On 14/4/25 下午4:37, Pinski, Andrew wrote: > > >> 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.
You mean using '__attribute__((aligned(8)))'? Sure of course that enlarges the alignment as expected, but sprinkling that over glibc, or getting it into the main glibc bits/time.h header is probably not going to happen... Thanks, Chung-Lin >> >> 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/
