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180 lines
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<div class="node">
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<a name="OpenRISC-Relocs"></a>
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<a name="OpenRISC_002dRelocs"></a>
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<p>
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Previous: <a rel="previous" accesskey="p" href="OpenRISC_002dRegs.html#OpenRISC_002dRegs">OpenRISC-Regs</a>,
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Up: <a rel="up" accesskey="u" href="OpenRISC_002dSyntax.html#OpenRISC_002dSyntax">OpenRISC-Syntax</a>
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</div>
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<h5 class="subsubsection">9.33.1.3 Relocations</h5>
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<p><a name="index-OpenRISC-relocations-1840"></a><a name="index-relocations_002c-OpenRISC-1841"></a>
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ELF relocations are available as defined in the OpenRISC architecture
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specification.
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<p><code>R_OR1K_HI_16_IN_INSN</code> is obtained using ‘<samp><span class="samp">hi</span></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><span class="samp">lo</span></samp>’. For signed offsets <code>R_OR1K_AHI16</code> is obtained from
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‘<samp><span class="samp">ha</span></samp>’. For 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>
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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>The PC relative relocation <code>R_OR1K_GOTPC_HI16</code> can be obtained by
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enclosing an operand inside of ‘<samp><span class="samp">gotpchi</span></samp>’. Likewise, the
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<code>R_OR1K_GOTPC_LO16</code> relocation can be obtained using ‘<samp><span class="samp">gotpclo</span></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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<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>
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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><span class="samp">got</span></samp>’. For example, assuming the GOT base is in
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register <code>r17</code>.
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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>
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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><span class="samp">gotoffha</span></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><span class="samp">gotofflo</span></samp>’. For example, assuming the GOT base is in register
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<code>rl7</code>:
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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>
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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><span class="samp">po</span></samp>’. For 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>
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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><span class="samp">got</span></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><span class="samp">gotpo</span></samp>’. For example to load the value of a GOT symbol into register
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‘<samp><span class="samp">r5</span></samp>’ we can do:
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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>
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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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<ul>
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<li><code>R_OR1K_TLS_GD_HI16</code> is requested using ‘<samp><span class="samp">tlsgdhi</span></samp>’.
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<li><code>R_OR1K_TLS_GD_LO16</code> is requested using ‘<samp><span class="samp">tlsgdlo</span></samp>’.
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<li><code>R_OR1K_TLS_GD_PG21</code> is requested using ‘<samp><span class="samp">tldgd</span></samp>’.
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<li><code>R_OR1K_TLS_GD_LO13</code> is requested using ‘<samp><span class="samp">tlsgdpo</span></samp>’.
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<li><code>R_OR1K_TLS_LDM_HI16</code> is requested using ‘<samp><span class="samp">tlsldmhi</span></samp>’.
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<li><code>R_OR1K_TLS_LDM_LO16</code> is requested using ‘<samp><span class="samp">tlsldmlo</span></samp>’.
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<li><code>R_OR1K_TLS_LDM_PG21</code> is requested using ‘<samp><span class="samp">tldldm</span></samp>’.
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<li><code>R_OR1K_TLS_LDM_LO13</code> is requested using ‘<samp><span class="samp">tlsldmpo</span></samp>’.
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<li><code>R_OR1K_TLS_LDO_HI16</code> is requested using ‘<samp><span class="samp">dtpoffhi</span></samp>’.
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<li><code>R_OR1K_TLS_LDO_LO16</code> is requested using ‘<samp><span class="samp">dtpofflo</span></samp>’.
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<li><code>R_OR1K_TLS_IE_HI16</code> is requested using ‘<samp><span class="samp">gottpoffhi</span></samp>’.
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<li><code>R_OR1K_TLS_IE_AHI16</code> is requested using ‘<samp><span class="samp">gottpoffha</span></samp>’.
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<li><code>R_OR1K_TLS_IE_LO16</code> is requested using ‘<samp><span class="samp">gottpofflo</span></samp>’.
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<li><code>R_OR1K_TLS_IE_PG21</code> is requested using ‘<samp><span class="samp">gottp</span></samp>’.
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<li><code>R_OR1K_TLS_IE_LO13</code> is requested using ‘<samp><span class="samp">gottppo</span></samp>’.
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<li><code>R_OR1K_TLS_LE_HI16</code> is requested using ‘<samp><span class="samp">tpoffhi</span></samp>’.
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<li><code>R_OR1K_TLS_LE_AHI16</code> is requested using ‘<samp><span class="samp">tpoffha</span></samp>’.
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<li><code>R_OR1K_TLS_LE_LO16</code> is requested using ‘<samp><span class="samp">tpofflo</span></samp>’.
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<li><code>R_OR1K_TLS_LE_SLO16</code> also is requested using ‘<samp><span class="samp">tpofflo</span></samp>’
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depending on the instruction format.
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</ul>
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<p>Here are some example TLS model sequences.
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<p>First, General Dynamic:
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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>
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<p>Initial Exec:
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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>
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<p>And finally, Local Exec:
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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>
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