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114 lines
5.4 KiB
HTML
114 lines
5.4 KiB
HTML
4 years ago
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<html lang="en">
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<head>
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<title>Per-Function Data - GNU Compiler Collection (GCC) Internals</title>
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<meta name="description" content="GNU Compiler Collection (GCC) Internals">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Target-Macros.html#Target-Macros" title="Target Macros">
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<link rel="prev" href="Run_002dtime-Target.html#Run_002dtime-Target" title="Run-time Target">
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<link rel="next" href="Storage-Layout.html#Storage-Layout" title="Storage Layout">
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<!--
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Copyright (C) 1988-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being ``Funding Free Software'', the Front-Cover
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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</head>
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<body>
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<div class="node">
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<a name="Per-Function-Data"></a>
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<a name="Per_002dFunction-Data"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Storage-Layout.html#Storage-Layout">Storage Layout</a>,
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Previous: <a rel="previous" accesskey="p" href="Run_002dtime-Target.html#Run_002dtime-Target">Run-time Target</a>,
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Up: <a rel="up" accesskey="u" href="Target-Macros.html#Target-Macros">Target Macros</a>
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<hr>
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</div>
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<h3 class="section">17.4 Defining data structures for per-function information.</h3>
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<p><a name="index-per_002dfunction-data-3920"></a><a name="index-data-structures-3921"></a>
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If the target needs to store information on a per-function basis, GCC
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provides a macro and a couple of variables to allow this. Note, just
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using statics to store the information is a bad idea, since GCC supports
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nested functions, so you can be halfway through encoding one function
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when another one comes along.
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<p>GCC defines a data structure called <code>struct function</code> which
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contains all of the data specific to an individual function. This
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structure contains a field called <code>machine</code> whose type is
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<code>struct machine_function *</code>, which can be used by targets to point
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to their own specific data.
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<p>If a target needs per-function specific data it should define the type
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<code>struct machine_function</code> and also the macro <code>INIT_EXPANDERS</code>.
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This macro should be used to initialize the function pointer
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<code>init_machine_status</code>. This pointer is explained below.
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<p>One typical use of per-function, target specific data is to create an
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RTX to hold the register containing the function's return address. This
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RTX can then be used to implement the <code>__builtin_return_address</code>
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function, for level 0.
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<p>Note—earlier implementations of GCC used a single data area to hold
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all of the per-function information. Thus when processing of a nested
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function began the old per-function data had to be pushed onto a
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stack, and when the processing was finished, it had to be popped off the
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stack. GCC used to provide function pointers called
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<code>save_machine_status</code> and <code>restore_machine_status</code> to handle
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the saving and restoring of the target specific information. Since the
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single data area approach is no longer used, these pointers are no
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longer supported.
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<div class="defun">
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— Macro: <b>INIT_EXPANDERS</b><var><a name="index-INIT_005fEXPANDERS-3922"></a></var><br>
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<blockquote><p>Macro called to initialize any target specific information. This macro
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is called once per function, before generation of any RTL has begun.
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The intention of this macro is to allow the initialization of the
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function pointer <code>init_machine_status</code>.
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</p></blockquote></div>
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<div class="defun">
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— Variable: void (*)(struct function *) <b>init_machine_status</b><var><a name="index-init_005fmachine_005fstatus-3923"></a></var><br>
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<blockquote><p>If this function pointer is non-<code>NULL</code> it will be called once per
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function, before function compilation starts, in order to allow the
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target to perform any target specific initialization of the
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<code>struct function</code> structure. It is intended that this would be
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used to initialize the <code>machine</code> of that structure.
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<p><code>struct machine_function</code> structures are expected to be freed by GC.
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Generally, any memory that they reference must be allocated by using
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GC allocation, including the structure itself.
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</p></blockquote></div>
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</body></html>
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