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229 lines
9.8 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- This file documents the GNU Assembler "as".
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Copyright (C) 1991-2019 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
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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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section entitled "GNU Free Documentation License".
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-->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>OpenRISC-Relocs (Using as)</title>
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<meta name="description" content="OpenRISC-Relocs (Using as)">
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<meta name="keywords" content="OpenRISC-Relocs (Using as)">
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<meta name="resource-type" content="document">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="AS-Index.html#AS-Index" rel="index" title="AS Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="OpenRISC_002dSyntax.html#OpenRISC_002dSyntax" rel="up" title="OpenRISC-Syntax">
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<link href="OpenRISC_002dFloat.html#OpenRISC_002dFloat" rel="next" title="OpenRISC-Float">
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<link href="OpenRISC_002dRegs.html#OpenRISC_002dRegs" rel="prev" title="OpenRISC-Regs">
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<style type="text/css">
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a.summary-letter {text-decoration: none}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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blockquote.smallquotation {font-size: smaller}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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div.lisp {margin-left: 3.2em}
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div.smalldisplay {margin-left: 3.2em}
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</style>
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</head>
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<body lang="en">
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<a name="OpenRISC_002dRelocs"></a>
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<div class="header">
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<p>
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Previous: <a href="OpenRISC_002dRegs.html#OpenRISC_002dRegs" accesskey="p" rel="prev">OpenRISC-Regs</a>, Up: <a href="OpenRISC_002dSyntax.html#OpenRISC_002dSyntax" accesskey="u" rel="up">OpenRISC-Syntax</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Relocations-3"></a>
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<h4 class="subsubsection">9.32.1.3 Relocations</h4>
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<a name="index-OpenRISC-relocations"></a>
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<a name="index-relocations_002c-OpenRISC"></a>
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<p>ELF relocations are available as defined in the OpenRISC architecture
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specification.
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</p>
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<p><code>R_OR1K_HI_16_IN_INSN</code> is obtained using ‘<samp>hi</samp>’ and
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<code>R_OR1K_LO_16_IN_INSN</code> and <code>R_OR1K_SLO16</code> are obtained using
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‘<samp>lo</samp>’. For signed offsets <code>R_OR1K_AHI16</code> is obtained from
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‘<samp>ha</samp>’. For example:
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</p>
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<div class="example">
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<pre class="example">l.movhi r5, hi(symbol)
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l.ori r5, r5, lo(symbol)
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l.movhi r5, ha(symbol)
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l.addi r5, r5, lo(symbol)
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</pre></div>
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<p>These “high” mnemonics extract bits 31:16 of their operand,
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and the “low” mnemonics extract bits 15:0 of their operand.
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</p>
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<p>The PC relative relocation <code>R_OR1K_GOTPC_HI16</code> can be obtained by
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enclosing an operand inside of ‘<samp>gotpchi</samp>’. Likewise, the
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<code>R_OR1K_GOTPC_LO16</code> relocation can be obtained using ‘<samp>gotpclo</samp>’.
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These are mostly used when assembling PIC code. For example, the
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standard PIC sequence on OpenRISC to get the base of the global offset
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table, PC relative, into a register, can be performed as:
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</p>
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<div class="example">
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<pre class="example">l.jal 0x8
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l.movhi r17, gotpchi(_GLOBAL_OFFSET_TABLE_-4)
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l.ori r17, r17, gotpclo(_GLOBAL_OFFSET_TABLE_+0)
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l.add r17, r17, r9
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</pre></div>
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<p>Several relocations exist to allow the link editor to perform GOT data
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references. The <code>R_OR1K_GOT16</code> relocation can obtained by enclosing an
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operand inside of ‘<samp>got</samp>’. For example, assuming the GOT base is in
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register <code>r17</code>.
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</p>
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<div class="example">
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<pre class="example">l.lwz r19, got(a)(r17)
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l.lwz r21, 0(r19)
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</pre></div>
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<p>Also, several relocations exist for local GOT references. The
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<code>R_OR1K_GOTOFF_AHI16</code> relocation can obtained by enclosing an operand
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inside of ‘<samp>gotoffha</samp>’. Likewise, <code>R_OR1K_GOTOFF_LO16</code> and
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<code>R_OR1K_GOTOFF_SLO16</code> can be obtained by enclosing an operand inside of
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‘<samp>gotofflo</samp>’. For example, assuming the GOT base is in register
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<code>rl7</code>:
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</p>
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<div class="example">
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<pre class="example">l.movhi r19, gotoffha(symbol)
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l.add r19, r19, r17
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l.lwz r19, gotofflo(symbol)(r19)
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</pre></div>
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<p>The above PC relative relocations use a <code>l.jal</code> (jump) instruction
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and reading of the link register to load the PC. OpenRISC also supports
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page offset PC relative locations without a jump instruction using the
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<code>l.adrp</code> instruction. By default the <code>l.adrp</code> instruction will
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create an <code>R_OR1K_PCREL_PG21</code> relocation.
