[PATCH 04/18] arm64: alternatives: Enforce alignment of struct alt_instr

[konrad.wilk@oracle.com (Konrad Rzeszutek Wilk)]

On Wed, Dec 06, 2017 at 02:57:29PM +0000, Marc Zyngier wrote:
> On 06/12/17 14:48, Konrad Rzeszutek Wilk wrote:
> > On Wed, Dec 06, 2017 at 02:38:25PM +0000, Marc Zyngier wrote:
> >> We're playing a dangerous game with struct alt_instr, as we produce
> >> it using assembly tricks, but parse them using the C structure.
> >> We just assume that the respective alignments of the two will
> >> be the same.
> >>
> >> But as we add more fields to this structure, the alignment requirements
> >> of the structure may change, and lead to all kind of funky bugs.
> >>
> >> TO solve this, let's move the definition of struct alt_instr to its
> >> own file, and use this to generate the alignment constraint from
> >> asm-offsets.c. The various macros are then patched to take the
> >> alignment into account.
> > 
> > Would it be better to use .p2align as on 32-bit ARM you must
> > have it 4-byte aligned. Or at least have and BUILD_BUG_ON
> > to make sure the size can be divided by four??
> > 
> > Oh wait. You are not even touching ARM-32, how come? The alternative
> > code can run on ARM-32 ...
> 
> How? Given that I haven't written yet, I'd be grateful if you could
> share your time machine...

Oh! I assumed it would be there as the Xen variant runs on ARM-32 and
it borrowed a bunch of code from Linux. 

Please disregard my comment. I will go back to tweaking the time machine.
> 
> Thanks,
> 
> 	M.
> -- 
> Jazz is not dead. It just smells funny...