The wiki page has recently been created, and at this time it's
just a stub. It's expected that support for WebAssembly will be
evolving over time, and the wiki page can be kept updated with
helpful information, how to get started, tips and tricks, etc.

Use present tense because it's expected that there will be more
general information added by the time Go 1.11 release happens.

Also add link to https://webassembly.org/ in first paragraph.

Change-Id: I139c2dcec8f0d7fd89401df38a3e12960946693f
Reviewed-on: https://go-review.googlesource.com/131078Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

gentraceback handles system stack transitions, but only when they're
done by systemstack(). Handle morestack() too.

I tried to do this generically but systemstack and morestack are
actually *very* different functions. Most notably, systemstack returns
"normally", just messes with $sp along the way. morestack never
returns at all -- it calls newstack, and newstack then jumps both
stacks and functions back to whoever called morestack. I couldn't
think of a way to handle both of them generically. So don't.

The current implementation does not include systemstack on the generated
traceback. That's partly because I don't know how to find its stack frame
reliably, and partly because the current structure of the code wants to
do the transition before the call, not after. If we're willing to
assume that morestack's stack frame is 0 size, this could probably be
fixed.

For posterity's sake, alternatives tried:

- Have morestack put a dummy function into schedbuf, like systemstack
does. This actually worked (see patchset 1) but more by a series of
coincidences than by deliberate design. The biggest coincidence was that
because morestack_switch was a RET and its stack was 0 size, it actually
worked to jump back to it at the end of newstack -- it would just return
to the caller of morestack. Way too subtle for me, and also a little
slower than just jumping directly.

- Put morestack's PC and SP into schedbuf, so that gentraceback could
treat it like a normal function except for the changing SP. This was a
terrible idea and caused newstack to reenter morestack in a completely
unreasonable state.

To make testing possible I did a small redesign of testCPUProfile to
take a callback that defines how to check if the conditions pass to it
are satisfied. This seemed better than making the syntax of the "need"
strings even more complicated.

Updates #25943

Change-Id: I9271a30a976f80a093a3d4d1c7e9ec226faf74b4
Reviewed-on: https://go-review.googlesource.com/126795
Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

gentraceback gets the currently running g to do some sanity checks, but
should use gp everywhere to do its actual work. Some noncritical checks
later accidentally used g instead of gp. This seems like it could be a
problem in many different contexts, but I noticed in Windows profiling,
where profilem calls gentraceback on a goroutine from a different
thread.

Change-Id: I3da27a43e833b257f6411ee6893bdece45a9323f
Reviewed-on: https://go-review.googlesource.com/128895
Run-TryBot: Heschi Kreinick <heschi@google.com>
Reviewed-by: Austin Clements <austin@google.com>

This turns

	panic: function name  is not a valid identifier

into
	panic: function name "" is not a valid identifier

and also makes it consistent with the func signature check.

This CL also makes the testBadFuncName func a test helper.

Change-Id: Id967cb61ac28228de81e1cd76a39f5195a5ebd11
Reviewed-on: https://go-review.googlesource.com/130998Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

We can no longer use the field's position for the duplicate field tag
warning - since we now check embedded tags, the positions may belong to
copmletely different packages.

Instead, keep track of the lowest field that's still part of the
top-level struct type that we are checking.

Finally, be careful to not repeat the independent struct field warnings
when checking fields again because they are embedded into another
struct. To do this, separate the duplicate tag value logic into a func
that recurses into embedded fields on a per-encoding basis.

Fixes #25593.

