Telling whether a string is a valid Go identifier can seem like an easy
task, but it's easy to forget about the edge cases. For example, some
implementations out there forget that an empty string or keywords like
"func" aren't valid identifiers.

Add a simple implementation with proper Unicode support, and start using
it in cmd/cover and cmd/doc. Other pieces of the standard library
reimplement part of this logic, but don't use a "func(string) bool"
signature, so we're leaving them untouched for now.

Add some tests too, to ensure that we actually got these edge cases
correctly.

Since telling whether a string is a valid identifier requires knowing
that it's not a valid keyword, add IsKeyword too. The internal map was
already accessible via Lookup, but "Lookup(str) != IDENT" isn't as easy
to understand as IsKeyword(str). And, as per Josh's suggestion, we could
have IsKeyword (and probably Lookup too) use a perfect hash function
instead of a global map.

Finally, for consistency with these new functions, add IsExported. That
makes go/ast.IsExported a bit redundant, so perhaps it can be deprecated
in favor of go/token.IsExported in the future. Clarify that
token.IsExported doesn't imply token.IsIdentifier, to avoid ambiguity.

Fixes #30064.

Change-Id: I0e0e49215fd7e47b603ebc2b5a44086c51ba57f7
Reviewed-on: https://go-review.googlesource.com/c/go/+/169018
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>

When string letters are all in lower/upper cases, both functions respectively
return original string.

Fixes #30987

Change-Id: Ie8d664f7af5e087f82c1bc156933e9a995645bf4
Reviewed-on: https://go-review.googlesource.com/c/go/+/171735Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Since CL 165799 was merged, VFP detection should work properly on FreeBSD.

Updates #27619

Change-Id: I386e856ceb54f0bf6e6bf83bf2d1e19154ba53f4
Reviewed-on: https://go-review.googlesource.com/c/go/+/171728
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

Merge case statement for OpARMSLL, OpARMSRL and OpARMSRA into an
existing one using the same logic.

Change-Id: Ic4224668228902e5188fb0559b5f1949cfea1381
Reviewed-on: https://go-review.googlesource.com/c/go/+/171724
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

This makes code more idiomatic and shows small performance gains of generic benchmarks.

Updates: #31456

name            old time/op    new time/op    delta
Hash8Bytes-8       275ns ± 4%     270ns ± 0%    ~     (p=0.213 n=9+8)
Hash320Bytes-8    1.46µs ± 5%    1.39µs ± 1%  -4.54%  (p=0.000 n=10+10)
Hash1K-8          3.99µs ± 5%    3.86µs ± 1%  -3.38%  (p=0.023 n=10+10)
Hash8K-8          28.9µs ± 0%    28.9µs ± 1%    ~     (p=0.315 n=10+10)

name            old speed      new speed      delta
Hash8Bytes-8    28.8MB/s ± 9%  29.6MB/s ± 0%    ~     (p=0.151 n=10+8)
Hash320Bytes-8   220MB/s ± 5%   230MB/s ± 1%  +4.65%  (p=0.000 n=10+10)
Hash1K-8         257MB/s ± 5%   265MB/s ± 1%  +3.38%  (p=0.023 n=10+10)
Hash8K-8         283MB/s ± 0%   284MB/s ± 1%    ~     (p=0.315 n=10+10)

Change-Id: Iee63aa042614e3bbeda9aaf5236180d4153f03c4
Reviewed-on: https://go-review.googlesource.com/c/go/+/171729Reviewed-by: Ilya Tokar <tocarip@gmail.com>
Run-TryBot: Ilya Tokar <tocarip@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

readValue is a hot function, clocking in at ~13% flat CPU use in
CodeDecoder. In particular, looping over the bytes is slow. That's
partially because the code contains a bounds check at the start of the
loop.

The source of the problem is that scanp is a signed integer, and comes
from a field, so the compiler doesn't know that it's non-negative. Help
it with a simple and comparatively cheap hint.

