These were new with TLS 1.2 and, reportedly, some servers require it.
Since it's easy, this change adds suport for three flavours of
AES-128-CBC with SHA-256 MACs.

Other testdata/ files have to be updated because this changes the list
of cipher suites offered by default by the client.

Fixes #15487.

Change-Id: I1b14330c31eeda20185409a37072343552c3464f
Reviewed-on: https://go-review.googlesource.com/27315
Run-TryBot: Adam Langley <agl@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Jonathan Rudenberg <jonathan@titanous.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Change-Id: I9a7654a6d623add8542a1c34ccc76ea136a9a7e3
Reviewed-on: https://go-review.googlesource.com/27359Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Change-Id: Ie6dd2318e031be445c0b1ae65d4c78723d5a1167
Reviewed-on: https://go-review.googlesource.com/27197
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

Syntax tree nodes, scanner, parser, basic printers.

Builds syntax trees for entire Go std lib at a rate of ~1.8M lines/s
in warmed up state (MacMini, 2.3 GHz Intel Core i7, 8GB RAM):

$ go test -run StdLib -fast
parsed 1074617 lines (2832 files) in 579.66364ms (1853863 lines/s)
allocated 282.212Mb (486.854Mb/s)
PASS

Change-Id: Ie26d9a7bf4e5ff07457aedfcc9b89f0eba72ae3f
Reviewed-on: https://go-review.googlesource.com/27195
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>

I accidentally included a modified spec in
https://go-review.googlesource.com/27290 .
Remove that change.

Change-Id: Icb62fe829072860e9eb74865d21e06f30efcfd26
Reviewed-on: https://go-review.googlesource.com/27357Reviewed-by: Robert Griesemer <gri@golang.org>

The changes match the existing compilers, and assume an adjusted
spec (per issue #16794).

Fixes #15686.

Change-Id: I72677ce75888c41a8f3c2963117a2f2d5501c42b
Reviewed-on: https://go-review.googlesource.com/27290Reviewed-by: Matthew Dempsky <mdempsky@google.com>

The trybot flakes are a nuisance.

Updates #16396

Change-Id: I8202adb554391676ba82bca44d784c6a81bf2085
Reviewed-on: https://go-review.googlesource.com/27313
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Fixes #14092.

Change-Id: I00692f60a416348e38cab256b94fda07e334d258
Reviewed-on: https://go-review.googlesource.com/27316Reviewed-by: Matthew Dempsky <mdempsky@google.com>

Follow-up to CL 27156

Change-Id: I4f1cfced2dced9c9fc8a05bbc00ec4229e85c5c9
Reviewed-on: https://go-review.googlesource.com/27314Reviewed-by: Ian Lance Taylor <iant@golang.org>

Only remove stores that is shadowed by another store with same or
larger size. Normally we don't need this check because we did check
the types, but unsafe pointer casting can get around it.

Fixes #16769.

Change-Id: I3f7c6c57807b590a2f735007dec6c65a4fa01a34
Reviewed-on: https://go-review.googlesource.com/27320
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

This time with the cherry-pick from the proper patch of
the old CL.

Stack size increased.
Corrected NaN-comparison glitches.
Marked g register as clobbered by calls.
Fixed shared libraries.

live_ssa.go still disabled because of differences.
Presumably turning on more optimization will fix
both the stack size and the live_ssa.go glitches.

Enhanced debugging output for shared libs test.

Rebased onto master.

Updates #16010.

Change-Id: I40864faf1ef32c118fb141b7ef8e854498e6b2c4
Reviewed-on: https://go-review.googlesource.com/27159
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

It is no longer used by Go.

It's now moved to golang.org/x/tools/cmd/goyacc for anybody who needs it.

Fixes #11229

Change-Id: Ia431d5a380c7ff784a2050dee2f5bc8acee015da
Reviewed-on: https://go-review.googlesource.com/27325
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

This is a copy of golang.org/cl/22092 by Ryan Brown.

Here's his original comment:
On my machine this increases the average time for 'go build cmd/go' from
2.25s to 2.36s. I tried to measure compile and link separately but saw
no significant change.

Change-Id: If0d2b756d52a0d30d4eda526929c82794d89dd7b
Reviewed-on: https://go-review.googlesource.com/25311
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

fmt treats interfaces as being transparent.
As a result, we cannot say with confidence
that any particular verb is wrong.