Change-Id: I3bd6e01306d8ec63c0314d25e3136d5e067a9517
Reviewed-on: https://go-review.googlesource.com/115677
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>

Change-Id: I3f99083b7d8ab06482c2c22eafda8b0141a872bd
Reviewed-on: https://go-review.googlesource.com/131076Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Change-Id: Iadb3c5de8ae9ea45855013997ed70f7929a88661
GitHub-Last-Rev: ae85bcf82be8fee533e2b9901c6133921382c70a
GitHub-Pull-Request: golang/go#26920
Reviewed-on: https://go-review.googlesource.com/128955Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Like the conv helper function but for creating OCONVNOP nodes
instead of OCONV nodes.

passes toolstash -cmp

Change-Id: Ib93ffe66590ebaa2b4fa552c81f1a2902e789d8e
Reviewed-on: https://go-review.googlesource.com/112597
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

This CL adds the source code of all inlined functions
into the function specified in $GOSSAFUNC.
The code is appended to the sources column of ssa.html.

ssaDumpInlined is populated with references to inlined functions.
Then it is used for dumping the sources in buildssa.

The source columns contains code in following order:
target function, inlined functions sorted by filename, lineno.

Fixes #25904

Change-Id: I4f6d4834376f1efdfda1f968a5335c0543ed36bc
Reviewed-on: https://go-review.googlesource.com/126606
Run-TryBot: Yury Smolsky <yury@smolsky.by>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

This CL exports the Func.Endlineno value for inlineable functions.
It is needed to grab the source code of an imported function
inlined into the function specified in $GOSSAFUNC.

See CL 126606 for details.

Updates #25904

Change-Id: I1e259e20445e4109b4621a95abb5bde1be457af1
Reviewed-on: https://go-review.googlesource.com/126605
Run-TryBot: Yury Smolsky <yury@smolsky.by>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

Since we print almost everything to ssa.html in the GOSSAFUNC mode,
there is a need to stop spamming stdout when user just wants to see
ssa.html.

This changes cleans output of the GOSSAFUNC debug mode.
To enable the dump of the debug data to stdout, one must
put suffix + after the function name like that:

GOSSAFUNC=Foo+

Otherwise gc will not print the IR and ASM to stdout after each phase.
AST IR is still sent to stdout because it is not included
into ssa.html. It will be fixed in a separate change.

The change adds printing out the full path to the ssa.html file.

Updates #25942

Change-Id: I711e145e05f0443c7df5459ca528dced273a62ee
Reviewed-on: https://go-review.googlesource.com/126603
Run-TryBot: Yury Smolsky <yury@smolsky.by>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

The current implementation removes all of the optimization flags from
the compiler.
Added the -O0 optimization flag after the removal loop, so go can
compile cgo on every OS consistently.

Fixes #26487

Change-Id: Ia98bca90def186dfe10f50b1787c2f40d85533da
Reviewed-on: https://go-review.googlesource.com/127755
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

The divLarge code contained "todo"s about avoiding alias
and clear calls in the initialization of variables.  By
rearranging the order of initialization and always using
an auxiliary variable for the shifted divisor, all of these
calls can be safely avoided.  On average, normalizing
the divisor (shift>0) is required 31/32 or 63/64 of the
time.  If one always performs the shift into an auxiliary
variable first, this avoids the need to check for aliasing of
vIn in the output variables u and z.  The remainder u is
initialized via a left shift of uIn and thus needs no
alias check against uIn.  Since uIn and vIn were both used,
z needs no alias checks except against u which is used for
storage of the remainder. This change has a minimal impact
on performance (see below), but cleans up the initialization
code and eliminates the "todo"s.

name                 old time/op  new time/op  delta
Div/20/10-4          86.7ns ± 6%  85.7ns ± 5%    ~     (p=0.841 n=5+5)
Div/200/100-4         523ns ± 5%   502ns ± 3%  -4.13%  (p=0.024 n=5+5)
Div/2000/1000-4      2.55µs ± 3%  2.59µs ± 5%    ~     (p=0.548 n=5+5)
Div/20000/10000-4    80.4µs ± 4%  80.0µs ± 2%    ~     (p=1.000 n=5+5)
Div/200000/100000-4  6.43ms ± 6%  6.35ms ± 4%    ~     (p=0.548 n=5+5)

Fixes #22928

Change-Id: I30d8498ef1cf8b69b0f827165c517bc25a5c32d7
Reviewed-on: https://go-review.googlesource.com/130775Reviewed-by: Robert Griesemer <gri@golang.org>

Use defined named constants instead of 0 literal in comparisons.

