[Bug libc/9894] Support for PI futexes wrongly marked as introduced in 2.6.18

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https://sourceware.org/bugzilla/show_bug.cgi?id=9894

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commit 47c5adebd2c864a098c3af66e61e1147dc3cf0b4
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Mon Mar 31 12:55:18 2014 +0000

    Correct robust mutex / PI futex kernel assumptions (bug 9894).

    This patch continues fixing __ASSUME_* issues in preparation for
    moving to a 2.6.32 minimum kernel version by addressing assumptions on
    robust mutex and PI futex support availability.  Those assumptions are
    bug 9894, but to be clear this patch does not address all the issues
    from that bug about wrong version assumptions, only those still
    applicable for --enable-kernel=2.6.32 or later (with the expectation
    that the move to that minimum kernel will obsolete the other parts of
    the bug).  The patch is independent of
    <https://sourceware.org/ml/libc-alpha/2014-03/msg00585.html>, my other
    pending-review patch preparing for the kernel version change; the two
    together complete all the changes I believe are needed in preparation
    regarding any macro in sysdeps/unix/sysv/linux/kernel-features.h that
    would be affected by such a change.  (I have not checked the
    correctness of macros whose conditions are unaffected by such a
    change, or macros only defined in other kernel-features.h files.)

    As discussed in that bug, robust mutexes and PI futexes need
    futex_atomic_cmpxchg_inatomic to be implemented, in addition to
    certain syscalls needed for robust mutexes (and
    architecture-independent kernel pieces for all the features in
    question).  That is, as I understand it, they need
    futex_atomic_cmpxchg_inatomic to *work* (not return an ENOSYS error).

    The issues identified in my analysis relate to ARM, M68K, MicroBlaze,
    MIPS and SPARC.

    On ARM, whether futex_atomic_cmpxchg_inatomic works depends on the
    kernel configuration.  As of 3.13, the condition for *not* working is
    CONFIG_CPU_USE_DOMAINS && CONFIG_SMP.  As of 2.6.32 it was simply
    CONFIG_SMP that meant the feature was not implemented.  I don't know
    if there are any circumstances in which we can say "we can assume a
    userspace glibc binary built with these options will never run on a
    kernel with the problematic configuration", but at least for now I'm
    just undefining the relevant __ASSUME_* macros for ARM.

    On M68K, two of the three macros are undefined for kernels before
    3.10, but as far as I can see __ASSUME_FUTEX_LOCK_PI is in the same
    group needing futex_atomic_cmpxchg_inatomic support and so should be
    undefined as well.

    On MicroBlaze the required support was added in 2.6.33.

    On MIPS, the support depends on cpu_has_llsc in the kernel - that is,
    actual hardware LL/SC support (GCC and glibc for MIPS GNU/Linux rely
    on the instructions being supported in some way, but it may be kernel
    emulation; futex_atomic_cmpxchg_inatomic doesn't work with that
    emulation).  The same condition as in GCC for indicating LL/SC support
    may not be available is used for undefining the macros in glibc,
    __mips == 1 || defined _MIPS_ARCH_R5900.  (Maybe we could in fact
    desupport MIPS processors without the hardware support in glibc.)

    On SPARC, 32-bit kernels don't support futex_atomic_cmpxchg_inatomic;
    __arch64__ || __sparc_v9__ is used as the condition for binaries that
    won't run on 32-bit kernels.

    This patch is not tested beyond the sanity check of an x86_64 build.

        [BZ #9894]
        * sysdeps/unix/sysv/linux/kernel-features.h
        [__sparc__ && !__arch64__ && !__sparc_v9__]
        (__ASSUME_SET_ROBUST_LIST): Do not define.
        [__sparc__ && !__arch64__ && !__sparc_v9__]
        (__ASSUME_FUTEX_LOCK_PI): Likewise.
        [__sparc__ && !__arch64__ && !__sparc_v9__] (__ASSUME_REQUEUE_PI):
        Likewise.
        * sysdeps/unix/sysv/linux/arm/kernel-features.h
        (__ASSUME_FUTEX_LOCK_PI): Undefine.
        (__ASSUME_REQUEUE_PI): Likewise.
        (__ASSUME_SET_ROBUST_LIST): Likewise.
        * sysdeps/unix/sysv/linux/m68k/kernel-features.h
        [__LINUX_KERNEL_VERSION < 0x030a00] (__ASSUME_FUTEX_LOCK_PI):
        Undefine.
        * sysdeps/unix/sysv/linux/microblaze/kernel-features.h
        [__LINUX_KERNEL_VERSION < 0x020621] (__ASSUME_FUTEX_LOCK_PI):
        Likewise.
        [__LINUX_KERNEL_VERSION < 0x020621] (__ASSUME_REQUEUE_PI):
        Likewise.
        [__LINUX_KERNEL_VERSION < 0x020621] (__ASSUME_SET_ROBUST_LIST):
        Likewise.
        * sysdeps/unix/sysv/linux/mips/kernel-features.h
        [__mips == 1 || _MIPS_ARCH_R5900] (__ASSUME_FUTEX_LOCK_PI):
        Undefine.
        [__mips == 1 || _MIPS_ARCH_R5900] (__ASSUME_REQUEUE_PI): Likewise.
        [__mips == 1 || _MIPS_ARCH_R5900] (__ASSUME_SET_ROBUST_LIST):
        Likewise.

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                                          |   29 ++++++++++++++++++++
 sysdeps/unix/sysv/linux/arm/kernel-features.h      |    7 +++++
 sysdeps/unix/sysv/linux/kernel-features.h          |   20 +++++++++----
 sysdeps/unix/sysv/linux/m68k/kernel-features.h     |    1 +
 .../unix/sysv/linux/microblaze/kernel-features.h   |    7 +++++
 sysdeps/unix/sysv/linux/mips/kernel-features.h     |    8 +++++
 6 files changed, 66 insertions(+), 6 deletions(-)

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