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doc/go1.4.html: GODEBUG and assembler changes

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https://golang.org/cl/160660046
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Rob Pike 2014-10-28 20:12:17 -07:00
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1 changed files with 56 additions and 9 deletions
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@ -157,7 +157,7 @@ for code that does unsafe things.
<p>
We have clarified this situation in the documentation included in the release.
The <a href="go1compat.html">Go compatibilty guidelines</a> and the
The <a href="go1compat.html">Go compatibility guidelines</a> and the
docs for the <a href="/pkg/unsafe/"><code>unsafe</code></a> package
are now explicit that unsafe code is not guaranteed to remain compatible.
</p>
@ -223,6 +223,61 @@ so the effect is minimal, but programs that store integers (for example) in
interfaces will see more allocations.
</p>
<p>
As of Go 1.3, the runtime crashes if it finds a memory word that should contain
a valid pointer but instead contains an obviously invalid pointer (for example, the value 3).
Programs that store integers in pointer values may run afoul of this check and crash.
In Go 1.4, setting the <a href="/pkg/runtime/"><code>GODEBUG</code></a> variable
<code>invalidptr=0</code> disables
the crash as a workaround, but we cannot guarantee that future releases will be
able to avoid the crash; the correct fix is to rewrite code not to alias integers and pointers.
</p>
<h3 id="asm">Assembly</h3>
<p>
The language accepted by the assemblers <code>cmd/5a</code>, <code>cmd/6a</code>
and <code>cmd/8a</code> has had several changes,
mostly to make it easier to deliver type information to the runtime.
</p>
<p>
First, the <code>textflag.h</code> file that defines flags for <code>TEXT</code> directives
has been copied from the linker source directory to a standard location so it can be
included with the simple directive
</p>
<pre>
#include "textflag.h"
</pre>
<p>
The more important changes are in how assembler source can define the necessary
type information.
For most programs it will suffice to move data
definitions (<code>DATA</code> and <code>GLOBL</code> directives)
out of assembly into Go files
and to write a Go declaration for each assembly function.
The <a href="/doc/asm#runtime">assembly document</a> describes what to do.
</p>
<p>
<em>Updating</em>:
Assembly files that include <code>textflag.h</code> from its old
location will still work, but should be updated.
For the type information, most assembly routines will need no change,
but all should be examined.
Assembly source files that define data,
functions with non-empty stack frames, or functions that return pointers
need particular attention.
A description of the necessary (but simple) changes
is in the <a href="/doc/asm#runtime">assembly document</a>.
</p>
<p>
More information about these changes is in the <a href="/doc/asm">assembly document</a>.
</p>
<h3 id="gccgo">Status of gccgo</h3>
<p>
@ -410,13 +465,6 @@ rebuild the standard library and commands, to avoid overwriting the installation
</ul>
<h3 id="cgo">Changes to cgo</h3>
<p>
TODO cgo news
</p>
<h3 id="godoc">Changes to godoc</h3>
<p>
TODO godoc news
@ -522,7 +570,6 @@ See the relevant package documentation for more information about each change.
cmd/6l, liblink: use pc-relative addressing for all memory references, so that linking Go binaries at high addresses works (CL 125140043). This cuts the maximum size of a Go binary's text+data+bss from 4GB to 2GB.
asm: make textflag.h available outside of cmd/ld (CL 128050043)
bufio: handling of empty tokens at EOF changed, may require scanner change (CL 145390043)
compress/flate, compress/gzip, compress/zlib: Reset support (https://codereview.appspot.com/97140043)
crypto/tls: add support for ALPN (RFC 7301) (CL 108710046)