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  1. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

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  62. <a name="OpenRISC_002dRelocs"></a>

  63. <div class="header">

  64. <p>

  65. 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> &nbsp; [<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>

  66. </div>

  67. <hr>

  68. <a name="Relocations-3"></a>

  69. <h4 class="subsubsection">9.33.1.3 Relocations</h4>

  70. <a name="index-OpenRISC-relocations"></a>

  71. <a name="index-relocations_002c-OpenRISC"></a>

  72. 

  73. <p>ELF relocations are available as defined in the OpenRISC architecture

  74. specification.

  75. </p>

  76. <p><code>R_OR1K_HI_16_IN_INSN</code> is obtained using &lsquo;<samp>hi</samp>&rsquo; and

  77. <code>R_OR1K_LO_16_IN_INSN</code> and <code>R_OR1K_SLO16</code> are obtained using

  78. &lsquo;<samp>lo</samp>&rsquo;.  For signed offsets <code>R_OR1K_AHI16</code> is obtained from

  79. &lsquo;<samp>ha</samp>&rsquo;.  For example:

  80. </p>

  81. <div class="example">

  82. <pre class="example">l.movhi r5, hi(symbol)

  83. l.ori   r5, r5, lo(symbol)

  84. 

  85. l.movhi r5, ha(symbol)

  86. l.addi  r5, r5, lo(symbol)

  87. </pre></div>

  88. 

  89. <p>These &ldquo;high&rdquo; mnemonics extract bits 31:16 of their operand,

  90. and the &ldquo;low&rdquo; mnemonics extract bits 15:0 of their operand.

  91. </p>

  92. <p>The PC relative relocation <code>R_OR1K_GOTPC_HI16</code> can be obtained by

  93. enclosing an operand inside of &lsquo;<samp>gotpchi</samp>&rsquo;.  Likewise, the

  94. <code>R_OR1K_GOTPC_LO16</code> relocation can be obtained using &lsquo;<samp>gotpclo</samp>&rsquo;.

  95. These are mostly used when assembling PIC code.  For example, the

  96. standard PIC sequence on OpenRISC to get the base of the global offset

  97. table, PC relative, into a register, can be performed as:

  98. </p>

  99. <div class="example">

  100. <pre class="example">l.jal   0x8

  101.  l.movhi r17, gotpchi(_GLOBAL_OFFSET_TABLE_-4)

  102. l.ori   r17, r17, gotpclo(_GLOBAL_OFFSET_TABLE_+0)

  103. l.add   r17, r17, r9

  104. </pre></div>

  105. 

  106. <p>Several relocations exist to allow the link editor to perform GOT data

  107. references.  The <code>R_OR1K_GOT16</code> relocation can obtained by enclosing an

  108. operand inside of &lsquo;<samp>got</samp>&rsquo;.  For example, assuming the GOT base is in

  109. register <code>r17</code>.

  110. </p>

  111. <div class="example">

  112. <pre class="example">l.lwz   r19, got(a)(r17)

  113. l.lwz   r21, 0(r19)

  114. </pre></div>

  115. 

  116. <p>Also, several relocations exist for local GOT references.  The

  117. <code>R_OR1K_GOTOFF_AHI16</code> relocation can obtained by enclosing an operand

  118. inside of &lsquo;<samp>gotoffha</samp>&rsquo;.  Likewise, <code>R_OR1K_GOTOFF_LO16</code> and

  119. <code>R_OR1K_GOTOFF_SLO16</code> can be obtained by enclosing an operand inside of

  120. &lsquo;<samp>gotofflo</samp>&rsquo;.  For example, assuming the GOT base is in register

  121. <code>rl7</code>:

  122. </p>

  123. <div class="example">

  124. <pre class="example">l.movhi r19, gotoffha(symbol)

  125. l.add   r19, r19, r17

  126. l.lwz   r19, gotofflo(symbol)(r19)

  127. </pre></div>

  128. 

  129. <p>The above PC relative relocations use a <code>l.jal</code> (jump) instruction

  130. and reading of the link register to load the PC.  OpenRISC also supports

  131. page offset PC relative locations without a jump instruction using the

  132. <code>l.adrp</code> instruction.  By default the <code>l.adrp</code> instruction will

  133. create an <code>R_OR1K_PCREL_PG21</code> relocation.

  134. Likewise, <code>BFD_RELOC_OR1K_LO13</code> and <code>BFD_RELOC_OR1K_SLO13</code> can

  135. be obtained by enclosing an operand inside of &lsquo;<samp>po</samp>&rsquo;.  For example:

  136. </p>

  137. <div class="example">

  138. <pre class="example">l.adrp  r3, symbol

  139. l.ori   r4, r3, po(symbol)

  140. l.lbz   r5, po(symbol)(r3)

  141. l.sb    po(symbol)(r3), r6

  142. </pre></div>

  143. 

