gogo called from GC is okay
for the same reasons that
gogo called from System or ExternalCode is okay.
All three are fake stack traces.

Fixes #8408.

LGTM=dvyukov, r
R=r, dvyukov
CC=golang-codereviews
https://golang.org/cl/152580043

This doesn't actually do anything. Maybe it will some day,
but maybe not.

TBR=r
CC=golang-codereviews
https://golang.org/cl/155490043

LGTM=iant
R=golang-codereviews, iant
CC=dvyukov, golang-codereviews, jamesr, nigeltao
https://golang.org/cl/155530043

Dmitriy believes this broke Windows.
It looks like build.golang.org stopped before that,
but it's worth a shot.

««« original CL description
runtime: make pprof a little nicer

Update #8942

This does not fully address issue 8942 but it does make
the profiles much more useful, until that issue can be
fixed completely.

LGTM=dvyukov
R=r, dvyukov
CC=golang-codereviews
https://golang.org/cl/159990043
»»»

TBR=dvyukov
CC=golang-codereviews
https://golang.org/cl/160030043

Fixes #8496.

LGTM=rsc, r, iant
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/148580043

LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/160920045

LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/159920044

Fixes #8849.

LGTM=bradfitz, aram
R=bradfitz, rsc, aram
CC=golang-codereviews
https://golang.org/cl/158970045

It cannot run 'go tool pprof'. There is no guarantee that's installed.
It needs to build a temporary pprof binary and run that.
It also needs to skip the test on systems that can't build and
run binaries, namely android and nacl.

See src/cmd/nm/nm_test.go's TestNM for a template.

Update #8867
Status: Accepted

TBR=dvyukov
CC=golang-codereviews
https://golang.org/cl/153710043

Update #8942

This does not fully address issue 8942 but it does make
the profiles much more useful, until that issue can be
fixed completely.

LGTM=dvyukov
R=r, dvyukov
CC=golang-codereviews
https://golang.org/cl/159990043

There are 3 issues:
1. Skip argument of callers is off by 3,
so that all allocations are deep inside of memory profiler.
2. Memory profiling statistics are not updated after runtime.GC.
3. Testing package does not update memory profiling statistics
before capturing the profile.
Also add an end-to-end test.
Fixes #8867.

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/148710043

Both of these forms can avoid writing to the base pointer in x
(in the slice, always, and in the append, most of the time).

For Go 1.5, will need to change the compilation of x = x[0:y]
to avoid writing to the base pointer, so that the elision is safe,
and will need to change the compilation of x = append(x, ...)
to write to the base pointer (through a barrier) only when
growing the underlying array, so that the general elision is safe.

For Go 1.4, elide the write barrier always, a change that should
have equivalent performance characteristics but is much
simpler and therefore safer.

benchmark                       old ns/op   new ns/op   delta
BenchmarkBinaryTree17           3910526122  3918802545  +0.21%
BenchmarkFannkuch11             3747650699  3732600693  -0.40%
BenchmarkFmtFprintfEmpty        106         98.7        -6.89%
BenchmarkFmtFprintfString       280         269         -3.93%
BenchmarkFmtFprintfInt          296         282         -4.73%
BenchmarkFmtFprintfIntInt       467         470         +0.64%
BenchmarkFmtFprintfPrefixedInt  418         398         -4.78%
BenchmarkFmtFprintfFloat        574         535         -6.79%
BenchmarkFmtManyArgs            1768        1818        +2.83%
BenchmarkGobDecode              14916799    14925182    +0.06%
BenchmarkGobEncode              14110076    13358298    -5.33%
BenchmarkGzip                   546609795   542630402   -0.73%
BenchmarkGunzip                 136270657   136496277   +0.17%
BenchmarkHTTPClientServer       126574      125245      -1.05%
BenchmarkJSONEncode             30006238    27862354    -7.14%
BenchmarkJSONDecode             106020889   102664600   -3.17%
BenchmarkMandelbrot200          5793550     5818320     +0.43%
BenchmarkGoParse                5437608     5463962     +0.48%
BenchmarkRegexpMatchEasy0_32    192         179         -6.77%
BenchmarkRegexpMatchEasy0_1K    462         460         -0.43%
BenchmarkRegexpMatchEasy1_32    168         153         -8.93%
BenchmarkRegexpMatchEasy1_1K    1420        1280        -9.86%
BenchmarkRegexpMatchMedium_32   338         286         -15.38%
BenchmarkRegexpMatchMedium_1K   107435      98027       -8.76%
BenchmarkRegexpMatchHard_32     5941        4846        -18.43%
BenchmarkRegexpMatchHard_1K     185965      153830      -17.28%
BenchmarkRevcomp                795497458   798447829   +0.37%
BenchmarkTemplate               132091559   134938425   +2.16%
BenchmarkTimeParse              604         608         +0.66%
BenchmarkTimeFormat             551         548         -0.54%

