64bit.html

unix 下的C开发手册,还用详细的例程。

The elements
<I>f_files</I>,
<I>f_ffree</I>,
and
<I>f_favail</I>
of the structure
<B>statvfs</B>
were changed to the new abstract
<B>fsfilcnt_t</B>
type.
<p>
To support the above changes, the following definitions were added to
<I>sys/types.h</I> :
<dl compact>
<p>
<dt><B>blkcnt_t</B><dd>A signed arithmetic type, used for file block counts.
<p>
<dt><B>fsblkcnt_t</B><dd>An arithmetic type, used for filesystem block counts.
<p>
<dt><B>fsfilcnt_t</B><dd>An arithmetic type, used for file serial numbers.
<p>
</dl>
<p>
<li>
<I>sys/time.h</I>
<p>
The
<I>tv_usec</I>
element of the
<B>timeval</B>
structure was of type
<B>long</B>.
This has been changed to use a new abstract data type for signed
integral time values, known as
<B>suseconds_t</B>.
<B>suseconds_t</B>
was added to
<I> sys/types.h</I> .
<p>
<li>
<I>msgrcv()</I>
<p>
In XSH, Issue&nbsp;4, Version&nbsp;2,
<I>msgrcv()</I>
returns the size of the message received as an integer value, but
the size of the message area is specified by a
<B>size_t</B>.
On 64-bit systems where
<B>size_t</B>
may be a different data type to
<B>int</B>,
this will cause problems.
XSH, Issue&nbsp;5 addresses this problem by changing the type of the
return value from
<B>int</B>
to
<B>ssize_t</B>,
and adding a warning to the Description about values of
<I>msgsz</I>
larger the {SSIZE_MAX}.
<p>
<li>
<I>sysconf()</I>
and
<I>unistd.h</I>
<p>
There is now a way to find out the data model supported by the platform.
This can be queried at compile time, using the constants defined in
<I>unistd.h</I> ,
or at run time using the
<I>sysconf()</I>
function.
<p>
The following symbolic constants are defined to have the value -1
if the implementation never provides the feature, and to have
a value other than -1 if the implementation always provides the
feature.
If these are undefined, the
<I>sysconf()</I>
function can be used to determine whether the feature is provided for a
particular invocation of the application.
<dl compact>
<p>
<dt>_XBS5_ILP32_OFF32<dd>Implementation provides a C-language compilation environment with 32-bit
<B>int</B>,
<B>long</B>,
<B>pointer</B>,
and
<B>off_t</B>
types.
<p>
<dt>_XBS5_ILP32_OFFBIG<dd>Implementation provides a C-language compilation environment with
32-bit
<B>int</B>,
<B>long</B>,
and
<B>pointer</B>
types, and an
<B>off_t</B>
type using at least 64 bits.
<p>
<dt>_XBS5_LP64_OFF64<dd>Implementation provides a C-language compilation environment with
32-bit
<B>int</B>
and 64-bit
<B>long</B>,
<B>pointer</B>,
and
<B>off_t</B>
types.
<p>
<dt>_XBS5_LPBIG_OFFBIG<dd>Implementation provides a C-language compilation environment with an
<B>int</B>
type using at least 32 bits and
<B>long</B>,
<B>pointer</B>,
and
<B>off_t</B>
types, using at least 64 bits.
<p>
</dl>
<p>
</ul>
<h4>Commands and Utilities, Issue 5 (XCU)</h4>
<p>
A new section of text was added to the end of the first paragraph of
Section 1.9, Utility Description Defaults, to align with requirements
in POSIX.2, and restates that integer variables and constants
used by utilities are permitted to be 64-bit values.
<h5>Programming Environments</h5>
<p>
The
<I>c89</I>
reference page has some new text describing programming environments.
All conforming implementations must support one of the following
programming environments by default.
Applications can use the
<I>sysconf()</I>
function or the
<I>getconf</I>
utility to determine which programming
environments the implementation supports.
<p>
The following table describes the supported programming environments.
