In external linking mode, the linker automatically imports
runtime/cgo.  When the user uses non-standard compilation options,
they have to know to run go install runtime/cgo.  When the go tool
adds non-standard compilation options itself, we can't force the user
to do that.  So add the dependency ourselves.

Bad news: we don't currently have a clean way to know whether we are
going to use external linking mode.  This CL duplicates logic split
between cmd/6l and cmd/internal/ld.

Good news: adding an unnecessary dependency on runtime/cgo does no
real harm.  We aren't going to force the linker to pull it in, we're
just going to build it so that its available if the linker wants it.

Change-Id: Ide676339d4e8b1c3d9792884a2cea921abb281b7
Reviewed-on: https://go-review.googlesource.com/9115Reviewed-by: David Crawshaw <crawshaw@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>

This change refactors reflect.Value to consistently use arrayAt when an element
of an array of bytes is indexed.

This effectively replaces:
 arr := unsafe.Pointer(...)
 arri := unsafe.Pointer(uintptr(arr) + uintptr(i)*elementSize)

with:
 arr := unsafe.Pointer(...)
 arri := arrayAt(arr, i, elementSize)

Change-Id: I53ffd0d6de693b43d5c10c0aa4cd6d4f5e95a1e3
Reviewed-on: https://go-review.googlesource.com/9183Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

This reduces the number of allocations in the compiler
while building the stdlib by 15.66%.

No functional changes. Passes toolstash -cmp.

Change-Id: Ia21b37134a8906a4e23d53fdc15235b4aa7bbb34
Reviewed-on: https://go-review.googlesource.com/9085Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Change-Id: I89704249218d4fdba11463c239c69143f8ad0051
Reviewed-on: https://go-review.googlesource.com/9185Reviewed-by: Ian Lance Taylor <iant@golang.org>

Currently, the GC controller computes the mutator assist ratio at the
beginning of the cycle by estimating that the marked heap size this
cycle will be the same as it was the previous cycle. It then uses that
assist ratio for the rest of the cycle. However, this means that if
the mutator is quickly growing its reachable heap, the heap size is
likely to exceed the heap goal and currently there's no additional
pressure on mutator assists when this happens. For example, 6g (with
GOMAXPROCS=1) frequently exceeds the goal heap size by ~25% because of
this.

This change makes GC revise its work estimate and the resulting assist
ratio every 10ms during the concurrent mark. Instead of
unconditionally using the marked heap size from the last cycle as an
estimate for this cycle, it takes the minimum of the previously marked
heap and the currently marked heap. As a result, as the cycle
approaches or exceeds its heap goal, this will increase the assist
ratio to put more pressure on the mutator assist to bring the cycle to
an end. For 6g, this causes the GC to always finish within 5% and
often within 1% of its heap goal.

Change-Id: I4333b92ad0878c704964be42c655c38a862b4224
Reviewed-on: https://go-review.googlesource.com/9070Reviewed-by: Rick Hudson <rlh@golang.org>
Run-TryBot: Austin Clements <austin@google.com>

Currently, in accordance with the GC pacing proposal, we schedule
background marking with a goal of achieving 25% utilization *total*
between mutator assists and background marking. This is stricter than
was set out in the Go 1.5 proposal, which suggests that the garbage
collector can use 25% just for itself and anything the mutator does to
help out is on top of that. It also has several technical
drawbacks. Because mutator assist time is constantly changing and we
can't have instantaneous information on background marking time, it
effectively requires hitting a moving target based on out-of-date
information. This works out in the long run, but works poorly for
short GC cycles and on short time scales. Also, this requires
time-multiplexing all Ps between the mutator and background GC since
the goal utilization of background GC constantly fluctuates. This
results in a complicated scheduling algorithm, poor affinity, and
extra overheads from context switching.

This change modifies the way we schedule and run background marking so
that background marking always consumes 25% of GOMAXPROCS and mutator
assist is in addition to this. This enables a much more robust
scheduling algorithm where we pre-determine the number of Ps we should
dedicate to background marking as well as the utilization goal for a
single floating "remainder" mark worker.

Change-Id: I187fa4c03ab6fe78012a84d95975167299eb9168
Reviewed-on: https://go-review.googlesource.com/9013Reviewed-by: Rick Hudson <rlh@golang.org>

Currently, the concurrent sweep follows a 1:1 rule: when allocation
needs a span, it sweeps a span (likewise, when a large allocation
needs N pages, it sweeps until it frees N pages). This rule worked
well for the STW collector (especially when GOGC==100) because it did
no more sweeping than necessary to keep the heap from growing, would
generally finish sweeping just before GC, and ensured good temporal
locality between sweeping a page and allocating from it.

