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content-class: urn:content-classes:message
Subject: Re: [PATCH] Restore module support.
Date: Fri, 7 Feb 2003 10:43:19 -0800
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Thread-Topic: Re: [PATCH] Restore module support.
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From: "Luck, Tony" <tony.luck@intel.com>
To: <linux-kernel@vger.kernel.org>
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> (2) has the disadvantage that its touching non-architecture specific
> code, but this is the option I'd prefer due to the obvious performance
> advantage.  However, I'm afraid that it isn't worth the effort to fix
> up vmalloc and /proc/kcore.  vmalloc fix appears simple, but /proc/kcore
> has issues (anyone know what KCORE_BASE is all about?)

KCORE_BASE is my fault ... it was an attempt to fix the "modules
below PAGE_OFFSET" problem for the ia64 port.  For a few nanoseconds
the code just here looked like this:

#if VMALLOC_START < PAGE_OFFSET
#define	KCORE_BASE	VMALLOC_START
#else
#define	KCORE_BASE	PAGE_OFFSET
#endif

Which worked great for ia64, but failed to even compile on i386
(because on i386 VMALLOC_START isn't a simple constant that cpp
can compare against).

Linus kept the bulk of my patch and just replaced the above code with
the "#define	KCORE_BASE	PAGE_OFFSET" that is there today, maybe
in the hope that I'd come back with a workable #ifdef ... but the only
one I've come up with so far is "#ifdef CONFIG_IA64" which can't be
right as ia64 isn't the only architecture with this issue.

There was some discussion on a better way to do this, by adding the
kernel itself to the vmlist, and eliminating all the special case code.
I took a brief look at this, but realised that there were all sorts
of ugly race conditions with /proc/kcore if a module is loaded/unloaded
after some process has read the Elf header.

-Tony Luck

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