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From: Rusty Russell <rusty@rustcorp.com.au>
To: Oleg Verych <olecom@flower.upol.cz>
Cc: Sam Ravnborg <sam@ravnborg.org>, Andi Kleen <ak@muc.de>,
	virtualization@lists.osdl.org,
	lkml - Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [q] kbuild for private asm-offsets (Re: [PATCH 6/10] lguest code: the little linux hypervisor.)
Date: Tue, 13 Feb 2007 10:41:36 +1100	[thread overview]
Message-ID: <1171323696.19842.29.camel@localhost.localdomain> (raw)
In-Reply-To: <E1HGbJz-0003Lc-6h@flower>

On Mon, 2007-02-12 at 14:34 +0100, Oleg Verych wrote:
> > I'd like my own, private "asm-offsets.h".  In this case, in
> > arch/i386/lguest/.  I guess it's a matter of extracting the core of the
> > asm-offsets.h magic and generalizing it.
> >
> > Have a good break!
> > Rusty.
> 
> If you will have time for newbie, to explain in a few words, what is it need
> for (whole idea, or key detail), and, maybe, why it is generated so ... interestingly:
> 
>             asm-offsets.c -> *.s -> *.h
>  (but this looks like interconnecting C and assembler, obviously)

Hi Oleg,

	Always happy to explain.  There's often a need to access constants in
assembler, which can only be derived from C, such as the size of a
structure, or the offset of a certain member within a structure.
Hardcoding the numbers in assembler is fragile leading to breakage when
something changes.

	So, asm-offsets.c is the solution: it uses asm() statements to emit
patterns in the assembler, with the compiler computing the actual
numbers, eg:

	#define DEFINE(sym, val) \
	        asm volatile("\n->" #sym " %0 " #val : : "i" (val))
	DEFINE(SIZEOF_FOOBAR, sizeof(foobar));

Becomes in asm-offsets.s:
	->SIZEOF_FOOBAR $10 sizeof(foobar)  #

This gets sed'd back into asm-offsets.h:
	#define SIZEOF_FOOBAR 10 /* SIZEOF_FOOBAR  # */

This can be included from .S files (which get passed through the
pre-processor).

Hope that helps!
Rusty.


  parent reply	other threads:[~2007-02-12 23:42 UTC|newest]

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-09  9:11 [PATCH 0/10] lguest Rusty Russell
2007-02-09  9:14 ` [PATCH 1/10] lguest: Don't rely on last-linked fallthru when no paravirt handler Rusty Russell
2007-02-09  9:15   ` [PATCH 2/10] lguest: Export symbols for lguest as a module Rusty Russell
2007-02-09  9:32     ` Andi Kleen
2007-02-09 12:06       ` Rusty Russell
2007-02-09 13:58         ` Andi Kleen
2007-02-10 11:39           ` Rusty Russell
2007-02-09  9:17   ` [PATCH 3/10] lguest: Expose get_futex_key, get_key_refs and drop_key_refs Rusty Russell
2007-02-09  9:18   ` [PATCH 4/10] lguest: Initialize esp0 properly all the time Rusty Russell
2007-02-09  9:19     ` [PATCH 5/10] Make hvc_console.c compile on non-PowerPC Rusty Russell
     [not found]       ` <1171012827.2718.42.camel@localhost.localdomain>
2007-02-09  9:22         ` [PATCH 7/10] lguest: Simple lguest network driver Rusty Russell
2007-02-09  9:23           ` [PATCH 8/10] lguest: console driver Rusty Russell
2007-02-09  9:24             ` [PATCH 9/10] lguest: block driver Rusty Russell
2007-02-09  9:25               ` [PATCH 10/10] lguest: documentatation including example launcher Rusty Russell
2007-02-09  9:35         ` [PATCH 6/10] lguest code: the little linux hypervisor Andrew Morton
2007-02-09 11:00           ` Rusty Russell
2007-02-09 11:13             ` Zachary Amsden
2007-02-09 11:50               ` Andi Kleen
2007-02-09 11:54                 ` Zachary Amsden
2007-02-09 11:57                   ` Andi Kleen
2007-02-09 12:08                     ` Zachary Amsden
2007-02-09 22:29                 ` David Miller
2007-02-09 10:09         ` Andi Kleen
2007-02-09 12:39           ` Rusty Russell
2007-02-09 13:57             ` Andi Kleen
2007-02-09 15:01               ` Rusty Russell
2007-02-09 14:17             ` Sam Ravnborg
2007-02-09 15:23               ` Rusty Russell
2007-02-12 13:34                 ` [q] kbuild for private asm-offsets (Re: [PATCH 6/10] lguest code: the little linux hypervisor.) Oleg Verych
2007-02-12 17:24                   ` Andi Kleen
2007-02-12 21:41                   ` Sam Ravnborg
2007-02-12 23:41                   ` Rusty Russell [this message]
2007-02-13  3:10                     ` Oleg Verych
2007-02-16 15:55                       ` [pp] kbuild: lguest with private asm-offsets (and some bloat) Oleg Verych
2007-02-16 15:59                         ` [pp] kbuild: asm-offsets generalized Oleg Verych
2007-02-16 18:56                           ` Sam Ravnborg
2007-02-16 21:56                             ` Oleg Verych
2007-02-17  4:43                               ` Rusty Russell
2007-02-17  5:33                                 ` Oleg Verych
2007-04-01 20:42                           ` Sam Ravnborg
2007-04-01 21:08                             ` Oleg Verych
2007-04-01 21:03                               ` Sam Ravnborg
2007-02-09 10:55       ` [PATCH 6a/10] lguest: Config and headers Rusty Russell
2007-02-09 10:56         ` [PATCH 6b/10] lguest: the host code (lg.ko) Rusty Russell
2007-02-09 10:57           ` [PATCH 6c/10] lguest: the guest code Rusty Russell
2007-02-09 10:58             ` [PATCH 6d/10] lguest: the Makefiles Rusty Russell
2007-02-09 17:06             ` [PATCH 6c/10] lguest: the guest code Len Brown
2007-02-09 17:14               ` James Morris
2007-02-09 17:49                 ` Len Brown
2007-02-09 23:48                   ` [PATCH 11/10] lguest: use disable_acpi() Rusty Russell
2007-02-09  9:31   ` [PATCH 1/10] lguest: Don't rely on last-linked fallthru when no paravirt handler Andi Kleen
2007-02-09 11:52     ` Rusty Russell
2007-02-09 20:49       ` Jeremy Fitzhardinge

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