linux-kernel - Re: [PATCH v2] efi: Fix warning of int-to-pointer-cast on x86 32-bit builds

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Message-ID: <CAKv+Gu8WPvG5rzBB57eK1_Ehj1wB19wR=zzBDRoQbmhRfpCGng@mail.gmail.com>
Date:	Fri, 23 Oct 2015 10:37:46 +0200
From:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:	Taku Izumi <izumi.taku@...fujitsu.com>,
	Matt Fleming <matt.fleming@...el.com>,
	Ingo Molnar <mingo.kernel.org@...il.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kamezawa.hiroyu@...fujitsu.com,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>
Subject: Re: [PATCH v2] efi: Fix warning of int-to-pointer-cast on x86 32-bit builds

On 23 October 2015 at 11:50, Taku Izumi <izumi.taku@...fujitsu.com> wrote:
> commit-0f96a99 introduces the following warning message:
>
>   drivers/firmware/efi/fake_mem.c:186:20: warning: cast to pointer
>   from integer of different size [-Wint-to-pointer-cast]
>
> new_memmap_phy was defined as a u64 value and casted to void*.
> This causes a warning of int-to-pointer-cast on x86 32-bit
> environment.
>
> This patch changes the type of "new_memmap_phy" variable
> from "u64" into "ulong" to avoid it.
>
> v1 -> v2:
>  - change the type of "new_memmap_phy" from phys_addr_t
>    into ulong according to Ard's comment
>
> Reported-by: Ingo Molnar <mingo@...nel.org>
> Signed-off-by: Taku Izumi <izumi.taku@...fujitsu.com>
> ---
>  drivers/firmware/efi/fake_mem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/firmware/efi/fake_mem.c b/drivers/firmware/efi/fake_mem.c
> index 32bcb14..1f483b4 100644
> --- a/drivers/firmware/efi/fake_mem.c
> +++ b/drivers/firmware/efi/fake_mem.c
> @@ -59,7 +59,7 @@ void __init efi_fake_memmap(void)
>         u64 start, end, m_start, m_end, m_attr;
>         int new_nr_map = memmap.nr_map;
>         efi_memory_desc_t *md;
> -       u64 new_memmap_phy;
> +       ulong new_memmap_phy;
>         void *new_memmap;
>         void *old, *new;
>         int i;

After looking at the original (already merged) patch 11/11 again, I
realize this is still not right: the problem is that efi_memory_map's
phys_map member uses a void* type to hold a physical address, which
happens to be correct in the normal case even when phys_addr_t is
larger than void* (like on ARM with LPAE enabled) since the address it
holds is the address of an allocation performed by the firmware, which
only uses 1:1 addressable memory.

However, overwriting memmap.phys_map with a value produced my
memblock_alloc() is problematic, since the allocation may be above 4
GB on 32-bit (L)PAE platforms. So the correct way to do this would be
to set the memblock limit to 4GB before memblock_alloc() on 32-bit
platforms, and restore it afterwards. This is a bit of a kludge,
though, and it would be more correct to change the type of
efi_memory_map::phys_map to phys_addr_t, although I don't know what
the potential fallout of that change is. Matt?

So that means your v1 of this patch is correct after all, and the
warning spotted by Ingo uncovered a problem with the original series
that requires an additional fix.

Regards,
Ard.
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