sdk/2.1/docs/man/restrictions.xml

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<refentry>
    <refentryinfo>
        <keywordset><keyword>restrictions</keyword></keywordset>
    </refentryinfo>
    <refmeta>
        <refentrytitle>restrictions</refentrytitle>
        <refmiscinfo>
            <copyright>
                <year>2007-2013</year>
                <holder>The Khronos Group Inc.
 Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and/or associated documentation files (the
"Materials"), to deal in the Materials without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Materials, and to
permit persons to whom the Materials are furnished to do so, subject to
the condition that this copyright notice and permission notice shall be included
in all copies or substantial portions of the Materials.</holder>
            </copyright>
        </refmiscinfo>
        <manvolnum>3</manvolnum>
    </refmeta>

<!-- ================================ SYNOPSIS -->

  <refnamediv id="restrictionsref">
    <refname>Restrictions</refname>
    <refpurpose> </refpurpose>
  </refnamediv>

    <refsect1 id="restrictions"><title></title>
      <itemizedlist mark="disc">
        <listitem>

<!-- RESTRICTION a  -->

            <para>The use of pointers is somewhat restricted. The following rules apply:</para>

            <itemizedlist mark="opencircle">
              <listitem>
                <para>
                  Arguments to kernel
                  functions declared in a program that are pointers must be declared with the
                  <citerefentry href="global"><refentrytitle>__global</refentrytitle></citerefentry>,
                  <citerefentry href="constant"><refentrytitle>__constant</refentrytitle></citerefentry>, or
                  <citerefentry href="local"><refentrytitle>__local</refentrytitle></citerefentry>
                  qualifier.
                </para>
              </listitem>

              <listitem>
                <para>
                    A pointer declared with the
                    <citerefentry href="constant"><refentrytitle>__constant</refentrytitle></citerefentry>
                    qualifier can only be assigned to a pointer declared with the __constant qualifier.
                </para>
              </listitem>

              <listitem>
                <para>Pointers to functions are not allowed.</para>
              </listitem>

            </itemizedlist>
        </listitem>

<!-- RESTRICTION b  -->

        <listitem>
          <para>
            An image type (
            <citerefentry href="otherDataTypes"><refentrytitle>image2d_t</refentrytitle></citerefentry>,
            <citerefentry href="otherDataTypes"><refentrytitle>image3d_t</refentrytitle></citerefentry>,
            <citerefentry href="otherDataTypes"><refentrytitle>image2d_array_t</refentrytitle></citerefentry>,
            <citerefentry href="otherDataTypes"><refentrytitle>image1d_t</refentrytitle></citerefentry>,
            <citerefentry href="otherDataTypes"><refentrytitle>image1d_buffer_t</refentrytitle></citerefentry>, or
            <citerefentry href="otherDataTypes"><refentrytitle>image1d_array_t</refentrytitle></citerefentry>)
            can only be used as the type of a function argument. An image function
            argument cannot be modified.  Elements of an image can only be accessed
            using the <citerefentry href="imageFunctions"><refentrytitle>Built-in Image
            Functions</refentrytitle></citerefentry>.
          </para>

          <para>
            An image type cannot be used to declare a variable, a structure or
            union field, an array of images, a pointer to an image, or the return
            type of a function. An image type cannot be used with the
            <citerefentry href="global"><refentrytitle>__global</refentrytitle></citerefentry>,
            <citerefentry href="private"><refentrytitle>__private</refentrytitle></citerefentry>,
            <citerefentry href="local"><refentrytitle>__local</refentrytitle></citerefentry> and
            <citerefentry href="constant"><refentrytitle>__constant</refentrytitle></citerefentry>
            address space qualifiers.
          </para>

          <para>
            The sampler type
            (<citerefentry><refentrytitle>sampler_t</refentrytitle></citerefentry>) can only be
            used as the type of a function argument or a variable declared in the program scope
            or the outermost scope of a kernel function. The behavior of a sampler variable
            declared in a non-outermost scope of a kernel function is implementation-defined. A
            sampler argument or variable cannot be modified.
          </para>

