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| <a name="OpenRISC-Relocs"></a> |
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| <p> |
| Previous: <a rel="previous" accesskey="p" href="OpenRISC_002dRegs.html#OpenRISC_002dRegs">OpenRISC-Regs</a>, |
| Up: <a rel="up" accesskey="u" href="OpenRISC_002dSyntax.html#OpenRISC_002dSyntax">OpenRISC-Syntax</a> |
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| |
| <h5 class="subsubsection">9.33.1.3 Relocations</h5> |
| |
| <p><a name="index-OpenRISC-relocations-1840"></a><a name="index-relocations_002c-OpenRISC-1841"></a> |
| ELF relocations are available as defined in the OpenRISC architecture |
| specification. |
| |
| <p><code>R_OR1K_HI_16_IN_INSN</code> is obtained using ‘<samp><span class="samp">hi</span></samp>’ and |
| <code>R_OR1K_LO_16_IN_INSN</code> and <code>R_OR1K_SLO16</code> are obtained using |
| ‘<samp><span class="samp">lo</span></samp>’. For signed offsets <code>R_OR1K_AHI16</code> is obtained from |
| ‘<samp><span class="samp">ha</span></samp>’. For example: |
| |
| <pre class="example"> l.movhi r5, hi(symbol) |
| l.ori r5, r5, lo(symbol) |
| |
| l.movhi r5, ha(symbol) |
| l.addi r5, r5, lo(symbol) |
| </pre> |
| <p>These “high” mnemonics extract bits 31:16 of their operand, |
| and the “low” mnemonics extract bits 15:0 of their operand. |
| |
| <p>The PC relative relocation <code>R_OR1K_GOTPC_HI16</code> can be obtained by |
| enclosing an operand inside of ‘<samp><span class="samp">gotpchi</span></samp>’. Likewise, the |
| <code>R_OR1K_GOTPC_LO16</code> relocation can be obtained using ‘<samp><span class="samp">gotpclo</span></samp>’. |
| These are mostly used when assembling PIC code. For example, the |
| standard PIC sequence on OpenRISC to get the base of the global offset |
| table, PC relative, into a register, can be performed as: |
| |
| <pre class="example"> l.jal 0x8 |
| l.movhi r17, gotpchi(_GLOBAL_OFFSET_TABLE_-4) |
| l.ori r17, r17, gotpclo(_GLOBAL_OFFSET_TABLE_+0) |
| l.add r17, r17, r9 |
| </pre> |
| <p>Several relocations exist to allow the link editor to perform GOT data |
| references. The <code>R_OR1K_GOT16</code> relocation can obtained by enclosing an |
| operand inside of ‘<samp><span class="samp">got</span></samp>’. For example, assuming the GOT base is in |
| register <code>r17</code>. |
| |
| <pre class="example"> l.lwz r19, got(a)(r17) |
| l.lwz r21, 0(r19) |
| </pre> |
| <p>Also, several relocations exist for local GOT references. The |
| <code>R_OR1K_GOTOFF_AHI16</code> relocation can obtained by enclosing an operand |
| inside of ‘<samp><span class="samp">gotoffha</span></samp>’. Likewise, <code>R_OR1K_GOTOFF_LO16</code> and |
| <code>R_OR1K_GOTOFF_SLO16</code> can be obtained by enclosing an operand inside of |
| ‘<samp><span class="samp">gotofflo</span></samp>’. For example, assuming the GOT base is in register |
| <code>rl7</code>: |
| |
| <pre class="example"> l.movhi r19, gotoffha(symbol) |
| l.add r19, r19, r17 |
| l.lwz r19, gotofflo(symbol)(r19) |
| </pre> |
| <p>The above PC relative relocations use a <code>l.jal</code> (jump) instruction |
| and reading of the link register to load the PC. OpenRISC also supports |
| page offset PC relative locations without a jump instruction using the |
| <code>l.adrp</code> instruction. By default the <code>l.adrp</code> instruction will |
| create an <code>R_OR1K_PCREL_PG21</code> relocation. |
| Likewise, <code>BFD_RELOC_OR1K_LO13</code> and <code>BFD_RELOC_OR1K_SLO13</code> can |
| be obtained by enclosing an operand inside of ‘<samp><span class="samp">po</span></samp>’. For example: |
| |
| <pre class="example"> l.adrp r3, symbol |
| l.ori r4, r3, po(symbol) |
| l.lbz r5, po(symbol)(r3) |
