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>The <SPAN
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><H1
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><A
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NAME="REF.IF-DEFINE"><SPAN
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CLASS="PROPERTY"
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>if_define</SPAN
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></H1
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><DIV
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CLASS="REFNAMEDIV"
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><A
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NAME="AEN4442"
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></A
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><H2
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>Name</H2
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>Property <SPAN
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CLASS="PROPERTY"
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>if_define</SPAN
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>&nbsp;--&nbsp;Output a common preprocessor construct to a configuration
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header file.</DIV
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><DIV
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CLASS="REFSYNOPSISDIV"
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><A
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NAME="AEN4446"><H2
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>Synopsis</H2
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><TABLE
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WIDTH="70%"
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><TR
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><TD
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><PRE
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CLASS="SYNOPSIS"
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>cdl_option &lt;name&gt; {
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    if_define [-file=&lt;filename&gt;] &lt;symbol1&gt; &lt;symbol2&gt;
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    &#8230;
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}</PRE
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></TD
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></TR
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></TABLE
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></DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="AEN4448"
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></A
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><H2
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>Description</H2
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><P
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>The purpose of the <SPAN
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CLASS="PROPERTY"
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>if_define</SPAN
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> property is best explained by an
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example. Suppose you want finer-grained control over assertions, say
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on a per-package or even a per-file basis rather than globally. The
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assertion macros can be defined by an exported header file in an
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infrastructure package, using code like the following:</P
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><TABLE
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WIDTH="70%"
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><TR
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>#ifdef CYGDBG_USE_ASSERTS
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# define CYG_ASSERT( _bool_, _msg_ )    \
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        CYG_MACRO_START                 \
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        if ( ! ( _bool_ ) )             \
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            CYG_ASSERT_DOCALL( _msg_ ); \
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        CYG_MACRO_END
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#else
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# define CYG_ASSERT( _bool_, _msg_ ) CYG_EMPTY_STATEMENT
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#endif</PRE
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></TD
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></TR
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></TABLE
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><P
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>Assuming this header file is <TT
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CLASS="LITERAL"
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>#include'd</TT
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> directly or
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indirectly by any code which may need to be built with assertions
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enabled, the challenge is now to control whether or not
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<TT
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CLASS="VARNAME"
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>CYGDBG_USE_ASSERTS</TT
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> is defined for any given source
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file. This is the purpose of the <SPAN
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CLASS="PROPERTY"
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>if_define</SPAN
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> property:</P
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><TABLE
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BGCOLOR="#E0E0F0"
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WIDTH="70%"
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><TR
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>cdl_option CYGDBG_KERNEL_USE_ASSERTS {
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    &#8230;
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    if_define CYGSRC_KERNEL CYGDBG_USE_ASSERTS
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    requires  CYGDBG_INFRA_ASSERTION_SUPPORT
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}</PRE
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></TD
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></TR
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></TABLE
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><P
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>If this option is active and enabled then the kernel's configuration
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header file would end up containing the following:</P
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>#ifdef CYGSRC_KERNEL
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# define CYGDBG_USE_ASSERTS 1
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#endif</PRE
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></TD
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></TR
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></TABLE
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><P
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>Kernel source code can now begin with the following construct:</P
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>#define CYGSRC_KERNEL 1
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#include &lt;pkgconf/kernel.h&gt;
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#include &lt;cyg/infra/cyg_ass.h&gt;</PRE
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></TD
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></TR
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></TABLE
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><P
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>The configuration option only affects kernel source code, assuming
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nothing else <TT
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CLASS="LITERAL"
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>#define's</TT
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> the symbol
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<TT
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CLASS="VARNAME"
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>CYGSRC_KERNEL</TT
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>. If the per-package assertion option
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is disabled then <TT
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CLASS="VARNAME"
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>CYGDBG_USE_ASSERTS</TT
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> will not get
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defined. If the option is enabled then
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<TT
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CLASS="VARNAME"
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>CYGDBG_USE_ASSERTS</TT
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> will get defined and assertions
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will be enabled for the kernel sources. It is possible to use the same
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mechanism for other facilities such as tracing, and to apply it at a
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finer grain such as individual source files by having multiple options
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with <SPAN
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CLASS="PROPERTY"
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>if_define</SPAN
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> properties and multiple symbols such as
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<TT
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CLASS="VARNAME"
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>CYGSRC_KERNEL_SCHED_BITMAP_CXX</TT
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>.</P
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><P
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>The <SPAN
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CLASS="PROPERTY"
