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SubjectRe: [PATCH] ftrace: fix ftrace_event_call alignment for use with gcc 4.5
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On Wed, 2010-02-24 at 14:33 -0500, Jeff Mahoney wrote:
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> On 02/24/2010 01:59 PM, Jeff Mahoney wrote:
> > GCC 4.5 introduces behavior that forces the alignment of structures to
> > use the largest possible value. The default value is 32 bytes, so if
> > some structures are defined with a 4-byte alignment and others aren't
> > declared with an alignment constraint at all - it will align at 32-bytes.
> >
> > For things like the ftrace events, this results in a non-standard array.
> > When initializing the ftrace subsystem, we traverse the _ftrace_events
> > section and call the initialization callback for each event. When the
> > structures are misaligned, we could be treating another part of the
> > structure (or the zeroed out space between them) as a function pointer.
> >
> > This patch forces the alignment for all the ftrace_event_call structures
> > to 4 bytes.
> >
> > Without this patch, the kernel fails to boot very early when built with
> > gcc 4.5.
> >
> > It's trivial to check the alignment of the members of the array, so it
> > might be worthwhile to add something to the build system to do that
> > automatically. Unfortunately, that only covers this case. I've asked one
> > of the gcc developers about adding a warning when this condition is seen.
>
> BTW, the analysis for this is available here:
>
> https://bugzilla.novell.com/show_bug.cgi?id=582222
>

Thanks! I'll apply this and push it forward (as well as to stable)

-- Steve



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