253 lines
8.1 KiB
Plaintext
253 lines
8.1 KiB
Plaintext
<!-- doc/src/sgml/dfunc.sgml -->
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<sect2 id="dfunc">
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<title>Compiling and Linking Dynamically-Loaded Functions</title>
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<para>
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Before you are able to use your
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<productname>PostgreSQL</productname> extension functions written in
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C, they must be compiled and linked in a special way to produce a
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file that can be dynamically loaded by the server. To be precise, a
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<firstterm>shared library</firstterm> needs to be
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created.<indexterm><primary>shared library</primary></indexterm>
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</para>
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<para>
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For information beyond what is contained in this section
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you should read the documentation of your
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operating system, in particular the manual pages for the C compiler,
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<command>cc</command>, and the link editor, <command>ld</command>.
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In addition, the <productname>PostgreSQL</productname> source code
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contains several working examples in the
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<filename>contrib</filename> directory. If you rely on these
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examples you will make your modules dependent on the availability
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of the <productname>PostgreSQL</productname> source code, however.
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</para>
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<para>
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Creating shared libraries is generally analogous to linking
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executables: first the source files are compiled into object files,
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then the object files are linked together. The object files need to
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be created as <firstterm>position-independent code</firstterm>
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(<acronym>PIC</acronym>),<indexterm><primary>PIC</primary></indexterm> which
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conceptually means that they can be placed at an arbitrary location
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in memory when they are loaded by the executable. (Object files
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intended for executables are usually not compiled that way.) The
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command to link a shared library contains special flags to
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distinguish it from linking an executable (at least in theory
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— on some systems the practice is much uglier).
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</para>
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<para>
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In the following examples we assume that your source code is in a
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file <filename>foo.c</filename> and we will create a shared library
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<filename>foo.so</filename>. The intermediate object file will be
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called <filename>foo.o</filename> unless otherwise noted. A shared
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library can contain more than one object file, but we only use one
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here.
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</para>
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<!--
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Note: Reading GNU Libtool sources is generally a good way of
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figuring out this information. The methods used within PostgreSQL
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source code are not necessarily ideal.
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-->
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<variablelist>
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<varlistentry>
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<term>
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<systemitem class="osname">FreeBSD</systemitem>
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<indexterm><primary>FreeBSD</primary><secondary>shared library</secondary></indexterm>
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</term>
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<listitem>
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<para>
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The compiler flag to create <acronym>PIC</acronym> is
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<option>-fPIC</option>. To create shared libraries the compiler
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flag is <option>-shared</option>.
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<programlisting>
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gcc -fPIC -c foo.c
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gcc -shared -o foo.so foo.o
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</programlisting>
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This is applicable as of version 3.0 of
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<systemitem class="osname">FreeBSD</systemitem>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<systemitem class="osname">HP-UX</systemitem>
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<indexterm><primary>HP-UX</primary><secondary>shared library</secondary></indexterm>
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</term>
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<listitem>
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<para>
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The compiler flag of the system compiler to create
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<acronym>PIC</acronym> is <option>+z</option>. When using
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<application>GCC</application> it's <option>-fPIC</option>. The
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linker flag for shared libraries is <option>-b</option>. So:
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<programlisting>
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cc +z -c foo.c
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</programlisting>
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or:
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<programlisting>
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gcc -fPIC -c foo.c
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</programlisting>
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and then:
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<programlisting>
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ld -b -o foo.sl foo.o
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</programlisting>
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<systemitem class="osname">HP-UX</systemitem> uses the extension
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<filename>.sl</filename> for shared libraries, unlike most other
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systems.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<systemitem class="osname">Linux</systemitem>
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<indexterm><primary>Linux</primary><secondary>shared library</secondary></indexterm>
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</term>
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<listitem>
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<para>
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The compiler flag to create <acronym>PIC</acronym> is
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<option>-fPIC</option>.
