Mac OS X for Unix Geeks

The BootX Loader

BootX is located in /System/Library/CoreServices . It draws the Apple logo on the screen and proceeds to set up the kernel environment. BootX first looks for kernel extensions (drivers, also known as kexts) that are cached in the mkext cache. If this cache does not exist, BootX loads only those extensions in /System/Library/Extensions that have the OSBundleRequired key in their Info.plist file. Each extension lives in a folder (ExtensionName.kext), and the Info.plist file is an XML document that resides in its Contents subfolder. Example 2-1 is an excerpt from the /System/Library/Extensions/System.kext/Contents/Info.plist file.

Example 2-1. A portion of a kernel extension’s Info.plist file

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" 
          "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
  <dict>
    <key>CFBundleDevelopmentRegion</key>
    <string>English</string>
    <!-- multiple keys and strings omitted -->
  </dict>
</plist>

After the required drivers are loaded, BootX hands off control to the kernel (/mach_kernel).