"archive/tar: reuse temporary buffer in writeHeader" introduced a
change which was supposed to help lower the number of allocations from
512 bytes for every call to writeHeader. This change broke the writing
of PAX headers.

writeHeader calls writePAXHeader and writePAXHeader calls writeHeader
again. writeHeader will end up writing the PAX header twice.

example broken header:
PaxHeaders.4007/NetLock_Arany_=Class_Gold=_Ftanstvny.crt0000000000000000000000000000007112301216634021512 xustar0000000000000000
PaxHeaders.4007/NetLock_Arany_=Class_Gold=_Ftanstvny.crt0000000000000000000000000000007112301216634021512 xustar0000000000000000

example correct header:
PaxHeaders.4290/NetLock_Arany_=Class_Gold=_Ftanstvny.crt0000000000000000000000000000007112301216634021516 xustar0000000000000000
0100644000000000000000000000270412301216634007250 0ustar0000000000000000

This commit adds a dedicated buffer for pax headers to the Writer
struct. This change increases the size of the struct by 512 bytes, but
allows tar/writer to avoid allocating 512 bytes for all written
headers and it avoids allocating 512 more bytes for pax headers.

LGTM=dsymonds
R=dsymonds, dave, iant
CC=golang-codereviews
https://golang.org/cl/110480043

Pending CL 113120043.

LGTM=dave
R=golang-codereviews, dave
CC=golang-codereviews
https://golang.org/cl/112290043

Fixes #6102.

LGTM=gri
R=ken, r, gri
CC=golang-codereviews
https://golang.org/cl/113120043

The garbage collector and stack scans are good enough now.

Fixes #7446.

LGTM=r
R=r, dvyukov
CC=golang-codereviews, mdempsky, mtj
https://golang.org/cl/112870046

As written, the ! applies before the &1.
This would crash writing out missing pcdata tables
if we ever used non-contiguous IDs in a function.
We don't, but fix anyway.

LGTM=iant, minux
R=minux, iant
CC=golang-codereviews
https://golang.org/cl/117810047

It's a bit slower, but not painfully so.  There is still room for
improvement (saving space so we can use nosplit, and removing the
requirement for hash/eq stubs).

benchmark                              old ns/op     new ns/op     delta
BenchmarkMegMap                        23.5          24.2          +2.98%
BenchmarkMegOneMap                     14.9          15.7          +5.37%
BenchmarkMegEqMap                      71668         72234         +0.79%
BenchmarkMegEmptyMap                   4.05          4.93          +21.73%
BenchmarkSmallStrMap                   21.9          22.5          +2.74%
BenchmarkMapStringKeysEight_16         23.1          26.3          +13.85%
BenchmarkMapStringKeysEight_32         21.9          25.0          +14.16%
BenchmarkMapStringKeysEight_64         21.9          25.1          +14.61%
BenchmarkMapStringKeysEight_1M         21.9          25.0          +14.16%
BenchmarkIntMap                        21.8          12.5          -42.66%
BenchmarkRepeatedLookupStrMapKey32     39.3          30.2          -23.16%
BenchmarkRepeatedLookupStrMapKey1M     322353        322675        +0.10%
BenchmarkNewEmptyMap                   129           136           +5.43%
BenchmarkMapIter                       137           107           -21.90%
BenchmarkMapIterEmpty                  7.14          8.71          +21.99%
BenchmarkSameLengthMap                 5.24          6.82          +30.15%
BenchmarkBigKeyMap                     34.5          35.3          +2.32%
BenchmarkBigValMap                     36.1          36.1          +0.00%
BenchmarkSmallKeyMap                   26.9          26.7          -0.74%

LGTM=rsc
R=golang-codereviews, dave, dvyukov, rsc, gobot, khr
CC=golang-codereviews
https://golang.org/cl/99380043

A byte order mark  (BOM) cannot be backquoted.

LGTM=r
R=golang-codereviews, gobot, r
CC=golang-codereviews
https://golang.org/cl/112310043

LGTM=r
R=golang-codereviews, gobot, r
CC=golang-codereviews
https://golang.org/cl/114850043

DWARF says only one is necessary.
The count is preferable because it admits 0-length arrays.
Update debug/dwarf to handle either form.

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/111230044

code.org exists

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/95500043

LGTM=rsc
R=golang-codereviews, rsc
CC=golang-codereviews, khr
https://golang.org/cl/117810043

Fixes 8363.

LGTM=bradfitz
R=bradfitz
CC=golang-codereviews
https://golang.org/cl/114810043

They can be large, so use a varint encoding rather than only one byte.

LGTM=iant, rsc
R=rsc, iant
CC=golang-codereviews
https://golang.org/cl/113180043

LGTM=minux, rsc
R=golang-codereviews, minux, rsc
CC=golang-codereviews
https://golang.org/cl/113970044

LGTM=iant
R=rsc, iant
CC=golang-codereviews
https://golang.org/cl/112320043

The issue is discovered during testing of a change to runtime.
Even if it is unlikely to happen, the comment can safe an hour
next person who hits it.

LGTM=khr
R=golang-codereviews, khr
CC=golang-codereviews, rlh, rsc
https://golang.org/cl/116790043

I don't see how it can lead to bad things today.
But it's better to kill it before it does.

LGTM=khr
R=golang-codereviews, khr
CC=golang-codereviews, rsc
https://golang.org/cl/111130045

Fixes #8252.

