Re: [RFC v6 07/23] RISC-V: Use 64-bit time_t and off_t for RV32 and RV64

From: Lukasz Majewski <lukma@denx.de>
To: Arnd Bergmann <arnd@arndb.de>, Joseph Myers <joseph@codesourcery.com>
Cc: "fweimer@redhat.com" <fweimer@redhat.com>,
	"libc-alpha@sourceware.org" <libc-alpha@sourceware.org>,
	Andreas Schwab <schwab@suse.de>,
	Vineet Gupta <Vineet.Gupta1@synopsys.com>,
	"palmerdabbelt@google.com" <palmerdabbelt@google.com>,
	"zongbox@gmail.com" <zongbox@gmail.com>,
	Alistair Francis <alistair.francis@wdc.com>,
	"adhemerval.zanella@linaro.org" <adhemerval.zanella@linaro.org>,
	"macro@wdc.com" <macro@wdc.com>,
	Alistair Francis <alistair23@gmail.com>,
	arcml <linux-snps-arc@lists.infradead.org>
Subject: Re: [RFC v6 07/23] RISC-V: Use 64-bit time_t and off_t for RV32 and RV64
Date: Thu, 20 Feb 2020 11:28:43 +0100
Message-ID: <20200220112843.76b8eb27@jawa> (raw)
In-Reply-To: <CAK8P3a3MTQf_fnEWiGVxzexZzYNQ34h29aNxH_YApmsVzY6OsA@mail.gmail.com>

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Hi Arnd, Joseph,

> On Thu, Feb 20, 2020 at 1:46 AM Joseph Myers
> <joseph@codesourcery.com> wrote:
> >
> > On Thu, 20 Feb 2020, Vineet Gupta wrote:
> >  
> > > The first 4 will need more work as sym aliasing like
> > >       strong_alias (__xstat64, __xstat)
> > >
> > > will be needed in those ARM files (which in turn use i386).  
> >
> > The situation for Arm is fundamentally different from that for ARC.
> >
> > For ARC, you only need a single public stat structure (using 64-bit
> > times and offsets).
> >
> > For Arm, a third public stat structure will need to be added
> > alongside the existing two, initially used internally in
> > 64-bit-time stat functions that aren't exported from glibc,
> > eventually to be used with _TIME_BITS=64 with the 64-bit-time stat
> > interfaces exported once all the _TIME_BITS=64 interfaces are
> > ready.  
> 
> But surely that structure layout would be the same on ARM and ARC
> as well as all other 32-bit architectures with _TIME_BITS=64, right?
> 

For ARM32 stat case (current):

./io/stat.c -> __xstat -> ./sysdeps/unix/sysv/linux/xstat64.c
and then struct stat64 buf is filled by the kernel.

The generic idea (which requires converting
./sysdeps/unix/sysv/linux/xstat64.c) would be to use statx always in
glibc instead of stat* syscalls (as it is done in
sysdeps/unix/sysv/linux/generic/wordsize-32/xstat64.c)

To do that we do need in-glibc internal new type - namely struct
stat64_time64

which would have always:

__time64_t st_atime; (and st_mtime, st_ctime).

instead of 

__time_t st_atime;

and also introduce __cp_stat64_time64_statx along with __cp_stat64_statx

as struct statx inherently support 64 bit time via struct
statx_timestamp even on 32 bit archs.

IMHO using statx as widely as possible in glibc is the easiest way to
convert stat* and friends functions to support Y2038.

> What's wrong with having a single implementation for the most
> recent set of stat syscalls, with the older variants being only
> compiled for architectures that need them to support _TIME_BITS=32
> and/or _FILE_OFFSET_BITS=32?
> 
>         Arnd

Best regards,

Lukasz Majewski

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