Re: [RFC][BZ #16549] Add sanity check for condvar alignment.

[Mike Frysinger <vapier at gentoo dot org>]

On Tuesday, February 11, 2014 17:26:38 OndÅej BÃlka wrote:
> On Tue, Feb 11, 2014 at 10:35:02AM -0500, Rich Felker wrote:
> > On Tue, Feb 11, 2014 at 01:43:46PM +0100, OndÅej BÃlka wrote:
> > > In this bug using misaligned condition variable causes a silent failure.
> > 
> > You cannot create a misaligned condvar without invoking undefined
> > behavior.
> > 
> > > There are two possibilities how to fix it. First one would be not lie
> > > about requirements and add attribute ((aligned)) to header. That could
> > > break programs by changing sizes of structures but these were broken in
> > > first place.
> > 
> > How is it lying about the requirements? The definition is visible and
> > it contains both ints and pointers in the union, so the alignment is
> > the maximum alignment needed for them. In practice this will be 4 on
> > 32-bit systems and 8 on 64-bit ones.
> > 
> > In any case, the bugreport is invalid. You can never take a pointer to
> > members of a #pragma packed struct and pass them to other functions.
> > For example, scanf("%d", &packed.x) is invalid because scanf has no
> > way of knowing it will get, much less dealing with, an
> > invalid/misaligned pointer. This is not specific to pthread
> > synchronization objects.
> 
> And by undefined behaviour we could format user harddisk. This is valid
> QoI issue as it aborting on undefined behaviour is prefered.

but you can make this argument for every single function that takes a pointer 
argument.  surely you can't be proposing that we add assert() to every 
function entry point to verify the user wasn't stupid ?  at some point the 
answer has to be "wtf go away".
-mike

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