On Windows, os.Chmod and syscall.Chmod toggle the FILE_ATTRIBUTES_
READONLY flag depending on the permission bits. That's a bit odd but I
guess some compromises were made at some point and this is what was
chosen to map to a Unix concept that Windows doesn't really have in the
same way. That's fine. However, the logic used in Chmod was forgotten
from os.Open and syscall.Open, which then manifested itself in various
places, most recently, go modules' read-only behavior.

This makes syscall.Open consistent with syscall.Chmod and adds a test
for the permission _behavior_ using ioutil. By testing the behavior
instead of explicitly testing for the attribute bits we care about, we
make sure this doesn't regress in unforeseen ways in the future, as well
as ensuring the test works on platforms other than Windows.

In the process, we fix some tests that never worked and relied on broken
behavior, as well as tests that were disabled on Windows due to the
broken behavior and had TODO notes.

Fixes #35033

Change-Id: I6f7cf54517cbe5f6b1678d1c24f2ab337edcc7f7
Reviewed-on: https://go-review.googlesource.com/c/go/+/202439
Run-TryBot: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Fixes #35045

Change-Id: I90ac29882c7d03936c98c4116a8bccdd2ecbf76b
Reviewed-on: https://go-review.googlesource.com/c/go/+/202445
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

Fixes #35053

Change-Id: I31853d434610880044c169e0c1e9732f97ff1bdb
Reviewed-on: https://go-review.googlesource.com/c/go/+/202444
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David du Colombier <0intro@gmail.com>

Change-Id: I96a9b34bf8e42c21a3e0258cbc8b1416328834be
GitHub-Last-Rev: 32709619a690459dc29a32f12cfbd3908ce270e3
GitHub-Pull-Request: golang/go#35066
Reviewed-on: https://go-review.googlesource.com/c/go/+/202598
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

Make go test -a -short -gcflags=all=-d=checkptr passes on darwin.

Update #34972

Change-Id: I71cf14ec1faccd4837713aa30c90ed665899b908
Reviewed-on: https://go-review.googlesource.com/c/go/+/202158
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Caught by go test -a -short -gcflags=all=-d=checkptr runtime

TestMincoreErrorSign intentionally uses uintptr(1) to get -EINVAL,
but it violates unsafe pointer rules 2. So use another misaligned
pointer add(new(int32), 1), but do not violate unsafe pointer rules.

TestEpollctlErrorSign passes an unsafe.Pointer of &struct{}{} to
Epollctl, which is then casted to epollevent, causes mis-alignment.
Fixing it by exporting epollevent on runtime_test package, so it can be
passed to Epollctl.

Updates #34972

Change-Id: I78ebfbeaf706fd1d372272af0bbc4e2cabca4631
Reviewed-on: https://go-review.googlesource.com/c/go/+/202157
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Add new fields to runtime.timer, and adjust the various timer
functions in preparation for adding timers to P's. This continues to
use the old timer code.

Updates #6239
Updates #27707

Change-Id: I9adb3814f657e083ec5e22736c4b5b52b77b6a3f
Reviewed-on: https://go-review.googlesource.com/c/go/+/171829
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

This matches the behavior and error of cmd/compile.

Fixes #34946.

Change-Id: I329ef358deea63d8425f76f1d54c95749b96c365
Reviewed-on: https://go-review.googlesource.com/c/go/+/202484Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Updates #6239
Updates #27707

Change-Id: I52cab8bf3dc8c552463725fc1d9e4e6b12230b03
Reviewed-on: https://go-review.googlesource.com/c/go/+/171828
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

Follow the idiom for allowing -d=checkptr to recognize and verify
correctness.

Updates #22218.
Updates #34972.

Change-Id: Ib6001c6f0e6dc535a36bcfaa1ae48e29e0c737f8
Reviewed-on: https://go-review.googlesource.com/c/go/+/202580
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

A common idiom for turning an unsafe.Pointer into a slice is to write:

    s := (*[Big]T)(ptr)[:n:m]

This technically violates Go's unsafe pointer rules (rule #1 says T2
can't be bigger than T1), but it's fairly common and not too difficult
to recognize, so might as well allow it for now so we can make
progress on #34972.

