linux-kernel - Re: [PATCH] x86-64: Clean up vdso/kernel shared variables

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Message-ID: <4D934648.7040500@kernel.org>
Date:	Wed, 30 Mar 2011 08:03:36 -0700
From:	"H. Peter Anvin" <hpa@...nel.org>
To:	Andy Lutomirski <luto@....edu>
CC:	x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86-64: Clean up vdso/kernel shared variables

On 03/29/2011 07:29 AM, Andy Lutomirski wrote:
> Variables that are shared between the vdso and the kernel are
> currently a bit of a mess.  They are each defined with their own
> magic, they are accessed differently in the kernel, the vsyscall page,
> and the vdso, and one of them (vsyscall_clock) doesn't even really
> exist.
> 
> This changes them all to use a common mechanism.  All of them are
> delcared in vvar.h with a fixed address (validated by the linker
> script).  In the kernel (as before), they look like ordinary
> read-write variables.  In the vsyscall page and the vdso, they are
> accessed through a new macro VVAR, which gives read-only access.
> 
> The vdso is now loaded verbatim into memory without any fixups.  As a
> side bonus, access from the vdso is faster because a level of
> indirection is removed.
> 
> Signed-off-by: Andy Lutomirski <luto@....edu>

How does this deal with variables which really should be shared with
multiple vdsos (in particular the 32-bit vdso and the 64-bit vdso)?
Part of me is wondering if it might not be simpler to put them all into
a structure?

	-hpa
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