While at it, use scanp as the index variable directly, removing the need
for a duplicate index variable which is later added back into scanp.

name           old time/op    new time/op    delta
CodeDecoder-8    11.3ms ± 1%    11.2ms ± 1%  -0.98%  (p=0.000 n=9+9)

name           old speed      new speed      delta
CodeDecoder-8   172MB/s ± 1%   174MB/s ± 1%  +0.99%  (p=0.000 n=9+9)

Updates #28923.

Change-Id: I138f83babdf316fc97697cc18f595c3403c1ddb7
Reviewed-on: https://go-review.googlesource.com/c/go/+/170939
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Make 'go test' command to pass the default timeout (10m) to test programs if the value is not given from command line.

Fixes #28147

Change-Id: I7856e452224a51a92da03bab8e3a0f9d7c41d32a
GitHub-Last-Rev: 66f9a6f90e9ffe7c58d5c1fe32af84e16ea74ab8
GitHub-Pull-Request: golang/go#30545
Reviewed-on: https://go-review.googlesource.com/c/go/+/164963
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

Fixes #7501

Change-Id: Iac7c79cd4b30a90b14ed84bf1eba758972232a6c
Reviewed-on: https://go-review.googlesource.com/c/go/+/171337
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Rename it to PCIter and convert it to use methods.

Set pcscale once, during construction, to make call sites clearer.

Change some ints to bools.

Use a simple iteration termination condition,
instead of the cap comparison from the c2go translation.

Instead of requiring a Pcdata, which requires one caller
to synthesize a fake Pcdata, just ask for a byte slice.

Passes toolstash-check.

Change-Id: I811da0e929cf4a806bd6d70357ccf2911cd0c737
Reviewed-on: https://go-review.googlesource.com/c/go/+/171770
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

This code was written before the c2go toolchain conversion.
Replace the handwritten varint encoding routines
and the handwritten unsigned-to-signed conversions
with calls to encoding/binary.

Passes toolstash-check.

Change-Id: I30d7f408cde3772ee98a3825e83075c4e1ec96d8
Reviewed-on: https://go-review.googlesource.com/c/go/+/171769
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

If preprocessing or assembling has failed, we should not proceed.
First, there's no point.
Second, I will shortly add some sanity checks to linkpcln
that will fail on malformed input.

Change-Id: I055eeab1c2f3a66b4b2cadb551bbf4ab55d176f4
Reviewed-on: https://go-review.googlesource.com/c/go/+/171886
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

On AIX, syscallX functions are using the first argument to retrieve the
next arguments when calling asmcgocall. Therefore,//go:cgo_unsafe_args
is needed.

Change-Id: I7fe0fbf0c961250a6573c66a8b0eb897dff94bfe
Reviewed-on: https://go-review.googlesource.com/c/go/+/171723
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Change-Id: I80cca386de23cde39ab4ed3be9878374dc7607ec
Reviewed-on: https://go-review.googlesource.com/c/go/+/171721Reviewed-by: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

This file was forgotten during the port of aix/ppc64. In order to make
its tests passed, a few things were added:
- Add termios.h to zerrors
- Add AF_LOCAL = AF_UNIX as this constant doesn't exits natively on AIX
- Fix the alignment in cmsghdr structure.

TestPassFD doesn't work on AIX TL<2 because getsockname isn't working as
expected with unix socket.

Change-Id: I928705bfc78ada29e66df61fe97d8f379f8c739b
Reviewed-on: https://go-review.googlesource.com/c/go/+/171339
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

The previous version was executing "oslevel -s" everytime testableNetwork
was called with unix/unixgram network. The current version retrieves if
the network is possible only once at the beginning of the tests.