Found using https://go-critic.github.io/overview.html#namedConst-ref

Change-Id: Ic075cece248f6e51db0b3d9d9eaba7d6409c9eef
Reviewed-on: https://go-review.googlesource.com/123376
Run-TryBot: Iskander Sharipov <iskander.sharipov@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

When this code was introduced, there were no R_MIPS, R_PPC64 and
R_390 and build would fail with this code uncommented.
Now we have those.

Change-Id: I18a54eaa250db12e293f8e4d1f080f1dd2e66a4f
Reviewed-on: https://go-review.googlesource.com/122896
Run-TryBot: Iskander Sharipov <iskander.sharipov@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Change-Id: I7c9c83ba236e1050e04377a7591fef7174df698b
Reviewed-on: https://go-review.googlesource.com/130415
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

As reported in #26650 and also cautioned on the man page
for fsync on OS X, fsync doesn't properly flush content
to permanent storage, and might cause corruption of data if
the OS crashes or if the drive loses power. Thus it is recommended
to use the F_FULLFSYNC fcntl, which flushes all buffered data to
permanent storage and is important for applications such as
databases that require a strict ordering of writes.

Also added a note in syscall_darwin.go that syscall.Fsync is
not invoked for os.File.Sync.

Fixes #26650.

Change-Id: Idecd9adbbdd640b9c5b02e73b60ed254c98b48b6
Reviewed-on: https://go-review.googlesource.com/130676
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

This comment has been the source of much confusion and broken dreams. We
can add it back if a tool ever gets released.

Updates #16742

Change-Id: I4b9c179b7c60274e6ff1bcb607b82029dd9a893f
Reviewed-on: https://go-review.googlesource.com/130876Reviewed-by: Matt Layher <mdlayher@gmail.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

If two goroutines are racing on a map, one of them will exit
cleanly, clearing the hashWriting bit, and the other will
likely notice and panic.  If we use XOR instead of OR to
set the bit in the first place, even numbers of racers will
hopefully all see the bit cleared and panic simultaneously,
giving the full set of available stacks.  If a third racer
sneaks in, we are no worse than the current code, and
the generated code should be no more expensive.

In practice, this catches most racing goroutines even in
very tight races.  See the demonstration program posted
on https://github.com/golang/go/issues/26703 for an example.

Fixes #26703

Change-Id: Idad17841a3127c24bd0a659b754734f70e307434
Reviewed-on: https://go-review.googlesource.com/126936
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

Previously fmt would first obtain a list of map keys
and then look up the value for each key. Since NaNs can
be map keys but cannot be fetched directly, the lookup would
fail and return a zero reflect.Value, which formats as <nil>.

golang.org/cl/33572 added a map iterator to the reflect package
that is used in this CL to retrieve the key and value from
the map and prints the correct value even for keys that are not
equal to themselves.

Fixes #14427

Change-Id: I9e1522959760b3de8b7ecf7a6e67cd603339632a
Reviewed-on: https://go-review.googlesource.com/129777Reviewed-by: Alan Donovan <adonovan@google.com>

Also remove lineno from typecheckdeftype since copytype was
the only user of it and typecheck uses lineno independently.

toolstach-check passed.

Updates #19683.

Change-Id: I1663fdb8cf519d505cc087c8657dcbff3c8b1a0a
Reviewed-on: https://go-review.googlesource.com/114875
Run-TryBot: Yury Smolsky <yury@smolsky.by>
Reviewed-by: Robert Griesemer <gri@golang.org>

Store the value of GOSSAFUNC in a global variable to avoid
multiple calls to os.Getenv from gc.buildssa and gc.mkinlcall1.
The latter is implemented in the CL 126606.

