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SubjectRe: [PATCH] Fix ARCH=um segfault on x86-64.
On Fri, Mar 06, 2009 at 12:42:14AM -0600, Rob Landley wrote:
>Apparently, nobody other than me has ever attempted to use User Mode Linux
>built from 2.6.28 on x86-64, because it doesn't work. It still doesn't work
>in current git. I complained about it not working back in January:
>
>http://sourceforge.net/mailarchive/forum.php?thread_name=200901130159.04389.rob%40landley.net&forum_name=user-
>mode-linux-devel
>http://lkml.indiana.edu/hypermail/linux/kernel/0901.2/00669.html
>
>And today, I bothered to track down why.
>
>This is the commit that broke it, when Peter Anvin merged x86 and x86-64 for
>ARCH=um: http://kernel.org/hg/linux-2.6/rev/117978
>
>Here's a patch that fixes it for me:

Thanks, Bob!

>
>Signed-off-by: Rob Landley <rob@landley.net>
>
>diff -r 178a096e9e38 arch/um/Kconfig.x86
>--- a/arch/um/Kconfig.x86 Fri Feb 27 16:49:46 2009 -0800
>+++ b/arch/um/Kconfig.x86 Thu Mar 05 23:35:55 2009 -0600
>@@ -26,9 +26,8 @@
> def_bool !X86_XADD
>
> config 3_LEVEL_PGTABLES
>- bool "Three-level pagetables (EXPERIMENTAL)" if !64BIT
>+ bool
> default 64BIT
>- depends on EXPERIMENTAL


So, on i386, it will not depend on EXPERIMENTAL any more, right?

How about changing it to the following?

depends on 64BIT || EXPERIMENTAL

> help
> Three-level pagetables will let UML have more than 4G of physical
> memory. All the memory that can't be mapped directly will be treated
>>What changed is that the resulting .config no longer contains the line
>"CONFIG_3_LEVEL_PGTABLES=y" (it's not visible, and thus not written out into
>the config file file). Without that symbol defined, x86-64 dies trying to
>boot. If you tweak the Kconfig so the symbol gets written out, it starts
>working again.
>
>I have no idea how ANYBODY has EVER managed to use 2.6.28 User Mode Linux on
>an x86-64 host. My theory is that nobody ever did. I suspect that very few
>people use UML anymore now that KVM and the rustyvisor and such are available,
>and those legacy users still fiddling with it are apparently all either using
>old versions or 32-bit hosts. (I still like being able to stick printfs into
>the kernel.)
>

I am sorry that I never have an x86_64 machine to use. :(

--
Do what you love, f**k the rest! F**k the regulations!



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