linux-kernel - Re: [PATCH] drm/i915/mtl: avoid stringop-overflow warning

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Message-ID: <20231024174153.byeq7ctssvxuwa4z@zenone.zhora.eu>
Date:   Tue, 24 Oct 2023 19:41:53 +0200
From:   Andi Shyti <andi.shyti@...nel.org>
To:     Jani Nikula <jani.nikula@...ux.intel.com>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Badal Nilawar <badal.nilawar@...el.com>,
        Ashutosh Dixit <ashutosh.dixit@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        Matt Roper <matthew.d.roper@...el.com>,
        Vinay Belgaumkar <vinay.belgaumkar@...el.com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org,
        Andi Shyti <andi.shyti@...ux.intel.com>
Subject: Re: [PATCH] drm/i915/mtl: avoid stringop-overflow warning

Hi Jani,

> >  static void rc6_res_reg_init(struct intel_rc6 *rc6)
> >  {
> > -	memset(rc6->res_reg, INVALID_MMIO_REG.reg, sizeof(rc6->res_reg));
> 
> That's just bollocks. memset() is byte granularity, while
> INVALID_MMIO_REG.reg is u32. If the value was anything other than 0,
> this would break.

Actually it's:

   void *memset(void *s, int c, size_t count)

> And you're not supposed to look at the guts of i915_reg_t to begin with,
> that's why it's a typedef. Basically any code that accesses the members
> of i915_reg_t outside of its implementation are doing it wrong.
> 
> Reviewed-by: Jani Nikula <jani.nikula@...el.com>

in any case, I agree with your argument, but why can't we simply
do:

   memset(rc6->res_reg, 0, sizeof(rc6->res_reg));

?

The patch looks to me like it's being more complex that it
should.

Andi