LGTM=r
R=r, dave
CC=golang-codereviews, iant, khr, rlh
https://golang.org/cl/159960043

A new attack on CBC padding in SSLv3 was released yesterday[1]. Go only
supports SSLv3 as a server, not as a client. An easy fix is to change
the default minimum version to TLS 1.0 but that seems a little much
this late in the 1.4 process as it may break some things.

Thus this patch adds server support for TLS_FALLBACK_SCSV[2] -- a
mechanism for solving the fallback problem overall. Chrome has
implemented this since February and Google has urged others to do so in
light of yesterday's news.

With this change, clients can indicate that they are doing a fallback
connection and Go servers will be able to correctly reject them.

[1] http://googleonlinesecurity.blogspot.com/2014/10/this-poodle-bites-exploiting-ssl-30.html
[2] https://tools.ietf.org/html/draft-ietf-tls-downgrade-scsv-00

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/157090043

Among other things, *x = T{} does not need a write barrier.
The changes here avoid an unnecessary copy even when
no pointers are involved, so it may have larger effects.

In 6g and 8g, avoid manually repeated STOSQ in favor of
writing explicit MOVs, under the theory that the MOVs
should have fewer dependencies and pipeline better.

Benchmarks compare best of 5 on a 2012 MacBook Pro Core i5
with TurboBoost disabled. Most improvements can be explained
by the changes in this CL.

The effect in Revcomp is real but harder to explain: none of
the instructions in the inner loop changed. I suspect loop
alignment but really have no idea.

benchmark                       old         new         delta
BenchmarkBinaryTree17           3809027371  3819907076  +0.29%
BenchmarkFannkuch11             3607547556  3686983012  +2.20%
BenchmarkFmtFprintfEmpty        118         103         -12.71%
BenchmarkFmtFprintfString       289         277         -4.15%
BenchmarkFmtFprintfInt          304         290         -4.61%
BenchmarkFmtFprintfIntInt       507         458         -9.66%
BenchmarkFmtFprintfPrefixedInt  425         408         -4.00%
BenchmarkFmtFprintfFloat        555         555         +0.00%
BenchmarkFmtManyArgs            1835        1733        -5.56%
BenchmarkGobDecode              14738209    14639331    -0.67%
BenchmarkGobEncode              14239039    13703571    -3.76%
BenchmarkGzip                   538211054   538701315   +0.09%
BenchmarkGunzip                 135430877   134818459   -0.45%
BenchmarkHTTPClientServer       116488      116618      +0.11%
BenchmarkJSONEncode             28923406    29294334    +1.28%
BenchmarkJSONDecode             105779820   104289543   -1.41%
BenchmarkMandelbrot200          5791758     5771964     -0.34%
BenchmarkGoParse                5376642     5310943     -1.22%
BenchmarkRegexpMatchEasy0_32    195         190         -2.56%
BenchmarkRegexpMatchEasy0_1K    477         455         -4.61%
BenchmarkRegexpMatchEasy1_32    170         165         -2.94%
BenchmarkRegexpMatchEasy1_1K    1410        1394        -1.13%
BenchmarkRegexpMatchMedium_32   336         329         -2.08%
BenchmarkRegexpMatchMedium_1K   108979      106328      -2.43%
BenchmarkRegexpMatchHard_32     5854        5821        -0.56%
BenchmarkRegexpMatchHard_1K     185089      182838      -1.22%
BenchmarkRevcomp                834920364   780202624   -6.55%
BenchmarkTemplate               137046937   129728756   -5.34%
BenchmarkTimeParse              600         594         -1.00%
BenchmarkTimeFormat             559         539         -3.58%

LGTM=r
R=r
CC=golang-codereviews, iant, khr, rlh
https://golang.org/cl/157910047

LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/157080043

Fixes #8828.

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/154410043

The general writebarrierfat needs a temporary for src,
because we need to pass the address of the temporary
to the writebarrierfat routine. But the new fixed-size
ones pass the value directly and don't need to introduce
the temporary.

Magnifies some of the effect of the custom write barrier change.