This should be revisited if #19367 is accepted.

Updates #22218.
Updates #34972.

Change-Id: Id824e2461904e770910b6e728b4234041d2cc8bc
Reviewed-on: https://go-review.googlesource.com/c/go/+/201839
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Fixes #34925

Change-Id: Iadf12ca47a69b62c3f48d732b430cc85cf62a91c
Reviewed-on: https://go-review.googlesource.com/c/go/+/202577Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

When we put timers on P's, the wasm code will not be able to rely on
the timer goroutine. Use the beforeIdle hook to schedule a wakeup.

Updates #6239
Updates #27707

Change-Id: Idf6309944778b8c3d7178f5d09431940843ea233
Reviewed-on: https://go-review.googlesource.com/c/go/+/171827
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

Slight differences existed due to a change in rulegen after the
FMA intrinsic code was generated.

Change-Id: Ieb6b3ec1b29985a18d1bbbc5a820ffea699306fd
Reviewed-on: https://go-review.googlesource.com/c/go/+/202443
Run-TryBot: Michael Munday <mike.munday@ibm.com>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Avoids false positive pointer arithmetic panic.

Fixes #35027.

Change-Id: Idd008caaab25fcf739327ac50a021b835ef13def
Reviewed-on: https://go-review.googlesource.com/c/go/+/202560
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

The parseURL variable was introduced in CL 49930 in order to work
around the fact that the name "url" was shadowed by a parameter of
exported functions, and couldn't be renamed without sacrificing
documentation readability. Documentation readability takes higher
priority than internal implementation details.

Back then, I considered renaming the net/url import but saw that it
would be too disruptive of a change to the large net/http package.

Now I see a better way: it's possible to import net/url both as url
and as urlpkg (the package is still imported just once, but it becomes
available via two names). This way we eliminate the need for wasting
(a little) memory on the parseURL variable, improve code readability
slightly, and delete some lines of code and comments.

Updates #21077

Change-Id: I42cd9833afdcf4a5f5874fb7ee9c8c11eae557dc
Reviewed-on: https://go-review.googlesource.com/c/go/+/202482Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

This var _ = log.Printf line was added 8 years ago, in CL 4973055,
which created the database/sql package and its tests. There was no
goimports back then, so this was likely added to make it easier to
use log package during development of tests.

It's no longer needed, so remove it. It can always be conveniently
re-added via goimports whenever needed.

Change-Id: I7c32ae3e593c194d970920084139dfa5a42386dc
Reviewed-on: https://go-review.googlesource.com/c/go/+/202481
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

localPipe currently flakes in various crypto/tls tests. Since that
function doesn't seem to flake anywhere else, I suspect a kernel bug.

To make the test less flaky, retry the Dial if we suspect that it is
affected. (Worst case, we delay the test by a few seconds before
erroring out as usual.)

Fixes #29583

Change-Id: I357990ffa316edb471bd7d46d6404fa0884da646
Reviewed-on: https://go-review.googlesource.com/c/go/+/202557
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

CL 200077 removed nacl bits in the toolchain, but it misses the code to
add pointer overflow padding, which is specific for nacl.

This CL removes that part.

Passes toolstash-check.

Updates #30439

Change-Id: I1e77cade9f31690e16cd13d3445a98b500671252
Reviewed-on: https://go-review.googlesource.com/c/go/+/202159
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

Change-Id: I224db88f3809001802e004077ce856f0e3347c67
Reviewed-on: https://go-review.googlesource.com/c/go/+/169017Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Makes TimeoutHandler consistent with other handlers, by
logging any spurious WriteHeader calls.

Fixes #30803

Change-Id: I693fbdf8378f31bca13d579eece8e8e00eb175bf
Reviewed-on: https://go-review.googlesource.com/c/go/+/200518
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Document that if either src implements the WriteTo interface
or if dst implements the ReaderFrom interface, then
buf will not be used.

