From mboxrd@z Thu Jan 1 00:00:00 1970 From: arnd@arndb.de (Arnd Bergmann) Date: Wed, 15 Apr 2015 14:47:37 +0200 Subject: [PATCH v4 00/24] ILP32 for ARM64 In-Reply-To: <20150414165459.GG14546@e104818-lin.cambridge.arm.com> References: <9F7FC15C-EED1-4939-B66A-1BC3119E0D9C@theobroma-systems.com> <20150414165459.GG14546@e104818-lin.cambridge.arm.com> Message-ID: <2059078.o6U5BYXcDP@wuerfel> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tuesday 14 April 2015 17:55:00 Catalin Marinas wrote: > On Tue, Apr 14, 2015 at 05:29:36PM +0200, Dr. Philipp Tomsich wrote: > > So tv_nsec needs to be 32bit on ILP32, as we would otherwise break the C > > language. Any program that assumes that tv_nsec is sizeof(long) would be > > correct and it would be unexpected and surprising behaviour [even though it > > would be consider a good programming style] if one would need to explicitly > > ask for the sizeof(ts.tv_nsec). Having the same problem on x32 doesn?t seem > > like a good justification to do the same. > > From a standards perspective, that's clear, and I'm fine with not making > the same choice as x32. I think on x32 it was a side-effect of glibc > defining tv_nsec as __syscall_slong_t and the kernel defining > __kernel_long_t to 64-bit. I'm pretty sure that this part of the x32 ABI was a deliberate choice in full knowledge of the tradeoffs. > > For time_t, I don?t see the need to have a 32bit type yet. > > As long as the the type is properly exposed through header files (and user > > programs can thus recreate the kernel?s data model), we should be safe. > > The problem with a 64-bit time_t is that the timespec structure looks > like neither compat32 nor native 64-bit. If we make the AArch32 and > native ILP32 exclusive and build time, it makes it easier, otherwise we > need to support a third ABI in the kernel. Exactly, which is why the layout was chosen to be the same as x86-64 for x32. > > Can we thus agree on the following for the next revision of the patch-set: > > (1) We retain a 64bit time_t, but implement different sizes (between ILP32 and > > LP64) for ?tv_nsec' in 'struct timespec?? > > (2) We use the 64bit system calls whereever possible (i.e. no register splitting). > > As I mentioned above, timespec and possibly other structures no longer > like any of the existing ABIs. Do we know how many syscalls are > affected? > > The alternative is 32-bit time_t which makes it easier to use the compat > syscall implementations (not numbers). It also depends on how we plan to > fix the 2038 problem. For new 32-bit only architectures, are we going to > require them to use a 64-bit time_t or we get alternative time64_t and > timespec64 specs? No, we had originally planned that a few years ago, but after deciding that we are fixing this problem for all 32-bit machines, and also seeing the magnitude of changes involved in that, I think we have a general consensus that we do not want to add special cases for architectures that use 64-bit time_t before everyone else does. Arnd