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Mathieu Desnoyers 6549864629 tracepoints: Fix section alignment using pointer array 
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 7e066fb8 tracepoints: add DECLARE_TRACE() and DEFINE_TRACE()
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.

One attempt was 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.

The reason is that the "aligned" attribute only specify the _minimum_ alignment
for a structure, leaving both the compiler and the linker free to align on
larger multiples. Because tracepoint.c expects the structures to be placed as an
array within each section, up-alignment cause NULL-pointer exceptions due to the
extra unexpected padding.

(this patch applies on top of -tip)

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: David S. Miller <davem@davemloft.net>
LKML-Reference: <20110126222622.GA10794@Krystal>
CC: Frederic Weisbecker <fweisbec@gmail.com>
CC: Ingo Molnar <mingo@elte.hu>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2011-02-03 09:28:46 -05:00
..
acpi Merge branch 'acpica' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux-acpi-2.6 2011-01-20 16:28:34 -08:00
asm-generic tracepoints: Fix section alignment using pointer array 2011-02-03 09:28:46 -05:00
crypto crypto: padlock - Move padlock.h into include/crypto 2011-01-07 14:52:00 +11:00
drm drm/radeon/kms: add new radeon_info ioctl query for clock crystal freq 2011-01-25 08:41:04 +10:00
keys keys: add new key-type encrypted 2010-11-29 08:55:29 +11:00
linux tracepoints: Fix section alignment using pointer array 2011-02-03 09:28:46 -05:00
math-emu
media [media] v4l: Include linux/videodev2.h in media/v4l2-ctrls.h 2011-01-19 11:52:09 -02:00
mtd
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6 2011-01-19 20:25:45 -08:00
pcmcia
rdma RDMA: Update workqueue usage 2011-01-16 21:16:31 -08:00
rxrpc
scsi Merge branch 'for-2.6.38/core' of git://git.kernel.dk/linux-2.6-block 2011-01-13 10:45:01 -08:00
sound ALSA: constify functions in ac97 2011-01-14 19:14:47 +01:00
target [SCSI] target: Add LIO target core v4.0.0-rc6 2011-01-14 10:12:29 -06:00
trace tracing: Replace trace_event struct array with pointer array 2011-02-02 21:37:13 -05:00
video Merge branch 'fbdev/udlfb' 2011-01-06 18:10:09 +09:00
xen Merge branch 'stable/gntdev' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen 2011-01-13 18:46:48 -08:00
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