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<h2 class="chapter">17 Target Description Macros and Functions</h2>
<p><a name="index-machine-description-macros-3850"></a><a name="index-target-description-macros-3851"></a><a name="index-macros_002c-target-description-3852"></a><a name="index-g_t_0040file_007btm_002eh_007d-macros-3853"></a>
In addition to the file <samp><var>machine</var><span class="file">.md</span></samp>, a machine description
includes a C header file conventionally given the name
<samp><var>machine</var><span class="file">.h</span></samp> and a C source file named <samp><var>machine</var><span class="file">.c</span></samp>.
The header file defines numerous macros that convey the information
about the target machine that does not fit into the scheme of the
<samp><span class="file">.md</span></samp> file. The file <samp><span class="file">tm.h</span></samp> should be a link to
<samp><var>machine</var><span class="file">.h</span></samp>. The header file <samp><span class="file">config.h</span></samp> includes
<samp><span class="file">tm.h</span></samp> and most compiler source files include <samp><span class="file">config.h</span></samp>. The
source file defines a variable <code>targetm</code>, which is a structure
containing pointers to functions and data relating to the target
machine. <samp><var>machine</var><span class="file">.c</span></samp> should also contain their definitions,
if they are not defined elsewhere in GCC, and other functions called
through the macros defined in the <samp><span class="file">.h</span></samp> file.
<ul class="menu">
<li><a accesskey="1" href="Target-Structure.html#Target-Structure">Target Structure</a>: The <code>targetm</code> variable.
<li><a accesskey="2" href="Driver.html#Driver">Driver</a>: Controlling how the driver runs the compilation passes.
<li><a accesskey="3" href="Run_002dtime-Target.html#Run_002dtime-Target">Run-time Target</a>: Defining ‘<samp><span class="samp">-m</span></samp>’ options like <samp><span class="option">-m68000</span></samp> and <samp><span class="option">-m68020</span></samp>.
<li><a accesskey="4" href="Per_002dFunction-Data.html#Per_002dFunction-Data">Per-Function Data</a>: Defining data structures for per-function information.
<li><a accesskey="5" href="Storage-Layout.html#Storage-Layout">Storage Layout</a>: Defining sizes and alignments of data.
<li><a accesskey="6" href="Type-Layout.html#Type-Layout">Type Layout</a>: Defining sizes and properties of basic user data types.
<li><a accesskey="7" href="Registers.html#Registers">Registers</a>: Naming and describing the hardware registers.
<li><a accesskey="8" href="Register-Classes.html#Register-Classes">Register Classes</a>: Defining the classes of hardware registers.
<li><a accesskey="9" href="Stack-and-Calling.html#Stack-and-Calling">Stack and Calling</a>: Defining which way the stack grows and by how much.
<li><a href="Varargs.html#Varargs">Varargs</a>: Defining the varargs macros.
<li><a href="Trampolines.html#Trampolines">Trampolines</a>: Code set up at run time to enter a nested function.
<li><a href="Library-Calls.html#Library-Calls">Library Calls</a>: Controlling how library routines are implicitly called.
<li><a href="Addressing-Modes.html#Addressing-Modes">Addressing Modes</a>: Defining addressing modes valid for memory operands.
<li><a href="Anchored-Addresses.html#Anchored-Addresses">Anchored Addresses</a>: Defining how <samp><span class="option">-fsection-anchors</span></samp> should work.
<li><a href="Condition-Code.html#Condition-Code">Condition Code</a>: Defining how insns update the condition code.
<li><a href="Costs.html#Costs">Costs</a>: Defining relative costs of different operations.
<li><a href="Scheduling.html#Scheduling">Scheduling</a>: Adjusting the behavior of the instruction scheduler.
<li><a href="Sections.html#Sections">Sections</a>: Dividing storage into text, data, and other sections.
<li><a href="PIC.html#PIC">PIC</a>: Macros for position independent code.
<li><a href="Assembler-Format.html#Assembler-Format">Assembler Format</a>: Defining how to write insns and pseudo-ops to output.
<li><a href="Debugging-Info.html#Debugging-Info">Debugging Info</a>: Defining the format of debugging output.
<li><a href="Floating-Point.html#Floating-Point">Floating Point</a>: Handling floating point for cross-compilers.
<li><a href="Mode-Switching.html#Mode-Switching">Mode Switching</a>: Insertion of mode-switching instructions.
<li><a href="Target-Attributes.html#Target-Attributes">Target Attributes</a>: Defining target-specific uses of <code>__attribute__</code>.
<li><a href="Emulated-TLS.html#Emulated-TLS">Emulated TLS</a>: Emulated TLS support.
<li><a href="MIPS-Coprocessors.html#MIPS-Coprocessors">MIPS Coprocessors</a>: MIPS coprocessor support and how to customize it.
<li><a href="PCH-Target.html#PCH-Target">PCH Target</a>: Validity checking for precompiled headers.
<li><a href="C_002b_002b-ABI.html#C_002b_002b-ABI">C++ ABI</a>: Controlling C++ ABI changes.
<li><a href="Named-Address-Spaces.html#Named-Address-Spaces">Named Address Spaces</a>: Adding support for named address spaces
<li><a href="Misc.html#Misc">Misc</a>: Everything else.
</ul>
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