| l.sb po(symbol)(r3), r6 |
| </pre> |
| <p>Likewise the page offset relocations can be used with GOT references. The |
| relocation <code>R_OR1K_GOT_PG21</code> can be obtained by enclosing an |
| <code>l.adrp</code> immediate operand inside of ‘<samp><span class="samp">got</span></samp>’. Likewise, |
| <code>R_OR1K_GOT_LO13</code> can be obtained by enclosing an operand inside of |
| ‘<samp><span class="samp">gotpo</span></samp>’. For example to load the value of a GOT symbol into register |
| ‘<samp><span class="samp">r5</span></samp>’ we can do: |
| |
| <pre class="example"> l.adrp r17, got(_GLOBAL_OFFSET_TABLE_) |
| l.lwz r5, gotpo(symbol)(r17) |
| </pre> |
| <p>There are many relocations that can be requested for access to |
| thread local storage variables. All of the OpenRISC TLS mnemonics |
| are supported: |
| |
| <ul> |
| <li><code>R_OR1K_TLS_GD_HI16</code> is requested using ‘<samp><span class="samp">tlsgdhi</span></samp>’. |
| <li><code>R_OR1K_TLS_GD_LO16</code> is requested using ‘<samp><span class="samp">tlsgdlo</span></samp>’. |
| <li><code>R_OR1K_TLS_GD_PG21</code> is requested using ‘<samp><span class="samp">tldgd</span></samp>’. |
| <li><code>R_OR1K_TLS_GD_LO13</code> is requested using ‘<samp><span class="samp">tlsgdpo</span></samp>’. |
| |
| <li><code>R_OR1K_TLS_LDM_HI16</code> is requested using ‘<samp><span class="samp">tlsldmhi</span></samp>’. |
| <li><code>R_OR1K_TLS_LDM_LO16</code> is requested using ‘<samp><span class="samp">tlsldmlo</span></samp>’. |
| <li><code>R_OR1K_TLS_LDM_PG21</code> is requested using ‘<samp><span class="samp">tldldm</span></samp>’. |
| <li><code>R_OR1K_TLS_LDM_LO13</code> is requested using ‘<samp><span class="samp">tlsldmpo</span></samp>’. |
| |
| <li><code>R_OR1K_TLS_LDO_HI16</code> is requested using ‘<samp><span class="samp">dtpoffhi</span></samp>’. |
| <li><code>R_OR1K_TLS_LDO_LO16</code> is requested using ‘<samp><span class="samp">dtpofflo</span></samp>’. |
| |
| <li><code>R_OR1K_TLS_IE_HI16</code> is requested using ‘<samp><span class="samp">gottpoffhi</span></samp>’. |
| <li><code>R_OR1K_TLS_IE_AHI16</code> is requested using ‘<samp><span class="samp">gottpoffha</span></samp>’. |
| <li><code>R_OR1K_TLS_IE_LO16</code> is requested using ‘<samp><span class="samp">gottpofflo</span></samp>’. |
| <li><code>R_OR1K_TLS_IE_PG21</code> is requested using ‘<samp><span class="samp">gottp</span></samp>’. |
| <li><code>R_OR1K_TLS_IE_LO13</code> is requested using ‘<samp><span class="samp">gottppo</span></samp>’. |
| |
| <li><code>R_OR1K_TLS_LE_HI16</code> is requested using ‘<samp><span class="samp">tpoffhi</span></samp>’. |
| <li><code>R_OR1K_TLS_LE_AHI16</code> is requested using ‘<samp><span class="samp">tpoffha</span></samp>’. |
| <li><code>R_OR1K_TLS_LE_LO16</code> is requested using ‘<samp><span class="samp">tpofflo</span></samp>’. |
| <li><code>R_OR1K_TLS_LE_SLO16</code> also is requested using ‘<samp><span class="samp">tpofflo</span></samp>’ |
| depending on the instruction format. |
| </ul> |
| |
| <p>Here are some example TLS model sequences. |
| |
| <p>First, General Dynamic: |
| |
| <pre class="example"> l.movhi r17, tlsgdhi(symbol) |
| l.ori r17, r17, tlsgdlo(symbol) |
| l.add r17, r17, r16 |
| l.or r3, r17, r17 |
| l.jal plt(__tls_get_addr) |
| l.nop |
| </pre> |
| <p>Initial Exec: |
| |
| <pre class="example"> l.movhi r17, gottpoffhi(symbol) |
| l.add r17, r17, r16 |
| l.lwz r17, gottpofflo(symbol)(r17) |
| l.add r17, r17, r10 |
| l.lbs r17, 0(r17) |
| </pre> |
| <p>And finally, Local Exec: |
| |
| <pre class="example"> l.movhi r17, tpoffha(symbol) |
| l.add r17, r17, r10 |
| l.addi r17, r17, tpofflo(symbol) |
| l.lbs r17, 0(r17) |
| </pre> |
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