1*e5dd7070Spatrick<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" 2*e5dd7070Spatrick "http://www.w3.org/TR/html4/strict.dtd"> 3*e5dd7070Spatrick<html> 4*e5dd7070Spatrick<head> 5*e5dd7070Spatrick <META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> 6*e5dd7070Spatrick <title>Clang - Universal Driver</title> 7*e5dd7070Spatrick <link type="text/css" rel="stylesheet" href="menu.css"> 8*e5dd7070Spatrick <link type="text/css" rel="stylesheet" href="content.css"> 9*e5dd7070Spatrick</head> 10*e5dd7070Spatrick<body> 11*e5dd7070Spatrick 12*e5dd7070Spatrick<!--#include virtual="menu.html.incl"--> 13*e5dd7070Spatrick 14*e5dd7070Spatrick<div id="content"> 15*e5dd7070Spatrick 16*e5dd7070Spatrick<h1>The Clang Universal Driver Project</h1> 17*e5dd7070Spatrick 18*e5dd7070Spatrick<p>Clang is inherently a cross compiler, in that it is always capable of 19*e5dd7070Spatrickbuilding code for targets which are a different architecture or even operating 20*e5dd7070Spatricksystem from the one running the compiler. However, actually cross compiling in 21*e5dd7070Spatrickpractice involves much more than just generating the right assembly code for a 22*e5dd7070Spatricktarget, it also requires having an appropriate tool chain (assemblers, linkers), 23*e5dd7070Spatrickaccess to header files and libraries for the target, and many other details (for 24*e5dd7070Spatrickexample, the calling convention or whether software floating point is in 25*e5dd7070Spatrickuse). Traditionally, compilers and development environments provide little 26*e5dd7070Spatrickassistance with this process, so users do not have easy access to the powerful 27*e5dd7070Spatrickunderlying cross-compilation abilities of clang.</p> 28*e5dd7070Spatrick 29*e5dd7070Spatrick<p>We would like to solve this problem by defining a new model for how cross 30*e5dd7070Spatrickcompilation is done, based on the idea of a <i>universal driver</i>. The key 31*e5dd7070Spatrickpoint of this model is that the user would always access the compiler through a 32*e5dd7070Spatricksingle entry point (e.g., <tt>/usr/bin/cc</tt>) and provide an argument 33*e5dd7070Spatrickspecifying the <i>configuration</i> they would like to target. Under the hood 34*e5dd7070Spatrickthis entry point (the universal driver) would have access to all the information 35*e5dd7070Spatrickthat the driver, compiler, and other tools need to build applications for that 36*e5dd7070Spatricktarget.</p> 37*e5dd7070Spatrick 38*e5dd7070Spatrick<p>This is a large and open-ended project. It's eventual success depends not 39*e5dd7070Spatrickjust on implementing the model, but also on getting buy-in from compiler 40*e5dd7070Spatrickdevelopers, operating system distribution vendors and the development community 41*e5dd7070Spatrickat large. Our plan is to begin by defining a clear list of the problems we want 42*e5dd7070Spatrickto solve and a proposed implementation (from the user perspective).</p> 43*e5dd7070Spatrick 44*e5dd7070Spatrick<p>This project is in the very early (i.e., thought experiment) stages of 45*e5dd7070Spatrickdevelopment. Stay tuned for more information, and of course, patches 46*e5dd7070Spatrickwelcome!</p> 47*e5dd7070Spatrick 48*e5dd7070Spatrick<p>See also <a href="https://llvm.org/PR4127">PR4127</a>.</p> 49*e5dd7070Spatrick 50*e5dd7070Spatrick<h2>Existing Solutions and Related Work</h2> 51*e5dd7070Spatrick 52*e5dd7070Spatrick<ul> 53*e5dd7070Spatrick <li>gcc's command line arguments <tt>-V</tt>, <tt>-B</tt>, <tt>-b</tt> are 54*e5dd7070Spatrick generic but limited solutions to related problems. Similarly, <tt>-m32</tt> 55*e5dd7070Spatrick and <tt>-m64</tt> solve a small subset of the problem for specific 56*e5dd7070Spatrick architectures.</li> 57*e5dd7070Spatrick 58*e5dd7070Spatrick <li>gcc's <a href="https://www.airs.com/ian/configure/configure_8.html">multilibs</a> 59*e5dd7070Spatrick solve the part of the problem that relates to finding appropriate libraries 60*e5dd7070Spatrick and include files based on particular feature support (soft float, 61*e5dd7070Spatrick etc.).</li> 62*e5dd7070Spatrick 63*e5dd7070Spatrick <li>Apple's "driver driver" supported by gcc and clang solve a subset of the 64*e5dd7070Spatrick problem by supporting <tt>-arch</tt>. Apple also provides a tool chain which 65*e5dd7070Spatrick supports <a href="https://en.wikipedia.org/wiki/Universal_binary">universal 66*e5dd7070Spatrick binaries</a> and object files which may include data for multiple 67*e5dd7070Spatrick architectures. See <a href="https://developer.apple.com/library/archive/technotes/tn2005/tn2137.html">TN2137</a> 68*e5dd7070Spatrick for an example of how this is used.</li> 69*e5dd7070Spatrick 70*e5dd7070Spatrick <li>Many operating systems and environments solve the problem by installing 71*e5dd7070Spatrick complete development environments (including the IDE, tools, header files, 72*e5dd7070Spatrick and libraries) for a single tool chain. This is cumbersome for users and 73*e5dd7070Spatrick does not match well with tools which are inherently capable of cross 74*e5dd7070Spatrick compiling.</li> 75*e5dd7070Spatrick 76*e5dd7070Spatrick <li>The Debian <a href="https://wiki.debian.org/ArmEabiPort">ArmEabiPort</a> 77*e5dd7070Spatrick wiki page for their work to support the ARM EABI provide an interesting 78*e5dd7070Spatrick glimpse into how related issues impact the operating system distribution.</li> 79*e5dd7070Spatrick 80*e5dd7070Spatrick <li><a href="https://icculus.org/fatelf/">FatELF</a> is a proposal for bringing 81*e5dd7070Spatrick Mac OS X like "Universal Binary" support to ELF based platforms.</li> 82*e5dd7070Spatrick 83*e5dd7070Spatrick</ul> 84*e5dd7070Spatrick 85*e5dd7070Spatrick</div> 86*e5dd7070Spatrick</body> 87*e5dd7070Spatrick</html> 88