Re: kgdb support in vanilla 2.6.2

[Piet Delaney <piet@www.piet.net>]

On Tue, 2004-02-10 at 13:56, George Anzinger wrote:

I thought I'd poke around an AMD64 with etherbased kgdb on 2.6.*.
I just picked up a used AMD64 K8D Master-F MS-9131 and thought I'd
install Fedora Core 1 test1 and the latest kernel from kernel.org.

It Might be interesting to try out a SuSE release also, I was wondering
if 9.0 from linuxiso.org might be best.

Last I worked with your kgdb patch for 2.6 Andrew's mm patch had the
latest code; Is that still the case?

-piet

> Andi Kleen wrote:
> > On Thu, 5 Feb 2004 23:20:04 +0530
> > "Amit S. Kale" <amitkale@emsyssoft.com> wrote:
> > 
> > 
> >>On Thursday 05 Feb 2004 8:41 am, Andi Kleen wrote:
> >>
> >>>Andrew Morton <akpm@osdl.org> writes:
> >>>
> >>>>need to take a look at such things and really convice ourselves that
> >>>>they're worthwhile.  Personally, I'd only be interested in the basic
> >>>>stub.
> >>>
> >>>What I found always extremly ugly in the i386 stub was that it uses
> >>>magic globals to talk to the page fault handler. For the x86-64
> >>>version I replaced that by just using __get/__put_user in the memory
> >>>accesses, which is much cleaner. I would suggest doing that for i386
> >>>too.
> >>
> >>May be I am missing something obvious. When debugging a page fault handler if 
> >>kgdb accesses an swapped-out user page doesn't it deadlock when trying to 
> >>hold mm semaphore?
> > 
> > 
> > Modern i386 kernels don't grab the mm semaphore when the access is >= TASK_SIZE
> > and the access came from kernel space (actually I see x86-64 still does, but that's 
> > a bug, will fix). You could only see a deadlock when using user addresses
> > and you already hold the mm semaphore for writing (normal read lock is ok). 
> > Just don't do that. 
> > 
> > 
> > 
> >>George has coded cfi directives i386 too. He can use them to backtrace past 
> >>irqs stack.
> > 
> > 
> > Problem is that he did it without binutils support. I don't think that's a good
> > idea because it makes the code basically unmaintainable for normal souls
> > (it's like writing assembly code directly in hex) 
> 
> Well, bin utils, at this time, makes it even worse in that it does not support 
> the expression syntax.  Also, it is not asm but dwarf2 and it is written in, 
> IMHO, useful macros (not hex :)
> 
> 
> 
> -- 
> George Anzinger   george@mvista.com
> High-res-timers:  http://sourceforge.net/projects/high-res-timers/
> Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml
> 
> -
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piet@www.piet.net