Arch Linux

dhiru1602

Member

Registered: 2015-01-28

Posts: 13

Very early kernel debugging to investigate kernel panic

Hi Guys,

I am currently having issues with kernel panics very early in the boot process on 2 of my motherboards when I enable intel_iommu=on boot parameter. IOMMU and VGA passthrough worked on the 4.1.21 kernel, but it's broken in the 4.2 kernel which no longer boots on 2 of my X58 boards. I am currently in the process of investigating the kernel panic log so that I can find the offending commit and report it. However, I can't get the kernel panic log to display up no matter what. All that I see is "Loading initial ramdisk" and the PC totally freezes.

I am currently running 4.5.0-1-ARCH. I have tried to boot with "debug ignore_loglevel LOGLEVEL=8 earlyprintk=vga,keep intel_iommu=on".

Is there any alternate way to grab kernel panic logs at very early boot process?

Last edited by dhiru1602 (2016-04-18 16:23:15)

wtx

Member

Registered: 2014-06-09

Posts: 76

Re: Very early kernel debugging to investigate kernel panic

There is some debugger kGDB, which can be used for debugging such a cases, but I'm not sure when it is called - before or after loading of initrd.
So the kernel hangs up after "Loading initial ramdisk"? You may try to use early_printk() and connect some serial console.