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

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Message-ID: <6bed42e871e74e898b400a404ec6d142@AcuMS.aculab.com>
Date:   Wed, 26 Jul 2023 09:19:48 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'kernel test robot' <lkp@...el.com>,
        "'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
        'Andy Shevchenko' <andriy.shevchenko@...ux.intel.com>,
        'Andrew Morton' <akpm@...ux-foundation.org>,
        "'Matthew Wilcox (Oracle)'" <willy@...radead.org>,
        'Christoph Hellwig' <hch@...radead.org>,
        "'Jason A. Donenfeld'" <Jason@...c4.com>
CC:     "llvm@...ts.linux.dev" <llvm@...ts.linux.dev>,
        "oe-kbuild-all@...ts.linux.dev" <oe-kbuild-all@...ts.linux.dev>,
        "Linux Memory Management List" <linux-mm@...ck.org>,
        "'maz@...nel.org'" <maz@...nel.org>, Rob Herring <robh@...nel.org>
Subject: RE: [PATCH next resend 2/5] minmax: Allow min()/max()/clamp() if the
 arguments have the same signedness.

> From: kernel test robot <lkp@...el.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.

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.

Possibly:
		.data = {sizeof ((fn) == (fn_type)(fn)) ? fn : fn }
would actually generate the required compile-time error.

	David

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