Messages in this thread |  | | | Date | Wed, 30 Mar 2005 15:31:08 -0800 | | From | "Randy.Dunlap" <> | | Subject | Re: How to debug kernel before there is no printk mechanism? |
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linux-os wrote: > On Wed, 30 Mar 2005, krishna wrote: > >> Hi all, >> >> How can one debug kernel before there is no printk mechanism in kernel. >> >> Regards, >> Krishna Chaitanya
Here's an implementation by Keith Owens: http://kernelnewbies.org/documents/videochar.txt
The patch there is to Linux 2.4.18, but should be workable on many versions.
> Write directly to screen memory at 0x000b8000, or write to the > RS-232C UART while polling the TX buf empty bit, or just write > bits that mean something to you out the printer port. > > Screen - memory is 16-bit words with the high-word being > an attibute byte. FYI 0x07 is a good B&W byte. You can > initialize a pointer to it as: > > unsigned short *screen = 0xc00b8000; Since low memory > is always mapped, the above cheat will work. The 0xc0000000 > is PAGE_OFFSET. > > An early '486 was brought up into a 32-bit protected-mode > (non linux) operating system using these debugging methods. > The first time I got to see some symbol written to the > screen in protected-mode marked the start of a week-end- > long party. Have fun!
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