This is clearly faster:
ok      net     74.045s
ok      net     5.098s

Change-Id: I12549da27721f85c007cf17cab5cfdbfeb839cf6
Reviewed-on: https://go-review.googlesource.com/c/go/+/171717
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Change-Id: Idbd6c97d754e3565aeade4d9e8011a76e8da19c2
GitHub-Last-Rev: 22e917e5ca429d76506346841e5b3c93c2a5f3fb
GitHub-Pull-Request: golang/go#31439
Reviewed-on: https://go-review.googlesource.com/c/go/+/171885Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Change-Id: I693250e980cc60ea151736b42ac6b1426ab801b3
Reviewed-on: https://go-review.googlesource.com/c/go/+/171765
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Since CL 170941 bootstrap.bash fails if no exec wrapper exists for a
given GOOS/GOARCH yet:

  #### Building ../../go-linux-arm-bootstrap

  Building Go cmd/dist using /usr/local/go.
  Building Go toolchain1 using /usr/local/go.
  Building Go bootstrap cmd/go (go_bootstrap) using Go toolchain1.
  Building Go toolchain2 using go_bootstrap and Go toolchain1.
  Building Go toolchain3 using go_bootstrap and Go toolchain2.
  Building packages and commands for host, linux/amd64.
  Building packages and commands for target, linux/arm.
  rm: cannot remove 'bin/go_linux_arm_exec': No such file or directory

Fix it by using 'rm -f' to ignore nonexisting files.

Change-Id: Ib4b1e19747052fa4dca06319f35cc25a0545c4f7
Reviewed-on: https://go-review.googlesource.com/c/go/+/171722
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Elias Naur <mail@eliasnaur.com>

ftabaddstring adds a string to the pclntab.
The pclntab uses C strings, so the code added 1 to the length.
However, it also added an extraneous 1 in the Grow call. Remove that.

While we're here, simplify, document, remove an unnecessary parameter,
and remove some unnecessary conversions.

Shaves off a few bytes here and there, and thus updates #6853.

file      before    after     Δ       %       
go        14671316  14659028  -12288  -0.084% 
addr2line 4280552   4276456   -4096   -0.096% 
api       6058936   6050744   -8192   -0.135% 
buildid   2861040   2856944   -4096   -0.143% 
cgo       4867912   4863816   -4096   -0.084% 
compile   25770104  25753720  -16384  -0.064% 
cover     5286888   5282792   -4096   -0.077% 
dist      3634048   3629952   -4096   -0.113% 
doc       4691000   4686904   -4096   -0.087% 
fix       3393736   3389640   -4096   -0.121% 
link      6109280   6105184   -4096   -0.067% 
nm        4225960   4221864   -4096   -0.097% 
objdump   4636520   4632424   -4096   -0.088% 
pack      2285200   2281104   -4096   -0.179% 
pprof     14657508  14645220  -12288  -0.084% 
test2json 2818568   2814472   -4096   -0.145% 
trace     11618524  11610332  -8192   -0.071% 
vet       8403544   8395352   -8192   -0.097% 

Change-Id: I20b1f541de5d3ed326dd937aad6a43801862df51
Reviewed-on: https://go-review.googlesource.com/c/go/+/171820
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Inside syscall_syscall6 function, libcall can directly be on the stack.
This is first function called with //go:nosplit, unlike runtime syscalls
which can be called during the sigtramp or by others //go:nosplit
functions.

Change-Id: Icc28def1a63e525850ec3bfb8184b995dfeaa736
Reviewed-on: https://go-review.googlesource.com/c/go/+/171338
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Fixes #31424

Change-Id: I8364578cbc77827552bd764c716f68495ec51547
Reviewed-on: https://go-review.googlesource.com/c/go/+/171763Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Failures here don't otherwise affect the build, but they do cause a
slow file leak in the user's temp directory. The user deserves at
least a cursory warning that something may be amiss.

