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| <a name="Named-Address-Spaces"></a> |
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| <a name="Adding-support-for-named-address-spaces"></a> |
| <h3 class="section">17.29 Adding support for named address spaces</h3> |
| <a name="index-named-address-spaces"></a> |
| |
| <p>The draft technical report of the ISO/IEC JTC1 S22 WG14 N1275 |
| standards committee, <cite>Programming Languages - C - Extensions to |
| support embedded processors</cite>, specifies a syntax for embedded |
| processors to specify alternate address spaces. You can configure a |
| GCC port to support section 5.1 of the draft report to add support for |
| address spaces other than the default address space. These address |
| spaces are new keywords that are similar to the <code>volatile</code> and |
| <code>const</code> type attributes. |
| </p> |
| <p>Pointers to named address spaces can have a different size than |
| pointers to the generic address space. |
| </p> |
| <p>For example, the SPU port uses the <code>__ea</code> address space to refer |
| to memory in the host processor, rather than memory local to the SPU |
| processor. Access to memory in the <code>__ea</code> address space involves |
| issuing DMA operations to move data between the host processor and the |
| local processor memory address space. Pointers in the <code>__ea</code> |
| address space are either 32 bits or 64 bits based on the |
| <samp>-mea32</samp> or <samp>-mea64</samp> switches (native SPU pointers are |
| always 32 bits). |
| </p> |
| <p>Internally, address spaces are represented as a small integer in the |
| range 0 to 15 with address space 0 being reserved for the generic |
| address space. |
| </p> |
| <p>To register a named address space qualifier keyword with the C front end, |
| the target may call the <code>c_register_addr_space</code> routine. For example, |
| the SPU port uses the following to declare <code>__ea</code> as the keyword for |
| named address space #1: |
| </p><div class="smallexample"> |
| <pre class="smallexample">#define ADDR_SPACE_EA 1 |
| c_register_addr_space ("__ea", ADDR_SPACE_EA); |
| </pre></div> |
| |
| <dl> |
| <dt><a name="index-TARGET_005fADDR_005fSPACE_005fPOINTER_005fMODE"></a>Target Hook: <em>machine_mode</em> <strong>TARGET_ADDR_SPACE_POINTER_MODE</strong> <em>(addr_space_t <var>address_space</var>)</em></dt> |
| <dd><p>Define this to return the machine mode to use for pointers to |
| <var>address_space</var> if the target supports named address spaces. |
| The default version of this hook returns <code>ptr_mode</code> for the |
| generic address space only. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-TARGET_005fADDR_005fSPACE_005fADDRESS_005fMODE"></a>Target Hook: <em>machine_mode</em> <strong>TARGET_ADDR_SPACE_ADDRESS_MODE</strong> <em>(addr_space_t <var>address_space</var>)</em></dt> |
| <dd><p>Define this to return the machine mode to use for addresses in |
| <var>address_space</var> if the target supports named address spaces. |
| The default version of this hook returns <code>Pmode</code> for the |
| generic address space only. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-TARGET_005fADDR_005fSPACE_005fVALID_005fPOINTER_005fMODE"></a>Target Hook: <em>bool</em> <strong>TARGET_ADDR_SPACE_VALID_POINTER_MODE</strong> <em>(machine_mode <var>mode</var>, addr_space_t <var>as</var>)</em></dt> |
| <dd><p>Define this to return nonzero if the port can handle pointers |
| with machine mode <var>mode</var> to address space <var>as</var>. This target |
| hook is the same as the <code>TARGET_VALID_POINTER_MODE</code> target hook, |
| except that it includes explicit named address space support. The default |
| version of this hook returns true for the modes returned by either the |
| <code>TARGET_ADDR_SPACE_POINTER_MODE</code> or <code>TARGET_ADDR_SPACE_ADDRESS_MODE</code> |
| target hooks for the given address space. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-TARGET_005fADDR_005fSPACE_005fLEGITIMATE_005fADDRESS_005fP"></a>Target Hook: <em>bool</em> <strong>TARGET_ADDR_SPACE_LEGITIMATE_ADDRESS_P</strong> <em>(machine_mode <var>mode</var>, rtx <var>exp</var>, bool <var>strict</var>, addr_space_t <var>as</var>)</em></dt> |
| <dd><p>Define this to return true if <var>exp</var> is a valid address for mode |
| <var>mode</var> in the named address space <var>as</var>. The <var>strict</var> |
| parameter says whether strict addressing is in effect after reload has |
| finished. This target hook is the same as the |
| <code>TARGET_LEGITIMATE_ADDRESS_P</code> target hook, except that it includes |
| explicit named address space support. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-TARGET_005fADDR_005fSPACE_005fLEGITIMIZE_005fADDRESS"></a>Target Hook: <em>rtx</em> <strong>TARGET_ADDR_SPACE_LEGITIMIZE_ADDRESS</strong> <em>(rtx <var>x</var>, rtx <var>oldx</var>, machine_mode <var>mode</var>, addr_space_t <var>as</var>)</em></dt> |
| <dd><p>Define this to modify an invalid address <var>x</var> to be a valid address |
| with mode <var>mode</var> in the named address space <var>as</var>. This target |
| hook is the same as the <code>TARGET_LEGITIMIZE_ADDRESS</code> target hook, |
| except that it includes explicit named address space support. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-TARGET_005fADDR_005fSPACE_005fSUBSET_005fP"></a>Target Hook: <em>bool</em> <strong>TARGET_ADDR_SPACE_SUBSET_P</strong> <em>(addr_space_t <var>subset</var>, addr_space_t <var>superset</var>)</em></dt> |
| <dd><p>Define this to return whether the <var>subset</var> named address space is |
| contained within the <var>superset</var> named address space. Pointers to |
| a named address space that is a subset of another named address space |
| will be converted automatically without a cast if used together in |
| arithmetic operations. Pointers to a superset address space can be |
| converted to pointers to a subset address space via explicit casts. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-TARGET_005fADDR_005fSPACE_005fCONVERT"></a>Target Hook: <em>rtx</em> <strong>TARGET_ADDR_SPACE_CONVERT</strong> <em>(rtx <var>op</var>, tree <var>from_type</var>, tree <var>to_type</var>)</em></dt> |
| <dd><p>Define this to convert the pointer expression represented by the RTL |
| <var>op</var> with type <var>from_type</var> that points to a named address |
| space to a new pointer expression with type <var>to_type</var> that points |
| to a different named address space. When this hook it called, it is |
| guaranteed that one of the two address spaces is a subset of the other, |
| as determined by the <code>TARGET_ADDR_SPACE_SUBSET_P</code> target hook. |
| </p></dd></dl> |
| |
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