This fixes the following vet false positives
in the standard library:

database/sql/sql_test.go:210: arg dep for printf verb %p of wrong type: sql.finalCloser
fmt/fmt_test.go:1663: arg nil for printf verb %s of wrong type: untyped nil
go/ast/commentmap.go:328: arg node for printf verb %p of wrong type: ast.Node
net/http/transport_test.go:120: arg c for printf verb %p of wrong type: net.Conn
net/http/httptest/server.go:198: arg c for printf verb %p of wrong type: net.Conn
net/http/httputil/dump_test.go:258: arg body for printf verb %p of wrong type: io.Reader
reflect/set_test.go:81: arg x for printf verb %p of wrong type: io.Writer
reflect/set_test.go:141: arg bb for printf verb %p of wrong type: io.Reader

Updates #11041
Updates #16314

Change-Id: I76df01abb3c34a97b6960f551bed9c1c91377cfc
Reviewed-on: https://go-review.googlesource.com/27127
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

CL 22720 hid all recently added functionality for go1.7.
Make everything exported again, so we could use it now.

Updates #15345

Change-Id: Id8ccba7199422b554407ec14c343d2c28fbb8f72
Reviewed-on: https://go-review.googlesource.com/27212
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

Although the term “RSA” is almost synonymous with PKCS#1 v1.5, that
standard is quite flawed, cryptographically speaking. Bellare and
Rogaway fixed PKCS#1 v1.5 with OAEP (for encryption) and PSS (for
signatures) but they only see a fraction of the use of v1.5.

This change adds support for creating and verifying X.509 certificates
that use PSS signatures. Sadly, every possible dimension of flexibility
seems to have been reflected in the integration of X.509 and PSS
resulting in a huge amount of excess complexity. This change only
supports one “sane” configuration for each of SHA-{256, 384, 512}.
Hopefully this is sufficient because it saves a lot of complexity in the
code.

Although X.509 certificates with PSS signatures are rare, I'm inclined
to look favourably on them because they are sufficiently superior.

Fixes #15958.

Change-Id: I7282e0b68ad0177209f8b2add473b94aa5224c07
Reviewed-on: https://go-review.googlesource.com/24743
Run-TryBot: Adam Langley <agl@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

The RFC is clear that the Parameters in an AlgorithmIdentifer for an RSA
public key must be NULL. BoringSSL enforces this so we have strong
evidence that this is a widely compatible change.

Embarrassingly enough, the major source of violations of this is us. Go
used to get this correct in only one of two places. This was only fixed
in 2013 (with 4874bc9b). That's why lots of test certificates are
updated in this change.

Fixes #16166.

Change-Id: Ib9a4551349354c66e730d44eb8cee4ec402ea8ab
Reviewed-on: https://go-review.googlesource.com/27312Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

name            old time/op  new time/op  delta
Encode/256-4     431ns ± 2%   391ns ± 2%   -9.36%  (p=0.000 n=8+8)
Encode/1024-4   1.68µs ± 0%  1.51µs ± 0%   -9.91%  (p=0.001 n=7+7)
Encode/4096-4   6.68µs ± 0%  6.03µs ± 1%   -9.69%  (p=0.000 n=8+8)
Encode/16384-4  27.0µs ± 1%  24.0µs ± 0%  -11.03%  (p=0.000 n=8+7)

Change-Id: I6994e02f77797349c4e188377d84f97dffe98399
Reviewed-on: https://go-review.googlesource.com/27254Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

This was fixed long ago but the test was not enabled.

For #8189.

Change-Id: Ia44ef752b6bf076f3e243d2d0db326a392a20193
Reviewed-on: https://go-review.googlesource.com/27310
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

subtle.ConstantTimeCompare now tests the length of the inputs (although
it didn't when this code was written) so this test in crypto/hmac is now
superfluous.

Fixes #16336.

Change-Id: Ic02d8537e776fa1dd5694d3af07a28c4d840d14b
Reviewed-on: https://go-review.googlesource.com/27239Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

If the SerialNumber is nil in the template then the resulting panic is
rather deep in encoding/asn1 and it's not obvious what went wrong.

This change tests and returns a more helpful error in this case.

Fixes #16603.