  144. <p>Likewise the page offset relocations can be used with GOT references.  The

  145. relocation <code>R_OR1K_GOT_PG21</code> can be obtained by enclosing an

  146. <code>l.adrp</code> immediate operand inside of &lsquo;<samp>got</samp>&rsquo;.  Likewise,

  147. <code>R_OR1K_GOT_LO13</code> can be obtained by enclosing an operand inside of

  148. &lsquo;<samp>gotpo</samp>&rsquo;.  For example to load the value of a GOT symbol into register

  149. &lsquo;<samp>r5</samp>&rsquo; we can do:

  150. </p>

  151. <div class="example">

  152. <pre class="example">l.adrp  r17, got(_GLOBAL_OFFSET_TABLE_)

  153. l.lwz   r5, gotpo(symbol)(r17)

  154. </pre></div>

  155. 

  156. <p>There are many relocations that can be requested for access to

  157. thread local storage variables.  All of the OpenRISC TLS mnemonics

  158. are supported:

  159. </p>

  160. <ul>

  161. <li> <code>R_OR1K_TLS_GD_HI16</code> is requested using &lsquo;<samp>tlsgdhi</samp>&rsquo;.

  162. </li><li> <code>R_OR1K_TLS_GD_LO16</code> is requested using &lsquo;<samp>tlsgdlo</samp>&rsquo;.

  163. </li><li> <code>R_OR1K_TLS_GD_PG21</code> is requested using &lsquo;<samp>tldgd</samp>&rsquo;.

  164. </li><li> <code>R_OR1K_TLS_GD_LO13</code> is requested using &lsquo;<samp>tlsgdpo</samp>&rsquo;.

  165. 

  166. </li><li> <code>R_OR1K_TLS_LDM_HI16</code> is requested using &lsquo;<samp>tlsldmhi</samp>&rsquo;.

  167. </li><li> <code>R_OR1K_TLS_LDM_LO16</code> is requested using &lsquo;<samp>tlsldmlo</samp>&rsquo;.

  168. </li><li> <code>R_OR1K_TLS_LDM_PG21</code> is requested using &lsquo;<samp>tldldm</samp>&rsquo;.

  169. </li><li> <code>R_OR1K_TLS_LDM_LO13</code> is requested using &lsquo;<samp>tlsldmpo</samp>&rsquo;.

  170. 

  171. </li><li> <code>R_OR1K_TLS_LDO_HI16</code> is requested using &lsquo;<samp>dtpoffhi</samp>&rsquo;.

  172. </li><li> <code>R_OR1K_TLS_LDO_LO16</code> is requested using &lsquo;<samp>dtpofflo</samp>&rsquo;.

  173. 

  174. </li><li> <code>R_OR1K_TLS_IE_HI16</code> is requested using &lsquo;<samp>gottpoffhi</samp>&rsquo;.

  175. </li><li> <code>R_OR1K_TLS_IE_AHI16</code> is requested using &lsquo;<samp>gottpoffha</samp>&rsquo;.

  176. </li><li> <code>R_OR1K_TLS_IE_LO16</code> is requested using &lsquo;<samp>gottpofflo</samp>&rsquo;.

  177. </li><li> <code>R_OR1K_TLS_IE_PG21</code> is requested using &lsquo;<samp>gottp</samp>&rsquo;.

  178. </li><li> <code>R_OR1K_TLS_IE_LO13</code> is requested using &lsquo;<samp>gottppo</samp>&rsquo;.

  179. 

  180. </li><li> <code>R_OR1K_TLS_LE_HI16</code> is requested using &lsquo;<samp>tpoffhi</samp>&rsquo;.

  181. </li><li> <code>R_OR1K_TLS_LE_AHI16</code> is requested using &lsquo;<samp>tpoffha</samp>&rsquo;.

  182. </li><li> <code>R_OR1K_TLS_LE_LO16</code> is requested using &lsquo;<samp>tpofflo</samp>&rsquo;.

  183. </li><li> <code>R_OR1K_TLS_LE_SLO16</code> also is requested using &lsquo;<samp>tpofflo</samp>&rsquo;

  184. depending on the instruction format.

  185. </li></ul>

  186. 

  187. <p>Here are some example TLS model sequences.

  188. </p>

  189. <p>First, General Dynamic:

  190. </p>

  191. <div class="example">

  192. <pre class="example">l.movhi r17, tlsgdhi(symbol)

  193. l.ori   r17, r17, tlsgdlo(symbol)

  194. l.add   r17, r17, r16

  195. l.or    r3, r17, r17

  196. l.jal   plt(__tls_get_addr)

  197.  l.nop

  198. </pre></div>

  199. 

  200. <p>Initial Exec:

  201. </p>

  202. <div class="example">

  203. <pre class="example">l.movhi r17, gottpoffhi(symbol)

  204. l.add   r17, r17, r16

  205. l.lwz   r17, gottpofflo(symbol)(r17)

  206. l.add   r17, r17, r10

  207. l.lbs   r17, 0(r17)

  208. </pre></div>

  209. 

  210. <p>And finally, Local Exec:

  211. </p>

  212. <div class="example">

  213. <pre class="example">l.movhi r17, tpoffha(symbol)

  214. l.add   r17, r17, r10

  215. l.addi  r17, r17, tpofflo(symbol)

  216. l.lbs   r17, 0(r17)

  217. </pre></div>

  218. 

  219. <hr>

  220. <div class="header">

  221. <p>

  222. 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> &nbsp; [<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>

  223. </div>

  224. 

  225. 

  226. 

  227. </body>

  228. </html>