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doc: tools for go1.5.html

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Don't know why, but git deleted the previous version of this change.
This is the same change as https://go-review.googlesource.com/11884,
which I will now abandon, with a couple of fixes.

Almost all done now. Could use help with the TODOs.

Major missing piece is the trace command. Vendoring
section is also weak, but it's also undocumented elsewhere.

Change-Id: I5d8556b23aa6628eb7bf0e330d4dd8d4ac2157c5
Reviewed-on: https://go-review.googlesource.com/11887
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Rob Pike 2015-07-06 09:01:32 +10:00
parent d5994f4f5e
commit ef37184c07
1 changed files with 304 additions and 75 deletions
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@ -28,7 +28,7 @@ once necessary for building the distribution is gone.
</li>
<li>
The garbage collector is now <a href="/s/go14gc">concurrent</a> and provides dramatically lower
The garbage collector is now <a href="https://golang.org/s/go14gc">concurrent</a> and provides dramatically lower
pause times by running, when possible, in parallel with other goroutines.
</li>
@ -43,10 +43,20 @@ is now provided for all repositories, not just the Go core.
</li>
<li>
The <code>go</code> command now provides <a href="/s/go15vendor">experimental
The <code>go</code> command now provides <a href="https://golang.org/s/go15vendor">experimental
support</a> for "vendoring" external dependencies.
</li>
<li>
A new <code>go tool trace</code> command supports fine-grained
tracing of program execution.
</li>
<li>
A new <code>go doc</code> command (distinct from <code>godoc</code>)
is customized for command-line use.
</li>
</ul>
<p>
@ -59,7 +69,7 @@ The release also contains one small language change involving map literals.
</p>
<p>
Finally, the timing of the <a href="/s/releasesched">release</a>
Finally, the timing of the <a href="https://golang.org/s/releasesched">release</a>
strays from the usual six-month interval,
both to provide more time to prepare this major release and to shift the schedule thereafter to
time the release dates more conveniently.
@ -67,7 +77,7 @@ time the release dates more conveniently.
<h2 id="language">Changes to the language</h2>
<h3 id="mapliterals">Map literals</h3>
<h3 id="map_literals">Map literals</h3>
<p>
Due to an oversight, the rule that allowed the element type to be elided from slice literals was not
@ -107,7 +117,7 @@ There was a C compiler in the tree in 1.4 and earlier.
It was used to build the runtime; a custom compiler was necessary in part to
guarantee the C code would work with the stack management of goroutines.
Since the runtime is in Go now, there is no need for this C compiler and it is gone.
Details of the process to eliminate C are discussed <a href="/s/go13compiler">elsewhere</a>.
Details of the process to eliminate C are discussed <a href="https://golang.org/s/go13compiler">elsewhere</a>.
</p>
<p>
@ -122,7 +132,7 @@ An overview of this process is available in the slides for
<a href="https://talks.golang.org/2015/gogo.slide">this presentation</a>.
</p>
<h3 id="compiler">Compiler and tools</h3>
<h3 id="compiler_and_tools">Compiler and tools</h3>
<p>
Independent of but encouraged by the move to Go, the names of the tools have changed.
@ -147,7 +157,23 @@ rather than <code>.8</code>, <code>.6</code>, etc.
<h3 id="gc">Garbage collector</h3>
<p>
TODO
The garbage collector has been re-engineered for 1.5 as part of the development
outlined in the <a href="https://golang.org/s/go14gc">design document</a>.
Expected latencies are much lower than with the collector
in prior releases, through a combination of advanced algorithms,
better <a href="https://golang.org/s/go15gcpacing">scheduling</a> of the collector,
and running more of the collection in parallel with the user program.
The "stop the world" phase of the collector
will almost always be under 10 milliseconds and usually much less.
</p>
<p>
For systems that benefit from low latency, such as user-responsive web sites,
the drop in expected latency with the new collector may be important.
</p>
<p>
Details of the new collector were presented in TODO: GopherCon talk.
</p>
<h3 id="runtime">Runtime</h3>
@ -182,7 +208,7 @@ must be available to compile the distribution from source.
Thus, to build the Go core, a working Go distribution must already be in place.
(Go programmers who do not work on the core are unaffected by this change.)
Any Go 1.4 or later distribution (including <code>gccgo</code>) will serve.
For details, see the <a href="/s/go15bootstrap">design document</a>.
For details, see the <a href="https://golang.org/s/go15bootstrap">design document</a>.