LGTM=adg
R=ruiu, josharian, adg
CC=golang-codereviews
https://golang.org/cl/102470046

        Fixes build failures on nacl/* and android/* platforms.

LGTM=adg
R=golang-codereviews, adg
CC=golang-codereviews
https://golang.org/cl/113140043

Make CanBackquote(invalid UTF-8) return false.

Also add two test which show that CanBackquote reports
true for strings containing a BOM.

Fixes #7572.

LGTM=r
R=golang-codereviews, bradfitz, r
CC=golang-codereviews
https://golang.org/cl/111780045

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/117790043

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/115820043

LGTM=adg
R=golang-codereviews, adg, minux
CC=golang-codereviews
https://golang.org/cl/106740044

TBR=dsymonds
R=golang-codereviews
CC=golang-codereviews
https://golang.org/cl/112300043

This CL adds 'dropg', which is called to drop the association
between m and its current goroutine, and it makes schedule
handle locked goroutines correctly, instead of requiring all
callers of schedule to do that.

The effect is that if you want to take over an m for, say,
garbage collection work while still allowing the current g
to run on some other m, you can do an mcall to a function
that is:

        // dissociate gp
        dropg();
        gp->status = Gwaiting; // for ready

        // put gp on run queue for others to find
        runtime·ready(gp);

        /* ... do other work here ... */

        // done with m, let it run goroutines again
        schedule();

Before this CL, the dropg() body had to be written explicitly,
and the check for lockedg before schedule had to be
written explicitly too, both of which make the code a bit
more fragile than it needs to be.

LGTM=iant
R=dvyukov, iant
CC=golang-codereviews, rlh
https://golang.org/cl/113110043

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/112970044

CC=golang-codereviews
https://golang.org/cl/110640044

This is a fully backward-compatible language change.

There are not a lot of cases in the std library, but
there are some. Arguably this makes the syntax a bit
more regular - any trailing index variable that is _
can be left away, and there's some analogy to type
switches where the temporary can be left away.

Implementation-wise the change should be trivial as
it can be done completely syntactically. For instance,
the respective change in go/parser is a dozen lines
(see https://golang.org/cl/112970044 ).

Fixes #6102.

LGTM=iant, r, rsc
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/104680043

This variable allows users to select the compiler when using the
gccgo toolchain.

LGTM=rsc
R=rsc, iant, minux, aram
CC=axwalk, golang-codereviews
https://golang.org/cl/106700044

Fixes #7806.

LGTM=minux
R=golang-codereviews, minux
CC=golang-codereviews
https://golang.org/cl/104690043

LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/116720043

warning: /usr/go/src/liblink/asm5.c:720 set and not used: m
warning: /usr/go/src/liblink/asm5.c:807 set and not used: c

LGTM=minux
R=minux
CC=golang-codereviews
https://golang.org/cl/108570043

The debug/dwarf package cannot parse the format generated here,
but the format can be changed so it does.
After this edit, tweaking the expression defining the offset
of a struct field, the dwarf package can parse the tables (again?).

LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/105710043

Fixes #6293.

Image "testdata/benchRGB-interlace.png" was generated by opening "testdata/benchRGB.png" in the editor Gimp and saving it with interlacing enabled.

Benchmark:
BenchmarkDecodeRGB        	     500	   7014194 ns/op	  37.37 MB/s
ok  	pkg/image/png	4.657s

BenchmarkDecodeInterlacing	     100	  10623241 ns/op	  24.68 MB/s
ok  	pkg/image/png	1.339s

LGTM=nigeltao
R=nigeltao, andybons, matrixik
CC=golang-codereviews
https://golang.org/cl/102130044

(This is a patch from the pkgsrc Go package.)

LGTM=iant
R=golang-codereviews, iant, joerg.sonnenberger, dave
CC=golang-codereviews, joerg
https://golang.org/cl/108340043

debug/elf: add (*File).DynamicSymbols, ErrNoSymbols, and tests for (*File).Symbols and (*File).DynamicSymbols, and formalize symbol order.

Added a complement to (*File).Symbols for the dynamic symbol table.
Would be useful, for instance, if seraching for certain shared objects
compatible with certain libraries (for instance, LADSPA requires an
exported symbol "ladspa_descriptor").

Added a variable ErrNoSymbols that canonicalizes a return from
(*File).Symbols and (*File).DyanmicSymbols if the file has no symbols.

Added tests for both (*File).Symbols and (*File).DynamicSymbols;
there was never a test for (*File).Symbols at all. A small C program using
libelf, included in the test data, was used to produce the golden
symbols to compare against.

As part of the requirements for testing, (*File).Symbols and (*File).DynamicSymbols now document the order in which the symbol tables are returned (in the order the symbols appear in the file).

All tests currently pass.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/107530043

The builder builds with GOROOT_FINAL=/usr/local/go set.

TBR=rsc
R=golang-codereviews
CC=golang-codereviews
https://golang.org/cl/112100043

Also detect GOARCH automatically based on `uname -m`.

LGTM=crawshaw, dave, rsc
R=rsc, iant, crawshaw, dave
CC=golang-codereviews
https://golang.org/cl/111780043

LGTM=dave, rsc
R=rsc, iant, dave
CC=golang-codereviews
https://golang.org/cl/109390043

LGTM=dave, rsc
R=rsc, iant, dave
CC=golang-codereviews
https://golang.org/cl/101590044