Updates #30789

Change-Id: Id0e72b1967e7f7c88cdc94d532554496653f264b
Reviewed-on: https://go-review.googlesource.com/c/go/+/171764
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

Updates #31293

Change-Id: I3d72f732be7b28059310ea6fc134c3bfac81492d
Reviewed-on: https://go-review.googlesource.com/c/go/+/171578Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

procresize is rather ungainly because it includes all of the code to
initialize new Ps and tear down unused Ps. Pull these out into their
own methods on the p type. This also tweaks the initialization loop in
procresize so we only initialize new Ps (and Ps we previously
destroyed) rather than asking each P "have you been initialized?"

This is for #10958 and #24543, but it's also just a nice cleanup.

Change-Id: Ic1242066f572c94a23cea8ea4dc47c918e31d559
Reviewed-on: https://go-review.googlesource.com/c/go/+/171762Reviewed-by: Michael Knyszek <mknyszek@google.com>

Change-Id: I8de5aa64a24e77e0ef876918fcace7668769ebc2
Reviewed-on: https://go-review.googlesource.com/c/go/+/171022Reviewed-by: Michael Knyszek <mknyszek@google.com>

Add a couple of testcase for a gccgo type checking bug.

Updates #31412.

Change-Id: I7a813dafde78e4add1432602d2af5fe879415e1c
Reviewed-on: https://go-review.googlesource.com/c/go/+/171761
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

The code to swap RemoveAllTestHook in and out in
TestRemoveAllWithMoreErrorThanReqSize was making a copy of the
RemoveAllTestHook pointer, then attempting to restore by loading from
the copy of that pointer. Since the two copies of the pointer aliased
the same address, the restore operation had no effect, and any
RemoveAll tests that happened to run after
TestRemoveAllWithMoreErrorThanReqSize would fail.

Fixes #31421

Change-Id: I7028475f5ceb3b0a2fa69d22af8d3379508c4531
Reviewed-on: https://go-review.googlesource.com/c/go/+/171777
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

For a failed interface conversion not in ",ok" form, getitab
calls itab.init to get the name of the missing method for the
panic message. itab.init will try to find the methods, populate
the method table as it goes. When some method is missing, it sets
itab.fun[0] to 0 before return. There is a small window that
itab.fun[0] could be non-zero.

If concurrently, another goroutine tries to do the same interface
conversion, it will read the same itab's fun[0]. If this happens
in the small window, it sees a non-zero fun[0] and thinks the
conversion succeeded, which is bad.

Fix the race by setting fun[0] to non-zero only when we know the
conversion succeeds. While here, also simplify the syntax
slightly.

Fixes #31419.

Change-Id: Ied34d3043079eb933e330c5877b85e13f98f1916
Reviewed-on: https://go-review.googlesource.com/c/go/+/171759
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

freebsd and netbsd require a minimum buffer size of 1K.

Note this doesn't quite fix freebsd, it has other bugs,
I'll file a separate issue.

Fixes #31403

Change-Id: I9d7e78f6d30859b34715afadc4b8bd3b1ecc606b
Reviewed-on: https://go-review.googlesource.com/c/go/+/171757
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

These workarounds predate proper DWARF support
and are no longer necessary.

Before this patch, running `/usr/bin/symbols go.o`
using the object in the c-archive would fail, causing
App Store rejections.

Fixes #31022 #28997

Change-Id: I6a210b6369c13038777c6e21e874e81afcb50c2f
Reviewed-on: https://go-review.googlesource.com/c/go/+/170377
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Currently which treap a span should be inserted into/removed from is
checked by looking at the span's properties. This logic is repeated in
four places. As this logic gets more complex, it makes sense to
de-duplicate this, so introduce treapForSpan instead which captures this
logic by returning the appropriate treap for the span.

For #30333.

Change-Id: I4bd933d93dc50c5fc7c7c7f56ceb95194dcbfbcc
Reviewed-on: https://go-review.googlesource.com/c/go/+/170857
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

This change exports the runtime mTreap in export_test.go and then adds a
series of tests which check that the invariants of the treap are
maintained under different operations. These tests also include tests
for the treap iterator type.