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The compiler flag to create a shared library is
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<option>-shared</option>. A complete example looks like this:
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<programlisting>
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cc -fPIC -c foo.c
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cc -shared -o foo.so foo.o
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</programlisting>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<systemitem class="osname">macOS</systemitem>
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<indexterm><primary>macOS</primary><secondary>shared library</secondary></indexterm>
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</term>
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<listitem>
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<para>
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Here is an example. It assumes the developer tools are installed.
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<programlisting>
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cc -c foo.c
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cc -bundle -flat_namespace -undefined suppress -o foo.so foo.o
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</programlisting>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<systemitem class="osname">NetBSD</systemitem>
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<indexterm><primary>NetBSD</primary><secondary>shared library</secondary></indexterm>
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</term>
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<listitem>
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<para>
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The compiler flag to create <acronym>PIC</acronym> is
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<option>-fPIC</option>. For <acronym>ELF</acronym> systems, the
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compiler with the flag <option>-shared</option> is used to link
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shared libraries. On the older non-ELF systems, <literal>ld
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-Bshareable</literal> is used.
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<programlisting>
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gcc -fPIC -c foo.c
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gcc -shared -o foo.so foo.o
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</programlisting>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<systemitem class="osname">OpenBSD</systemitem>
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<indexterm><primary>OpenBSD</primary><secondary>shared library</secondary></indexterm>
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</term>
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<listitem>
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<para>
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The compiler flag to create <acronym>PIC</acronym> is
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<option>-fPIC</option>. <literal>ld -Bshareable</literal> is
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used to link shared libraries.
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<programlisting>
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gcc -fPIC -c foo.c
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ld -Bshareable -o foo.so foo.o
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</programlisting>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<systemitem class="osname">Solaris</systemitem>
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<indexterm><primary>Solaris</primary><secondary>shared library</secondary></indexterm>
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</term>
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<listitem>
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<para>
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The compiler flag to create <acronym>PIC</acronym> is
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<option>-KPIC</option> with the Sun compiler and
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<option>-fPIC</option> with <application>GCC</application>. To
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link shared libraries, the compiler option is
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<option>-G</option> with either compiler or alternatively
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<option>-shared</option> with <application>GCC</application>.
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<programlisting>
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cc -KPIC -c foo.c
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cc -G -o foo.so foo.o
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</programlisting>
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or
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<programlisting>
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gcc -fPIC -c foo.c
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gcc -G -o foo.so foo.o
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</programlisting>
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<tip>
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<para>
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If this is too complicated for you, you should consider using
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<ulink url="http://www.gnu.org/software/libtool/">
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<productname>GNU Libtool</productname></ulink>,
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which hides the platform differences behind a uniform interface.
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</para>
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</tip>
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<para>
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The resulting shared library file can then be loaded into
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<productname>PostgreSQL</productname>. When specifying the file name
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to the <command>CREATE FUNCTION</command> command, one must give it
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the name of the shared library file, not the intermediate object file.
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Note that the system's standard shared-library extension (usually
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<literal>.so</literal> or <literal>.sl</literal>) can be omitted from
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the <command>CREATE FUNCTION</command> command, and normally should
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be omitted for best portability.
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</para>
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<para>
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Refer back to <xref linkend="xfunc-c-dynload"/> about where the
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server expects to find the shared library files.
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</para>
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<!--
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Under AIX, object files are compiled normally but building the shared
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library requires a couple of steps. First, create the object file:
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.nf
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cc <other flags> -c foo.c
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.fi
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You must then create a symbol \*(lqexports\*(rq file for the object
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file:
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.nf
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mkldexport foo.o `pwd` > foo.exp
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.fi
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Finally, you can create the shared library:
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.nf
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ld <other flags> -H512 -T512 -o foo.so -e _nostart \e
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-bI:.../lib/postgres.exp -bE:foo.exp foo.o \e
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-lm -lc 2>/dev/null
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.fi
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-->
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</sect2>
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