It doesn't work well with concurrent GC. Since concurrent GC requires
starting GC earlier (sometimes much earlier), the sweep often won't be
done when GC starts. Unfortunately, the first thing GC has to do is
finish the sweep. In the mean time, the mutator can continue
allocating, pushing the heap size even closer to the goal size. This
worked okay with the 7/8ths trigger, but it gets into a vicious cycle
with the GC trigger controller: if the mutator is allocating quickly
and driving the trigger lower, more and more sweep work will be left
to GC; this both causes GC to take longer (allowing the mutator to
allocate more during GC) and delays the start of the concurrent mark
phase, which throws off the GC controller's statistics and generally
causes it to push the trigger even lower.

As an example of a particularly bad case, the garbage benchmark with
GOMAXPROCS=4 and -benchmem 512 (MB) spends the first 0.4-0.8 seconds
of each GC cycle sweeping, during which the heap grows by between
109MB and 252MB.

To fix this, this change replaces the 1:1 sweep rule with a
proportional sweep rule. At the end of GC, GC knows exactly how much
heap allocation will occur before the next concurrent GC as well as
how many span pages must be swept. This change computes this "sweep
ratio" and when the mallocgc asks for a span, the mcentral sweeps
enough spans to bring the swept span count into ratio with the
allocated byte count.

On the benchmark from above, this entirely eliminates sweeping at the
beginning of GC, which reduces the time between startGC readying the
GC goroutine and GC stopping the world for sweep termination to ~100µs
during which the heap grows at most 134KB.

Change-Id: I35422d6bba0c2310d48bb1f8f30a72d29e98c1af
Reviewed-on: https://go-review.googlesource.com/8921Reviewed-by: Rick Hudson <rlh@golang.org>

This field used to decrease with sweeps (and potentially go
negative). Now it is always zero or positive, so change it to a
uintptr so it meshes better with other memory stats.

Change-Id: I6a50a956ddc6077eeaf92011c51743cb69540a3c
Reviewed-on: https://go-review.googlesource.com/8899Reviewed-by: Rick Hudson <rlh@golang.org>

Currently, concurrent GC triggers at a fixed 7/8*GOGC heap growth. For
mutators that allocate slowly, this means GC will trigger too early
and run too often, wasting CPU time on GC. For mutators that allocate
quickly, this means GC will trigger too late, causing the program to
exceed the GOGC heap growth goal and/or to exceed CPU goals because of
a high mutator assist ratio.

This change adds a feedback control loop to dynamically adjust the GC
trigger from cycle to cycle. By monitoring the heap growth and GC CPU
utilization from cycle to cycle, this adjusts the Go garbage collector
to target the GOGC heap growth goal and the 25% CPU utilization goal.

Change-Id: Ic82eef288c1fa122f73b69fe604d32cbb219e293
Reviewed-on: https://go-review.googlesource.com/8851Reviewed-by: Rick Hudson <rlh@golang.org>

Currently, the concurrent mark phase is performed by the main GC
goroutine. Prior to the previous commit enabling preemption, this
caused marking to always consume 1/GOMAXPROCS of the available CPU
time. If GOMAXPROCS=1, this meant background GC would consume 100% of
the CPU (effectively a STW). If GOMAXPROCS>4, background GC would use
less than the goal of 25%. If GOMAXPROCS=4, background GC would use
the goal 25%, but if the mutator wasn't using the remaining 75%,
background marking wouldn't take advantage of the idle time. Enabling
preemption in the previous commit made GC miss CPU targets in
completely different ways, but set us up to bring everything back in
line.

This change replaces the fixed GC goroutine with per-P background mark
goroutines. Once started, these goroutines don't go in the standard
run queues; instead, they are scheduled specially such that the time
spent in mutator assists and the background mark goroutines totals 25%
of the CPU time available to the program. Furthermore, this lets
background marking take advantage of idle Ps, which significantly
boosts GC performance for applications that under-utilize the CPU.

This requires also changing how time is reported for gctrace, so this
change splits the concurrent mark CPU time into assist/background/idle
scanning.

This also requires increasing the size of the StackRecord slice used
in a GoroutineProfile test.

