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    SubjectRe: [Fastboot] [PATCH 1/1] Allow i386 crash kernels to handle x86_64 dumps
    On 3/16/07, Horms <horms@verge.net.au> wrote:
    > On Thu, Mar 15, 2007 at 06:56:16PM +0530, Vivek Goyal wrote:
    > > On Thu, Mar 15, 2007 at 12:22:57PM +0000, Ian Campbell wrote:
    > > > On Thu, 2007-03-15 at 11:17 +0530, Vivek Goyal wrote:
    > > > > > > But I think changing this macro might run into issues. It is
    > > > > > > being used at few places in kernel, for example while loading
    > > > > > > module. This will essentially mean that we allow loading 64bit
    > > > > > > x86_64 modules on 32bit i386 systems?
    > > >
    > > > Yes, not sure how I missed that fact...
    > > >
    > > > > Kexec will also not allow loading an x86_64 kernel on a 32bit machine.
    > > >
    > > > For crash kernel only or for regular kexec too?
    > > >
    > >
    > > I think for both. One of the possible reasons I think is that one never
    > > knows is underlying machine has got 64bit extensions or not. So even if
    > > we load the kernel it will never boot. Secondly, we might not be able to
    > > handle 64bit address in 32bit kernel/user space?
    >
    > Perhaps I am miss-understanding what you are saying, but I do
    > recally kexecing from 32->64 and 64->32 bit kernels on x86_64 hardware.
    > I can run these checks again if it helps.

    I recall kexecing a bzImage for x86_64 on i386, but I'm not 100% sure.
    I think it worked because the bzImage loader code was regular 32 bit
    x86 code, but that may be wrong as well.

    > Won't the above change break non i386 archtectures as
    > vmcore_elf_check_arch_cross isn't defined for them?

    Right. And maybe it's a good idea to make sure that this feature is
    actually supported by kexec-tools before adding code to the kernel?

    My gut feeling about this is that you are begging for trouble. The
    kexec/kdump solution is fragile just by itself, and trying to go
    between architectures is just going to be painful.

    / magnus
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