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132 lines
6.2 KiB
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<title>CRIS-Pic - Using as</title>
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<!--
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This file documents the GNU Assembler "as".
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Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002,
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2006, 2007 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 1.1
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, with no Front-Cover Texts, and with no
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Back-Cover Texts. A copy of the license is included in the
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<div class="node">
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<p>
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<a name="CRIS_002dPic"></a>Next: <a rel="next" accesskey="n" href="CRIS_002dRegs.html#CRIS_002dRegs">CRIS-Regs</a>,
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Previous: <a rel="previous" accesskey="p" href="CRIS_002dChars.html#CRIS_002dChars">CRIS-Chars</a>,
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Up: <a rel="up" accesskey="u" href="CRIS_002dSyntax.html#CRIS_002dSyntax">CRIS-Syntax</a>
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<hr><br>
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</div>
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<h5 class="subsubsection">9.7.4.2 Symbols in position-independent code</h5>
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<p><a name="index-Symbols-in-position_002dindependent-code_002c-CRIS-701"></a><a name="index-CRIS-symbols-in-position_002dindependent-code-702"></a><a name="index-Position_002dindependent-code_002c-symbols-in_002c-CRIS-703"></a>
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When generating <a name="crispic"></a>position-independent code (SVR4
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PIC) for use in cris-axis-linux-gnu or crisv32-axis-linux-gnu
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shared libraries, symbol
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suffixes are used to specify what kind of run-time symbol lookup
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will be used, expressed in the object as different
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<em>relocation types</em>. Usually, all absolute symbol values
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must be located in a table, the <em>global offset table</em>,
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leaving the code position-independent; independent of values of
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global symbols and independent of the address of the code. The
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suffix modifies the value of the symbol, into for example an
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index into the global offset table where the real symbol value
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is entered, or a PC-relative value, or a value relative to the
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start of the global offset table. All symbol suffixes start
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with the character <span class="samp">:</span> (omitted in the list below). Every
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symbol use in code or a read-only section must therefore have a
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PIC suffix to enable a useful shared library to be created.
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Usually, these constructs must not be used with an additive
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constant offset as is usually allowed, i.e. no 4 as in
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<code>symbol + 4</code> is allowed. This restriction is checked at
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link-time, not at assembly-time.
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<dl>
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<dt><code>GOT</code><dd>
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Attaching this suffix to a symbol in an instruction causes the
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symbol to be entered into the global offset table. The value is
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a 32-bit index for that symbol into the global offset table.
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The name of the corresponding relocation is
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<span class="samp">R_CRIS_32_GOT</span>. Example: <code>move.d
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[$r0+extsym:GOT],$r9</code>
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<br><dt><code>GOT16</code><dd>
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Same as for <span class="samp">GOT</span>, but the value is a 16-bit index into the
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global offset table. The corresponding relocation is
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<span class="samp">R_CRIS_16_GOT</span>. Example: <code>move.d
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[$r0+asymbol:GOT16],$r10</code>
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<br><dt><code>PLT</code><dd>
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This suffix is used for function symbols. It causes a
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<em>procedure linkage table</em>, an array of code stubs, to be
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created at the time the shared object is created or linked
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against, together with a global offset table entry. The value
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is a pc-relative offset to the corresponding stub code in the
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procedure linkage table. This arrangement causes the run-time
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symbol resolver to be called to look up and set the value of the
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symbol the first time the function is called (at latest;
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depending environment variables). It is only safe to leave the
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symbol unresolved this way if all references are function calls.
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The name of the relocation is <span class="samp">R_CRIS_32_PLT_PCREL</span>.
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Example: <code>add.d fnname:PLT,$pc</code>
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<br><dt><code>PLTG</code><dd>
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Like PLT, but the value is relative to the beginning of the
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global offset table. The relocation is
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<span class="samp">R_CRIS_32_PLT_GOTREL</span>. Example: <code>move.d
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fnname:PLTG,$r3</code>
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<br><dt><code>GOTPLT</code><dd>
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Similar to <span class="samp">PLT</span>, but the value of the symbol is a 32-bit
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index into the global offset table. This is somewhat of a mix
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between the effect of the <span class="samp">GOT</span> and the <span class="samp">PLT</span> suffix;
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the difference to <span class="samp">GOT</span> is that there will be a procedure
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linkage table entry created, and that the symbol is assumed to
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be a function entry and will be resolved by the run-time
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resolver as with <span class="samp">PLT</span>. The relocation is
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<span class="samp">R_CRIS_32_GOTPLT</span>. Example: <code>jsr
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[$r0+fnname:GOTPLT]</code>
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<br><dt><code>GOTPLT16</code><dd>
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A variant of <span class="samp">GOTPLT</span> giving a 16-bit value. Its
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relocation name is <span class="samp">R_CRIS_16_GOTPLT</span>. Example: <code>jsr
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[$r0+fnname:GOTPLT16]</code>
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<br><dt><code>GOTOFF</code><dd>
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This suffix must only be attached to a local symbol, but may be
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used in an expression adding an offset. The value is the
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address of the symbol relative to the start of the global offset
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table. The relocation name is <span class="samp">R_CRIS_32_GOTREL</span>.
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Example: <code>move.d [$r0+localsym:GOTOFF],r3</code>
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</dl>
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</body></html>
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