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88 строки
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88 строки
4.1 KiB
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<h1>The Clang Universal Driver Project</h1>
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<p>Clang is inherently a cross compiler, in that it is always capable of
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building code for targets which are a different architecture or even operating
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system from the one running the compiler. However, actually cross compiling in
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practice involves much more than just generating the right assembly code for a
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target, it also requires having an appropriate tool chain (assemblers, linkers),
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access to header files and libraries for the target, and many other details (for
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example, the calling convention or whether software floating point is in
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use). Traditionally, compilers and development environments provide little
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assistance with this process, so users do not have easy access to the powerful
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underlying cross-compilation abilities of clang.</p>
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<p>We would like to solve this problem by defining a new model for how cross
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compilation is done, based on the idea of a <i>universal driver</i>. The key
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point of this model is that the user would always access the compiler through a
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single entry point (e.g., <tt>/usr/bin/cc</tt>) and provide an argument
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specifying the <i>configuration</i> they would like to target. Under the hood
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this entry point (the universal driver) would have access to all the information
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that the driver, compiler, and other tools need to build applications for that
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target.</p>
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<p>This is a large and open-ended project. It's eventual success depends not
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just on implementing the model, but also on getting buy-in from compiler
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developers, operating system distribution vendors and the development community
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at large. Our plan is to begin by defining a clear list of the problems we want
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to solve and a proposed implementation (from the user perspective).</p>
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<p>This project is in the very early (i.e., thought experiment) stages of
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development. Stay tuned for more information, and of course, patches
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welcome!</p>
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<p>See also <a href="http://llvm.org/PR4127">PR4127</a>.</p>
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<h2>Existing Solutions and Related Work</h2>
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<ul>
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<li>gcc's command line arguments <tt>-V</tt>, <tt>-B</tt>, <tt>-b</tt> are
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generic but limited solutions to related problems. Similarly, <tt>-m32</tt>
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and <tt>-m64</tt> solve a small subset of the problem for specific
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architectures.</li>
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<li>gcc's <a href="http://www.airs.com/ian/configure/configure_8.html">multilibs</a>
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solve the part of the problem that relates to finding appropriate libraries
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and include files based on particular feature support (soft float,
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etc.).</li>
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<li>Apple's "driver driver" supported by gcc and clang solve a subset of the
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problem by supporting <tt>-arch</tt>. Apple also provides a tool chain which
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supports <a href="http://en.wikipedia.org/wiki/Universal_binary">universal
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binaries</a> and object files which may include data for multiple
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architectures. See <a href="http://developer.apple.com/mac/library/technotes/tn2005/tn2137.html">TN2137</a>
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for an example of how this is used.</li>
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<li>Many operating systems and environments solve the problem by installing
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complete development environments (including the IDE, tools, header files,
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and libraries) for a single tool chain. This is cumbersome for users and
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does not match well with tools which are inherently capable of cross
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compiling.</li>
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<li>The Debian <a href="http://wiki.debian.org/ArmEabiPort">ArmEabiPort</a>
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wiki page for their work to support the ARM EABI provide an interesting
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glimpse into how related issues impact the operating system distribution.</li>
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<li><a href="http://icculus.org/fatelf/">FatELF</a> is a proposal for bringing
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Mac OS X like "Universal Binary" support to ELF based platforms.</li>
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</ul>
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