Fixes #32276

Change-Id: Id0a69c90e255e694e7ec9f79ffe4d8391441e59e
GitHub-Last-Rev: 750e7e86d5d9b985fae7f2329fd219cacf72a62b
GitHub-Pull-Request: golang/go#32279
Reviewed-on: https://go-review.googlesource.com/c/go/+/179137Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

This change introduces an arm intrinsic that generates the FMULAD
instruction for the fused-multiply-add operation on systems that
support it. System support is detected via cpu.ARM.HasVFPv4. A rewrite
rule translates the generic intrinsic to FMULAD.

Updates #25819.

Change-Id: I8459e5dd1cdbdca35f88a78dbeb7d387f1e20efa
Reviewed-on: https://go-review.googlesource.com/c/go/+/142117
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

Add support to the main scheduler loop for handling timers on P's.
This is not used yet, as timers are not yet put on P's.

Updates #6239
Updates #27707

Change-Id: I6a359df408629f333a9232142ce19e8be8496dae
Reviewed-on: https://go-review.googlesource.com/c/go/+/171826
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

Fixes #35015

Change-Id: I7a1ed9cfa219ad88014aad033e3a01f9dffc3eb3
Reviewed-on: https://go-review.googlesource.com/c/go/+/202239
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

As a small step toward speeding up timers, restrict modification
of the timer.when field to the timer code itself. Other code that
wants to change the when field of an existing timer must now call
resettimer rather than changing the when field and calling addtimer.
The new resettimer function also works for a new timer.

This is just a refactoring in preparation for later code.

Updates #27707

Change-Id: Iccd5dcad415ffbeac4c2a3cf015e91f82692acf8
Reviewed-on: https://go-review.googlesource.com/c/go/+/171825
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

To permit ssa-level optimization, this change introduces an amd64 intrinsic
that generates the VFMADD231SD instruction for the fused-multiply-add
operation on systems that support it. System support is detected via
cpu.X86.HasFMA. A rewrite rule can then translate the generic ssa intrinsic
("Fma") to VFMADD231SD.

The benchmark compares the software implementation (old) with the intrinsic
(new).

name   old time/op  new time/op  delta
Fma-4  27.2ns ± 1%   1.0ns ± 9%  -96.48%  (p=0.008 n=5+5)

Updates #25819.

Change-Id: I966655e5f96817a5d06dff5942418a3915b09584
Reviewed-on: https://go-review.googlesource.com/c/go/+/137156
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

The new netpollBreak function can be used to interrupt a blocking netpoll.
This function is not currently used; it will be used by later CLs.

Updates #27707

Change-Id: I5cb936609ba13c3c127ea1368a49194fc58c9f4d
Reviewed-on: https://go-review.googlesource.com/c/go/+/171824
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

In order to make math.FMA a compiler intrinsic for ISAs like ARM64,
PPC64[le], and S390X, a generic 3-argument opcode "Fma" is provided and
rewritten as

    ARM64: (Fma x y z) -> (FMADDD z x y)
    PPC64: (Fma x y z) -> (FMADD x y z)
    S390X: (Fma x y z) -> (FMADD z x y)

Updates #25819.

Change-Id: Ie5bc628311e6feeb28ddf9adaa6e702c8c291efa
Reviewed-on: https://go-review.googlesource.com/c/go/+/131959
Run-TryBot: Akhil Indurti <aindurti@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

Currently, the precision of the float64 multiply-add operation
(x * y) + z varies across architectures. While generated code for
ppc64, s390x, and arm64 can guarantee that there is no intermediate
rounding on those platforms, other architectures like x86, mips, and
arm will exhibit different behavior depending on available instruction
set. Consequently, applications cannot rely on results being identical
across GOARCH-dependent codepaths.

This CL introduces a software implementation that performs an IEEE 754
double-precision fused-multiply-add operation. The only supported
rounding mode is round-to-nearest ties-to-even. Separate CLs include
hardware implementations when available. Otherwise, this software
fallback is given as the default implementation.