Change-Id: I0936ff907d2cee6cb687a208f2df47e8988e3157
Reviewed-on: https://go-review.googlesource.com/8850Reviewed-by: Rick Hudson <rlh@golang.org>

Currently, the entire GC process runs with g.m.preemptoff set. In the
concurrent phases, the parts that actually need preemption disabled
are run on a system stack and there's no overall need to stay on the
same M or P during the concurrent phases. Hence, move the setting of
g.m.preemptoff to when we start mark termination, at which point we
really do need preemption disabled.

This dramatically changes the scheduling behavior of the concurrent
mark phase. Currently, since this is non-preemptible, concurrent mark
gets one dedicated P (so 1/GOMAXPROCS utilization). With this change,
the GC goroutine is scheduled like any other goroutine during
concurrent mark, so it gets 1/<runnable goroutines> utilization.

You might think it's not even necessary to set g.m.preemptoff at that
point since the world is stopped, but stackalloc/stackfree use this as
a signal that the per-P pools are not safe to access without
synchronization.

Change-Id: I08aebe8179a7d304650fb8449ff36262b3771099
Reviewed-on: https://go-review.googlesource.com/8839Reviewed-by: Rick Hudson <rlh@golang.org>

This time is tracked per P and periodically flushed to the global
controller state. This will be used to compute mutator assist
utilization in order to schedule background GC work.

Change-Id: Ib94f90903d426a02cf488bf0e2ef67a068eb3eec
Reviewed-on: https://go-review.googlesource.com/8837Reviewed-by: Rick Hudson <rlh@golang.org>

Currently, mutator allocation periodically assists the garbage
collector by performing a small, fixed amount of scanning work.
However, to control heap growth, mutators need to perform scanning
work *proportional* to their allocation rate.

This change implements proportional mutator assists. This uses the
scan work estimate computed by the garbage collector at the beginning
of each cycle to compute how much scan work must be performed per
allocation byte to complete the estimated scan work by the time the
heap reaches the goal size. When allocation triggers an assist, it
uses this ratio and the amount allocated since the last assist to
compute the assist work, then attempts to steal as much of this work
as possible from the background collector's credit, and then performs
any remaining scan work itself.

Change-Id: I98b2078147a60d01d6228b99afd414ef857e4fba
Reviewed-on: https://go-review.googlesource.com/8836Reviewed-by: Rick Hudson <rlh@golang.org>

Currently, the "n" in gcDrainN is in terms of objects to scan. This is
used by gchelpwork to perform a limited amount of work on allocation,
but is a pretty arbitrary way to bound this amount of work since the
number of objects has little relation to how long they take to scan.

Modify gcDrainN to perform a fixed amount of scan work instead. For
now, gchelpwork still performs a fairly arbitrary amount of scan work,
but at least this is much more closely related to how long the work
will take. Shortly, we'll use this to precisely control the scan work
performed by mutator assists during allocation to achieve the heap
size goal.

Change-Id: I3cd07fe0516304298a0af188d0ccdf621d4651cc
Reviewed-on: https://go-review.googlesource.com/8835Reviewed-by: Rick Hudson <rlh@golang.org>

This tracks scan work done by background GC in a global pool. Mutator
assists will draw on this credit to avoid doing work when background
GC is staying ahead.

Unlike the other GC controller tracking variables, this will be both
written and read throughout the cycle. Hence, we can't arbitrarily
delay updates like we can for scan work and bytes marked. However, we
still want to minimize contention, so this global credit pool is
allowed some error from the "true" amount of credit. Background GC
accumulates credit locally up to a limit and only then flushes to the
global pool. Similarly, mutator assists will draw from the credit pool
in batches.

Change-Id: I1aa4fc604b63bf53d1ee2a967694dffdfc3e255e
Reviewed-on: https://go-review.googlesource.com/8834Reviewed-by: Rick Hudson <rlh@golang.org>

This implements tracking the scan work ratio of a GC cycle and using
this to estimate the scan work that will be required by the next GC
cycle. Currently this estimate is unused; it will be used to drive
mutator assists.

Change-Id: I8685b59d89cf1d83eddfc9b30d84da4e3a7f4b72
Reviewed-on: https://go-review.googlesource.com/8833Reviewed-by: Rick Hudson <rlh@golang.org>

This tracks the amount of scan work in terms of scanned pointers
during the concurrent mark phase. We'll use this information to
estimate scan work for the next cycle.