Change-Id: Ib30d652555191eb78f705dff8d909e4b5808f9ca
Reviewed-on: https://go-review.googlesource.com/27238Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Change-Id: I82eaf5c14a5b8b9ec088409f946adf7b5fd5dbe3
Reviewed-on: https://go-review.googlesource.com/27311Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Fixes #13993

Change-Id: Ic61b2bcd9f4f71457d3a8581574633d505d5750e
Reviewed-on: https://go-review.googlesource.com/27240
Run-TryBot: Rob Pike <r@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

Now matches the gc compiler.

Fixes #15594.

Change-Id: I9f3942367bc0acf883c6216b8ca44820832f5fe3
Reviewed-on: https://go-review.googlesource.com/27241
TryBot-Result: Gobot Gobot <gobot@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

This commit improves the processing of the final few bytes in
castagnoliSSE42: instead of processing one byte at a time, we use all
versions of the CRC32 instruction to process 4 bytes, then 2, then 1.
The difference is only noticeable for small "odd" sized buffers.

We do the similar improvement for processing the first few bytes in
the case of unaligned buffer.

Fixing the test which was not actually verifying the results for
misaligned buffers (WriteString was creating an internal copy which
was aligned).

Adding benchmarks for length 15 (aligned and misaligned), results
below.

name                          old time/op    new time/op    delta
CastagnoliCrc15B-4              25.1ns ± 0%    22.1ns ± 1%  -12.14%
CastagnoliCrc15BMisaligned-4    25.2ns ± 0%    22.9ns ± 1%   -9.03%
CastagnoliCrc40B-4              23.1ns ± 0%    23.4ns ± 0%   +1.08%
CastagnoliCrc1KB-4               127ns ± 0%     128ns ± 0%   +1.18%
CastagnoliCrc4KB-4               462ns ± 0%     464ns ± 0%     ~
CastagnoliCrc32KB-4             3.58µs ± 0%    3.60µs ± 0%   +0.58%

name                          old speed      new speed      delta
CastagnoliCrc15B-4             597MB/s ± 0%   679MB/s ± 1%  +13.77%
CastagnoliCrc15BMisaligned-4   596MB/s ± 0%   655MB/s ± 1%   +9.94%
CastagnoliCrc40B-4            1.73GB/s ± 0%  1.71GB/s ± 0%   -1.14%
CastagnoliCrc1KB-4            8.01GB/s ± 0%  7.93GB/s ± 1%   -1.06%
CastagnoliCrc4KB-4            8.86GB/s ± 0%  8.83GB/s ± 0%     ~
CastagnoliCrc32KB-4           9.14GB/s ± 0%  9.09GB/s ± 0%   -0.58%

Change-Id: I499e37af2241d28e3e5d522bbab836c1a718430a
Reviewed-on: https://go-review.googlesource.com/24470Reviewed-by: Keith Randall <khr@golang.org>

In CSE if a tuple generator is CSE'd to a different block, its
selectors are copied to the same block. In this case, also CES
the copied selectors.

Test copied from Keith's CL 27202.

Fixes #16741.

Change-Id: I2fc8b9513d430f10d6104275cfff5fb75d3ef3d9
Reviewed-on: https://go-review.googlesource.com/27236
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

If we cannot infer the asm arch from the filename
or the build tags, assume that it is the
current build arch. Assembly files with no
restrictions ought to be usable on all arches.

Updates #11041

Change-Id: I0ae807dbbd5fb67ca21d0157fe180237a074113a
Reviewed-on: https://go-review.googlesource.com/27151
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

The unsafe.Pointer check allows adding to
and subtracting from uintptrs in order to do
arithmetic.

Some code needs to round uintptrs.
Allow &^ for that purpose.

Updates #11041

Change-Id: Ib90dd2954bb6c78427058271e13f2ce4c4af38fb
Reviewed-on: https://go-review.googlesource.com/27156
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

Moves the state.ServerName assignment to outside the if
statement that checks for handshakeComplete.