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>if_define</SPAN
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> property takes two arguments, both of which must be
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valid C preprocessor symbols. If the current option is active and
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enabled then three lines will be output to the configuration header
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file:</P
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><TABLE
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BGCOLOR="#E0E0F0"
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WIDTH="70%"
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><TR
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>#ifdef &lt;symbol1&gt;
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# define &lt;symbol2&gt;
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#endif</PRE
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></TD
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></TR
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></TABLE
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><P
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>If the option is inactive or disabled then these lines will not be
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output. By default the current package's configuration header file
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will be used, but it is possible to specify an alternative destination
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using a <TT
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CLASS="LITERAL"
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>-file</TT
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> option. At present the only
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legitimate alternative destination is <TT
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CLASS="LITERAL"
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>system.h</TT
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>, the
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global configuration header. <SPAN
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CLASS="PROPERTY"
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>if_define</SPAN
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> processing happens in
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addition to, not instead of, the normal <TT
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CLASS="LITERAL"
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>#define</TT
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>
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processing or the handling of other header-file related properties.</P
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><DIV
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CLASS="NOTE"
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><BLOCKQUOTE
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CLASS="NOTE"
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><P
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><B
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>Note: </B
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>The infrastructure in the current <SPAN
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CLASS="APPLICATION"
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>eCos</SPAN
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> release does not yet work
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this way. In future it may do so, and the intention is that suitable
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configuration options get generated semi-automatically by the
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configuration system rather than having to be defined explicitly.</P
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></BLOCKQUOTE
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></DIV
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><DIV
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CLASS="TIP"
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><BLOCKQUOTE
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CLASS="TIP"
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><P
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><B
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>Tip: </B
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>As an alternative to changing the configuration, updating the build
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tree, and so on, it is possible to enable assertions by editing a
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source file directly, for example:</P
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><PRE
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CLASS="PROGRAMLISTING"
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>#define CYGSRC_KERNEL 1
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#define CYGDBG_USE_ASSERTS 1
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#include &lt;pkgconf/kernel.h&gt;
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#include &lt;cyg/infra/cyg_ass.h&gt;</PRE
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></TD
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></TR
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></TABLE
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><P
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>The assertion header file does not care whether
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<TT
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CLASS="VARNAME"
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>CYGDBG_USE_ASSERTS</TT
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> is <TT
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CLASS="LITERAL"
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>#define'd</TT
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>
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via a configuration option or by explicit code. This technique can be
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useful to component writers when debugging their source code, although
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care has to be taken to remove any such <TT
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CLASS="LITERAL"
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>#define's</TT
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>
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later on.</P
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></BLOCKQUOTE
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CLASS="REFSECT1"
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><A
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NAME="AEN4487"
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></A
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><H2
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>Example</H2
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WIDTH="70%"
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><TR
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>cdl_option CYGDBG_KERNEL_USE_ASSERTS {
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    display "Assertions in the kernel package"
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    &#8230;
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    if_define CYGSRC_KERNEL CYGDBG_USE_ASSERTS
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    requires  CYGDBG_INFRA_ASSERTION_SUPPORT
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}</PRE
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></TD
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></TR
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></TABLE
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></DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="AEN4490"
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></A
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><H2
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>See Also</H2
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><P
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>Properties <A
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HREF="ref.define.html"
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><SPAN
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CLASS="PROPERTY"
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>define</SPAN
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></A
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>,
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<A
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HREF="ref.define-format.html"
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><SPAN
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CLASS="PROPERTY"
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>define_format</SPAN
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></A
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>,
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<A
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HREF="ref.define-header.html"
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><SPAN
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CLASS="PROPERTY"
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>define_header</SPAN
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></A
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>,
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<A
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HREF="ref.define-proc.html"
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><SPAN
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CLASS="PROPERTY"
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>define_proc</SPAN
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></A
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> and
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<A
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HREF="ref.no-define.html"
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><SPAN
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CLASS="PROPERTY"
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>no_define</SPAN
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></A
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>.</P
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