Wednesday 23 October 2013

Debugging Stop 0x124 - Calculating Clockspeed (Without !sysinfo cpuspeed)

We all know that Stop 0x124 contain very little practical information to work with, the stack consists of WHEA reporting routines and many commands have no significance to a Stop 0x124.

The first thing to look at with a Stop 0x124 is the clock speed of the processor, generally a overclocked processor will mean that the user has most likely overclocked their GPU or RAM, and also changed the voltage settings. However, the !sysinfo cpuspeed extension does not always work like below:

This is quite annoying, but there are other ways to view the clockspeed of a processor, we can see the !prcb extension to view the Processor Control Block, which is a private kernel data structure used to store thread scheduling information; DPC queue, detailed CPU vendor information and cache sizes etc.

Using the !prcb extension doesn't provide much information, but using the address fffff780ffff0000 with the _KPRCB data structure will provide some very detailed information. Please be aware that not specifying the processor number with !prcb extension will default to the context of the current processor.

This is not the entire data structure, you can enter the command yourself, if you wish to view the entire data structure, but for the purposes of this blog post the MHz field is what we are interested in the most.

The hexadecimal value of 0xa21 doesn't give much information and is practically useless. Using the ? (evaluate expression) command we can convert this into something readable.

We can see that the processor is running at 2.6 GHz, the .formats command will give similar information:

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