[SeaBIOS] Problem with Debug lvl under XEN

Daniel Castro evil.dani at gmail.com
Tue Feb 14 00:21:24 CET 2012

On Tue, Feb 14, 2012 at 5:50 AM, Ian Campbell <Ian.Campbell at citrix.com> wrote:
> On Mon, 2012-02-13 at 23:21 +0900, Daniel Castro wrote:
>> Hello,
>> I have encountered something a little strange, if I set up the debug
>> lvl to 3 or more Y will get a Triple VCPU fault. If I set it to 1 the
>> bios runs normally but I loose a lot of information that I need to
>> debug. Sometimes if I try to print char * variables regardless of the
>> debug level I still get the fault.
>> Any ideas why?
> My guess is that there is a debug print at lvl>=3 which ends up
> dereferencing a NULL pointer in one of its arguments (probably a %s) and
> this leads to a page fault. This in turn leads to a double fault because
> SeaBIOS does not install a page fault handler and then a triple fault
> because it also does not install a double fault handler. Likewise when
> you are printing "char * variables regardless of the debug level".
> You could test this by adding an explicit check for null in the bit of
> bvprintf which handles %s, perhaps putc()ing "(null)" instead.

Thanks for the response, I will try what you suggest.

>> Thanks for the ideas/pointers/ anything!
>> Daniel

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