Fixes #15571

Change-Id: I6c4131ddb16389aed1c410a975f9aa3b52816965
Reviewed-on: https://go-review.googlesource.com/22862
Run-TryBot: Adam Langley <agl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>

- Use machine instructions for uint64<->float conversions
- Do not enforce alignment on Zero/Move
	ARM64 supports unaligned load/stores, but only aligned offset
	or small offset can be encoded into instructions.
- Do combined loads

Change-Id: Iffca7dd0f13070b17b784861ce5a30af584680eb
Reviewed-on: https://go-review.googlesource.com/27086Reviewed-by: David Chase <drchase@google.com>

name               old time/op    new time/op    delta
FloatAdd/10-4         116ns ± 1%      82ns ± 0%   -28.74%  (p=0.008 n=5+5)
FloatAdd/100-4        124ns ± 0%      86ns ± 1%   -30.34%  (p=0.016 n=4+5)
FloatAdd/1000-4       192ns ± 1%     123ns ± 0%   -35.94%  (p=0.008 n=5+5)
FloatAdd/10000-4      826ns ± 0%     438ns ± 0%   -46.99%  (p=0.000 n=4+5)
FloatAdd/100000-4    6.82µs ± 1%    3.36µs ± 0%   -50.74%  (p=0.008 n=5+5)
FloatSub/10-4         108ns ± 1%      77ns ± 1%   -29.06%  (p=0.008 n=5+5)
FloatSub/100-4        115ns ± 0%      79ns ± 0%   -31.48%  (p=0.029 n=4+4)
FloatSub/1000-4       168ns ± 0%      99ns ± 0%   -41.09%  (p=0.029 n=4+4)
FloatSub/10000-4      690ns ± 2%     288ns ± 1%   -58.24%  (p=0.008 n=5+5)
FloatSub/100000-4    5.37µs ± 1%    2.10µs ± 1%   -60.89%  (p=0.008 n=5+5)

name               old alloc/op   new alloc/op   delta
FloatAdd/10-4         48.0B ± 0%     0.0B ±NaN%  -100.00%  (p=0.008 n=5+5)
FloatAdd/100-4        64.0B ± 0%     0.0B ±NaN%  -100.00%  (p=0.008 n=5+5)
FloatAdd/1000-4        176B ± 0%       0B ±NaN%  -100.00%  (p=0.008 n=5+5)
FloatAdd/10000-4     1.41kB ± 0%   0.00kB ±NaN%  -100.00%  (p=0.008 n=5+5)
FloatAdd/100000-4    13.6kB ± 0%    0.0kB ±NaN%  -100.00%  (p=0.008 n=5+5)
FloatSub/10-4         48.0B ± 0%     0.0B ±NaN%  -100.00%  (p=0.008 n=5+5)
FloatSub/100-4        64.0B ± 0%     0.0B ±NaN%  -100.00%  (p=0.008 n=5+5)
FloatSub/1000-4        176B ± 0%       0B ±NaN%  -100.00%  (p=0.008 n=5+5)
FloatSub/10000-4     1.41kB ± 0%   0.00kB ±NaN%  -100.00%  (p=0.008 n=5+5)
FloatSub/100000-4    13.6kB ± 0%    0.0kB ±NaN%  -100.00%  (p=0.008 n=5+5)

Fixes #14868

Change-Id: Ia2b8b1a8ef0868288ecb25f812b17bd03ff40d1c
Reviewed-on: https://go-review.googlesource.com/23568Reviewed-by: Robert Griesemer <gri@golang.org>

Timings is a simple data structure that collects times of labeled
Start/Stop events describing timed phases, which later can be written
to a file.

Adjacent phases with common label prefix are automatically collected
in a group together with the accumulated phase time.

Timing data can be appended to a file in benchmark data format
using the new -bench flag:

$ go build -gcflags="-bench=/dev/stdout" -o /dev/null go/types
commit: devel +8847c6b Mon Aug 15 17:51:53 2016 -0700
goos: darwin
goarch: amd64
BenchmarkCompile:go/types:fe:init              1       663292 ns/op      0.07 %
BenchmarkCompile:go/types:fe:loadsys           1      1337371 ns/op      0.14 %
BenchmarkCompile:go/types:fe:parse             1     47008869 ns/op      4.91 %    10824 lines    230254 lines/s
BenchmarkCompile:go/types:fe:typecheck:top1    1      2843343 ns/op      0.30 %
BenchmarkCompile:go/types:fe:typecheck:top2    1       447457 ns/op      0.05 %
BenchmarkCompile:go/types:fe:typecheck:func    1     15119595 ns/op      1.58 %      427 funcs     28241 funcs/s
BenchmarkCompile:go/types:fe:capturevars       1        56314 ns/op      0.01 %
BenchmarkCompile:go/types:fe:inlining          1      9805767 ns/op      1.02 %
BenchmarkCompile:go/types:fe:escapes           1     53598646 ns/op      5.60 %
BenchmarkCompile:go/types:fe:xclosures         1       199302 ns/op      0.02 %
BenchmarkCompile:go/types:fe:subtotal          1    131079956 ns/op     13.70 %
BenchmarkCompile:go/types:be:compilefuncs      1    692009428 ns/op     72.33 %      427 funcs       617 funcs/s
BenchmarkCompile:go/types:be:externaldcls      1        54591 ns/op      0.01 %
BenchmarkCompile:go/types:be:dumpobj           1    133478173 ns/op     13.95 %
BenchmarkCompile:go/types:be:subtotal          1    825542192 ns/op     86.29 %
BenchmarkCompile:go/types:unaccounted          1       106101 ns/op      0.01 %
BenchmarkCompile:go/types:total                1    956728249 ns/op    100.00 %

