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| <h4 class="subsection">3.17.41 SPU Options</h4> |
| |
| <p><a name="index-SPU-options-2219"></a> |
| These ‘<samp><span class="samp">-m</span></samp>’ options are supported on the SPU: |
| |
| <dl> |
| <dt><code>-mwarn-reloc</code><dt><code>-merror-reloc</code><dd><a name="index-mwarn_002dreloc-2220"></a><a name="index-merror_002dreloc-2221"></a> |
| The loader for SPU does not handle dynamic relocations. By default, GCC |
| gives an error when it generates code that requires a dynamic |
| relocation. <samp><span class="option">-mno-error-reloc</span></samp> disables the error, |
| <samp><span class="option">-mwarn-reloc</span></samp> generates a warning instead. |
| |
| <br><dt><code>-msafe-dma</code><dt><code>-munsafe-dma</code><dd><a name="index-msafe_002ddma-2222"></a><a name="index-munsafe_002ddma-2223"></a> |
| Instructions that initiate or test completion of DMA must not be |
| reordered with respect to loads and stores of the memory that is being |
| accessed. |
| With <samp><span class="option">-munsafe-dma</span></samp> you must use the <code>volatile</code> keyword to protect |
| memory accesses, but that can lead to inefficient code in places where the |
| memory is known to not change. Rather than mark the memory as volatile, |
| you can use <samp><span class="option">-msafe-dma</span></samp> to tell the compiler to treat |
| the DMA instructions as potentially affecting all memory. |
| |
| <br><dt><code>-mbranch-hints</code><dd><a name="index-mbranch_002dhints-2224"></a> |
| By default, GCC generates a branch hint instruction to avoid |
| pipeline stalls for always-taken or probably-taken branches. A hint |
| is not generated closer than 8 instructions away from its branch. |
| There is little reason to disable them, except for debugging purposes, |
| or to make an object a little bit smaller. |
| |
| <br><dt><code>-msmall-mem</code><dt><code>-mlarge-mem</code><dd><a name="index-msmall_002dmem-2225"></a><a name="index-mlarge_002dmem-2226"></a> |
| By default, GCC generates code assuming that addresses are never larger |
| than 18 bits. With <samp><span class="option">-mlarge-mem</span></samp> code is generated that assumes |
| a full 32-bit address. |
| |
| <br><dt><code>-mstdmain</code><dd><a name="index-mstdmain-2227"></a> |
| By default, GCC links against startup code that assumes the SPU-style |
| main function interface (which has an unconventional parameter list). |
| With <samp><span class="option">-mstdmain</span></samp>, GCC links your program against startup |
| code that assumes a C99-style interface to <code>main</code>, including a |
| local copy of <code>argv</code> strings. |
| |
| <br><dt><code>-mfixed-range=</code><var>register-range</var><dd><a name="index-mfixed_002drange-2228"></a>Generate code treating the given register range as fixed registers. |
| A fixed register is one that the register allocator cannot use. This is |
| useful when compiling kernel code. A register range is specified as |
| two registers separated by a dash. Multiple register ranges can be |
| specified separated by a comma. |
| |
| <br><dt><code>-mea32</code><dt><code>-mea64</code><dd><a name="index-mea32-2229"></a><a name="index-mea64-2230"></a>Compile code assuming that pointers to the PPU address space accessed |
| via the <code>__ea</code> named address space qualifier are either 32 or 64 |
| bits wide. The default is 32 bits. As this is an ABI-changing option, |
| all object code in an executable must be compiled with the same setting. |
| |
| <br><dt><code>-maddress-space-conversion</code><dt><code>-mno-address-space-conversion</code><dd><a name="index-maddress_002dspace_002dconversion-2231"></a><a name="index-mno_002daddress_002dspace_002dconversion-2232"></a>Allow/disallow treating the <code>__ea</code> address space as superset |
| of the generic address space. This enables explicit type casts |
| between <code>__ea</code> and generic pointer as well as implicit |
| conversions of generic pointers to <code>__ea</code> pointers. The |
| default is to allow address space pointer conversions. |
| |
| <br><dt><code>-mcache-size=</code><var>cache-size</var><dd><a name="index-mcache_002dsize-2233"></a>This option controls the version of libgcc that the compiler links to an |
| executable and selects a software-managed cache for accessing variables |
| in the <code>__ea</code> address space with a particular cache size. Possible |
| options for <var>cache-size</var> are ‘<samp><span class="samp">8</span></samp>’, ‘<samp><span class="samp">16</span></samp>’, ‘<samp><span class="samp">32</span></samp>’, ‘<samp><span class="samp">64</span></samp>’ |
| and ‘<samp><span class="samp">128</span></samp>’. The default cache size is 64KB. |
| |
| <br><dt><code>-matomic-updates</code><dt><code>-mno-atomic-updates</code><dd><a name="index-matomic_002dupdates-2234"></a><a name="index-mno_002datomic_002dupdates-2235"></a>This option controls the version of libgcc that the compiler links to an |
| executable and selects whether atomic updates to the software-managed |
| cache of PPU-side variables are used. If you use atomic updates, changes |
| to a PPU variable from SPU code using the <code>__ea</code> named address space |
| qualifier do not interfere with changes to other PPU variables residing |
| in the same cache line from PPU code. If you do not use atomic updates, |
| such interference may occur; however, writing back cache lines is |
| more efficient. The default behavior is to use atomic updates. |
| |
| <br><dt><code>-mdual-nops</code><dt><code>-mdual-nops=</code><var>n</var><dd><a name="index-mdual_002dnops-2236"></a>By default, GCC inserts nops to increase dual issue when it expects |
| it to increase performance. <var>n</var> can be a value from 0 to 10. A |
| smaller <var>n</var> inserts fewer nops. 10 is the default, 0 is the |
| same as <samp><span class="option">-mno-dual-nops</span></samp>. Disabled with <samp><span class="option">-Os</span></samp>. |
| |
| <br><dt><code>-mhint-max-nops=</code><var>n</var><dd><a name="index-mhint_002dmax_002dnops-2237"></a>Maximum number of nops to insert for a branch hint. A branch hint must |
| be at least 8 instructions away from the branch it is affecting. GCC |
| inserts up to <var>n</var> nops to enforce this, otherwise it does not |
| generate the branch hint. |
| |
| <br><dt><code>-mhint-max-distance=</code><var>n</var><dd><a name="index-mhint_002dmax_002ddistance-2238"></a>The encoding of the branch hint instruction limits the hint to be within |
| 256 instructions of the branch it is affecting. By default, GCC makes |
| sure it is within 125. |
| |
| <br><dt><code>-msafe-hints</code><dd><a name="index-msafe_002dhints-2239"></a>Work around a hardware bug that causes the SPU to stall indefinitely. |
| By default, GCC inserts the <code>hbrp</code> instruction to make sure |
| this stall won't happen. |
| |
| </dl> |
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