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Re: [PATCH 1/2] y2038: make CONFIG_64BIT_TIME unconditional
- From: Stepan Golosunov <stepan at golosunov dot pp dot ru>
- To: Lukasz Majewski <lukma at denx dot de>
- Cc: Arnd Bergmann <arnd at arndb dot de>, Thomas Gleixner <tglx at linutronix dot de>, Joseph Myers <joseph at codesourcery dot com>, libc-alpha at sourceware dot org, linux-api at vger dot kernel dot org, linux-kernel at vger dot kernel dot org, Deepa Dinamani <deepa dot kernel at gmail dot com>
- Date: Sat, 27 Apr 2019 13:54:18 +0400
- Subject: Re: [PATCH 1/2] y2038: make CONFIG_64BIT_TIME unconditional
- References: <firstname.lastname@example.org> <20190427004653.3cecd1cb@jawa>
27.04.2019 в 00:46:53 +0200 Lukasz Majewski написал:
> Hi Arnd,
> > As Stepan Golosunov points out, we made a small mistake in the
> > get_timespec64() function in the kernel. It was originally added under
> > the assumption that CONFIG_64BIT_TIME would get enabled on all 32-bit
> > and 64-bit architectures, but when I did the conversion, I only turned
> > it on for 32-bit ones.
> > The effect is that the get_timespec64() function never clears the
> > upper half of the tv_nsec field for 32-bit tasks in compat mode.
> > Clearing this is required for POSIX compliant behavior of functions
> > that pass a 'timespec' structure with a 64-bit tv_sec and a 32-bit
> > tv_nsec, plus uninitialized padding.
> At least for my setup (32bit ARM with 64 bit time support) this patch is
> not fixing anything.
The patch is not supposed to fix anything on 32-bit architectures as
in-kernel struct timespec64 has 32-bit tv_nsec there. Thus truncation
should happen automatically. I also missed that fact when I was
reading get_timespec64 code.
(I am wondering whether such trucation is undefined behaviour in C and
whether there should be sign-extension instead of zeroing-out for the
in_compat_syscall() case though.)
> > The easiest fix for linux-5.1 is to just make the Kconfig symbol
> > unconditional, as it was originally intended. As a follow-up,
> > we should remove any #ifdef CONFIG_64BIT_TIME completely.
> > Link:
> > email@example.com/">https://firstname.lastname@example.org/
> > Cc: Lukasz Majewski <email@example.com> Cc: Stepan Golosunov
> > <firstname.lastname@example.org> Signed-off-by: Arnd Bergmann <email@example.com>
> > ---
> > Please apply this one as a bugfix for 5.1
> > ---
> > arch/Kconfig | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> > diff --git a/arch/Kconfig b/arch/Kconfig
> > index 33687dddd86a..9092e0ffe4d3 100644
> > --- a/arch/Kconfig
> > +++ b/arch/Kconfig
> > @@ -764,7 +764,7 @@ config COMPAT_OLD_SIGACTION
> > bool
> > config 64BIT_TIME
> > - def_bool ARCH_HAS_64BIT_TIME
> > + def_bool y
> > help
> > This should be selected by all architectures that need to
> > support new system calls with a 64-bit time_t. This is relevant on
> > all 32-bit