<pre>
<P><table  bordercolor=#000000 border=1 align=center><tr valign=top><th align=center>&nbsp;<b>Programming Environment</b>
<th align=center>&nbsp;<b>int</b>
<th align=center>&nbsp;<b>long</b>
<th align=center>&nbsp;<b>pointer</b>
<th align=center>&nbsp;<b>off_t</b>
<tr valign=top><td align=left>&nbsp;XBS5_ILP32_OFF32
<td align=left>&nbsp;32
<td align=left>&nbsp;32
<td align=left>&nbsp;32
<td align=left>&nbsp;32
<tr valign=top><td align=left>&nbsp;XBS5_ILP32_OFFBIG
<td align=left>&nbsp;32
<td align=left>&nbsp;32
<td align=left>&nbsp;32
<td align=left>&nbsp;&gt;=64
<tr valign=top><td align=left>&nbsp;XBS5_LP64_OFF64
<td align=left>&nbsp;32
<td align=left>&nbsp;64
<td align=left>&nbsp;64
<td align=left>&nbsp;64
<tr valign=top><td align=left>&nbsp;XBS5_LPBIG_OFFBIG
<td align=left>&nbsp;&gt;= 32
<td align=left>&nbsp;&gt;= 64
<td align=left>&nbsp;&gt;= 64
<td align=left>&nbsp;&gt;= 64
</table>
</pre>
<p>
The
<I>c89</I>
reference page also has text describing new support in
<I>getconf</I>
and
<I>sysconf()</I>
to determine configuration strings for C compiler flags,
linker/loader flags, and libraries for each supported environment.
<p>
When an application wishes to use a specific programming environment
rather than an implementation's default programming environment
while compiling, the application must first verify that the
implementation supports the desired environment.
If the desired programming environment is supported, the application
can then invoke
<I>c89</I>
with the appropriate C compiler flags as the
first options for the compile, the appropriate linker/loader flags
after any other options but before any operands, and the
appropriate libraries at the end of the operands.
<p>
The following table shows the various options available:
<pre>
<P><table  bordercolor=#000000 border=1 align=center><tr valign=top><th align=center>&nbsp;<b>Programming Environment</b>
<th align=center>&nbsp;<b>Use</b>
<th align=center>&nbsp;<b>Compiler Flags</b>
<tr valign=top><td align=left>&nbsp;XBS5_ILP32_OFF32
<td align=left>&nbsp;C Compiler Flags
<td align=left>&nbsp;XBS5_ILP32_OFF32_CFLAGS
<tr valign=top><td align=left>&nbsp;
<td align=left>&nbsp;Linker/Loader Flags
<td align=left>&nbsp;XBS5_ILP32_OFF32_LDFLAGS
<tr valign=top><td align=left>&nbsp;
<td align=left>&nbsp;Libraries Flags
<td align=left>&nbsp;XBS5_ILP32_OFF32_LIBS
<tr valign=top><td align=left>&nbsp;XBS5_ILP32_OFFBIG
<td align=left>&nbsp;C Compiler Flags
<td align=left>&nbsp;XBS5_ILP32_OFFBIG_CFLAGS
<tr valign=top><td align=left>&nbsp;
<td align=left>&nbsp;Linker/Loader Flags
<td align=left>&nbsp;XBS5_ILP32_OFFBIG_LDFLAGS
<tr valign=top><td align=left>&nbsp;
<td align=left>&nbsp;Libraries Flags
<td align=left>&nbsp;XBS5_ILP32_OFFBIG_LIBS
<tr valign=top><td align=left>&nbsp;XBS5_LP64_OFF64
<td align=left>&nbsp;C Compiler Flags
<td align=left>&nbsp;XBS5_LP64_OFF64_CFLAG
<tr valign=top><td align=left>&nbsp;
<td align=left>&nbsp;Linker/Loader Flags
<td align=left>&nbsp;XBS5_LP64_OFF64_LDFLAGS
<tr valign=top><td align=left>&nbsp;
<td align=left>&nbsp;Libraries Flags
<td align=left>&nbsp;XBS5_LP64_OFF64_LIBS
<tr valign=top><td align=left>&nbsp;XBS5_LPBIG_OFFBIG
<td align=left>&nbsp;C Compiler Flags
<td align=left>&nbsp;XBS5_LPBIG_OFFBIG_CFLAGS
<tr valign=top><td align=left>&nbsp;
<td align=left>&nbsp;Linker/Loader Flags
<td align=left>&nbsp;XBS5_LPBIG_OFFBIG_LDFLAGS
<tr valign=top><td align=left>&nbsp;
<td align=left>&nbsp;Libraries Flags
<td align=left>&nbsp;XBS5_LPBIG_OFFBIG_LIBS
</table>
</pre>
<h3>Porting Issues</h3>
<p>
Porting an application to a 64-bit UNIX system can be accomplished
with a minimal amount of effort if the application was developed
using good modern software engineering practices such as:
<ul>
<p>
<li>
ISO&nbsp;C function prototypes
<p>
<li>
consistent and careful use of data types
<p>
<li>
all declarations are in headers.
