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<title>GNU Compiler Collection (GCC) Internals: Named Address Spaces</title>
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<a name="Named-Address-Spaces"></a>
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<p>
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Next: <a href="Misc.html#Misc" accesskey="n" rel="next">Misc</a>, Previous: <a href="C_002b_002b-ABI.html#C_002b_002b-ABI" accesskey="p" rel="prev">C++ ABI</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Adding-support-for-named-address-spaces"></a>
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<h3 class="section">17.29 Adding support for named address spaces</h3>
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<a name="index-named-address-spaces"></a>
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<p>The draft technical report of the ISO/IEC JTC1 S22 WG14 N1275
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standards committee, <cite>Programming Languages - C - Extensions to
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support embedded processors</cite>, specifies a syntax for embedded
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processors to specify alternate address spaces. You can configure a
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GCC port to support section 5.1 of the draft report to add support for
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address spaces other than the default address space. These address
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spaces are new keywords that are similar to the <code>volatile</code> and
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<code>const</code> type attributes.
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</p>
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<p>Pointers to named address spaces can have a different size than
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pointers to the generic address space.
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</p>
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<p>For example, the SPU port uses the <code>__ea</code> address space to refer
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to memory in the host processor, rather than memory local to the SPU
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processor. Access to memory in the <code>__ea</code> address space involves
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issuing DMA operations to move data between the host processor and the
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local processor memory address space. Pointers in the <code>__ea</code>
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address space are either 32 bits or 64 bits based on the
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<samp>-mea32</samp> or <samp>-mea64</samp> switches (native SPU pointers are
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always 32 bits).
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</p>
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<p>Internally, address spaces are represented as a small integer in the
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range 0 to 15 with address space 0 being reserved for the generic
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address space.
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</p>
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<p>To register a named address space qualifier keyword with the C front end,
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the target may call the <code>c_register_addr_space</code> routine. For example,
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the SPU port uses the following to declare <code>__ea</code> as the keyword for
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named address space #1:
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</p><div class="smallexample">
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<pre class="smallexample">#define ADDR_SPACE_EA 1
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c_register_addr_space ("__ea", ADDR_SPACE_EA);
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</pre></div>
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<dl>
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<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>
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<dd><p>Define this to return the machine mode to use for pointers to
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<var>address_space</var> if the target supports named address spaces.
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The default version of this hook returns <code>ptr_mode</code>.
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</p></dd></dl>
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<dl>
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<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>
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<dd><p>Define this to return the machine mode to use for addresses in
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<var>address_space</var> if the target supports named address spaces.
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The default version of this hook returns <code>Pmode</code>.
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</p></dd></dl>
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<dl>
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<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>
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<dd><p>Define this to return nonzero if the port can handle pointers
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with machine mode <var>mode</var> to address space <var>as</var>. This target
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hook is the same as the <code>TARGET_VALID_POINTER_MODE</code> target hook,
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except that it includes explicit named address space support. The default
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version of this hook returns true for the modes returned by either the
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<code>TARGET_ADDR_SPACE_POINTER_MODE</code> or <code>TARGET_ADDR_SPACE_ADDRESS_MODE</code>
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target hooks for the given address space.
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</p></dd></dl>
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<dl>
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<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>
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<dd><p>Define this to return true if <var>exp</var> is a valid address for mode
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<var>mode</var> in the named address space <var>as</var>. The <var>strict</var>
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parameter says whether strict addressing is in effect after reload has
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finished. This target hook is the same as the
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<code>TARGET_LEGITIMATE_ADDRESS_P</code> target hook, except that it includes
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explicit named address space support.
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</p></dd></dl>
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<dl>
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<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>
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<dd><p>Define this to modify an invalid address <var>x</var> to be a valid address
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with mode <var>mode</var> in the named address space <var>as</var>. This target
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hook is the same as the <code>TARGET_LEGITIMIZE_ADDRESS</code> target hook,
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except that it includes explicit named address space support.
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</p></dd></dl>
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<dl>
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<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>
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<dd><p>Define this to return whether the <var>subset</var> named address space is
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contained within the <var>superset</var> named address space. Pointers to
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a named address space that is a subset of another named address space
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will be converted automatically without a cast if used together in
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arithmetic operations. Pointers to a superset address space can be
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converted to pointers to a subset address space via explicit casts.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fADDR_005fSPACE_005fZERO_005fADDRESS_005fVALID"></a>Target Hook: <em>bool</em> <strong>TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID</strong> <em>(addr_space_t <var>as</var>)</em></dt>
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<dd><p>Define this to modify the default handling of address 0 for the
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address space. Return true if 0 should be considered a valid address.
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</p></dd></dl>
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<dl>
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<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>
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<dd><p>Define this to convert the pointer expression represented by the RTL
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<var>op</var> with type <var>from_type</var> that points to a named address
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space to a new pointer expression with type <var>to_type</var> that points
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to a different named address space. When this hook it called, it is
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guaranteed that one of the two address spaces is a subset of the other,
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as determined by the <code>TARGET_ADDR_SPACE_SUBSET_P</code> target hook.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fADDR_005fSPACE_005fDEBUG"></a>Target Hook: <em>int</em> <strong>TARGET_ADDR_SPACE_DEBUG</strong> <em>(addr_space_t <var>as</var>)</em></dt>
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<dd><p>Define this to define how the address space is encoded in dwarf.
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The result is the value to be used with <code>DW_AT_address_class</code>.
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</p></dd></dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Misc.html#Misc" accesskey="n" rel="next">Misc</a>, Previous: <a href="C_002b_002b-ABI.html#C_002b_002b-ABI" accesskey="p" rel="prev">C++ ABI</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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