Comparing best of 5 with TurboBoost turned off,
on a 2012 Retina MacBook Pro Core i5.
Still not completely confident in these numbers,
but the fmt, regexp, and revcomp improvements seem real.

benchmark                      old ns/op  new ns/op  delta
BenchmarkBinaryTree17          3942965521 3929654940 -0.34%
BenchmarkFannkuch11            3707543350 3699566011 -0.22%
BenchmarkFmtFprintfEmpty       119        119        +0.00%
BenchmarkFmtFprintfString      295        296        +0.34%
BenchmarkFmtFprintfInt         313        314        +0.32%
BenchmarkFmtFprintfIntInt      517        484        -6.38%
BenchmarkFmtFprintfPrefixedInt 439        429        -2.28%
BenchmarkFmtFprintfFloat       571        569        -0.35%
BenchmarkFmtManyArgs           1899       1820       -4.16%
BenchmarkGobDecode             15507208   15325649   -1.17%
BenchmarkGobEncode             14811710   14715434   -0.65%
BenchmarkGzip                  561144467  549624323  -2.05%
BenchmarkGunzip                137377667  137691087  +0.23%
BenchmarkHTTPClientServer      126632     124717     -1.51%
BenchmarkJSONEncode            29944112   29526629   -1.39%
BenchmarkJSONDecode            108954913  107339551  -1.48%
BenchmarkMandelbrot200         5828755    5821659    -0.12%
BenchmarkGoParse               5577437    5521895    -1.00%
BenchmarkRegexpMatchEasy0_32   198        193        -2.53%
BenchmarkRegexpMatchEasy0_1K   486        469        -3.50%
BenchmarkRegexpMatchEasy1_32   175        167        -4.57%
BenchmarkRegexpMatchEasy1_1K   1450       1419       -2.14%
BenchmarkRegexpMatchMedium_32  344        338        -1.74%
BenchmarkRegexpMatchMedium_1K  112088     109855     -1.99%
BenchmarkRegexpMatchHard_32    6078       6003       -1.23%
BenchmarkRegexpMatchHard_1K    191166     187499     -1.92%
BenchmarkRevcomp               854870445  799012851  -6.53%
BenchmarkTemplate              141572691  141508105  -0.05%
BenchmarkTimeParse             604        603        -0.17%
BenchmarkTimeFormat            579        560        -3.28%

LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/155450043

scalar is no longer needed, now that
interfaces always hold pointers.

Comparing best of 5 with TurboBoost turned off,
on a 2012 Retina MacBook Pro Core i5.
Still not completely confident in these numbers,
but the gob and template improvements seem real.

benchmark                       old ns/op   new ns/op   delta
BenchmarkBinaryTree17           3819892491  3803008185  -0.44%
BenchmarkFannkuch11             3623876405  3611776426  -0.33%
BenchmarkFmtFprintfEmpty        119         118         -0.84%
BenchmarkFmtFprintfString       294         292         -0.68%
BenchmarkFmtFprintfInt          310         304         -1.94%
BenchmarkFmtFprintfIntInt       513         507         -1.17%
BenchmarkFmtFprintfPrefixedInt  427         426         -0.23%
BenchmarkFmtFprintfFloat        562         554         -1.42%
BenchmarkFmtManyArgs            1873        1832        -2.19%
BenchmarkGobDecode              15824504    14746565    -6.81%
BenchmarkGobEncode              14347378    14208743    -0.97%
BenchmarkGzip                   537229271   537973492   +0.14%
BenchmarkGunzip                 134996775   135406149   +0.30%
BenchmarkHTTPClientServer       119065      116937      -1.79%
BenchmarkJSONEncode             29134359    28928099    -0.71%
BenchmarkJSONDecode             106867289   105770161   -1.03%
BenchmarkMandelbrot200          5798475     5791433     -0.12%
BenchmarkGoParse                5299169     5379201     +1.51%
BenchmarkRegexpMatchEasy0_32    195         195         +0.00%
BenchmarkRegexpMatchEasy0_1K    477         477         +0.00%
BenchmarkRegexpMatchEasy1_32    170         170         +0.00%
BenchmarkRegexpMatchEasy1_1K    1412        1397        -1.06%
BenchmarkRegexpMatchMedium_32   336         337         +0.30%
BenchmarkRegexpMatchMedium_1K   109025      108977      -0.04%
BenchmarkRegexpMatchHard_32     5854        5856        +0.03%
BenchmarkRegexpMatchHard_1K     184914      184748      -0.09%
BenchmarkRevcomp                829233526   836598734   +0.89%
BenchmarkTemplate               142055312   137016166   -3.55%
BenchmarkTimeParse              598         597         -0.17%
BenchmarkTimeFormat             564         568         +0.71%

Fixes #7425.