</p>
<h2 id="ports">Ports</h2>
@ -217,57 +243,105 @@ On NaCl, Go 1.5 requires SDK version pepper-39 or above because it now uses the
<h2 id="tools">Tools</h2>
<pre>
build: external linking support for windows (https://golang.org/cl/7163, 7282, 7283, 7284, 7534, 7535)
cmd/cover: tool now lives in the standard repository (https://golang.org/cl/9560)
cmd/gc: constant arithmetic is based on math/big (https://golang.org/cl/7830, 7851, 7857, 8426, 7858, 7912, 8171)
cmd/go, go/build: add ${SRCDIR} variable expansion to cgo lines (https://golang.org/cl/1756)
cmd/go: add $DOLLAR to generate's variables (https://golang.org/cl/8091)
cmd/go: std wildcard now excludes commands in main repo (https://golang.org/cl/5550)
cmd/go: .swig/.swigcxx files now require SWIG 3.0.6 or later
cmd/go: add -run flag to go generate (https://golang.org/cl/9005)
cmd/go: add $GOLINE to generate's variables (https://golang.org/cl/9007)
cmd/go: add go doc (https://golang.org/cl/9227)
cmd/go: internal enforced even outside standard library (golang.org/s/go14internal; https://golang.org/cl/9156)
cmd/go, testing: add go test -count (https://golang.org/cl/10669)
cmd/go: add preliminary support for vendor directories (https://golang.org/cl/10923)
cmd/vet: better validation of struct tags (https://golang.org/cl/2685)
cmd/ld: no longer record build timestamp in Windows PE file header (https://golang.org/cl/3740)
cmd/go: add -toolexec build option
cmd/go: drop -ccflags build option
cmd/go: add -asmflags build option
cmd/go: add -buildmode build option
cmd/gc: add -dynlink option (for amd64 only)
cmd/ld: add -buildmode option
cmd/trace: new command to view traces (https://golang.org/cl/3601)
<h3 id="translate">Translating</h3>
<p>
As part of the process to eliminate C from the tree, the compiler and
linker were translated from C to Go.
It was a genuine (machine assisted) translation, so the new programs are essentially
the old programs translated rather than new ones with new bugs.
We are confident the translation process has introduced few if any new bugs,
and in fact uncovered a number of previously unknown bugs, now fixed.
</p>
<p>
The assembler is a new program, however; it is described below.
</p>
<h3 id="rename">Renaming</h3>
<p>
The suites of programs that were the compilers (<code>6g</code>, <code>8g</code>, etc.),
the assemblers (<code>6a</code>, <code>8a</code>, etc.),
and the linkers (<code>6l</code>, <code>8l</code>, etc.)
have each been consolidated into a single tool that is configured
by the environment variables <code>GOOS</code> and <code>GOARCH</code>.
The old names are gone; the new tools are available through the <code>go</code> <code>tool</code>
mechanism as <code>go tool compile</code>,
<code>go tool asm</code>,
<code>and go tool link</code>.
Also, the file suffixes <code>.6</code>, <code>.8</code> etc. for the
intermediate object files are also gone; now they are just plain <code>.o</code> files.
</p>
<p>
For example, to build and link a program on amd64 for Darwin
using the tools directly, rather than through <code>go build</code>,
one would run:
</p>
<pre>
$ export GOOS=darwin GOARCH=amd64
$ go tool compile program.go
$ go tool link program.o
</pre>
<h3 id="moving">Moving</h3>
<p>
Because the <a href="/pkg/go/types/"><code>go/types</code></a> package
has now moved into the main repository (see below),
the <a href="/cmd/vet"><code>vet</code></a> and
<a href="/cmd/cover"><code>cover</code></a>
tools have also been moved.
They are no longer maintained in the external <code>golang.org/x/tools</code> repository,
although (deprecated) source still resides there for compatibility with old releases.
</p>
<h3 id="compiler">Compiler</h3>
<p>
As described above, the compiler in Go 1.5 is a single Go program,
translated from the old C source, that replaces <code>6g</code>, <code>8g</code>,
and so on.
Its target is configured by the environment variables <code>GOOS</code> and <code>GOARCH</code>.
</p>
<p>
The 1.5 compiler is mostly equivalent to the old,
but some internal details have changed.
One significant change is that evaluation of constants now uses
the <a href="/pkg/math/big/"><code>math/big</code></a> package
rather than a custom (and less well tested) implementation of high precision
arithmetic.
We do not expect this to affect the results.
</p>
<p>
For the amd64 architecture only, the compiler has a new option, <code>-dynlink</code>,
that assists dynamic linking by supporting references to Go symbols
defined in external shared libraries.
</p>
<h3 id="assembler">Assembler</h3>
<p>
The assembler in Go 1.5 is a single new Go program that replaces
the suite of C-language assemblers (<code>6a</code>,
<code>8a</code>, etc.) in previous releases.
The values of the environment variables
Like the compiler and linker, the assembler in Go 1.5 is a single program
that replaces the suite of assemblers (<code>6a</code>,
<code>8a</code>, etc.) and the environment variables
<code>GOARCH</code> and <code>GOOS</code>
choose which architecture and operating system the generated
code will be for.
