[PATCH v2 2/3] Y2038: nptl: Provide futex_abstimed_wait64 supporting 64 bit time
Lukasz Majewski
lukma@denx.de
Wed Sep 30 13:39:53 GMT 2020
Hi Adhemerval,
> On 30/09/2020 09:47, Lukasz Majewski wrote:
> > Hi Adhemerval,
> >
> >> On 19/09/2020 10:07, Lukasz Majewski wrote:
> >>> This is the helper function, which uses struct __timespec64
> >>> to provide 64 bit absolute time to futex syscalls.
> >>>
> >>> The aim of this function is to move convoluted pre-processor
> >>> macro code from sysdeps/nptl/lowlevellock-futex.h to C
> >>> function in futex-internal.c
> >>>
> >>> The futex_abstimed_wait64 function has been put into a separate
> >>> file on the purpose - to avoid issues apparent on the m68k
> >>> architecture related to small number of available registers (there
> >>> is not enough registers to put all necessary arguments in them if
> >>> the above function would be added to futex-internal.h with
> >>> __always_inline attribute).
> >>>
> >>> Additional precautions for m68k port have been taken - the
> >>> futex-internal.c file will be compiled with -fno-inline flag.
> >>
> >> LGTM with a nit regarding style and a clarification about
> >> '-fno-inline'.
> >
> > Please find the explanation below.
> >
> >>
> >>>
> >>> ---
> >>> Changes for v2:
> >>> - Handle the case when *abstime pointer is NULL
> >>> ---
> >>> sysdeps/nptl/futex-internal.c | 70
> >>> +++++++++++++++++++++++++++ sysdeps/nptl/futex-internal.h
> >>> | 6 +++ sysdeps/unix/sysv/linux/m68k/Makefile | 2 +
> >>> 3 files changed, 78 insertions(+)
> >>>
> >>> diff --git a/sysdeps/nptl/futex-internal.c
> >>> b/sysdeps/nptl/futex-internal.c index 3366aac162..3211b4c94f
> >>> 100644 --- a/sysdeps/nptl/futex-internal.c
> >>> +++ b/sysdeps/nptl/futex-internal.c
> >>> @@ -45,6 +45,29 @@ __futex_abstimed_wait_cancelable32 (unsigned
> >>> int* futex_word, abstime != NULL ? &ts32 : NULL,
> >>> NULL /* Unused. */,
> >>> FUTEX_BITSET_MATCH_ANY); }
> >>> +
> >>> +static int
> >>> +__futex_abstimed_wait32 (unsigned int* futex_word,
> >>> + unsigned int expected, clockid_t
> >>> clockid,
> >>> + const struct __timespec64* abstime,
> >>> + int private)
> >>> +{
> >>> + struct timespec ts32;
> >>> +
> >>> + if (abstime != NULL && ! in_time_t_range (abstime->tv_sec))
> >>> + return -EOVERFLOW;
> >>> +
> >>> + unsigned int clockbit = (clockid == CLOCK_REALTIME) ?
> >>> + FUTEX_CLOCK_REALTIME : 0;
> >>> + int op = __lll_private_flag (FUTEX_WAIT_BITSET | clockbit,
> >>> private); +
> >>> + if (abstime != NULL)
> >>> + ts32 = valid_timespec64_to_timespec (*abstime);
> >>> +
> >>> + return INTERNAL_SYSCALL_CALL (futex, futex_word, op, expected,
> >>> + abstime != NULL ? &ts32 : NULL,
> >>> + NULL /* Unused. */,
> >>> FUTEX_BITSET_MATCH_ANY); +}
> >>> #endif
> >>>
> >>> int
> >>
> >> Ok.
> >>
> >>> @@ -97,3 +120,50 @@ __futex_abstimed_wait_cancelable64 (unsigned
> >>> int* futex_word, futex_fatal_error ();
> >>> }
> >>> }
> >>> +
> >>> +int
> >>> +__futex_abstimed_wait64 (unsigned int* futex_word, unsigned int
> >>> expected,
> >>> + clockid_t clockid,
> >>> + const struct __timespec64* abstime, int
> >>> private) +{
> >>> + unsigned int clockbit;
> >>> + int err;
> >>> +
> >>> + /* Work around the fact that the kernel rejects negative
> >>> timeout values
> >>> + despite them being valid. */
> >>> + if (__glibc_unlikely ((abstime != NULL) && (abstime->tv_sec <
> >>> 0)))
> >>> + return ETIMEDOUT;
> >>> +
> >>> + if (! lll_futex_supported_clockid(clockid))
> >>> + return EINVAL;
> >>
> >> Space before parentheses.
