linux-kernel - Re: [PATCH] tracing: properly align linker defined symbols

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Message-ID: <AANLkTil4eO0TW34ggl16lA9BTx5gObKQl4P3etzZI0MK@mail.gmail.com>
Date:	Sat, 10 Jul 2010 16:06:05 +0300
From:	Zeev Tarantov <zeev.tarantov@...il.com>
To:	rostedt@...dmis.org
Cc:	Sam Ravnborg <sam@...nborg.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [PATCH] tracing: properly align linker defined symbols

On Sat, Jul 10, 2010 at 14:34, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Sat, 2010-07-10 at 13:18 +0300, Zeev Tarantov wrote:
>> On Sat, Jul 10, 2010 at 09:35, Sam Ravnborg <sam@...nborg.org> wrote:
>
>> > +/*
>> > + * Align to a 32 byte boundary equal to the
>> > + * alignment gcc 4.5 uses for a struct
>> > + */
>> > +#define STRUCT_ALIGN() . = ALIGN(32)
>> > +
>
> What I'm nervous about is when gcc 4.8 decides to up the alignment to
> 64.
>
> Maybe we should have both patches, just to be safe.
>
> -- Steve
>

I don't want to post obvious or inane suggests to the mailing list,
but if you're worried about gcc changing the default alignment, the
solution seems to be one of:
1. Not relying on the default alignment and specifying explicitly what you want.
2. Querying the default alignment before compilation, either using an
API gcc may provide or (cumbersomely) by testing.

-Zeev
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