Re: [PATCH next resend 2/5] minmax: Allow min()/max()/clamp() if the arguments have the same signedness.

[Marc Zyngier <maz@kernel.org>]

On Wed, 26 Jul 2023 10:19:48 +0100,
David Laight <David.Laight@ACULAB.COM> wrote:
> 
> > From: kernel test robot <lkp@intel.com>
> > Sent: 25 July 2023 19:33
> ...
> > 
> > All errors (new ones prefixed by >>):
> > 
> > >> drivers/irqchip/irq-mips-cpu.c:288:1: error: call to undeclared function '__typecheck'; ISO C99 and
> > later do not support implicit function declarations [-Wimplicit-function-declaration]
> >      288 | IRQCHIP_DECLARE(cpu_intc, "mti,cpu-interrupt-controller", mips_cpu_irq_of_init);
> >          | ^
> >    include/linux/irqchip.h:37:38: note: expanded from macro 'IRQCHIP_DECLARE'
> >       37 |         OF_DECLARE_2(irqchip, name, compat, typecheck_irq_init_cb(fn))
> >          |                                             ^
> >    include/linux/irqchip.h:24:3: note: expanded from macro 'typecheck_irq_init_cb'
> >       24 |         (__typecheck(typecheck_irq_init_cb, &fn) ? fn : fn)
> >          |          ^
> > >> drivers/irqchip/irq-mips-cpu.c:288:1: error: initializer element is not a compile-time constant
> >      288 | IRQCHIP_DECLARE(cpu_intc, "mti,cpu-interrupt-controller", mips_cpu_irq_of_init);
> >          | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >    include/linux/irqchip.h:37:2: note: expanded from macro 'IRQCHIP_DECLARE'
> >       37 |         OF_DECLARE_2(irqchip, name, compat, typecheck_irq_init_cb(fn))
> >          |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >    include/linux/of.h:1493:3: note: expanded from macro 'OF_DECLARE_2'
> >     1493 |                 _OF_DECLARE(table, name, compat, fn, of_init_fn_2)
> >          |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >    include/linux/of.h:1481:2: note: expanded from macro '_OF_DECLARE'
> >     1481 |         _OF_DECLARE_STUB(table, name, compat, fn, fn_type)
> >          |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >    include/linux/of.h:1470:16: note: expanded from macro '_OF_DECLARE_STUB'
> >     1470 |                      .data = (fn == (fn_type)NULL) ? fn : fn }
> >          |                              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> It looks like irqchip.h is using __typecheck() which is really
> an internal part of the implementation of min() and max().
> The patched version doesn't use it - hence the build fail.
> I can re-instate it, but this all looks wrong to me.

Please see f1985002839a ("irqchip: Provide stronger type checking for
IRQCHIP_MATCH/IRQCHIP_DECLARE") for the rationale.

Given that this has uncovered a number of bugs, I'm not letting this
go without an equivalent replacement.

> The type of typecheck_irq_init_cb is the same as that of fn_type (although
> they are defined separately).
> Both headers seem to be testing the type - and it must match both.
> So if the test in of.h worked the one in irqchip.h wouldn't have been added.
> So I suspect it doesn't actually do anything - the RHS is NULL, the type
> probably doesn't matter.

They are used in different contexts. See IRQCHIP_MATCH().

	M.

-- 
Without deviation from the norm, progress is not possible.