> On Apr 24, 2014, at 11:06 PM, "Chung-Lin Tang" <clt...@codesourcery.com> > wrote: > >> On 2014/4/25 02:42 AM, Pinski, Andrew wrote: >> >> >>>> On Apr 24, 2014, at 11:37 AM, "Chung-Lin Tang" <clt...@codesourcery.com> >>>> wrote: >>>> >>>>> On 2014/4/24 11:28 PM, Catalin Marinas wrote: >>>>>> On Thu, Apr 24, 2014 at 09:55:25AM +0100, Chung-Lin Tang wrote: >>>>>>> On 2014/4/24 02:26 PM, Chung-Lin Tang wrote: >>>>>>> On 2014/4/24 上午 02:15, Pinski, Andrew wrote: >>>>>>> >>>>>>>>> On Apr 23, 2014, at 10:59 AM, "Chung-Lin Tang" >>>>>>>>> <clt...@codesourcery.com> wrote: >>>>>>>>> >>>>>>>>>>> On 2014/4/22 07:20 PM, Ley Foon Tan wrote: >>>>>>>>>>> On Tue, Apr 22, 2014 at 6:56 PM, Arnd Bergmann <a...@arndb.de> >>>>>>>>>>> wrote: >>>>>>>>>>>>>>> On Tuesday 22 April 2014 18:37:11 Ley Foon Tan wrote: >>>>>>>>>>>>>>>>>>> Hi Arnd and Peter Anvin, >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> Other than 64-bit time_t, clock_t and suseconds_t, can you >>>>>>>>>>>>>>>>>>> confirm >>>>>>>>>>>>>>>>>>> that we don't need to have 64 bit off_t? See detail in link >>>>>>>>>>>>>>>>>>> below. >>>>>>>>>>>>>>>>>>> I can submit the patches for 64-bit time changes >>>>>>>>>>>>>>>>>>> (include/asm-generic/posix_types.h and other archs) if >>>>>>>>>>>>>>>>>>> everyone is >>>>>>>>>>>>>>>>>>> agreed on this. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Yes. >>>>>>>>>>> Okay, will doing that. >>>>>>>>> >>>>>>>>> I believe that arm64 ILP32 will also be affected. What is the status >>>>>>>>> of >>>>>>>>> this configuration? Has the glibc/kernel ABI been finalized? >>>>>>> Not yet. I am still working out the signal handling part. But we >>>>>>> already agreed on 64bit time_t, clock_t, and suseconds_t. And we >>>>>>> agreed to a 64bit offset_t too. >>>>>>> >>>>>>> On a related note suseconds in the timespec in posix is defined to >>>>>>> be long. So it would nice if the kernel ignores the upper 32bits so >>>>>>> we (glibc developers) can fix this for new targets including x32 >>>>>>> and arm64/ilp32. >>>>>> >>>>>> Hmm, but that means for purely 32-bit architectures like nios2, which >>>>>> unlike x86_64 or arm64, never has a 64-bit mode, suseconds_t as a 64-bit >>>>>> type in the kernel is simply wasted. >>>>> >>>>> The more I think of this, the more I feel that suseconds_t should jsut >>>>> be 'long', not strictly 64-bitified. An ILP32 sub-mode in a 64-bit >>>>> kernel should be using compat_* code paths, something like a >>>>> COMPAT_USE_32BIT_SUSECONDS case. >>>> >>>> ILP32 mode should use LP64 syscalls as much as possible and that's the >>>> aim with arm64 as well (of course, we still have a few that wouldn't be >>>> possible and we route them via compat). >>>> >>>> But here if time_t is 64-bit while susecconds_t is 32-bit, the compat >>>> code wouldn't help. >>> >>> Why not? You can define the arm64 'struct compat_timeval' with >>> suseconds_t as s32, and add the 32<-->64 case in the >>> compat_get/put_timeval path, triggered when the process is ILP32 (test >>> wrapped in the above hypothetical COMPAT_USE_32BIT_SUSECONDS macro). >>> Similar to how x32 does COMPAT_USE_64BIT_TIME. >> >> We would three timeval then. One for aarch32, one for lp64 and one for >> ilp32. We really don't want three. Two is already one too many in my mind >> after developing the ilp32 syscall abi. >> >> Thanks, >> Andrew > > Okay I now see you're already doing that for 32-bit ARM. > > Still, you would probably just need to have an arm64-ILP32 specific case > to be careful about the last padding word upon kernel entry/exit. > (accommodating the difference in sizeof(long)) Penalizing all > architectures does not seem like the best solution.
Considering the alignment of long long would be 64bits, the struct does not change sizes if suseconds_t is 32bits or 64bits. > > Having suseconds_t as a strictly 64-bit C type in the kernel, while > defined as <= long in user-space may cause other problems. > > I'll try to explain a probable situation for Nios II. I'm not sure about > other soft-cores, but nios2 is sort of uncommon in that the maximum > alignment is 4-bytes (32-bits), even for doubles/long-longs. Yes does that include even if users of aligned? If so that seems broken. Also yes nios ii is unstandard when it comes to alignment here. > > So if time_t is 64-bits (which makes sense), then struct timeval, which > is time_t+suseconds_t in userspace is 12-bytes/aligned-4 (unlike many > archs where a 64-bit time_t will expand the size to 16-bytes, due to > align-8) Unlike most other targets where the struct would 16bits no matter what. Thanks, Andrew > > If the kernel suseconds_t is forced to be 64-bits, then nios2 will have > a 16-byte kernel timeval vs. 12-byte userspace timeval situation. Just > this will require us to do something using compat_*, or weird hacks in > glibc, which is unfair. Nios II has no "other-mode". We are just > strictly ILP32, everywhere. > > Of course, we can probably still at the end just use a Nios II specific > posix_types.h header to override things, but I'm just stating this as a > matter of which are the most reasonable default settings in the generic > headers. Making pure ILP32 archs diverge from POSIX standards by default > does not seem to be right. > > Thanks, > Chung-Lin > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