Updates #25942

Change-Id: I58caaef2fee23694d80dc5a561a2e809bf077fa4
Reviewed-on: https://go-review.googlesource.com/126604
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Fixes #27085

Change-Id: I4eb3ff7c76e0b8e4d8fe0298f739b0284d74a031
Reviewed-on: https://go-review.googlesource.com/130855Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

The Sqrt code previously used explicit constants for 2 and 1/2.  This change
replaces multiplication by these constants with increment and decrement of
the floating point exponent directly.  This improves performance by ~7-10%
for small inputs and minimal improvement for large inputs.

name                 old time/op    new time/op    delta
FloatSqrt/64-4         1.39µs ± 0%    1.29µs ± 3%   -7.01%  (p=0.016 n=4+5)
FloatSqrt/128-4        2.84µs ± 0%    2.60µs ± 1%   -8.33%  (p=0.008 n=5+5)
FloatSqrt/256-4        3.24µs ± 1%    2.91µs ± 2%  -10.00%  (p=0.008 n=5+5)
FloatSqrt/1000-4       7.42µs ± 1%    6.74µs ± 0%   -9.16%  (p=0.008 n=5+5)
FloatSqrt/10000-4      65.9µs ± 1%    65.3µs ± 4%     ~     (p=0.310 n=5+5)
FloatSqrt/100000-4     1.57ms ± 8%    1.52ms ± 1%     ~     (p=0.111 n=5+4)
FloatSqrt/1000000-4     127ms ± 1%     126ms ± 1%     ~     (p=0.690 n=5+5)

Change-Id: Id81ac842a9d64981e001c4ca3ff129eebd227593
Reviewed-on: https://go-review.googlesource.com/130835Reviewed-by: Robert Griesemer <gri@golang.org>

This is causing failures on TryBots and BuildBots:
--- FAIL: TestGcSys (0.06s)
    gc_test.go:27: expected "OK\n", but got "using too much memory: 39882752 bytes\n"
FAIL

Updates #27156

Change-Id: I418bbec89002574cd583c97422e433f042c07492
Reviewed-on: https://go-review.googlesource.com/130875
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Example of use:

	iter := reflect.ValueOf(m).MapRange()
 	for iter.Next() {
		k := iter.Key()
		v := iter.Value()
		...
	}

See issue golang/go#11104

Q. Are there any benchmarks that would exercise the new calls to
   copyval in existing code?

Change-Id: Ic469fcab5f1d9d853e76225f89bde01ee1d36e7a
Reviewed-on: https://go-review.googlesource.com/33572Reviewed-by: Keith Randall <khr@golang.org>

This CL adds the "sources" column at the beginning of SSA table.
This column displays the source code for the function being passed
in the GOSSAFUNC env variable.

Also UI was extended so that clicking on particular line will
highlight all places this line is referenced.

JS code was cleaned and formatted.

This CL does not handle inlined functions. See issue 25904.

Change-Id: Ic7833a0b05e38795f4cf090f3dc82abf62d97026
Reviewed-on: https://go-review.googlesource.com/119035
Run-TryBot: Yury Smolsky <yury@smolsky.by>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

I merged CL 115835 without testing it after a rebase. My bad.

Change-Id: I0acc6ed78ea7d718ac2df11d509cfcf4364dfaee
Reviewed-on: https://go-review.googlesource.com/130815
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Martin Möhrmann <moehrmann@google.com>

Replaces legacy Go syntax for pointer struct member access
with more modern auto-deref alternative.

Found using https://go-critic.github.io/overview#underef-ref

Change-Id: I71a3c424126c4ff5d89f9e4bacb6cc01c6fa2ddf
Reviewed-on: https://go-review.googlesource.com/122895
Run-TryBot: Iskander Sharipov <iskander.sharipov@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Replace `x[:]` where x is a slice with just `x`.

Found using https://go-critic.github.io/overview.html#unslice-ref

Change-Id: Ib0ee16e1d49b2a875b6b92a770049acc33208362
Reviewed-on: https://go-review.googlesource.com/123375
Run-TryBot: Iskander Sharipov <iskander.sharipov@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

The workthegc function was being inlined, and the slice did not
escape, so there was no memory allocation. Use a sink variable to
force memory allocation, at least for now.

