Debugging the Linux kernel with JTAG

Alexander Sirotkin, FemtoLinux
8/29/2010 5:31 PM EDT

As with many Linux-related topics, the issue of using debuggers to troubleshoot the Linux kernel is not only technical--it's political. Linux is being mostly developed on the x86 platform, which does not have JTAG debugging capabilities, and software-only kernel debuggers are complex and unreliable. Because of this and other reasons, Linus Torvalds objected for a long time to inclusion of the KGDB (Linux kernel debugger) patch in the main Linux tree until Ingo Molnar managed to get a rather slimmed down KGDB variant into the 2.6.26 version. Putting politics aside, I believe that most developers would agree with me, that at least in the embedded world, a kernel debugger is a must-have tool for many tasks, BSP (board support package) development being probably the most obvious example.

Fortunately, compared with the world of x86, embedded platforms introduce not only additional challenges but also a good tool to help us tackle the problem--a JTAG debugger. It's easy to use, reliable, provides some nice features that are not available in software-only debuggers and is free from any controversy that is always associated with invasive Linux kernel patches, such as the original KGDB.

I assume that the topic of JTAG debugging is not new to you--as an experienced embedded systems developer, you have probably used something like Wind River's On-Chip Debugging in the past. I will go very briefly over general JTAG debugging capabilities and show you the peculiarities of Linux kernel debugging using JTAG.

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