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    SubjectRe: kgdb support in vanilla 2.6.2
    Date
    On Friday 06 Feb 2004 7:50 am, 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.

    OK. It don't deadlock when kgdb accesses kernel addresses.

    When a user space address is accessed through kgdb, won't the kernel attempt
    to fault in the user page? We don't want that to happen inside kgdb.

    -Amit


    >
    > > 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)
    >
    > -Andi

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