Subject: Re: [PATCH 0/2] jump label: update for .39
From: Steven Rostedt <rostedt@goodmis.org>
To: David Daney <ddaney@caviumnetworks.com>
Cc: Jason Baron <jbaron@redhat.com>,
        Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>, peterz@infradead.org,
        hpa@zytor.com, mingo@elte.hu, tglx@linutronix.de, andi@firstfloor.org,
        roland@redhat.com, rth@redhat.com, masami.hiramatsu.pt@hitachi.com,
        fweisbec@gmail.com, avi@redhat.com, davem@davemloft.net,
        sam@ravnborg.org, michael@ellerman.id.au, linux-kernel@vger.kernel.org,
        Ralf Baechle <ralf@linux-mips.org>
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Date: Thu, 10 Mar 2011 14:25:43 -0500
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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.

-- Steve


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