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

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Message-ID: <alpine.LFD.2.00.1103110029090.2787@localhost6.localdomain6>
Date:	Fri, 11 Mar 2011 00:32:02 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	David Daney <ddaney@...iumnetworks.com>
cc:	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Jason Baron <jbaron@...hat.com>, peterz@...radead.org,
	hpa@...or.com, mingo@...e.hu, 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, 10 Mar 2011, David Daney wrote:

> On 03/10/2011 03:16 PM, Steven Rostedt wrote:
> > On Thu, 2011-03-10 at 17:48 -0500, Mathieu Desnoyers wrote:
> > > * Steven Rostedt (rostedt@...dmis.org) wrote:
> > > > On Thu, 2011-03-10 at 16:22 -0500, Mathieu Desnoyers wrote:
> > > > 
> > > > > > 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.
> > > > > 
> > > > > You seem to be contradicting yourself here. I'm concerned about having
> > > > > "structures" of a size not power of two. Can we simply either
> > > > 
> > > > But we don't have structures. We have data that has been allocated in
> > > > assembly. Come to think of it, it may be best to keep these as
> > > > ".align 4".
> > > 
> > > The .align 4 is certainly not the right answer, because it will trigger
> > > unaligned accesses on some 64-bit architectures, as we have faced with
> > > trace event.
> > 
> > Will it? Seems that sparc does this regardless.
> > 
> > Remember, this is 3 natural word sized objects, and vmlinux.ld starts
> > the section off with .ALIGN 8, hence, the section is already 8 byte
> > aligned, all objects within this section are 8 bytes (for 64bit archs,
> > and 4 bytes for 32bit), why would saying ".align 4" cause the linker to
> > add holes to make it 4 byte aligned when it is already 8 byte aligned.
> > The ".align 4" should work with both 32bit and 64bit archs.
> > 
> 
> It should work, but it hurts my eyes to see the source code forcing a 64-bit
> word to 32-bit alignment.

We solved such stuff with macros in other places already.

#ifdef 64bit
# define BLA 8
#else
# define BLA 4
#endif

and then use 

.aling BLA

Where is the problem?

Thanks,

	tglx
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