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SubjectRe: [PATCH 2/2] Tracepoints: Fix section alignment using pointer array
* Steven Rostedt (rostedt@goodmis.org) wrote:
> On Wed, 2011-02-02 at 13:31 -0500, Mathieu Desnoyers wrote:
>
> > > 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.
>
> OK, I just did a git commit --amend to fix it. Here's the new text:
>
>
> commit 7e066fb870fcd1025ec3ba7bbde5d541094f4ce1 added the aligned(32) type a
> 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 apply
> both the variable and type attribute to tracepoint structures definitions an
> declarations. It worked fine with gcc 4.5.1, but broke with gcc 4.4.4 and 4.
>
> The reason is that the "aligned" attribute only specify the _minimum_ alignm
> 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 a
> array within each section, up-alignment cause NULL-pointer exceptions due to
> extra unexpected padding.
>
> This version has just been pushed. I just changed the wording to leave
> out the reference to the reverted commit.

Looks good!

Thanks,

Mathieu

>
> -- Steve
>
>

--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com


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