<p>
</ul>
<p>
First of all, determine which data model is available on the platform
you are porting to.
The data model you are porting to will have a major impact
on the amount of work required to achieve a successful port.
<p>
Then take the time to create and use ISO&nbsp;C function prototypes
if they are absent from the source code.
Unfortunately large quantities of perfectly good legacy code
developed in the days before portability was a major issue
may not have function prototypes.
Fortunately many compilers have an option to generate ISO&nbsp;C function
prototypes.
<p>
The remainder of this article assumes that you are porting to an
LP64 platform since this is the data model of choice amongst major
vendors, but the issues raised are equally valid on some or all
of the other 64-bit data models.
<h4>General</h4>
<p>
Use utilities such as
<I>grep</I>
to locate and check all instances of the following:
<ul>
<p>
<li>
Shift and complement operators; that is, &quot;&lt;&lt;&quot;, &quot;&gt;&gt;&quot;, &quot;~&quot;.
If used with
<B>long</B>,<B>&quot;.</B>
add &quot;L&quot; to value shifted to avoid an incorrect result.
<p>
<li>
Addresses of &quot;&amp;&quot;.
Make sure they are not being stored in an
<B>int</B>.
<p>
<li>
Declarations of type
<B>long</B>.
Many of these can be converted to type
<B>int</B>
to save space.
This is particularly true for network code.
<p>
<li>
The functions
<I>lseek()</I> ,
<I>fseek()</I> ,
<I>ftell()</I> ,
<I>fgetpos()</I> ,
and so on.
Use either
<B>off_t</B>
or
<B>fpos_t</B>
as appropriate for offset arguments.
Do not use
<B>int</B>
or
<B>long</B>
to store file offsets.
<p>
<li>
All (
<B>int *</B>)
and (
<B>long *</B>)
casts.
<p>
<li>
Use of (
<B>char *</B>)
0 for zero or (
<B>char *</B>)
comparisons.
Use NULL instead.
<p>
<li>
Hard-coded byte counts or memory sizes.
These will be wrong if they assume
<B>long</B>s
or
<B>pointer</B>s
are 32 bits.
Applications should use the
<I>sizeof()</I>
operator to avoid such problems.
<p>
</ul>
<h4>Declarations</h4>
<p>
To enable application code to work on both 32-bit and 64-bit platforms,
check all
<B>int</B>
and
<B>long</B>
declarations.
Declare integer constants using &quot;L&quot; or &quot;U&quot; as appropriate.
Ensure an
<B>unsigned int</B>
is used where appropriate to prevent sign extension.
If you have specific variables that need to be 32 bits on both
platforms, define the type to be
<B>int</B>.
If the variable should be 32 bits on an ILP32 platform and 64 bits on
an LP64 platform, define the variables to be
<B>long</B>.
<p>
Declare numeric variables as
<B>int</B>
or
<B>long</B>
for alignment and performance.
Don't worry about trying to save bytes by using
<B>char</B>
or
<B>short</B>.
Remember that if the type specifier is missing from a declaration,
it defaults to an
<B>int</B>.
Declare character pointers and character bytes as
<B>unsigned</B>
to avoid sign extension problems with 8-bit characters.
<h4>Assignments and Function Parameters</h4>
<p>
All assignments require checking.
Since
<B>pointer</B>,
<B>int</B>,
and
<B>long</B>
are no longer the same size on LP64 platforms, problems may arise
depending on how the variables are assigned and used within
an application.
<p>
Do not use
<B>int</B>
and
<B>long</B>
interchangeably because of the possible truncation of significant
digits, as shown in the following example:
<pre>