linux-kernel - Re: [PATCH] drm/amdgpu: fix 32-bit compiler warning

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Message-ID: <20151007092101.GD27939@nuc-i3427.alporthouse.com>
Date:	Wed, 7 Oct 2015 10:21:01 +0100
From:	Chris Wilson <chris@...is-wilson.co.uk>
To:	Christian König <christian.koenig@....com>
Cc:	Arnd Bergmann <arnd@...db.de>, David Airlie <airlied@...ux.ie>,
	marek.olsak@....com, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	linux-arm-kernel@...ts.infradead.org,
	Alex Deucher <alexander.deucher@....com>,
	"monk.liu" <monk.liu@....com>
Subject: Re: [PATCH] drm/amdgpu: fix 32-bit compiler warning

On Wed, Oct 07, 2015 at 10:57:11AM +0200, Christian König wrote:
> On 07.10.2015 09:41, Arnd Bergmann wrote:
> >The new amdgpu driver passes a user space pointer in a 64-bit structure
> >member, which is the correct way to do it, but it attempts to
> >directly cast it to a __user pointer in the kernel, which causes
> >a warning in three places:
> >
> >drm/amd/amdgpu/amdgpu_cs.c: In function 'amdgpu_cs_parser_init':
> >drm/amd/amdgpu/amdgpu_cs.c:180:21: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
> >   chunk_array_user = (uint64_t __user *)(cs->in.chunks);
> >
> >This changes all three to add an intermediate cast to 'unsigned long'
> >as other drivers do. This avoids the warning and works correctly on
> >both 32-bit and 64-bit architectures.
> >
> >Signed-off-by: Arnd Bergmann <arnd@...db.de>
> 
> Well if I'm not completely mistaken this is the second time we need
> to fix this because somebody thought the cast was unnecessary.
> 
> Anyway the patch is Reviewed-by: Christian König
> <christian.koenig@....com> and I'm going to keep an eye open for the
> next time somebody tries to remove this.

We use

static inline void __user *to_user_ptr(u64 address)
{
        return (void __user *)(uintptr_t)address;
}

to make the intention clear and hide the cast from prying eyes.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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