LGTM=r
R=golang-codereviews, r
CC=golang-codereviews, iant, khr
https://golang.org/cl/158890043

LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/152640043

A Go prototype can be used instead now, and the compiler
will do a better job than we will doing it by hand.
(We got it wrong in amd64p32, causing the current build
breakage.)

The auto-prototype-matching only applies to functions
without an explicit package path, so the TEXT lines for
reflectcall and callXX are s/runtime·/·/.

LGTM=khr
R=khr
CC=golang-codereviews, iant, r
https://golang.org/cl/153600043

Fixes #7969.

LGTM=bradfitz
R=bradfitz
CC=golang-codereviews
https://golang.org/cl/158950043

Fixes #7990.

LGTM=iant, bradfitz
R=bradfitz, iant, robryk
CC=golang-codereviews
https://golang.org/cl/156220043

Fixes #6606.

LGTM=rsc
R=rsc
CC=golang-codereviews, gri
https://golang.org/cl/156210044

The http package by default adds "Accept-Encoding: gzip" to outgoing
requests, unless it's a bad idea, or the user requested otherwise.
Only when the http package adds its own implicit Accept-Encoding header
does the http package also transparently un-gzip the response.

If the user requested part of a document (e.g. bytes 40 to 50), it appears
that Github/Varnish send:
        range(gzip(content), 40, 50)

And not:
        gzip(range(content, 40, 50))

The RFC 2616 set of replacements (with the purpose of
clarifying ambiguities since 1999) has an RFC about Range
requests (http://tools.ietf.org/html/rfc7233) but does not
mention the interaction with encodings.

Regardless of whether range(gzip(content)) or gzip(range(content)) is
correct, this change prevents the Go package from asking for gzip
in requests if we're also asking for Range, avoiding the issue.
If the user cared, they can do it themselves. But Go transparently
un-gzipping a fragment of gzip is never useful.

Fixes #8923

LGTM=adg
R=adg
CC=golang-codereviews
https://golang.org/cl/155420044

Fixes #8534

LGTM=adg
R=adg
CC=golang-codereviews
https://golang.org/cl/149340044

Fixes #8936.

LGTM=bradfitz
R=agl, bradfitz
CC=golang-codereviews
https://golang.org/cl/152590043

The assembler could give a better error, but this one
is good enough for now.

Fixes #8880.

LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/153610043

When the Import function in go/build encounters a directory
without any buildable Go source files, it returns a handy
NoGoError. Now if, instead it encounters multiple Go source files
from multiple packages, it returns a handy MultiplePackageError.

A new test for NoGoError and MultiplePackageError is also provided.

Fixes #8286.

LGTM=adg, rsc
R=bradfitz, rsc, adg
CC=golang-codereviews
https://golang.org/cl/155050043

The racewalk code was not updated for the new write barriers.
Make it more future-proof.

The new write barrier code assumed that +1 pointer would
be aligned properly for any type that might follow, but that's
not true on 32-bit systems where some types are 64-bit aligned.
The only system like that today is nacl/amd64p32.
Insert a dummy pointer so that the ambiguously typed
value is at +2 pointers, which is always max-aligned.

LGTM=r
R=r
CC=golang-codereviews, iant, khr
https://golang.org/cl/158890046

FieldByIndex never returns an invalid Value, so the validity
test can be avoided if the field is not indirect.

BenchmarkGobEncode     12768642      12424022      -2.70%
BenchmarkGobEncode     60.11        61.78        1.03x

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/158890045

Fixes #7960.

LGTM=rsc
R=rsc
CC=golang-codereviews, gri
https://golang.org/cl/159800045

includes undo of 22318cd31d7d and also:
- always use SetUnhandledExceptionFilter on windows-386;
- crash when receive EXCEPTION_BREAKPOINT in exception handler.

Fixes #8006.

LGTM=rsc
R=golang-codereviews, rsc
CC=golang-codereviews
https://golang.org/cl/155360043

The inverse is defined whenever the element and the
modulus are relatively prime.  The code already handles
this situation, but the spec does not.

Test that it does indeed work.

Fixes #8875

LGTM=agl
R=agl
CC=golang-codereviews
https://golang.org/cl/155010043

Assignments of 2-, 3-, and 4-word values were handled
by individual MOV instructions (and for scalars still are).
But if there are pointers involved, those assignments now
go through the write barrier routine. Before this CL, they
went to writebarrierfat, which calls memmove.
Memmove is too much overhead for these small
amounts of data.

