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157 lines
8.4 KiB
HTML
4 years ago
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<html lang="en">
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<title>Named Address Spaces - GNU Compiler Collection (GCC) Internals</title>
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<meta name="description" content="GNU Compiler Collection (GCC) Internals">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Target-Macros.html#Target-Macros" title="Target Macros">
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<link rel="prev" href="C_002b_002b-ABI.html#C_002b_002b-ABI" title="C++ ABI">
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<link rel="next" href="Misc.html#Misc" title="Misc">
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Copyright (C) 1988-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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</head>
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<body>
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<div class="node">
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<a name="Named-Address-Spaces"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Misc.html#Misc">Misc</a>,
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Previous: <a rel="previous" accesskey="p" href="C_002b_002b-ABI.html#C_002b_002b-ABI">C++ ABI</a>,
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Up: <a rel="up" accesskey="u" href="Target-Macros.html#Target-Macros">Target Macros</a>
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<hr>
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</div>
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<h3 class="section">17.29 Adding support for named address spaces</h3>
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<p><a name="index-named-address-spaces-4883"></a>
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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>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>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><span class="option">-mea32</span></samp> or <samp><span class="option">-mea64</span></samp> switches (native SPU pointers are
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always 32 bits).
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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>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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<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>
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<div class="defun">
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— Target Hook: machine_mode <b>TARGET_ADDR_SPACE_POINTER_MODE</b> (<var>addr_space_t address_space</var>)<var><a name="index-TARGET_005fADDR_005fSPACE_005fPOINTER_005fMODE-4884"></a></var><br>
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<blockquote><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> for the
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generic address space only.
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</p></blockquote></div>
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<div class="defun">
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— Target Hook: machine_mode <b>TARGET_ADDR_SPACE_ADDRESS_MODE</b> (<var>addr_space_t address_space</var>)<var><a name="index-TARGET_005fADDR_005fSPACE_005fADDRESS_005fMODE-4885"></a></var><br>
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<blockquote><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> for the
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generic address space only.
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</p></blockquote></div>
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<div class="defun">
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— Target Hook: bool <b>TARGET_ADDR_SPACE_VALID_POINTER_MODE</b> (<var>machine_mode mode, addr_space_t as</var>)<var><a name="index-TARGET_005fADDR_005fSPACE_005fVALID_005fPOINTER_005fMODE-4886"></a></var><br>
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<blockquote><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></blockquote></div>
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<div class="defun">
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— Target Hook: bool <b>TARGET_ADDR_SPACE_LEGITIMATE_ADDRESS_P</b> (<var>machine_mode mode, rtx exp, bool strict, addr_space_t as</var>)<var><a name="index-TARGET_005fADDR_005fSPACE_005fLEGITIMATE_005fADDRESS_005fP-4887"></a></var><br>
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<blockquote><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></blockquote></div>
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<div class="defun">
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— Target Hook: rtx <b>TARGET_ADDR_SPACE_LEGITIMIZE_ADDRESS</b> (<var>rtx x, rtx oldx, machine_mode mode, addr_space_t as</var>)<var><a name="index-TARGET_005fADDR_005fSPACE_005fLEGITIMIZE_005fADDRESS-4888"></a></var><br>
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<blockquote><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></blockquote></div>
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<div class="defun">
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— Target Hook: bool <b>TARGET_ADDR_SPACE_SUBSET_P</b> (<var>addr_space_t subset, addr_space_t superset</var>)<var><a name="index-TARGET_005fADDR_005fSPACE_005fSUBSET_005fP-4889"></a></var><br>
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<blockquote><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></blockquote></div>
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<div class="defun">
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— Target Hook: rtx <b>TARGET_ADDR_SPACE_CONVERT</b> (<var>rtx op, tree from_type, tree to_type</var>)<var><a name="index-TARGET_005fADDR_005fSPACE_005fCONVERT-4890"></a></var><br>
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<blockquote><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></blockquote></div>
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</body></html>
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