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| <h3 class="section">4.2 <samp><span class="command">ld</span></samp> and the Motorola 68HC11 and 68HC12 families</h3> |
| |
| <p><a name="index-M68HC11-and-68HC12-support-625"></a> |
| |
| <h4 class="subsection">4.2.1 Linker Relaxation</h4> |
| |
| <p>For the Motorola 68HC11, <samp><span class="command">ld</span></samp> can perform these global |
| optimizations when you specify the ‘<samp><span class="samp">--relax</span></samp>’ command-line option. |
| |
| |
| <a name="index-relaxing-on-M68HC11-626"></a> |
| <dl><dt><em>relaxing address modes</em><dd><samp><span class="command">ld</span></samp> finds all <code>jsr</code> and <code>jmp</code> instructions whose |
| targets are within eight bits, and turns them into eight-bit |
| program-counter relative <code>bsr</code> and <code>bra</code> instructions, |
| respectively. |
| |
| <p><samp><span class="command">ld</span></samp> also looks at all 16-bit extended addressing modes and |
| transforms them in a direct addressing mode when the address is in |
| page 0 (between 0 and 0x0ff). |
| |
| <br><dt><em>relaxing gcc instruction group</em><dd>When <samp><span class="command">gcc</span></samp> is called with <samp><span class="option">-mrelax</span></samp>, it can emit group |
| of instructions that the linker can optimize to use a 68HC11 direct |
| addressing mode. These instructions consists of <code>bclr</code> or |
| <code>bset</code> instructions. |
| |
| </dl> |
| |
| <h4 class="subsection">4.2.2 Trampoline Generation</h4> |
| |
| <p><a name="index-trampoline-generation-on-M68HC11-627"></a><a name="index-trampoline-generation-on-M68HC12-628"></a>For 68HC11 and 68HC12, <samp><span class="command">ld</span></samp> can generate trampoline code to |
| call a far function using a normal <code>jsr</code> instruction. The linker |
| will also change the relocation to some far function to use the |
| trampoline address instead of the function address. This is typically the |
| case when a pointer to a function is taken. The pointer will in fact |
| point to the function trampoline. |
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