Currently this aggregates the work counter in gcWork and dispose
atomically aggregates this into a global work counter. dispose happens
relatively infrequently, so the contention on the global counter
should be low. If this turns out to be an issue, we can reduce the
number of disposes, and if it's still a problem, we can switch to
per-P counters.

Change-Id: Iac0364c466ee35fab781dbbbe7970a5f3c4e1fc1
Reviewed-on: https://go-review.googlesource.com/8832Reviewed-by: Rick Hudson <rlh@golang.org>

These currently use portable implementations in terms of their uint64
counterparts.

Change-Id: Icba5f7134cfcf9d0429edabcdd73091d97e5e905
Reviewed-on: https://go-review.googlesource.com/8831Reviewed-by: Rick Hudson <rlh@golang.org>

This change exposes reflect.ArrayOf to create new reflect.Type array
types at runtime, when given a reflect.Type element.

- reflect: implement ArrayOf
- reflect: tests for ArrayOf
- runtime: document that typeAlg is used by reflect and must be kept in
  synchronized

Fixes #5996.

Change-Id: I5d07213364ca915c25612deea390507c19461758
Reviewed-on: https://go-review.googlesource.com/4111Reviewed-by: Keith Randall <khr@golang.org>

Update #10512.

Change-Id: Ifdc59c3a5d8aba420b34ae4e37b3c2315dd7c783
Reviewed-on: https://go-review.googlesource.com/9162Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

Fixes #10516.

Change-Id: Ia93f53d4e752bbcca6112bc75f6c3dbe30b90dac
Reviewed-on: https://go-review.googlesource.com/9192Reviewed-by: Ian Lance Taylor <iant@golang.org>

This change fixes inconsistent error values on
Lookup{Addr,CNAME,Host,IP.MX,NS,Port,SRV,TXT}.

Updates #4856.

Change-Id: I059bc8ffb96ee74dff8a8c4e8e6ae3e4a462a7ef
Reviewed-on: https://go-review.googlesource.com/9108Reviewed-by: Ian Lance Taylor <iant@golang.org>

This change fixes inconsistent error values on Interfaces,
InterfaceAddrs, InterfaceBy{Index,Name}, and Addrs and MulticastAddrs
methods of Interface.

Updates #4856.

Change-Id: I09e65522a22f45c641792d774ebf7a0081b874ad
Reviewed-on: https://go-review.googlesource.com/9140Reviewed-by: Ian Lance Taylor <iant@golang.org>

This change fixes inconsistent error values on
Set{Deadline,ReadDeadline,WriteDeadline,ReadBuffer,WriteBuffer} for
Conn, Listener and PacketConn, and
Set{KeepAlive,KeepAlivePeriod,Linger,NoDelay} for TCPConn.

Updates #4856.

Change-Id: I34ca5e98f6de72863f85b2527478b20d8d5394dd
Reviewed-on: https://go-review.googlesource.com/9109Reviewed-by: Ian Lance Taylor <iant@golang.org>

This change fixes inconsistent error values on
File{Conn,Listener,PacketConn} and File method of Conn, Listener.

Updates #4856.

Change-Id: I3197b9277bef0e034427e3a44fa77523acaa2520
Reviewed-on: https://go-review.googlesource.com/9101Reviewed-by: Ian Lance Taylor <iant@golang.org>

They don't really make any sense on this side of the compiler/linker divide.

Some of the code touching these fields was the support for R_TLS when
thechar=='6' which turns out to be dead and so I just removed all of that.

Change-Id: I4e265613c4e7fcc30a965fffb7fd5f45017f06f3
Reviewed-on: https://go-review.googlesource.com/9107
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Also moves a few server test helpers into mockserver_test.go.

Change-Id: I5a95c9bc6f0c4683751bcca77e26a8586a377466
Reviewed-on: https://go-review.googlesource.com/9106Reviewed-by: Ian Lance Taylor <iant@golang.org>

Change-Id: I1ea4175466c9113c1f41b012ba8266ee2b06e3a3
Reviewed-on: https://go-review.googlesource.com/8522Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Thanks to Russ for the hints.