          <para>
            The sampler type cannot be used to declare a structure or union field, an array of
            samplers, a pointer to a sampler, or the return type of a function. The sampler type
            cannot be used with the 
            <citerefentry href="local"><refentrytitle>__local</refentrytitle></citerefentry> and 
            <citerefentry href="global"><refentrytitle>__global</refentrytitle></citerefentry> 
            address space qualifiers.
          </para>
        </listitem>

<!-- RESTRICTION c   -->

        <listitem>
          <para>Bit-fields struct members are currently not supported.</para>
        </listitem>

<!-- RESTRICTION d - removed -->
<!-- RESTRICTION d - added again in ver 2.1 -->

        <listitem>
          <para>Variable length arrays and structures with 
                flexible (or unsized) arrays are not supported.</para>
        </listitem>

<!-- RESTRICTION e   -->

        <listitem>
          <para>Variadic macros and functions with the exception of 
          <citerefentry href="printfFunction"><refentrytitle>printf</refentrytitle></citerefentry> and 
          <citerefentry><refentrytitle>enqueue_kernel</refentrytitle></citerefentry> 
          are not supported.</para>
        </listitem>

<!-- RESTRICTION f  -->

        <listitem>
          <para>
            The library functions defined in the C99 standard headers <code>assert.h</code>,
            <code>ctype.h</code>, <code>complex.h</code>, <code>errno.h</code>,
            <code>fenv.h</code>, <code>float.h</code>, <code>inttypes.h</code>,
            <code>limits.h</code>, <code>locale.h</code>, <code>setjmp.h</code>,
            <code>signal.h</code>, <code>stdarg.h</code>, <code>stdio.h</code>,
            <code>stdlib.h</code>, <code>string.h</code>, <code>tgmath.h</code>,
            <code>time.h</code>, <code>wchar.h</code>, and <code>wctype.h</code> are not
            available and cannot be included by a program.
          </para>
        </listitem>

<!-- RESTRICTION g   -->

        <listitem>
          <para>
             The <code>auto</code> and <code>register</code> 
             storage-class specifiers are not supported.
          </para>
        </listitem>

<!-- RESTRICTION h deleted with rev 13 of the 1.2 specification   -->

<!-- RESTRICTION i   -->

        <listitem>
          <para>Recursion is not supported.</para>
        </listitem>

<!-- RESTRICTION j  -->

        <listitem>
          <para>
            The return type of a kernel function must be <type>void</type>.
          </para>
        </listitem>

<!-- RESTRICTION k -->

        <listitem>
          <para>
            Arguments to kernel functions in a program cannot be declared with the built-in
            scalar types <type>bool</type>, <type>half</type>, <type>size_t</type>,
            <type>ptrdiff_t</type>, <type>intptr_t</type>, and <type>uintptr_t</type>, or
            a struct and/or union that contain fields declared to be one of these built-in
            scalar types. The size in bytes of these types except <type>half</type> are
            implementation-defined and in addition can also be different for the OpenCL device
            and the host processor making it difficult to allocate buffer objects to be passed
            as arguments to a kernel declared as pointer to these types. <type>half</type> is
            not supported as <type>half</type> can be used as a storage format only (unless the
            <citerefentry><refentrytitle>cl_khr_fp16</refentrytitle></citerefentry> extension is
            supported) and is not a data type on which floating-point arithmetic can be performed.
          </para>
        </listitem>

<!-- RESTRICTION l  -->

        <listitem>
          <para>Whether or not irreducible control flow is illegal is implementation defined.</para>
        </listitem>

