loader crash / BTX halted on 9.0-RC2 DVD with AMD pseudo-RAID

John Baldwin jhb at freebsd.org
Mon Nov 28 22:21:09 UTC 2011

On Tuesday, November 22, 2011 10:07:52 pm John Nielsen wrote:
> On Nov 22, 2011, at 10:26 AM, John Baldwin <jhb at freebsd.org> wrote:
> > On Monday, November 21, 2011 1:45:36 pm John Nielsen wrote:
> >> This weekend I downloaded the Freebsd 9.0 RC2 amd64 ISO image and burned it 
> > to a DVD. I have a computer that currently runs Windows 7 but I plan to 
> > install FreeBSD on it in the near future so I booted it up from the DVD to 
> > check the hardware/driver status. Much to my dismay, the boot loader crashed 
> > right away (register dump followed by "BTX halted") and the computer 
> > immediately rebooted. I took a video with my phone so I could capture the 
> > crash message, screenshot here:
> >> 
> >> http://picpaste.com/pics/BTXcrash.1321899682.jpg
> >> 
> >> I then tried tweaking a few BIOS settings and found that turning off the 
> > built-in pseudo-RAID allowed the DVD to boot normally. I changed the SATA type 
> > from "RAID" to "AHCI". Fortunately I plan to use the controller in AHCI mode 
> > for the FreeBSD installation so this won't end up being a problem for me, but 
> > I still thought it was worth reporting.
> > 
> > Hmmm, so this is odd.  It died with an Invalid TSS exception on the iret 
> > instruction at the end of the return-from-real-mode trampoline in BTX.  
> > Looking at the dump I noticed that PSL_NT is set in %eflags, so for some 
> > reason the iret was trying to do a nested task return.  We shouldn't let
> > that flag leak out of any real mode code.  Try this patch perhaps:
> Thanks for looking!
> I put gptboot on a USB stick and tried it with and without the patch.
> Identical behavior in both cases to booting from the DVD (only faster)--BTX
> dump and an instant reboot. I didn't do a screen capture yet but will be
> happy to tomorrow if it will help.

A screen capture would be useful.  It may be that I did not fix the right
copy of the flags.

John Baldwin

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