Re: switching ARC to 64-bit time_t (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>
Cc: Florian Weimer <fweimer@redhat.com>,
	Helmut Grohne <helmutg@debian.org>,
	GNU C Library <libc-alpha@sourceware.org>,
	Viresh Kumar <vireshk@kernel.org>,
	Vineet Gupta <Vineet.Gupta1@synopsys.com>,
	Palmer Dabbelt <palmerdabbelt@google.com>,
	Zong Li <zongbox@gmail.com>,
	debian-arm@lists.debian.org,
	Alistair Francis <alistair.francis@wdc.com>,
	Adhemerval Zanella <adhemerval.zanella@linaro.org>,
	"Maciej W. Rozycki" <macro@wdc.com>,
	Alistair Francis <alistair23@gmail.com>,
	arcml <linux-snps-arc@lists.infradead.org>,
	Joseph Myers <joseph@codesourcery.com>
Subject: Re: switching ARC to 64-bit time_t (Re: [RFC v6 07/23] RISC-V: Use 64-bit time_t and off_t for RV32 and RV64)
Date: Thu, 20 Feb 2020 17:31:32 +0100	[thread overview]
Message-ID: <20200220173132.05f2fad5@jawa> (raw)
In-Reply-To: <CAK8P3a2vvuqzLQqrYkyyYBFATDjCpBuR2Zquu-xB2BWmc5GQWA@mail.gmail.com>

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Hi Arnd,

> On Thu, Feb 20, 2020 at 4:42 PM Lukasz Majewski <lukma@denx.de> wrote:
> > > On Thu, Feb 20, 2020 at 2:15 PM Lukasz Majewski <lukma@denx.de>
> > > wrote:  
> 
> >
> > I do see two approaches here:
> >
> > 1. In glibc:
> >
> > When -D_TIME_BITS=64 is set - redirections are enabled for syscall
> > wrappers; for example __clock_settime64 is used instead of
> > __clock_settime (e.g. sysdeps/unix/sysv/linux/clock_settime).
> >
> > The latter is guarded by #ifdef __TIMESIZE != 64 so we could change
> > mechanically that __clock_settime returns -1 and sets errno to
> > -ENOTSUPP  
> 
> What I meant is to remove the __clock_settime function from the
> library entirely to cause a link failure. I suppose replacing most
> "__TIMESIZE != 64" with '0' would do that. Ideally I'd just set

I think that replacing "__TIMESIZE != 64" with '0' would be the
simplest option.

> __TIMESIZE to 64, but doing that would make the ABI incompatible
> with mainline glibc.
> 
> > 2. In kernel - return -ENOTSUPP when clock_settime syscall instead
> > of clock_settime64 is invoked.  
> 
> We already have that with CONFIG_COMPAT_32BIT_TIME, but
> at the moment I think that still breaks glibc's usage of __NR_futex,
> and a compile-time error is always better than a runtime error,
> as it's easier to catch them reliably

Ok.

> 
>       Arnd

Best regards,

Lukasz Majewski

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