linux-kernel - Re: [PATCH] bootwrapper: mspsc.c: fix pointer-to-int-cast warnings

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Message-ID: <87o9o6wi9j.fsf@concordia.ellerman.id.au>
Date:   Mon, 13 Nov 2017 22:05:44 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Michal Suchanek <msuchanek@...e.de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michal Suchanek <msuchanek@...e.de>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bootwrapper: mspsc.c: fix pointer-to-int-cast warnings

Hi Michal,

Thanks for trying to fix this.

Michal Suchanek <msuchanek@...e.de> writes:
> I get these warnings:
>
> ../arch/powerpc/boot/mpsc.c: In function 'mpsc_get_virtreg_of_phandle':
> ../arch/powerpc/boot/mpsc.c:113:35: warning: cast from pointer to
> integer of different size [-Wpointer-to-int-cast]
>
> ../arch/powerpc/boot/mpsc.c: In function 'mpsc_console_init':
> ../arch/powerpc/boot/mpsc.c:147:12: warning: cast from pointer to
> integer of different size [-Wpointer-to-int-cast]
>
> Presumably the patch below fixes these, and presumably the DT defines
> that pointes and integers have the same size in the DT so this is fine

Actually no it doesn't. A device tree doesn't contain pointers, and it
doesn't say anything about the size of a pointer on a platform that uses
that device tree.

phandles are not pointers, they are handles, and they are always 32-bit.
So this code is just wrong on 64-bit, you can't safely cast from a
64-bit pointer to a phandle.

But I think this warning has actually been fixed differently by commit:

  866bfc75f40e ("powerpc: conditionally compile platform-specific serial drivers")

If you're still seeing the warning let me know.

cheers