<!-- RESTRICTION m  -->
<!-- Restriction m is removed -->

<!-- RESTRICTION n  -->

        <listitem>
          <para>
            The type qualifiers <code>const</code>, <code>restrict</code> 
            and <code>volatile</code> as defined by the C99 
            specification are supported. These qualifiers cannot be used with 
            <citerefentry href="otherDataTypes"><refentrytitle>image2d_t</refentrytitle></citerefentry>, 
            <citerefentry href="otherDataTypes"><refentrytitle>image3d_t</refentrytitle></citerefentry>, 
            <citerefentry href="otherDataTypes"><refentrytitle>image2d_array_t</refentrytitle></citerefentry>, 
            <citerefentry href="otherDataTypes"><refentrytitle>image2d_depth_t</refentrytitle></citerefentry>,
            <citerefentry href="otherDataTypes"><refentrytitle>image2d_array_depth_t</refentrytitle></citerefentry>, 
            <citerefentry href="otherDataTypes"><refentrytitle>image1d_t</refentrytitle></citerefentry>, 
            <citerefentry href="otherDataTypes"><refentrytitle>image1d_buffer_t</refentrytitle></citerefentry> and 
            <citerefentry href="otherDataTypes"><refentrytitle>image1d_array_t</refentrytitle></citerefentry> 
            types. Types other than pointer types shall not use the 
            <code>restrict</code> qualifier.
          </para>
        </listitem>

<!-- RESTRICTION o -->

        <listitem>
          <para>
            The event type 
            (<citerefentry href="otherDataTypes"><refentrytitle>event_t</refentrytitle></citerefentry>) 
            cannot be used as the type of a kernel function argument. 
            The event type cannot be used to declare a program scope variable. The event type 
            cannot be used to declare a structure or union field. The event type cannot be used with the 
            <citerefentry href="local"><refentrytitle>__local</refentrytitle></citerefentry>, 
            <citerefentry href="constant"><refentrytitle>__constant</refentrytitle></citerefentry> and 
            <citerefentry href="global"><refentrytitle>__global</refentrytitle></citerefentry> 
            address space qualifiers.
          </para>
        </listitem>

<!-- RESTRICTION p  -->

        <listitem>
          <para>
            The <type>clk_event_t</type>, <type>ndrange_t</type> and 
            <type>reserve_id_t</type> types cannot be used as arguments to 
            kernel functions that get enqueued from the host. The 
            <type>clk_event_t</type> and <type>reserve_id_t</type> types 
            cannot be declared in program scope.
          </para>
        </listitem>

<!-- RESTRICTION q-->

        <listitem>
          <para>
            The behavior of applying the <code>sizeof</code> operator 
            to the <type>queue_t</type>, <type>clk_event_t</type>, 
            <type>ndrange_t</type> and <type>reserve_id_t</type> 
            types is implementation-defined.
          </para>
        </listitem>

<!-- RESTRICTION r -->

        <listitem>
          <para>
            Kernels enqueued by the host must continue to have 
            their arguments that are a pointer to 
            a type declared to point to a named address space.
          </para>
        </listitem>

<!-- RESTRICTION s -->

        <listitem>
          <para>
            A function in an OpenCL program cannot be called <code>main</code>.
          </para>
        </listitem>

      </itemizedlist>
    </refsect1>

<!-- ================================ SPECIFICATION  -->
<!-- Set the "uri" attribute in the <olink /> element to the "named destination" for the PDF page
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    <refsect1 id="specification"><title>Specification</title>
        <para><imageobject><imagedata fileref="pdficon_small1.gif" format="gif" /></imageobject>
            <olink uri="restrictions">OpenCL Specification</olink>
        </para>
    </refsect1>

<!-- ================================ ALSO SEE  -->
    <refsect1 id="seealso"><title>Also see</title>
        <para>
            <citerefentry href="imageFunctions"><refentrytitle>Image Functions</refentrytitle></citerefentry>,
            <citerefentry href="functionQualifiers"><refentrytitle>Function Qualifiers</refentrytitle></citerefentry>,
            <citerefentry href="qualifiers"><refentrytitle>Qualifiers</refentrytitle></citerefentry>
        </para>
    </refsect1>

<!-- ============================== COPYRIGHT -->
<!-- Content included from copyright.inc.xsl -->

    <refsect3 id="Copyright"><title></title>
        <imageobject>
                <imagedata fileref="KhronosLogo.jpg" format="jpg" />
        </imageobject>
        <para />
    </refsect3>

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