linux-kernel - Re: [PATCH v1] x86/platform/intel-mid: Revert "Make 'bt_sfi

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Date:   Thu, 28 Dec 2017 11:34:56 +0100 (CET)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     Ingo Molnar <mingo@...nel.org>
cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
        Darren Hart <dvhart@...radead.org>,
        platform-driver-x86@...r.kernel.org,
        Bhumika Goyal <bhumirks@...il.com>,
        Julia Lawall <julia.lawall@...6.fr>
Subject: Re: [PATCH v1] x86/platform/intel-mid: Revert "Make 'bt_sfi_data'
 const"



On Thu, 28 Dec 2017, Ingo Molnar wrote:

>
> * Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
>
> > The annoying static analyzer follow up patches make a pain rather then
> > fixing issues.
> >
> > The one done by commit 276c87054751
> >
> > ("x86/platform/intel-mid: Make 'bt_sfi_data' const")
> >
> > made an obvious regression [BugLink] since the struct bt_sfi_data used
> > as a temporary container for important data that is used to fill
> > 'parent' and 'name' fields in struct platform_device_info.
> >
> > That's why revert the commit which had been apparently done w/o reading
> > the code.
> >
> > BugLink: https://github.com/andy-shev/linux/issues/20
> > Cc: Bhumika Goyal <bhumirks@...il.com>
> > Cc: julia.lawall@...6.fr
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > ---
> >  arch/x86/platform/intel-mid/device_libs/platform_bt.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/platform/intel-mid/device_libs/platform_bt.c b/arch/x86/platform/intel-mid/device_libs/platform_bt.c
> > index dc036e511f48..5a0483e7bf66 100644
> > --- a/arch/x86/platform/intel-mid/device_libs/platform_bt.c
> > +++ b/arch/x86/platform/intel-mid/device_libs/platform_bt.c
> > @@ -60,7 +60,7 @@ static int __init tng_bt_sfi_setup(struct bt_sfi_data *ddata)
> >  	return 0;
> >  }
> >
> > -static const struct bt_sfi_data tng_bt_sfi_data __initdata = {
> > +static struct bt_sfi_data tng_bt_sfi_data __initdata = {
> >  	.setup	= tng_bt_sfi_setup,
> >  };
>
> This is nasty, why didn't the compiler warn about this bug?
>
> Normally when using a const data structure for a non-const purpose. (Unless
> there's a type cast which loses the type - one of the many reasons why type casts
> should be avoided.)

Indeed, because there is a cast:

#define ICPU(model, ddata)      \
        { X86_VENDOR_INTEL, 6, model, X86_FEATURE_ANY, (kernel_ulong_t)&ddata }

static const struct x86_cpu_id bt_sfi_cpu_ids[] = {
	ICPU(INTEL_FAM6_ATOM_MERRIFIELD, tng_bt_sfi_data),
        {}
};

julia