Fixes #23343

Change-Id: I02f4618e343c8b6cb552cb4e9f272e112785f7cf
Reviewed-on: https://go-review.googlesource.com/122576
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Fixes #26437

Change-Id: Id47b3bcc23ea7b7b17b55dd96b5830c48fd8d53d
Reviewed-on: https://go-review.googlesource.com/124895Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

The implementation of cputicks has been wrong for ppc64x. The
previous code sequence is for 32 bit, not 64 bit.

Change-Id: I308ae6cf9131f53a0100cd3f8ae4e16601f2d553
Reviewed-on: https://go-review.googlesource.com/129595
Run-TryBot: Lynn Boger <laboger@linux.vnet.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Carlos Eduardo Seo <cseo@linux.vnet.ibm.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Fixes #26970

Change-Id: I0f2695434a53550cf84f702e9d8d02a37448d396
Reviewed-on: https://go-review.googlesource.com/129195Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Also adds some missing asmdecl comments for funcs with Go proto.

Change-Id: Iabc68e8c0ad936e06ed719e0f030bfc5f6f6e168
Reviewed-on: https://go-review.googlesource.com/127760
Run-TryBot: Iskander Sharipov <iskander.sharipov@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

The hasprefix function is redundant and can be removed since it has
the same implementation as hasPrefix modulo variable names.

Fixes #25688

Change-Id: I499cc24a2b5c38d1301718a4e66f555fd138386f
Reviewed-on: https://go-review.googlesource.com/115835
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ilya Tocar <ilya.tocar@intel.com>

Change-Id: I2ecbd68b1b30ab64e64ae120101761400c22457b
Reviewed-on: https://go-review.googlesource.com/129757Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

First, use a dummy slice access on decode64 and decode32 to ensure that
there is a single bounds check for src.

Second, move the PutUint64/PutUint32 calls out of these functions,
meaning that they are simpler and smaller. This may also open the door
to inlineability in the future, but for now, they both go past the
budget.

While at it, get rid of the ilen and olen variables, which have no
impact whatsoever on performance. At least, not measurable by any of the
benchmarks.

name                 old time/op    new time/op    delta
DecodeString/2-4       54.3ns ± 1%    55.2ns ± 2%   +1.60%  (p=0.017 n=5+6)
DecodeString/4-4       66.6ns ± 1%    66.8ns ± 2%     ~     (p=0.903 n=6+6)
DecodeString/8-4       79.3ns ± 2%    79.6ns ± 1%     ~     (p=0.448 n=6+6)
DecodeString/64-4       300ns ± 1%     281ns ± 3%   -6.54%  (p=0.002 n=6+6)
DecodeString/8192-4    27.4µs ± 1%    23.7µs ± 2%  -13.47%  (p=0.002 n=6+6)

name                 old speed      new speed      delta
DecodeString/2-4     73.7MB/s ± 1%  72.5MB/s ± 2%   -1.55%  (p=0.026 n=5+6)
DecodeString/4-4      120MB/s ± 1%   120MB/s ± 2%     ~     (p=0.851 n=6+6)
DecodeString/8-4      151MB/s ± 2%   151MB/s ± 1%     ~     (p=0.485 n=6+6)
DecodeString/64-4     292MB/s ± 1%   313MB/s ± 3%   +7.03%  (p=0.002 n=6+6)
DecodeString/8192-4   399MB/s ± 1%   461MB/s ± 2%  +15.58%  (p=0.002 n=6+6)

For #19636.

Change-Id: I0dfbdafa2a41dc4c582f63aef94b90b8e473731c
Reviewed-on: https://go-review.googlesource.com/113776Reviewed-by: Ian Lance Taylor <iant@golang.org>

Tests in test/safe were neglected after moving to the run.go
framework. This change restores them.

These tests are skipped for go/types via -+ option.

Fixes #25668

Change-Id: I8fe26574a76fa7afa8664c467d7c2e6334f1bba9
Reviewed-on: https://go-review.googlesource.com/124660Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Updates #26148

Change-Id: I008502232642237270b7c8a2efb4a378345d06fd
Reviewed-on: https://go-review.googlesource.com/128716
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>