From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH v2] efi: Fix warning of int-to-pointer-cast on x86 32-bit builds Date: Fri, 23 Oct 2015 10:50:11 +0200 Message-ID: <20151023085011.GB21631@gmail.com> References: <1445593826-4578-1-git-send-email-izumi.taku@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Ard Biesheuvel Cc: Taku Izumi , Matt Fleming , Ingo Molnar , "linux-kernel@vger.kernel.org" , kamezawa.hiroyu@jp.fujitsu.com, "linux-efi@vger.kernel.org" List-Id: linux-efi@vger.kernel.org * Ard Biesheuvel wrote: > On 23 October 2015 at 11:50, Taku Izumi 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 > > Signed-off-by: Taku Izumi > > --- > > 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. No, v1 is not right either. This type cast loses information: memmap.phys_map = (void *)new_memmap_phy; Because there are countless platforms where 'void *' is 32-bit while physical addresses are wider. No way of fudging around the type of 'new_memmap_phy' will solve that bug, it might only make the symptoms and the warning go away ... The real problem is with the inappropriate (too narrow) type of memmap.phys_map, not with the type of new_memmap_phy. The cast just hides it. One more page in the '1000 real-life examples of why type casts are evil' book. Thanks, Ingo