Change-Id: Ie35a71d432b9d68bd30c7a364b4dce1bd3db806e
Reviewed-on: https://go-review.googlesource.com/9102Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Change-Id: I1cf94377c613fb51ae77f4fe1e3439268b1606a9
Reviewed-on: https://go-review.googlesource.com/9161Reviewed-by: Ian Lance Taylor <iant@golang.org>

Optimized heapBitsForObject by special casing
objects whose size is a power of two. When a
span holding such objects is initialized I
added a mask that when &ed with an interior pointer
results in the base of the pointer. For the garbage
benchmark this resulted in CPU_CLK_UNHALTED in
heapBitsForObject going from 7.7% down to 5.9%
of the total, INST_RETIRED went from 12.2 -> 8.7.

Here are the benchmarks that were at lease plus or minus 1%.

benchmark                          old ns/op      new ns/op      delta
BenchmarkFmtFprintfString          249            221            -11.24%
BenchmarkFmtFprintfInt             247            223            -9.72%
BenchmarkFmtFprintfEmpty           76.5           69.6           -9.02%
BenchmarkBinaryTree17              4106631412     3744550160     -8.82%
BenchmarkFmtFprintfFloat           424            399            -5.90%
BenchmarkGoParse                   4484421        4242115        -5.40%
BenchmarkGobEncode                 8803668        8449107        -4.03%
BenchmarkFmtManyArgs               1494           1436           -3.88%
BenchmarkGobDecode                 10431051       10032606       -3.82%
BenchmarkFannkuch11                2591306713     2517400464     -2.85%
BenchmarkTimeParse                 361            371            +2.77%
BenchmarkJSONDecode                70620492       68830357       -2.53%
BenchmarkRegexpMatchMedium_1K      54693          53343          -2.47%
BenchmarkTemplate                  90008879       91929940       +2.13%
BenchmarkTimeFormat                380            387            +1.84%
BenchmarkRegexpMatchEasy1_32       111            113            +1.80%
BenchmarkJSONEncode                21359159       21007583       -1.65%
BenchmarkRegexpMatchEasy1_1K       603            613            +1.66%
BenchmarkRegexpMatchEasy0_32       127            129            +1.57%
BenchmarkFmtFprintfIntInt          399            393            -1.50%
BenchmarkRegexpMatchEasy0_1K       373            378            +1.34%

Change-Id: I78e297161026f8b5cc7507c965fd3e486f81ed29
Reviewed-on: https://go-review.googlesource.com/8980Reviewed-by: Austin Clements <austin@google.com>

http://golang.org/cl/7623 refactored how line history works and
introduced a new TrimPathPrefix field to replace the existing Trimpath
field, but never removed the latter or updated its users.

Fixes #10503.

Change-Id: Ief90a55b6cef2e8062b59856a4c7dcc0df01d3f2
Reviewed-on: https://go-review.googlesource.com/9113Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>

Fixes #9496
Fixes #9946
Fixes #10474
Fixes #10405

Change-Id: I4e65f1706e46499811d9ebf4ad6d83a5dfb2ddaa
Reviewed-on: https://go-review.googlesource.com/8550Reviewed-by: Daniel Morsing <daniel.morsing@gmail.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>

This is primarily about making the code clearer, but as part of the cleanup
componentgen is now much more consistent about what it does and does
not attempt.

The new limit is to 8 move instructions.

The old limit was either 3 or 4 small things but in the details it was
quite inconsistent: ints, interfaces, strings, and slices all counted as small;
it handled a struct containing two ints, but not a struct containing a struct
containing two ints; it handled slices and interfaces and a struct containing
a slice but not a struct containing an interface; and so on.

The new code runs at about the same speed as the old code if limited to 4 moves,
but that's much more restrictive when the pieces are strings or interfaces.
With the limit raised to 8 moves, this CL is sometimes a significant improvement:

benchmark                          old ns/op      new ns/op      delta
BenchmarkBinaryTree17              4361174290     4362870005     +0.04%
BenchmarkFannkuch11                3008201483     2974408533     -1.12%
BenchmarkFmtFprintfEmpty           79.0           79.5           +0.63%
BenchmarkFmtFprintfString          281            261            -7.12%
BenchmarkFmtFprintfInt             264            262            -0.76%
BenchmarkFmtFprintfIntInt          447            443            -0.89%
BenchmarkFmtFprintfPrefixedInt     354            361            +1.98%
BenchmarkFmtFprintfFloat           500            452            -9.60%
BenchmarkFmtManyArgs               1688           1693           +0.30%
BenchmarkGobDecode                 11718456       11741179       +0.19%
BenchmarkGobEncode                 10144620       10161627       +0.17%
BenchmarkGzip                      437631642      435271877      -0.54%
BenchmarkGunzip                    109468858      110173606      +0.64%
BenchmarkHTTPClientServer          76248          75362          -1.16%
BenchmarkJSONEncode                24160474       23753091       -1.69%
BenchmarkJSONDecode                84470041       82902026       -1.86%
BenchmarkMandelbrot200             4676857        4687040        +0.22%
BenchmarkGoParse                   4954602        4923965        -0.62%
BenchmarkRegexpMatchEasy0_32       151            151            +0.00%
BenchmarkRegexpMatchEasy0_1K       450            452            +0.44%
BenchmarkRegexpMatchEasy1_32       131            130            -0.76%
BenchmarkRegexpMatchEasy1_1K       713            695            -2.52%
BenchmarkRegexpMatchMedium_32      227            218            -3.96%
BenchmarkRegexpMatchMedium_1K      63911          62966          -1.48%
BenchmarkRegexpMatchHard_32        3163           3026           -4.33%
BenchmarkRegexpMatchHard_1K        93985          90266          -3.96%
BenchmarkRevcomp                   650697093      649211600      -0.23%
BenchmarkTemplate                  107049170      106804076      -0.23%
BenchmarkTimeParse                 448            452            +0.89%
BenchmarkTimeFormat                468            460            -1.71%

Change-Id: I08563133883e88bb9db9e9e4dee438a5af2787da
Reviewed-on: https://go-review.googlesource.com/9004Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

This CL revises CL 7504 to use explicitly uintptr types for the
struct fields that are going to be updated sometimes without
write barriers. The result is that the fields are now updated *always*
without write barriers.

This approach has two important properties:

1) Now the GC never looks at the field, so if the missing reference
could cause a problem, it will do so all the time, not just when the
write barrier is missed at just the right moment.

2) Now a write barrier never happens for the field, avoiding the
(correct) detection of inconsistent write barriers when GODEBUG=wbshadow=1.

Change-Id: Iebd3962c727c0046495cc08914a8dc0808460e0e
Reviewed-on: https://go-review.googlesource.com/9019Reviewed-by: Austin Clements <austin@google.com>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

The majority of this CL was prepared via scripted invocations of
`gofmt -w -r "$SYM -> obj.$SYM" cmd/internal/ld/*.go` and `gofmt -w -r
"ld.$SYM -> obj.$SYM" cmd/?l/*.go`.

Because of issue #7417, that was followed by repeatedly running an AWK
script to identify lines that differed other than whitespace changes
or "ld." or "obj." prefixes and manually restoring comments.

Finally, the redundant constants from cmd/internal/ld/link.go were
removed, and "goimports -w" was used to cleanup import lines.

Passes rsc.io/toolstash/buildall, even when modified to also build cmd.

Fixes #10055.

Change-Id: Icd5dbe819a3b6520ce883748e60017dc8e9a2e85
Reviewed-on: https://go-review.googlesource.com/9112Reviewed-by: Michael Hudson-Doyle <michael.hudson@canonical.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

The go command prints paths in errors relative to its current directory.
Since all.bash and run.bash are run in $GOROOT/src, prefer to run
the go command, so that the relative paths are correct.

Before this CL, running all.bash in $GOROOT/src:

	##### Testing race detector
	# net/http
	src/net/http/transport.go:1257: cannot take the address of <node EFACE>

This is wrong (or at least less useful) because there is no $GOROOT/src/src/net/http directory.

Change-Id: I0c0d52c22830d79b3715f51a6329a3d33de52a72
Reviewed-on: https://go-review.googlesource.com/9157Reviewed-by: Rob Pike <r@golang.org>

The callee-saved registers must be saved because for the c-shared case
this code is invoked from C code in the system library, and that code
expects the registers to be saved.  The tests were passing because in
the normal case the code calls a cgo function that naturally saves
callee-saved registers anyhow.  However, it fails when the code takes
the non-cgo path.

Change-Id: I9c1f5e884f5a72db9614478049b1863641c8b2b9
Reviewed-on: https://go-review.googlesource.com/9114Reviewed-by: David Crawshaw <crawshaw@golang.org>

Change-Id: I4ee6dac32bd3759aabdfdc92b235282785fbcca9
Reviewed-on: https://go-review.googlesource.com/9083Reviewed-by: David Crawshaw <crawshaw@golang.org>

Change-Id: I5964fc55157dc1df7be400dfa0df591d6163e25e
Reviewed-on: https://go-review.googlesource.com/9084Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>