linux-kernel - Re: [patch 1/7] Immediate Values - Architecture Independent Code

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Message-Id: <200709182101.12284.vda.linux@googlemail.com>
Date:	Tue, 18 Sep 2007 21:01:12 +0100
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 1/7] Immediate Values - Architecture Independent Code

On Tuesday 18 September 2007 18:59, Mathieu Desnoyers wrote:
> * Denys Vlasenko (vda.linux@...glemail.com) wrote:
> > On Monday 17 September 2007 19:42, Mathieu Desnoyers wrote:
> > > Index: linux-2.6-lttng/include/asm-generic/vmlinux.lds.h
> > > ===================================================================
> > > --- linux-2.6-lttng.orig/include/asm-generic/vmlinux.lds.h	2007-09-17 13:25:06.000000000 -0400
> > > +++ linux-2.6-lttng/include/asm-generic/vmlinux.lds.h	2007-09-17 13:35:50.000000000 -0400
> > > @@ -122,6 +122,13 @@
> > >  		VMLINUX_SYMBOL(__stop___kcrctab_gpl_future) = .;	\
> > >  	}								\
> > >  									\
> > > +	/* Immediate values: pointers */				\
> > > +	__immediate : AT(ADDR(__immediate) - LOAD_OFFSET) {		\
> > > +		VMLINUX_SYMBOL(__start___immediate) = .;		\
> > > +		*(__immediate)						\
> > > +		VMLINUX_SYMBOL(__stop___immediate) = .;			\
> > > +	}								\
> > > +									\
> > 
> > Why do you need an output section for that? IOW: will this work too?
> > 
> > .data : ... { 
> > ...
> > 
> > 		VMLINUX_SYMBOL(__start___immediate) = .;		\
> > 		*(__immediate)						\
> > 		VMLINUX_SYMBOL(__stop___immediate) = .;			\
> > ...
> > }
> > 
> 
> This last one could cause alignment problems. We either have to use the
> proper ALIGN() before the section, or let AT(ADDR(__immediate) -
> LOAD_OFFSET) take care of it. I prefer the latter.

This adds yet another output section in vmlinux, and there is
no tools which need that. We already have 30+ sections there while we need ~20.

I am trying to fix the mess. Please don't add to it.

Re alignment: (1) do you really realy REALLY need it? Last I checked,
i386 was handling unaligned accesses just fine; and
(2) this works:

		. = ALIGN(4)
 		VMLINUX_SYMBOL(__start___immediate) = .;		\
 		*(__immediate)						\
 		VMLINUX_SYMBOL(__stop___immediate) = .;			\


--
vda
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