Specifically,
    - arm64, ppc64, s390x: Uses the FMA instruction provided by all
      of these ISAs.
    - mips[64][le]: Falls back to this software implementation. Only
      release 6 of the ISA includes a strict FMA instruction with
      MADDF.D (not implementation defined). Because the number of R6
      processors in the wild is scarce, the assembly implementation
      is left as a future optimization.
    - x86: Guards the use of VFMADD213SD by checking cpu.X86.HasFMA.
    - arm: Guards the use of VFMA by checking cpu.ARM.HasVFPv4.
    - software fallback: Uses mostly integer arithmetic except
      for input that involves Inf, NaN, or zero.

Updates #25819.

Change-Id: Iadadff2219638bacc9fec78d3ab885393fea4a08
Reviewed-on: https://go-review.googlesource.com/c/go/+/127458
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

This change adds the '-modcacherw' build flag, which leaves
newly-created directories (but not the files!) in the module cache
read-write instead of making them unwritable.

Fixes #31481

Change-Id: I7c21a53dd145676627c3b51096914ce797991d99
Reviewed-on: https://go-review.googlesource.com/c/go/+/202079
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

The internal read and write functions used to return -1 on error;
change them to return a negative errno value instead.
This will be used by later CLs in this series.

For most targets this is a simplification, although for ones that call
into libc it is a complication.

Updates #27707

Change-Id: Id02bf9487f03e7e88e4f2b85e899e986738697ad
Reviewed-on: https://go-review.googlesource.com/c/go/+/171823
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

This picks up CL 202317 which fixes golang.org/x/net for Dragonfly
master (upcoming 5.8 release). Also re-enable the interface tests
disabled in CL 201482.

Vendored using:

    $ go get golang.org/x/net@24d2ffbea1e8
    $ go mod tidy
    $ go mod vendor

Fixes #34368

Change-Id: Iac152b7ffaa607bfedbb4024b4e1ffc9b649d689
Reviewed-on: https://go-review.googlesource.com/c/go/+/202438
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

On MIPS, pipe returns two values rather than taking a pointer.

On MIPS64, call pipe2 rather than pipe.

Also, use the correct system call number for fcntl on mips64.

Change-Id: Ie72acdefeb593f44cb98735fc40eac99cf73509e
Reviewed-on: https://go-review.googlesource.com/c/go/+/202417
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Updates golang/go#20821

Change-Id: I186356a78ac385a15b4604e0ea6110c4c212ebc4
Reviewed-on: https://go-review.googlesource.com/c/go/+/202357Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

This requires defining pipe, pipe2, and setNonblock for various platforms.

The new function is currently only used on AIX. It will be used by
later CLs in this series.

Updates #27707

Change-Id: Id2f987b66b4c66a3ef40c22484ff1d14f58e9b31
Reviewed-on: https://go-review.googlesource.com/c/go/+/171822
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

On case insensitive filesystems, '.S' is interpreted as '.s' so,
providing option to use '.sx' extension for '.S' files as an alternative.

Fixes #32434

Change-Id: Ie2f7e5e2f3f12690ce18659e30ca94252a8f7bfc
GitHub-Last-Rev: dcca989ec41ddc1d06ea509b78dce7d70bc996ed
GitHub-Pull-Request: golang/go#32557
Reviewed-on: https://go-review.googlesource.com/c/go/+/181699
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Fixes #34730

Change-Id: I2a16bbbd7af386e0abf59e1cc4b7d6e4ca3047c6
GitHub-Last-Rev: 096ff5a59ace36ac6ed5a0c87b4eef061be6b937
GitHub-Pull-Request: golang/go#34899
Reviewed-on: https://go-review.googlesource.com/c/go/+/201039
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Use 32-bit alignment for versions before the September 2019 ABI changes
http://lists.dragonflybsd.org/pipermail/users/2019-September/358280.html

Fixes #34958

Change-Id: Iab4b23083a7c9ca7e96a737b03e75cd36d98ee24
Reviewed-on: https://go-review.googlesource.com/c/go/+/201977
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Instead of using a two-slot array and having to remember which
index is the signed poset, and which is the unsigned one, just
use two different variables.

Change-Id: Ic7f7676436c51bf43a182e999a926f8b7f69434b
Reviewed-on: https://go-review.googlesource.com/c/go/+/196678Reviewed-by: Keith Randall <khr@golang.org>