linux-kernel - Re: [PATCH] drivers/irqchip: Remove function callback casts

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Message-ID: <b0bd9442c1ba63c38d25ade479885cbd@kernel.org>
Date:   Sun, 24 May 2020 17:16:41 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Oscar Carter <oscar.carter@....com>
Cc:     Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers/irqchip: Remove function callback casts

On 2020-05-24 17:06, Oscar Carter wrote:
> Hi Marc,
> 
> On Sun, May 24, 2020 at 12:46:34PM +0100, Marc Zyngier wrote:
>> On Sun, 24 May 2020 10:09:10 +0200
>> Oscar Carter <oscar.carter@....com> wrote:
>> 
>> Hi Oscar,
>> 
>> Thanks for this. Comments below.
>> 
>> > In an effort to enable -Wcast-function-type in the top-level Makefile to
>> > support Control Flow Integrity builds, remove all the function callback
>> > casts.
>> >
>> > To do this, modify the IRQCHIP_ACPI_DECLARE macro initializing the
>> > acpi_probe_entry struct directly instead of use the existent macro
>> > ACPI_DECLARE_PROBE_ENTRY.
>> >
>> > In this new initialization use the probe_subtbl field instead of the
>> > probe_table field use in the ACPI_DECLARE_PROBE_ENTRY macro.
>> 
>> Please add *why* this is a valid transformation (probe_table and
>> probe_subtbl are part of a union).
> 
> Ok, I will add a more detailed explanation.
> 
>> > Signed-off-by: Oscar Carter <oscar.carter@....com>
>> > ---
>> >  include/linux/irqchip.h | 10 ++++++++--
>> >  1 file changed, 8 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/include/linux/irqchip.h b/include/linux/irqchip.h
>> > index 950e4b2458f0..1f464fd10df0 100644
>> > --- a/include/linux/irqchip.h
>> > +++ b/include/linux/irqchip.h
>> > @@ -39,8 +39,14 @@
>> >   * @fn: initialization function
>> >   */
>> >  #define IRQCHIP_ACPI_DECLARE(name, subtable, validate, data, fn)	\
>> > -	ACPI_DECLARE_PROBE_ENTRY(irqchip, name, ACPI_SIG_MADT, 		\
>> > -				 subtable, validate, data, fn)
>> > +	static const struct acpi_probe_entry __acpi_probe_##name	\
>> > +		__used __section(__irqchip_acpi_probe_table) = {	\
>> > +			.id = ACPI_SIG_MADT,				\
>> > +			.type = subtable,				\
>> > +			.subtable_valid = validate,			\
>> > +			.probe_subtbl = (acpi_tbl_entry_handler)fn,	\
>> > +			.driver_data = data,				\
>> > +		}
>> >
>> 
>> I'd rather you add an ACPI_DECLARE_SUBTABLE_PROBE_ENTRY to acpi.h, and
>> use that here so that we can keep the ACPI gunk in a single place.
> 
> Ok, I will do the changes you suggested and I will resend a new 
> version.
> Later, I will also send a series to clean up the checkpatch warnings 
> and
> errors for the acpi.h header.

Not necessarily a good idea. Churn for the sake of keeping checkpatch
at bay is pretty pointless. Do fix bugs if you spot any, but please
exercise judgement.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...