1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" 2 "http://www.w3.org/TR/html4/strict.dtd"> 3 <html> 4 <head> 5 <META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" /> 6 <title>Clang - Universal Driver</title> 7 <link type="text/css" rel="stylesheet" href="menu.css" /> 8 <link type="text/css" rel="stylesheet" href="content.css" /> 9 </head> 10 <body> 11 12 <!--#include virtual="menu.html.incl"--> 13 14 <div id="content"> 15 16 <h1>The Clang Universal Driver Project</h1> 17 18 <p>Clang is inherently a cross compiler, in that it is always capable of 19 building code for targets which are a different architecture or even operating 20 system from the one running the compiler. However, actually cross compiling in 21 practice involves much more than just generating the right assembly code for a 22 target, it also requires having an appropriate tool chain (assemblers, linkers), 23 access to header files and libraries for the target, and many other details (for 24 example, the calling convention or whether software floating point is in 25 use). Traditionally, compilers and development environments provide little 26 assistance with this process, so users do not have easy access to the powerful 27 underlying cross-compilation abilities of clang.</p> 28 29 <p>We would like to solve this problem by defining a new model for how cross 30 compilation is done, based on the idea of a <i>universal driver</i>. The key 31 point of this model is that the user would always access the compiler through a 32 single entry point (e.g., <tt>/usr/bin/cc</tt>) and provide an argument 33 specifying the <i>configuration</i> they would like to target. Under the hood 34 this entry point (the universal driver) would have access to all the information 35 that the driver, compiler, and other tools need to build applications for that 36 target.</p> 37 38 <p>This is a large and open-ended project. It's eventual success depends not 39 just on implementing the model, but also on getting buy-in from compiler 40 developers, operating system distribution vendors and the development community 41 at large. Our plan is to begin by defining a clear list of the problems we want 42 to solve and a proposed implementation (from the user perspective).</p> 43 44 <p>This project is in the very early (i.e., thought experiment) stages of 45 development. Stay tuned for more information, and of course, patches 46 welcome!</p> 47 48 <p>See also <a href="http://llvm.org/PR4127">PR4127</a>.</p> 49 50 <h2>Existing Solutions and Related Work</h2> 51 52 <ul> 53 <li>gcc's command line arguments <tt>-V</tt>, <tt>-B</tt>, <tt>-b</tt> are 54 generic but limited solutions to related problems. Similarly, <tt>-m32</tt> 55 and <tt>-m64</tt> solve a small subset of the problem for specific 56 architectures.</li> 57 58 <li>gcc's <a href="http://www.airs.com/ian/configure/configure_8.html">multilibs</a> 59 solve the part of the problem that relates to finding appropriate libraries 60 and include files based on particular feature support (soft float, 61 etc.).</li> 62 63 <li>Apple's "driver driver" supported by gcc and clang solve a subset of the 64 problem by supporting <tt>-arch</tt>. Apple also provides a tool chain which 65 supports <a href="http://en.wikipedia.org/wiki/Universal_binary">universal 66 binaries</a> and object files which may include data for multiple 67 architectures. See <a href="http://developer.apple.com/mac/library/technotes/tn2005/tn2137.html">TN2137</a> 68 for an example of how this is used.</li> 69 70 <li>Many operating systems and environments solve the problem by installing 71 complete development environments (including the IDE, tools, header files, 72 and libraries) for a single tool chain. This is cumbersome for users and 73 does not match well with tools which are inherently capable of cross 74 compiling.</li> 75 76 <li>The Debian <a href="http://wiki.debian.org/ArmEabiPort">ArmEabiPort</a> 77 wiki page for their work to support the ARM EABI provide an interesting 78 glimpse into how related issues impact the operating system distribution.</li> 79 80 <li><a href="http://icculus.org/fatelf/">FatELF</a> is a proposal for bringing 81 Mac OS X like "Universal Binary" support to ELF based platforms.</li> 82 83 </ul> 84 85 </div> 86 </body> 87 </html> 88
