dutifully pushes a call to
sigpanic onto the stack and returns to it.
We're now executing on the m->curg stack but with
g=m->g0. Sigpanic does a stack split check, sees that
the SP is not in range (50% chance depending on relative
ordering of m->g0's and m->curg's stacks), and then
calls morestack. Morestack sees that g=m->g0 and
crashes the program.

The fix is to replace every change of g in asm_arm.s
with a call to a function that both updates g and
saves the updated g to TLS.

Why did it start happening? That's unclear.
Unfortunately there were other bugs in the initial
checkin that mask exactly which of a sequence of
CLs started the behavior where sigpanic would end
up tripping the stack split.

Fixes arm build.
Fixes #8675.

LGTM=iant
R=golang-codereviews, iant
CC=dave, golang-codereviews, khr, minux, r
https://golang.org/cl/135570043

Maybe will help us understand Solaris build failure.

TBR=aram
CC=golang-codereviews
https://golang.org/cl/139290043

Fixes arm build.

TBR=khr
CC=golang-codereviews
https://golang.org/cl/132700043

The Unix make.bash builds cmd/dist from *.c.
make.bat apparently does not.

TBR=r
CC=golang-codereviews
https://golang.org/cl/137280043

After the three pending CLs listed below, there will be no more .goc files.

134580043	runtime: move stubs.goc code into runtime.c
133670043	runtime: fix windows syscalls for copying stacks
141180043	runtime: eliminate Go -> C -> block paths for Solaris

LGTM=bradfitz
R=golang-codereviews, bradfitz, dave
CC=golang-codereviews, iant, r
https://golang.org/cl/132680043

Update #8675
Fixes nacl/amd64p32 build.

TBR=khr
CC=golang-codereviews
https://golang.org/cl/141140045

Syscall and everything it calls must be nosplit:
we cannot split a stack once Syscall has been invoked,
because we don't know which of its arguments are
pointers.

LGTM=khr, r, alex.brainman
R=dvyukov, iant, khr, r, bradfitz, alex.brainman
CC=golang-codereviews
https://golang.org/cl/133670043

LGTM=aram, r
R=golang-codereviews, aram, r
CC=golang-codereviews, iant, khr
https://golang.org/cl/141180043

Increase NOSPLIT reservation from 192 to 384 bytes.
The problem is that the non-Unix systems (Solaris and Windows)
just can't make system calls in a small amount of space,
and then worse they do things that are complex enough
to warrant calling runtime.throw on failure.
We don't have time to rewrite the code to use less stack.

I'm not happy about this, but it's still a small amount.

The good news is that we're doing this to get to only
using copying stacks for stack growth. Once that is true,
we can drop the default stack size from 8k to 4k, which
should more than make up for the bytes we're losing here.

LGTM=r
R=iant, r, bradfitz, aram.h
CC=golang-codereviews
https://golang.org/cl/140350043

LGTM=bradfitz
R=adg, bradfitz, minux
CC=golang-codereviews
https://golang.org/cl/140310045

This will keep the go command from trying to build it
when the cmd/ tree is no longer a special case.

Also update doc.go to refer to the correct location.
(It was incorrect even before this CL.)

LGTM=r
R=iant, r
CC=golang-codereviews
https://golang.org/cl/134560043

This will withstand the src/pkg/ to src/ move.

LGTM=r
R=iant, r
CC=golang-codereviews
https://golang.org/cl/134530044

Now that the calling conventions are the same,
there's no danger to using plain C for these.

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=dvyukov, golang-codereviews, iant, khr, r
https://golang.org/cl/134580043

This was supposed to be in CL 135490044
but got lost in a transfer from machine to machine.

TBR=khr
R=khr
CC=golang-codereviews
https://golang.org/cl/135560043

LGTM=dave, rsc
R=khr, dvyukov, dave, gobot, rsc
CC=golang-codereviews, rsc
https://golang.org/cl/133220044

The gp->panicwrap adjustment is just fatally flawed.
Now that there is a Panic.argp field, update that instead.
That can be done on entry only, so that unwinding doesn't
need to worry about undoing anything. The wrappers
emit a few more instructions in the prologue but everything
else in the system gets much simpler.

It also fixes (without trying) a broken test I never checked in.

Fixes #7491.

LGTM=khr
R=khr
CC=dvyukov, golang-codereviews, iant, r
https://golang.org/cl/135490044

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/136260043

testSchedLocal* tests need to malloc now because their
stack frames are too big to fit on the G0 stack.

LGTM=iant
R=golang-codereviews, iant, khr
CC=golang-codereviews
https://golang.org/cl/133660043

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/141150043

LGTM=rsc
R=rsc, khr
CC=golang-codereviews
https://golang.org/cl/132660043

I forgot to clear this before submitting.

TBR=khr
CC=golang-codereviews
https://golang.org/cl/132640044

newstackcall creates a new stack segment, and we want to
be able to throw away all that code.

LGTM=khr
R=khr, iant
CC=dvyukov, golang-codereviews, r
https://golang.org/cl/139270043