Kernel extension mac os x

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Contents:
  1. How to Load & Unload Kernel Extensions in OS X
  2. In-Depth Explanation
  3. Kernel Extensions for OS X
  4. Kernel Extension Overview

How to Load & Unload Kernel Extensions in OS X

It is important to list all dependencies for each KEXT. Dependencies in KEXTs can be considered analogous to required header files or libraries in code development; in fact, the Kernel Extension Manager uses the standard linker to resolve KEXT requirements. Any errors in the source code are brought to your attention during the build and you are given the chance to edit your source files and try again.

If you work in the Terminal application, you must view system messages in the log file or in the Console application.

In-Depth Explanation

You also need to log in to the root account or use the su or sudo command , since only the root account can load kernel extensions. When testing your KEXT, you can load and unload it manually, as well as check the load status. You can use the kextload command to load any KEXT.


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A manual page for kextload is included in OS X. On OS X prior to Note that this command is useful only when developing a KEXT. Then, it will be loaded and unloaded automatically at system startup and shutdown or whenever it is needed such as when a new device is detected.

Implementation of a Kernel Extension (KEXT)

KEXT debugging can be complicated. Before you can debug a KEXT, you must first enable kernel debugging, as OS X is not normally configured to permit debugging the kernel.

Only the root account can enable kernel debugging, and you need to reboot OS X for the changes to take effect. Kernel debugging is performed using two OS X computers, called the development or debug host and the debug target. These computers must be connected over a reliable network connection on the same subnet or within a single local network. Specifically, there must not be any intervening IP routers or other devices that could make hardware-based Ethernet addressing impossible.


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The KEXT is registered and loaded and run on the target. The debugger is launched and run on the debug host. You can also rebuild your KEXT on the debug host, after you fix any errors you find. Debugging must be performed in this fashion because you must temporarily halt the kernel on the target in order to use the debugger. When you halt the kernel, all other processes on that computer stop.

However, a debugger running remotely can continue to run and can continue to examine or modify the kernel on the target. Note that bugs in KEXTs may cause the target kernel to freeze or panic. If this happens, you may not be able to continue debugging, even over a remote connection; you have to reboot the target and start over, setting a breakpoint just before the code where the KEXT crashed and working very carefully up to the crash point.

Developers generally debug KEXTs using gdb , a source-level debugger with a command-line interface.

Kernel Extensions for OS X

You will need to work in the Terminal application to run gdb. For detailed information about using gdb , see the documentation included with OS X. You can also use the help command from within gdb. Some features of gdb are unavailable when debugging KEXTs because of implementation limitations.

Kernel Extension Overview

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  • How to Load & Unload Kernel Extensions in OS X.
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  • Kernel Extensions for OS X;

Load and unload. Commands associated with KEXT must be run as root, e. There are different mechanisms for the interaction between KEXT and the user-space. This method allows to interact between user and kernel via special sockets. Different clients in user-space can connect to the KEXT socket and send there interaction commands. Kernel Events Notifications allows applications to receive notifications about a particular event that occurred in the kernel.

How to Repair and Fix Kexts - MacOs (Mac OS X)

This interaction is also based on the sockets. One of the most frequently asked questions is the question of how to implement reading the settings from the file when KEXT starts. To perform this, KEXT must work in conjunction with daemon, which works in user-mode. At launch, daemon reads the data from the configuration file, connects to KEXT using the tools described above, and passes settings to it. Unlike other platforms, Kernel extension programming under macOS is much easier and more comfortable. KEXT can be developed in Xcode - a powerful development environment that is provided by Apple for free.

In addition to direct KEXT developing, Xcode allows to combine and collect all the necessary related products in one project. Since errors in kernel extensions are critical can involve OS crash , thoroughly testing and debugging a Kernel extension is a must. At the same time, KEXT is in the kernel, and it is not possible to use usual debug techniques.