Instead, call writebarrierfat{2,3,4}, which are specialized
for the specific amount of data being copied.
Today the write barrier does not care which words are
pointers, so size alone is enough to distinguish the cases.
If we keep these distinctions in Go 1.5 we will need to
expand them for all the pointer-vs-scalar possibilities,
so the current 3 functions will become 3+7+15 = 25,
still not a large burden (we deleted more morestack
functions than that when we dropped segmented stacks).

BenchmarkBinaryTree17           3250972583  3123910344  -3.91%
BenchmarkFannkuch11             3067605223  2964737839  -3.35%
BenchmarkFmtFprintfEmpty        101         96.0        -4.95%
BenchmarkFmtFprintfString       267         235         -11.99%
BenchmarkFmtFprintfInt          261         253         -3.07%
BenchmarkFmtFprintfIntInt       444         402         -9.46%
BenchmarkFmtFprintfPrefixedInt  374         346         -7.49%
BenchmarkFmtFprintfFloat        472         449         -4.87%
BenchmarkFmtManyArgs            1537        1476        -3.97%
BenchmarkGobDecode              13986528    12432985    -11.11%
BenchmarkGobEncode              13120323    12537420    -4.44%
BenchmarkGzip                   451925758   437500578   -3.19%
BenchmarkGunzip                 113267612   110053644   -2.84%
BenchmarkHTTPClientServer       103151      77100       -25.26%
BenchmarkJSONEncode             25002733    23435278    -6.27%
BenchmarkJSONDecode             94213717    82568789    -12.36%
BenchmarkMandelbrot200          4804246     4713070     -1.90%
BenchmarkGoParse                4646114     4379456     -5.74%
BenchmarkRegexpMatchEasy0_32    163         158         -3.07%
BenchmarkRegexpMatchEasy0_1K    433         391         -9.70%
BenchmarkRegexpMatchEasy1_32    154         138         -10.39%
BenchmarkRegexpMatchEasy1_1K    1481        1132        -23.57%
BenchmarkRegexpMatchMedium_32   282         270         -4.26%
BenchmarkRegexpMatchMedium_1K   92421       86149       -6.79%
BenchmarkRegexpMatchHard_32     5209        4718        -9.43%
BenchmarkRegexpMatchHard_1K     158141      147921      -6.46%
BenchmarkRevcomp                699818791   642222464   -8.23%
BenchmarkTemplate               132402383   108269713   -18.23%
BenchmarkTimeParse              509         478         -6.09%
BenchmarkTimeFormat             462         456         -1.30%

LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/156200043

Right now, go tool 6g -A fails complaining about 'any' type.

TBR=r
CC=golang-codereviews
https://golang.org/cl/156200044

Lowers gc pause time by 5-10% on test/bench/garbage

LGTM=rsc, dvyukov
R=rsc, dvyukov
CC=golang-codereviews
https://golang.org/cl/157810043

In [1] the behaviour of encoding/asn1 with respect to marshaling
optional integers was changed. Previously, a zero valued integer would
be omitted when marshaling. After the change, if a default value was
set then the integer would only be omitted if it was the default value.

This changed the behaviour of crypto/x509 because
Certificate.MaxPathLen has a default value of -1 and thus zero valued
MaxPathLens would no longer be omitted when marshaling. This is
arguably a bug-fix -- a value of zero for MaxPathLen is valid and
meaningful and now could be expressed. However it broke users
(including Docker) who were not setting MaxPathLen at all.

This change again causes a zero-valued MaxPathLen to be omitted and
introduces a ZeroMathPathLen member that indicates that, yes, one
really does want a zero. This is ugly, but we value not breaking users.

[1] https://code.google.com/p/go/source/detail?r=4218b3544610e8d9771b89126553177e32687adf

LGTM=rsc
R=rsc
CC=golang-codereviews, golang-dev
https://golang.org/cl/153420045

(*Rat).SetString checks for denominator.

LGTM=gri
R=golang-codereviews, gri
CC=golang-codereviews
https://golang.org/cl/159760043

LGTM=gri
R=gri
CC=golang-codereviews, iant
https://golang.org/cl/159850044

This error is returned by lib9p when removing a file
without parent. It should fix TestRemoveAllRace
when running on ramfs.

LGTM=bradfitz, aram
R=rsc, bradfitz, aram
CC=golang-codereviews, mischief
https://golang.org/cl/153410044