This is practical because the assembly language syntax has always
been idiosyncratic and nearly uniform across architectures;
what differs is just the list of instructions available and the
syntax of some addressing modes.
With the variation easily configured at startup, a single
assembler binary can cover all architectures.
(See the updated <a href="/doc/asm">assembler guide</a>
for more information about the language and some of
the changes listed below.)
configure the architecture and operating system.
Unlike the other programs, the assembler is a wholly new program
written in Go.
</p>
<p>
The new assembler is very nearly compatible with the previous
one, but there are a few changes that may affect some
ones, but there are a few changes that may affect some
assembler source files.
See the updated <a href="/doc/asm">assembler guide</a>
for more specific information about these changes. In summary:
</p>
<p>
@ -276,10 +350,8 @@ different.
It now uses unsigned 64-bit arithmetic and the precedence
of operators (<code>+</code>, <code>-</code>, <code><<</code>, etc.)
comes from Go, not C.
Since there are few assembly programs to start with, and few use
complex arithmetic expressions,
and of those even fewer will be affected by these changes, we expect
almost no programs will need to be updated.
We expect these changes to affect very few programs but
manual verification may be required.
</p>
<p>
@ -321,33 +393,190 @@ supported (the assembler includes an implementation
of a simplified C preprocessor), the feature was removed.
</p>
<h2 id="performance">Performance</h2>
<h3 id="link">Linker</h3>
<p>
The linker in Go 1.5 is now one Go program,
that replaces <code>6l</code>, <code>8l</code>, etc.
Its operating system and instruction set are specified
by the environment variables <code>GOOS</code> and <code>GOARCH</code>.
</p>
<p>
There are a couple of other changes.
The more significant is the addition of a <code>-buildmode</code> option that
expands the style of linking; it now supports
situations such as building shared libraries and allowing other languages
to call into Go libraries.
Some of these were outlined in a <a href="https://golang.org/s/execmodes">design document</a>.
For a list of the available build modes and their use, run
</p>
<pre>
cmd/gc: evaluate concrete == interface without allocating (https://golang.org/cl/2096)
cmd/gc: optimize memclr of slices and arrays (https://golang.org/cl/2520)
cmd/gc: transform closure calls to function calls (https://golang.org/cl/4050)
cmd/gc: transitive inlining (https://golang.org/cl/5952)
cmd/gc, runtime: speed up some cases of _, ok := i.(T) (https://golang.org/cl/7697)
cmd/gc: speed up large string switches (https://golang.org/cl/7698)
cmd/gc: inline x := y.(*T) and x, ok := y.(*T) (https://golang.org/cl/7862)
cmd/gc: allocate backing storage for non-escaping interfaces on stack (https://golang.org/cl/8201)
encoding/xml: avoid an allocation for tags without attributes (https://golang.org/cl/4160)
image: many optimizations
runtime: add ARM runtime.cmpstring and bytes.Compare (https://golang.org/cl/8010)
runtime: do not scan maps when k/v do not contain pointers (https://golang.org/cl/3288)
runtime: reduce thrashing of gs between ps (https://golang.org/cl/9872)
sort: number of Sort performance optimizations (https://golang.org/cl/2100, https://golang.org/cl/2614, ...)
strconv: optimize decimal to string conversion (https://golang.org/cl/2105)
strconv: optimize float to string conversion (https://golang.org/cl/5600)
sync: add active spinning to Mutex (https://golang.org/cl/5430)
math/big: faster assembly kernels for amd64 and 386 (https://golang.org/cl/2503, https://golang.org/cl/2560)
math/big: faster "pure Go" kernels for platforms w/o assembly kernels (https://golang.org/cl/2480)
regexp: port RE2's bitstate backtracker to the regexp package (https://golang.org/cl/2153)
$ go help buildmode
</pre>
<h3 id="library">Core library</h3>
<p>
Another minor change is that the linker no longer records build time stamps in
the header of Windows executables.
Also, although this may be fixed, Windows cgo executables are missing some
DWARF information.
</p>
<h3 id="go_command">Go command</h3>
<p>
The <a href="/cmd/go"><code>go</code></a> command's basic operation
is unchanged, but there are a number of changes worth noting.
</p>
<p>
The previous release introduced the idea of a directory internal to a package
being unimportable through the <code>go</code> command.
In 1.4, it was tested with the introduction of some internal elements
in the core repository.
As suggested in the <a href="https://golang.org/s/go14internal">design document</a>,
that change is now being made available to all repositories.
The rules are explained in the design document, but in summary any
package in or under a directory named <code>internal</code> may
be imported by packages rooted in the same subtree.
