Messages in this thread |  | | Date | Sat, 20 Apr 2019 13:21:12 +0200 | From | Lukasz Majewski <> | Subject | Re: [PATCH 3/6] y2038: linux: Provide __clock_settime64 implementation |
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Hi Stepan,
> 15.04.2019 в 00:08:38 +0200 Lukasz Majewski написал: > > +# if defined __NR_clock_settime64 > > + /* Make sure that passed __timespec64 struct pad is 0. */ > > + struct __timespec64 ts = *tp; > > + ts.tv_pad = 0; > > + return INLINE_SYSCALL_CALL (clock_settime64, clock_id, &ts); > > Isn't kernel supposed to zero out padding on its own? > At least comment in kernel's get_timespec64 says so: > > /* Zero out the padding for 32 bit systems or in compat mode > */ if (IS_ENABLED(CONFIG_64BIT_TIME) && in_compat_syscall()) > kts.tv_nsec &= 0xFFFFFFFFUL; >
For ARM (and x86) 32 bit machines I do use following syscalls (like clock_settime64): https://elixir.bootlin.com/linux/v5.1-rc4/source/arch/arm/tools/syscall.tbl#L420
which are providing 64 bit time support on 32 bit systems.
Yes. In those systems the upper part (32 bits) of tv_nsec is cleared up with mask in the kernel. However, I would prefer not to pass random data to the kernel, and hence I do clear it up explicitly in glibc.
> The code looks buggy though. It fails to zero out the padding in > 32-bit kernels.
For the 32 bit systems without Y2038 support enabled in glibc - the clock_settime would be used, which corresponds to sys_clock_settime32() in the kernel.
> That part is probably broken since > 98f76206b3350 ("compat: Cleanup in_compat_syscall() callers"). > > And, hmm, is CONFIG_64BIT_TIME enabled anywhere?
When I do use clock_settime64 on the glibc side (with _TIME_BITS=64), I do not need to enable such config in the kernel.
If the kernel supports this call (5.1+), then use it, otherwise fallback to clock_settime().
For 64 bit systems, I do not change the execution path.
If you are interested, please look on the following repo (which has some more commits than those posted to the mailing list): https://github.com/lmajewski/y2038_glibc/commits/Y2038-2.29-glibc-__clock-internal-struct-timespec-v1
And meta layer for testing.
https://github.com/lmajewski/meta-y2038
Best regards,
Lukasz Majewski
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