Also, we note that the find() operation on the treap never actually was
best-fit, so the tests just ensure that it returns an appropriately
sized span.

For #30333.

Change-Id: If81f7c746dda6677ebca925cb0a940134701b894
Reviewed-on: https://go-review.googlesource.com/c/go/+/164100
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

Currently when coalescing if two adjacent spans are scavenged, we
subtract their sizes from memstats and re-scavenge the new combined
span. This is wasteful however, since the realignment semantics make
this case of having to re-scavenge impossible.

In realign() inside of coalesce(), there was also a bug: on systems
where physPageSize > pageSize, we wouldn't realign because a condition
had the wrong sign. This wasteful re-scavenging has been masking this
bug this whole time. So, this change fixes that first.

Then this change gets rid of the needsScavenge logic and instead checks
explicitly for the possibility of unscavenged pages near the physical
page boundary. If the possibility exists, it throws. The intent of
throwing here is to catch changes to the runtime which cause this
invariant to no longer hold, at which point it would likely be
appropriate to scavenge the additional pages (and only the additional
pages) at that point.

Change-Id: I185e3d7b53e36e90cf9ace5fa297a9e8008d75f3
Reviewed-on: https://go-review.googlesource.com/c/go/+/158377
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

This allows passing custom LDFLAGS while building the bootstrapping
tool.

Afterwards, GO_LDFLAGS will be used as usual.

Change-Id: I1e224e3ce8bf7b2ce1ef8fec1894720338f04396
GitHub-Last-Rev: 17d40dc2dd2f0815331cb2f8de3445f86687cc45
GitHub-Pull-Request: golang/go#31298
Reviewed-on: https://go-review.googlesource.com/c/go/+/171037
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

golang.org/cl/121255 added close and re-open the directory when looping, prevent
us from missing some if previous iteration deleted files.

The CL introdued a bug. If we can not delete all entries in one request,
the looping never exits, causing RemoveAll hangs.

To fix that, simply discard the entries if we can not delete all of them
in one iteration, then continue reading entries and delete them.

Also make sure removeall_at return first error it encounters.

Fixes #29921

Change-Id: I8ec3a4c822d8d2d95d9f1ab71547879da395bc4a
Reviewed-on: https://go-review.googlesource.com/c/go/+/171099
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Multiple calls to ReadDirent expect to return subsequent
portions of the directory listing. There's no place to store
our progress other than the file descriptor offset.

Fortunately, the file descriptor offset doesn't need to be
a real offset. We can store any int64 we want there.

Fixes #31368

Change-Id: I49e4e0e7ff707d3e96aa5d43e3b0199531013cde
Reviewed-on: https://go-review.googlesource.com/c/go/+/171477
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Fixes #30970

Change-Id: I333676b55a2364e329fffeafca8fc57d45a0b84b
Reviewed-on: https://go-review.googlesource.com/c/go/+/168598Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

The check of MADD&MSUB was added to the function IsMIPSMUL in
a previous commit, and the comments should also be updated.

Change-Id: I2d3da055d55b459b908714c542dff99ab5c6cf99
Reviewed-on: https://go-review.googlesource.com/c/go/+/171102Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

CL 170955 set tlsg to the Android Q free TLS slot offset in the linker
data (16 on amd64, 8 on 386), offsetting all TLS relative access.
We need the 0'th slot (TLS_SLOT_SELF) at initialization, so
compensate with a corresponding negative offset.

Fixes the android/386 and android/amd64 builders broken by CL 170955.

Change-Id: I9882088c0c8bc6a777d2aabc9404cb76f02b6cea
Reviewed-on: https://go-review.googlesource.com/c/go/+/170956
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

Change-Id: I209b75dc8dc4da881b68e5c5d98cbf08c1032dfc
Reviewed-on: https://go-review.googlesource.com/c/go/+/171098Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>