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Re: [PATCH v2 2/7] y2038: Introduce __ASSUME_64BIT_TIME define
- From: Joseph Myers <joseph at codesourcery dot com>
- To: Lukasz Majewski <lukma at denx dot de>
- Cc: <libc-alpha at sourceware dot org>, Stepan Golosunov <stepan at golosunov dot pp dot ru>, Arnd Bergmann <arnd at arndb dot de>, Paul Eggert <eggert at cs dot ucla dot edu>
- Date: Thu, 9 May 2019 15:46:01 +0000
- Subject: Re: [PATCH v2 2/7] y2038: Introduce __ASSUME_64BIT_TIME define
- References: <20190414220841.20243-1-lukma@denx.de> <20190429104613.16209-1-lukma@denx.de> <20190429104613.16209-3-lukma@denx.de> <alpine.DEB.2.21.1904292138430.21580@digraph.polyomino.org.uk> <20190430110505.2a0c7d1a@jawa> <alpine.DEB.2.21.1905021431060.4027@digraph.polyomino.org.uk> <20190506165510.7a6c20d1@jawa> <alpine.DEB.2.21.1905071523000.3445@digraph.polyomino.org.uk> <20190508121840.39aaedcb@jawa>
On Wed, 8 May 2019, Lukasz Majewski wrote:
> The 64 bit versions of syscalls (like clock_settime64 or
> clock_gettime64) are available since 5.1 kernel (as you posted already
> the following patch: "Update syscall-names.list for Linux 5.1" .
>
> I've now only focused on clock_settime(64) to make the discussion more
> concrete.
The following will be relevant for use of clock_gettime64, but is not
immediately relevant for clock_settime64:
clock_gettime64 will complicate things because the present clock_gettime
code uses the vDSO on some architectures. Is clock_gettime64 available in
the vDSO in 5.1 on all architectures where clock_gettime is? If it is,
with the same symbol version as used for existing vDSO symbols, or a
different symbol version? If not in the vDSO, are there any performance
implications from using a clock_gettime64 syscall in place of a
clock_gettime call to the vDSO?
(I think the code using the vDSO will automatically fall back to a
corresponding syscall if the vDSO symbol isn't there, but answers to those
questions will still be relevant for reviewing any patch for
clock_gettime64 and understanding exactly what code paths it will use.)
--
Joseph S. Myers
joseph@codesourcery.com