linux-kernel - Re: [PATCH 0/2] jump label: update for .39

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Date:	Thu, 10 Mar 2011 14:45:29 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	David Daney <ddaney@...iumnetworks.com>
Cc:	Jason Baron <jbaron@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	peterz@...radead.org, hpa@...or.com, mingo@...e.hu,
	tglx@...utronix.de, andi@...stfloor.org, roland@...hat.com,
	rth@...hat.com, masami.hiramatsu.pt@...achi.com,
	fweisbec@...il.com, avi@...hat.com, davem@...emloft.net,
	sam@...nborg.org, michael@...erman.id.au,
	linux-kernel@...r.kernel.org, Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: [PATCH 0/2] jump label: update for .39

On Thu, 2011-03-10 at 14:25 -0500, Steven Rostedt wrote:
> On Thu, 2011-03-10 at 10:57 -0800, David Daney wrote:
> > On 03/10/2011 10:53 AM, Steven Rostedt wrote:
> > > On Thu, 2011-03-10 at 10:47 -0800, David Daney wrote:
> > >
> > >> The alignment requested by the assembler will have to satisfy *all* the
> > >> requested alignments, so manually forcing everything to .align 8 (or
> > >> .align 4 for 32-bit) should ensure that the linker doesn't put in any holes.
> > >
> > > I would agree with the assessment although, I don't know that it is
> > > documented anywhere that this is what happens. As the previous "bug"
> > > with the trace_events was solved by me adding .align(4) everywhere, I
> > > would think that .align(sizeof(long)) would work here too.
> > >
> > > It may be a good ideal to force this alignment, and not add wasted
> > > space. If anything, if this (hypothetical) bug appears, it will most
> > > likely show up as a crash on boot up. I'm not too concerned about it.
> > >
> > 
> > If the linker put in gratuitous holes, things like  __ex_table would 
> > break too.
> 
> Again, as I have said (although I said extable not __ex_table), there
> seems to be no problem when the data is of a power of 2 as well. As
> __ex_table size is a power of 2. We just don't know if the linker will
> add holes when the size is something other than power of 2.

Anyway, I think the best thing for now is to have Jason add
the .align(sizeof(long)) in the inline assembly for all locations and be
done with it.

-- Steve


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