> >
> > Ok. Fixed.
> >
> >>
> >>> +
> >>> + clockbit = (clockid == CLOCK_REALTIME) ? FUTEX_CLOCK_REALTIME :
> >>> 0;
> >>> + int op = __lll_private_flag (FUTEX_WAIT_BITSET | clockbit,
> >>> private); +
> >>> + err = INTERNAL_SYSCALL_CALL (futex_time64, futex_word, op,
> >>> expected,
> >>> + abstime, NULL /* Unused. */,
> >>> + FUTEX_BITSET_MATCH_ANY);
> >>> +#ifndef __ASSUME_TIME64_SYSCALLS
> >>> + if (err == -ENOSYS)
> >>> + err = __futex_abstimed_wait32 (futex_word, expected,
> >>> + clockid, abstime, private);
> >>> +#endif
> >>> + switch (err)
> >>> + {
> >>> + case 0:
> >>> + case -EAGAIN:
> >>> + case -EINTR:
> >>> + case -ETIMEDOUT:
> >>> + return -err;
> >>> +
> >>> + case -EFAULT: /* Must have been caused by a glibc or
> >>> application bug. */
> >>> + case -EINVAL: /* Either due to wrong alignment, unsupported
> >>> + clockid or due to the timeout not being
> >>> + normalized. Must have been caused by a glibc
> >>> or
> >>> + application bug. */
> >>> + case -ENOSYS: /* Must have been caused by a glibc bug. */
> >>> + /* No other errors are documented at this time. */
> >>> + default:
> >>> + futex_fatal_error ();
> >>> + }
> >>> +}
> >>
> >> Ok.
> >>
> >>> diff --git a/sysdeps/nptl/futex-internal.h
> >>> b/sysdeps/nptl/futex-internal.h index 7f3910ad98..1ba0d61938
> >>> 100644 --- a/sysdeps/nptl/futex-internal.h
> >>> +++ b/sysdeps/nptl/futex-internal.h
> >>> @@ -529,4 +529,10 @@ __futex_abstimed_wait_cancelable64 (unsigned
> >>> int* futex_word, const struct __timespec64* abstime,
> >>> int private)
> >>> attribute_hidden;
> >>> +int
> >>> +__futex_abstimed_wait64 (unsigned int* futex_word, unsigned int
> >>> expected,
> >>> + clockid_t clockid,
> >>> + const struct __timespec64* abstime,
> >>> + int private) attribute_hidden;
> >>> +
> >>> #endif /* futex-internal.h */
> >>
> >> Ok.
> >>
> >>> diff --git a/sysdeps/unix/sysv/linux/m68k/Makefile
> >>> b/sysdeps/unix/sysv/linux/m68k/Makefile index
> >>> be40fae68a..65164c5752 100644 ---
> >>> a/sysdeps/unix/sysv/linux/m68k/Makefile +++
> >>> b/sysdeps/unix/sysv/linux/m68k/Makefile @@ -21,3 +21,5 @@
> >>> sysdep-dl-routines += dl-static sysdep-others += lddlibc4
> >>> install-bin += lddlibc4
> >>> endif
> >>> +
> >>> +CFLAGS-futex-internal.c += -fno-inline
> >>>
> >>
> >> Do we still need it?
> >
> > Unfortunately, yes. The m68k architecture has the issue with
> > properly compiling this code (in futex-internal.c) as it has very
> > limited number of registers (8 x 32 bit IIRC).
> >
> > I did some investigation and it looks like static inline
> > in_time_t_range() function affects the compiler capabilities to
> > generate correct code.
> >
> > It can be easily inlined on any architecture but m68k.
> >
> > As m68k has issues with this code compilation - it is IMHO better to
> > disable inlining (-fno-inline) on this particular port.
> >
> > As a result we would have slower execution only on relevant
> > functions, but 64 bit time support would be provided.
>
> I recall this was need on first patch for the cancellable 64-bit
> futex_abstimed_wait where it embedded the 32-bit fallback in the
> __futex_abstimed_wait_cancelable64. And my suggestion to move it to
> an external function seems to avoid the extra compiler flag.
>
> This patchset uses the same strategy and I checked both patches
> and it seems that -fno-inline is not required to build m68k.
As fair as I can tell (at the time I tested it) - it was necessary to
have -fno-inline when this patch was applied on top of the one which is
now in the -master branch (in futex-internal.c).
I will double check it now with:
glibc/glibc-many-build --keep failed glibcs
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
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