Bug#642762: xulrunner-6.0: console flooded with unaligned access messages on ia64 (IA-64/IPF/Itanium) platform

[Mike Hommey]

On Tue, Oct 04, 2011 at 08:11:17PM +0200, Émeric Maschino wrote:
> Sorry for the late reply.
> 
> 2011/9/28 Mike Hommey <mh at glandium.org>:
> > On Tue, Sep 27, 2011 at 10:32:17PM +0200, Émeric Maschino wrote:
> >
> > Thanks so in fact the error is on the next line, and is due to this
> > code:
> >  inline PRBool Equals(const nsID& other) const {
> >    return
> >      ((PRUint64*) &m0)[0] == ((PRUint64*) &other.m0)[0] &&
> >      ((PRUint64*) &m0)[1] == ((PRUint64*) &other.m0)[1];
> >  }
> >
> > Mike
> 
> Wow! How did you figure this? From the assembly output?
> 
> I still understand what's wrong with this code. nsID is defined as:
> 
> struct nsID {
>   PRUint32 m0;
>   PRUint16 m1;
>   PRUint16 m2;
>   PRUint8 m3[8];
>   ...
> };
> 
> It seems 64-bit aligned to me.
> 
> And if I understand Equals code correctly, (PRUint64*)[0] is a 64-bit
> word with packed data of m0, m1 and m2 (32+16+16 = 64 bits) and
> (PRUint64*)[1] is another 64-bit word with m3 data (8*8 = 64 bits).
> 
> Am I right? How can this be unaligned then?

Because the struct you copy/pasted is 32-bits aligned.

Mike