Existing packages with directory elements named <code>internal</code> may be
inadvertently broken by this change, which was why it was advertised
in the last release.
</p>
<p>
Another change in how packages are handled is the experimental
addition of support for "vendoring".
TODO: This is undocumented in the go command itself.
TODO: Preliminary design in https://golang.org/s/go15vendor should be updated.
</p>
<p>
There have also been several minor changes.
Read the <a href="/cmd/go">documentation</a> for full details.
</p>
<ul>
<li>
SWIG support has been updated such that
<code>.swig</code> and <code>.swigcxx</code>
now require SWIG 3.0.6 or later.
</li>
<li>
The <code>std</code> (standard library) wildcard package name
now excludes commands.
A new <code>cmd</code> wildcard covers the commands.
</li>
<li>
A new <code>-toolexec</code> flag for building
allows substitution of a different command to invoke
the compiler and so on.
This acts as a custom replacement for <code>go tool</code>.
</li>
<li>
The build subcommand has a <code>-buildmode</code> option tied to the linker,
as described above.
</li>
<li>
An <code>-asmflags</code> build option has been added to provide
flags to the assembler.
However,
the <code>-ccflags</code> build option has been dropped. TODO: why?
</li>
<li>
cmd/go, testing: add go test -count (https://golang.org/cl/10669)
</li>
<li>
The <code>generate</code> subcommand has a couple of new features.
The <code>-run</code> option specifies a regular expression to select which directives
to execute; this was proposed but never implemented in 1.4.
The executing pattern now has access to two new environment variables:
<code>$GOLINE</code> returns the source line number of the directive
and <code>$DOLLAR</code> expands to a dollar sign.
</li>
</ul>
<h3 id="vet_command">Go vet command</h3>
<p>
The <a href="/cmd/vet"><code>go tool vet</code></a> command now does
more thorough validation of struct tags.
</p>
<h3 id="trace_command">Trace command</h3>
<pre>
TODO
cmd/trace: new command to view traces (https://golang.org/cl/3601)
</pre>
<h3 id="doc_command">Go doc command</h3>
<p>
A few releases back, the <code>go doc</code>
command was deleted as being unnecessary.
One could always run "<code>godoc .</code>" instead.
The 1.5 release introduces a new <a href="/cmd/doc"><code>go doc</code></a>
command with a more convenient command-line interface than
<code>godoc</code>'s.
It is designed for command-line usage specifically, and provides a more
compact and focused presentation of the documentation for a package
or its elements, according to the invocation.
It also provides case-insensitive matching and
support for showing the documentation for unexported symbols.
For details run "<code>go help doc</code>".
</p>
<h3 id="cgo">Cgo</h3>
<p>
When parsing <code>#cgo</code> lines,
the invocation <code>${SRCDIR}</code> is now
expanded into the path to the source directory.
This allows options to be passed to the
compiler and linker that involve file paths relative to the
source code directory. Without the expansion the paths would be
invalid when the current working directory changes.
</p>
<p>
On Windows, cgo now uses external linking by default.
</p>
<h2 id="performance">Performance</h2>
<p>
As always, the changes are so general and varied that precise statements
about performance are difficult to make.
The changes are even broader ranging than usual in this release, which
includes a new garbage collector and a conversion of the runtime to Go.
Some programs may run faster, some slower.
On average the programs in the Go 1 benchmark suite run a few percent faster in Go 1.5
than they did in Go 1.4,
while as mentioned above the garbage collector's pauses are
dramatically shorter, and almost always under 10 milliseconds.
</p>
<p>
Builds in Go 1.5 will be slower by a factor of about two.
The automatic translation of the compiler and linker from C to Go resulted in
unidiomatic Go code that performs poorly compared to well-written Go.
Analysis tools and refactoring helped to improve the code, but much remains to be done.
Further profiling and optimization will continue in Go 1.6 and future releases.
For more details, see these <a href="https://talks.golang.org/2015/gogo.slide">slides</a>
and associated <a href="https://www.youtube.com/watch?v=cF1zJYkBW4A">video</a>.
</p>
<h2 id="library">Core library</h2>
<h3 id="flag">Flag</h3>
@ -569,7 +798,7 @@ Also, the <a href="/pkg/crypto/tls/"><code>crypto/tls</code></a> package
now supports Signed Certificate Timestamps (SCTs) as specified in RFC 6962.
The server serves them if they are listed in the
<a href="/pkg/crypto/tls/#Certificate"><code>Certificate</code></a> struct,
and the client reqeusts them and exposes them, if present,
and the client requests them and exposes them, if present,
in its <a href="/pkg/crypto/tls/#ConnectionState"><code>ConnectionState</code></a> struct.
The <a href="/pkg/crytpo/tls/"><code>crytpo/tls</code></a> server implementation
will also now always call the