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144 lines
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144 lines
7.1 KiB
HTML
4 years ago
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<html lang="en">
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<title>Emulated TLS - 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="Target-Attributes.html#Target-Attributes" title="Target Attributes">
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<link rel="next" href="MIPS-Coprocessors.html#MIPS-Coprocessors" title="MIPS Coprocessors">
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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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any later version published by the Free Software Foundation; with the
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Invariant Sections being ``Funding Free Software'', the Front-Cover
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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="Emulated-TLS"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="MIPS-Coprocessors.html#MIPS-Coprocessors">MIPS Coprocessors</a>,
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Previous: <a rel="previous" accesskey="p" href="Target-Attributes.html#Target-Attributes">Target Attributes</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">17.25 Emulating TLS</h3>
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<p><a name="index-Emulated-TLS-4851"></a>
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For targets whose psABI does not provide Thread Local Storage via
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specific relocations and instruction sequences, an emulation layer is
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used. A set of target hooks allows this emulation layer to be
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configured for the requirements of a particular target. For instance
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the psABI may in fact specify TLS support in terms of an emulation
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layer.
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<p>The emulation layer works by creating a control object for every TLS
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object. To access the TLS object, a lookup function is provided
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which, when given the address of the control object, will return the
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address of the current thread's instance of the TLS object.
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<div class="defun">
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— Target Hook: const char * <b>TARGET_EMUTLS_GET_ADDRESS</b><var><a name="index-TARGET_005fEMUTLS_005fGET_005fADDRESS-4852"></a></var><br>
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<blockquote><p>Contains the name of the helper function that uses a TLS control
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object to locate a TLS instance. The default causes libgcc's
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emulated TLS helper function to be used.
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</p></blockquote></div>
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<div class="defun">
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— Target Hook: const char * <b>TARGET_EMUTLS_REGISTER_COMMON</b><var><a name="index-TARGET_005fEMUTLS_005fREGISTER_005fCOMMON-4853"></a></var><br>
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<blockquote><p>Contains the name of the helper function that should be used at
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program startup to register TLS objects that are implicitly
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initialized to zero. If this is <code>NULL</code>, all TLS objects will
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have explicit initializers. The default causes libgcc's emulated TLS
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registration function to be used.
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</p></blockquote></div>
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<div class="defun">
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— Target Hook: const char * <b>TARGET_EMUTLS_VAR_SECTION</b><var><a name="index-TARGET_005fEMUTLS_005fVAR_005fSECTION-4854"></a></var><br>
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<blockquote><p>Contains the name of the section in which TLS control variables should
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be placed. The default of <code>NULL</code> allows these to be placed in
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any section.
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</p></blockquote></div>
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<div class="defun">
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— Target Hook: const char * <b>TARGET_EMUTLS_TMPL_SECTION</b><var><a name="index-TARGET_005fEMUTLS_005fTMPL_005fSECTION-4855"></a></var><br>
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<blockquote><p>Contains the name of the section in which TLS initializers should be
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placed. The default of <code>NULL</code> allows these to be placed in any
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section.
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</p></blockquote></div>
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<div class="defun">
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— Target Hook: const char * <b>TARGET_EMUTLS_VAR_PREFIX</b><var><a name="index-TARGET_005fEMUTLS_005fVAR_005fPREFIX-4856"></a></var><br>
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<blockquote><p>Contains the prefix to be prepended to TLS control variable names.
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The default of <code>NULL</code> uses a target-specific prefix.
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</p></blockquote></div>
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<div class="defun">
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— Target Hook: const char * <b>TARGET_EMUTLS_TMPL_PREFIX</b><var><a name="index-TARGET_005fEMUTLS_005fTMPL_005fPREFIX-4857"></a></var><br>
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<blockquote><p>Contains the prefix to be prepended to TLS initializer objects. The
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default of <code>NULL</code> uses a target-specific prefix.
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</p></blockquote></div>
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<div class="defun">
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— Target Hook: tree <b>TARGET_EMUTLS_VAR_FIELDS</b> (<var>tree type, tree *name</var>)<var><a name="index-TARGET_005fEMUTLS_005fVAR_005fFIELDS-4858"></a></var><br>
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<blockquote><p>Specifies a function that generates the FIELD_DECLs for a TLS control
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object type. <var>type</var> is the RECORD_TYPE the fields are for and
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<var>name</var> should be filled with the structure tag, if the default of
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<code>__emutls_object</code> is unsuitable. The default creates a type suitable
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for libgcc's emulated TLS function.
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</p></blockquote></div>
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<div class="defun">
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— Target Hook: tree <b>TARGET_EMUTLS_VAR_INIT</b> (<var>tree var, tree decl, tree tmpl_addr</var>)<var><a name="index-TARGET_005fEMUTLS_005fVAR_005fINIT-4859"></a></var><br>
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<blockquote><p>Specifies a function that generates the CONSTRUCTOR to initialize a
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TLS control object. <var>var</var> is the TLS control object, <var>decl</var>
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is the TLS object and <var>tmpl_addr</var> is the address of the
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initializer. The default initializes libgcc's emulated TLS control object.
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</p></blockquote></div>
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<div class="defun">
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— Target Hook: bool <b>TARGET_EMUTLS_VAR_ALIGN_FIXED</b><var><a name="index-TARGET_005fEMUTLS_005fVAR_005fALIGN_005fFIXED-4860"></a></var><br>
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<blockquote><p>Specifies whether the alignment of TLS control variable objects is
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fixed and should not be increased as some backends may do to optimize
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single objects. The default is false.
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</p></blockquote></div>
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<div class="defun">
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— Target Hook: bool <b>TARGET_EMUTLS_DEBUG_FORM_TLS_ADDRESS</b><var><a name="index-TARGET_005fEMUTLS_005fDEBUG_005fFORM_005fTLS_005fADDRESS-4861"></a></var><br>
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<blockquote><p>Specifies whether a DWARF <code>DW_OP_form_tls_address</code> location descriptor
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may be used to describe emulated TLS control objects.
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</p></blockquote></div>
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</body></html>
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