RE: [RFC][PATCH 2/3] locking,entry: #PF vs TRACE_IRQFLAGS

[David Laight]

From: peterz@xxxxxxxxxxxxx
> Sent: 10 August 2020 12:58
> 
...
> > > --- a/include/linux/entry-common.h
> > > +++ b/include/linux/entry-common.h
> > > @@ -310,6 +310,7 @@ void irqentry_exit_to_user_mode(struct p
> > >  #ifndef irqentry_state
> > >  typedef struct irqentry_state {
> > >  	bool	exit_rcu;
> > > +	bool	irqs_enabled;
> >
> > Instead of passing a structure around, should we look at converting
> > "irqentry_state" into a flags field?
> 
> Probably, on x86_64-linux sizeof(_Bool) == 1, so it's two bytes and that
> fits perfectly fine in a normal return value, but yeah, this is common
> code now and we can't rely on sizeof(_Bool) being sane.

I'd check the arm ABI(s).
IIRC 'sizeof bool' changed - but I can't remember which way :-)

There are probably other ABI where a 'struct' return value
is always implemented as a 'pass by reference' parameter
(Probably M68k?).

	David

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