Re: [RFC v6 04/23] linux: Use 32-bit time_t for itimerval

[Alistair Francis <alistair23 at gmail dot com>]

On Tue, Jan 14, 2020 at 8:58 PM Lukasz Majewski <lukma@denx.de> wrote:
>
> Hi Alistair,
>
> > The Linux kernel expects itimerval to use a 32-bit time_t, even on
> > archs with a 64-bit time_t (like RV32). To address this let's convert
> > itimerval to/from 32-bit and 64-bit to ensure the kernel always gets
> > a 32-bit time_t.
> >
> > This means that all 32-bit architectures with a 64-bit time_t will be
> > able to use this generic implementation.
> >
> > This code is bsaed on similar code in alpha, but adjusted to pass the
> > 32-bit time_t to the kernel.
> >
> > We can't directly call the __getitimer/__setitimer functions as they
> > expect a struct itimerval but we need to pass in a struct itimerval32.
> > ---
> >  .../linux/generic/wordsize-32/getitimer.c     | 42 +++++++++++++++
> >  .../linux/generic/wordsize-32/setitimer.c     | 53
> > +++++++++++++++++++ .../linux/generic/wordsize-32/tv32-compat.h   |
> > 35 ++++++++++++ 3 files changed, 130 insertions(+)
> >  create mode 100644
> > sysdeps/unix/sysv/linux/generic/wordsize-32/getitimer.c create mode
> > 100644 sysdeps/unix/sysv/linux/generic/wordsize-32/setitimer.c create
> > mode 100644 sysdeps/unix/sysv/linux/generic/wordsize-32/tv32-compat.h
> >
> > diff --git a/sysdeps/unix/sysv/linux/generic/wordsize-32/getitimer.c
> > b/sysdeps/unix/sysv/linux/generic/wordsize-32/getitimer.c new file
> > mode 100644 index 0000000000..b279acbc2e
> > --- /dev/null
> > +++ b/sysdeps/unix/sysv/linux/generic/wordsize-32/getitimer.c
> > @@ -0,0 +1,42 @@
> > +/* getitimer -- Get the state of an interval timer.  Linux/RV32/tv32
> > version.
> > +   Copyright (C) 2020 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be
> > useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <http://www.gnu.org/licenses/>.  */
> > +
> > +#include <sys/time.h>
> > +#include <sysdep.h>
> > +#include <tv32-compat.h>
> > +
> > +int
> > +__getitimer (__itimer_which_t which, struct itimerval *curr_value)
> > +{
> > +#if __TIMESIZE == 64
> > +  struct itimerval32 curr_value_32;
> > +  if (INLINE_SYSCALL_CALL (getitimer, which, &curr_value_32) == -1)
> > +    return -1;
> > +
> > +  /* Write all fields of 'curr_value' regardless of overflow.  */
> > +  curr_value->it_interval
> > +    = valid_timeval_long_to_timeval64 (curr_value_32.it_interval);
> > +  curr_value->it_value
> > +    = valid_timeval_long_to_timeval64 (curr_value_32.it_value);
> > +  return 0;
> > +#else
> > +  return INLINE_SYSCALL_CALL (getitimer, which, curr_value);
> > +#endif
> > +}
> > +
> > +weak_alias (__getitimer, getitimer)
> > diff --git a/sysdeps/unix/sysv/linux/generic/wordsize-32/setitimer.c
> > b/sysdeps/unix/sysv/linux/generic/wordsize-32/setitimer.c new file
> > mode 100644 index 0000000000..807683ccae
> > --- /dev/null
> > +++ b/sysdeps/unix/sysv/linux/generic/wordsize-32/setitimer.c
> > @@ -0,0 +1,53 @@
> > +/* getitimer -- Get the state of an interval timer.  Linux/RV32/tv32
> > version.
>
> Please update the header info. I suppose you refer to setitimer here.

Fixed!

>
> > +   Copyright (C) 2020 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be
> > useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <http://www.gnu.org/licenses/>.  */
> > +
> > +#include <sys/time.h>
> > +#include <sysdep.h>
> > +#include <tv32-compat.h>
> > +
> > +int
> > +__setitimer (__itimer_which_t which,
> > +             const struct itimerval *restrict new_value,
> > +             struct itimerval *restrict old_value)
> > +{
> > +#if __TIMESIZE == 64
>
> I think that Y2038 safe systems with __WORDSIZE == 32 && __TIMESIZE ==
> 32 (for now?) also could reuse this work.
>
> To allow it this syscall wrapper shall be converted (written) in the
> same way as e.g:
>
> ./sysdeps/unix/sysv/linux/clock_settime.c
>
> (the same issue is with getitimer).
>
> Then only redirection when __USE_TIME_BITS64 is set are needed to use
> __setitimer64/__getitimer64 on Y2038 safe systems.

I'm not sure what you mean here.

There is no setitimer64/getitimer64 syscall so we need to make sure we
pass a 32-bit time_t here. If __TIMESIZE == 32 then we don't need any
changes and can just directly make the syscall (as we do in this
patch). The conversion is only required if __TIMESIZE == 64 as we need
to convert to/from a 32-bit time_t.

Alistair

>
> > +  struct itimerval32 new_value_32;
> > +  new_value_32.it_interval
> > +    = valid_timeval64_to_timeval_long (new_value->it_interval);
> > +  new_value_32.it_value
> > +    = valid_timeval64_to_timeval_long (new_value->it_value);
> > +
> > +  if (old_value == NULL)
> > +    return INLINE_SYSCALL_CALL (setitimer, which, &new_value_32,
> > NULL); +
> > +  struct itimerval32 old_value_32;
> > +  if (INLINE_SYSCALL_CALL (setitimer, which, &new_value_32,
> > &old_value_32) == -1)
> > +    return -1;
> > +
> > +  /* Write all fields of 'old_value' regardless of overflow.  */
> > +  old_value->it_interval
> > +     = valid_timeval_long_to_timeval64 (old_value_32.it_interval);
> > +  old_value->it_value
> > +     = valid_timeval_long_to_timeval64 (old_value_32.it_value);
> > +  return 0;
> > +#else
> > +  return INLINE_SYSCALL_CALL (setitimer, which, new_value,
> > old_value); +#endif
> > +}
> > +
> > +weak_alias (__setitimer, setitimer)
> > diff --git
> > a/sysdeps/unix/sysv/linux/generic/wordsize-32/tv32-compat.h
> > b/sysdeps/unix/sysv/linux/generic/wordsize-32/tv32-compat.h new file
> > mode 100644 index 0000000000..aa960a6632 --- /dev/null
> > +++ b/sysdeps/unix/sysv/linux/generic/wordsize-32/tv32-compat.h
> > @@ -0,0 +1,35 @@
> > +/* Compatibility definitions for `struct timeval' with 32-bit time_t.
> > +   Copyright (C) 2020 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be
> > useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <http://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef _TV32_COMPAT_H
> > +#define _TV32_COMPAT_H 1
> > +
> > +#include <features.h>
> > +
> > +#include <bits/types.h>
> > +#include <bits/types/time_t.h>
> > +#include <bits/types/struct_timeval.h>
> > +
> > +/* Structures containing 'struct timeval' with 32-bit time_t.  */
> > +struct itimerval32
> > +{
> > +  struct __timeval_long it_interval;
> > +  struct __timeval_long it_value;
> > +};
> > +
> > +#endif /* tv32-compat.h */
>
>
> Best regards,
>
> Lukasz Majewski
>
> --
>
> DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
> Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email: lukma@denx.de