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Likewise, <code>BFD_RELOC_OR1K_LO13</code> and <code>BFD_RELOC_OR1K_SLO13</code> can
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be obtained by enclosing an operand inside of ‘<samp>po</samp>’. For example:
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</p>
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<div class="example">
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<pre class="example">l.adrp r3, symbol
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l.ori r4, r3, po(symbol)
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l.lbz r5, po(symbol)(r3)
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l.sb po(symbol)(r3), r6
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</pre></div>
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<p>Likewise the page offset relocations can be used with GOT references. The
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relocation <code>R_OR1K_GOT_PG21</code> can be obtained by enclosing an
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<code>l.adrp</code> immediate operand inside of ‘<samp>got</samp>’. Likewise,
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<code>R_OR1K_GOT_LO13</code> can be obtained by enclosing an operand inside of
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‘<samp>gotpo</samp>’. For example to load the value of a GOT symbol into register
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‘<samp>r5</samp>’ we can do:
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</p>
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<div class="example">
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<pre class="example">l.adrp r17, got(_GLOBAL_OFFSET_TABLE_)
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l.lwz r5, gotpo(symbol)(r17)
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</pre></div>
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<p>There are many relocations that can be requested for access to
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thread local storage variables. All of the OpenRISC TLS mnemonics
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are supported:
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</p>
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<ul>
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<li> <code>R_OR1K_TLS_GD_HI16</code> is requested using ‘<samp>tlsgdhi</samp>’.
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</li><li> <code>R_OR1K_TLS_GD_LO16</code> is requested using ‘<samp>tlsgdlo</samp>’.
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</li><li> <code>R_OR1K_TLS_GD_PG21</code> is requested using ‘<samp>tldgd</samp>’.
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</li><li> <code>R_OR1K_TLS_GD_LO13</code> is requested using ‘<samp>tlsgdpo</samp>’.
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</li><li> <code>R_OR1K_TLS_LDM_HI16</code> is requested using ‘<samp>tlsldmhi</samp>’.
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</li><li> <code>R_OR1K_TLS_LDM_LO16</code> is requested using ‘<samp>tlsldmlo</samp>’.
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</li><li> <code>R_OR1K_TLS_LDM_PG21</code> is requested using ‘<samp>tldldm</samp>’.
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</li><li> <code>R_OR1K_TLS_LDM_LO13</code> is requested using ‘<samp>tlsldmpo</samp>’.
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</li><li> <code>R_OR1K_TLS_LDO_HI16</code> is requested using ‘<samp>dtpoffhi</samp>’.
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</li><li> <code>R_OR1K_TLS_LDO_LO16</code> is requested using ‘<samp>dtpofflo</samp>’.
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</li><li> <code>R_OR1K_TLS_IE_HI16</code> is requested using ‘<samp>gottpoffhi</samp>’.
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</li><li> <code>R_OR1K_TLS_IE_AHI16</code> is requested using ‘<samp>gottpoffha</samp>’.
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</li><li> <code>R_OR1K_TLS_IE_LO16</code> is requested using ‘<samp>gottpofflo</samp>’.
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</li><li> <code>R_OR1K_TLS_IE_PG21</code> is requested using ‘<samp>gottp</samp>’.
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</li><li> <code>R_OR1K_TLS_IE_LO13</code> is requested using ‘<samp>gottppo</samp>’.
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</li><li> <code>R_OR1K_TLS_LE_HI16</code> is requested using ‘<samp>tpoffhi</samp>’.
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</li><li> <code>R_OR1K_TLS_LE_AHI16</code> is requested using ‘<samp>tpoffha</samp>’.
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</li><li> <code>R_OR1K_TLS_LE_LO16</code> is requested using ‘<samp>tpofflo</samp>’.
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</li><li> <code>R_OR1K_TLS_LE_SLO16</code> also is requested using ‘<samp>tpofflo</samp>’
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depending on the instruction format.
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</li></ul>
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<p>Here are some example TLS model sequences.
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</p>
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<p>First, General Dynamic:
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</p>
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<div class="example">
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<pre class="example">l.movhi r17, tlsgdhi(symbol)
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l.ori r17, r17, tlsgdlo(symbol)
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l.add r17, r17, r16
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l.or r3, r17, r17
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l.jal plt(__tls_get_addr)
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l.nop
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</pre></div>
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<p>Initial Exec:
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</p>
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<div class="example">
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<pre class="example">l.movhi r17, gottpoffhi(symbol)
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l.add r17, r17, r16
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l.lwz r17, gottpofflo(symbol)(r17)
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l.add r17, r17, r10
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l.lbs r17, 0(r17)
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</pre></div>
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<p>And finally, Local Exec:
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</p>
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<div class="example">
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<pre class="example">l.movhi r17, tpoffha(symbol)
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l.add r17, r17, r10
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l.addi r17, r17, tpofflo(symbol)
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l.lbs r17, 0(r17)
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</pre></div>
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<hr>
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<div class="header">
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<p>
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Previous: <a href="OpenRISC_002dRegs.html#OpenRISC_002dRegs" accesskey="p" rel="prev">OpenRISC-Regs</a>, Up: <a href="OpenRISC_002dSyntax.html#OpenRISC_002dSyntax" accesskey="u" rel="up">OpenRISC-Syntax</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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