Re: [PATCH] b43: Fix possible unaligned u32 access

["John W. Linville" <linville@tuxdriver.com>]

On Fri, Jun 05, 2009 at 02:53:07PM -0400, John W. Linville wrote:
> On Fri, Jun 05, 2009 at 05:03:57PM +0200, castet.matthieu@free.fr wrote:
> > Quoting "John W. Linville" <linville@tuxdriver.com>:
> > 
> > > On Thu, Jun 04, 2009 at 11:18:33PM +0200, Michael Buesch wrote:
> > > > From: Matthieu CASTET <castet.matthieu@free.fr>
> > > >
> > > > Fix possible unaligned u32 access in b43_generate_plcp_hdr().
> > > > Unaligned data is read/write with a u32 pointer instead of using the
> > > > packed structure. Some versions of gcc ignore the "packed" attribute, if
> > > the
> > > > structure element is accessed through a local pointer.
> > > >
> > > > Signed-off-by: Matthieu CASTET <castet.matthieu@free.fr>
> > > > Signed-off-by: Michael Buesch <mb@bu3sch.de>
> > >
> > > That seems pretty brain-dead...can you cite a source for this
> > > information?
> > The test I did with the attached test case in the first post.
> 
> Link?
> 
> > I don't see why gcc should propagate packed structure info to assignment.
> > That will be impossible to handle (think of passing it to function parameter).
> 
> Perhaps this is obvious to you, but it isn't to me.

OK, I got an explanation from Kyle McMartin that I grok...

> > 
> > > The patch seems like a no-op...
> > At least the code produced on mips is different.
> 
> Then why aren't you trying to get the mips gcc guys to fix it?

Still worth wondering...anyway, the patch is fine -- I just didn't
grok the explanation.

John
-- 
John W. Linville		Someday the world will need a hero, and you
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