linux-kernel - Re: [PATCH 2/2] Tracepoints: Fix section alignment using pointer array

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Date:	Wed, 02 Feb 2011 13:47:17 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 2/2] Tracepoints: Fix section alignment using pointer
 array

On Wed, 2011-02-02 at 13:31 -0500, Mathieu Desnoyers wrote:
> * Steven Rostedt (rostedt@...dmis.org) wrote:
> > From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> > 
> > Make the tracepoints more robust, making them solid enough to handle compiler
> > changes by not relying on anything based on compiler-specific behavior with
> > respect to structure alignment. Implement an approach proposed by David Miller:
> > use an array of const pointers to refer to the individual structures, and export
> > this pointer array through the linker script rather than the structures per se.
> > It will consume 32 extra bytes per tracepoint (24 for structure padding and 8
> > for the pointers), but are less likely to break due to compiler changes.
> > 
> > History:
> > 
> > commit 7e066fb870fcd1025ec3ba7bbde5d541094f4ce1 added the aligned(32) type and
> > variable attribute to the tracepoint structures to deal with gcc happily
> > aligning statically defined structures on 32-byte multiples.
> > 
> > commit 15e3540ce2159705f18fad6147ffedf04445ad64 tried to use a 8-byte alignment
> > for tracepoint structures by applying both the variable and type attribute to
> > tracepoint structures definitions and declarations. It worked fine with gcc
> > 4.5.1, but broke with gcc 4.4.4 and 4.4.5.
> 
> Small nit: this reference to commit 15e3540ce2159705f18fad6147ffedf04445ad64
> should be changed to a non-commit-id-related explanation, because the commit has
> been rolled back from -tip.

Yeah, I noticed this too, right after I posted it.

> 
> The rest looks good.

OK, I'll rebase by just removing the reverted commit reference.

Thanks,

-- Steve


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