For #16169.

Change-Id: I93265fe0cb08e47cd413608d0824c5dd35ba7899
Reviewed-on: https://go-review.googlesource.com/24462Reviewed-by: Matthew Dempsky <mdempsky@google.com>

.local addresses are used by things like Kubernetes and Weave DNS; Go
should not avoid resolving them.

This is a partial revert of https://golang.org/cl/21328 which was too
strict of an interpretation of RFC 6762.

Fixes #16739

Change-Id: I349415b4eab5d61240dd18217bd95dc7d2105cd5
Reviewed-on: https://go-review.googlesource.com/27250Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

The Width{int,ptr,reg} assignments are no longer necessary since
golang.org/cl/21623. The other arch's betypeinit functions were
cleaned up, but apparently this one was missed.

Change-Id: I1c7f074d7864a561659c1f98aef604f57f285fd0
Reviewed-on: https://go-review.googlesource.com/27272
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Michael Munday <munday@ca.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Updates #15419.

Change-Id: If7c80adcb38b5731e337b2ae2d9d76fcf8513d8e
Reviewed-on: https://go-review.googlesource.com/27271Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

BIND libresolv allows values from 0 to 15.

For invalid values and negative numbers, 0 is used.
For numbers greater than 15, 15 is used.

Fixes #15419

Change-Id: I1009bc119c3e87919bcb55a80a35532e9fc3ba52
Reviewed-on: https://go-review.googlesource.com/24901Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Test nil check removal for access of PAUTOHEAP.

Change-Id: Id739a9cda7cd3ff173bdcccfedcad93ee90711ef
Reviewed-on: https://go-review.googlesource.com/27232
Run-TryBot: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

The Source provided by math/rand relies on an array of cooked
pseudo-random 63bit integers for seeding. The origin of these
numbers is undocumented.

Add a standalone program in math/rand folder that generates
the 63bit integer array as well as a 64bit version supporting
extension of the Source to 64bit pseudo-random number
generation while maintaining the current sequence in the
lower 63bit.

The code is largely based on the initial implementation of the
random number generator in the go repository by Ken Thompson
(revision 399).

Change-Id: Ib4192aea8127595027116a0f5a7be53f11dc110b
Reviewed-on: https://go-review.googlesource.com/22230Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

sysUnused (e.g., madvise MADV_FREE) is only sensible to call on
physical page boundaries, so scavengelist rounds in the bounds of the
region being released to the nearest physical page boundaries.
However, if the region is smaller than a physical page and neither the
start nor end fall on a boundary, then rounding the start up to a page
boundary and the end down to a page boundary will result in end < start.
Currently, we only give up on the region if start == end, so if we
encounter end < start, we'll call madvise with a negative length and
the madvise will fail.

Issue #16644 gives a concrete example of this:

    start = 0x1285ac000
    end   = 0x1285ae000 (1 8K page)

This leads to the rounded values

    start = 0x1285b0000
    end   = 0x1285a0000

which leads to len = -65536.

Fix this by giving up on the region if end <= start, not just if
end == start.

Fixes #16644.

Change-Id: I8300db492dbadc82ac1ad878318b36bcb7c39524
Reviewed-on: https://go-review.googlesource.com/27230Reviewed-by: Keith Randall <khr@golang.org>

fixes #16493

Change-Id: I86bec2f9bd7965449c43e94733791f7cb18c5c4c
Reviewed-on: https://go-review.googlesource.com/25165Reviewed-by: Alex Brainman <alex.brainman@gmail.com>