• Jim Wilson's avatar
    RISC-V: Add futex support. · b90edb33
    Jim Wilson authored
    Here is an attempt to add the missing futex support.  I started with the MIPS
    version of futex.h and modified it until I got it working.  I tested it on
    a HiFive Unleashed running Fedora Core 29 using the fc29 4.15 version of the
    kernel.  This was tested against the glibc testsuite, where it fixes 14 nptl
    related testsuite failures.  That unfortunately only tests the cmpxchg support,
    so I also used the testcase at the end of
    
        https://lwn.net/Articles/148830/
    
    which tests the atomic_op functionality, except that it doesn't verify that
    the operations are atomic, which they obviously are.  This testcase runs
    successfully with the patch and fails without it.
    
    I'm not a kernel expert, so there could be details I got wrong here.  I wasn't
    sure about the memory model support, so I used aqrl which seemed safest, and
    didn't add fences which seemed unnecessary.  I'm not sure about the copyright
    statements, I left in Ralf Baechle's line because I started with his code.
    Checkpatch reports some style problems, but it is the same style as the MIPS
    futex.h, and the uses of ENOSYS appear correct even though it complains about
    them.  I don't know if any of that matters.
    
    This patch was tested on qemu with the glibc nptl/tst-cond-except
    testcase, and the wake_op testcase from above.
    Signed-off-by: default avatarJim Wilson <jimw@sifive.com>
    Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
    Signed-off-by: default avatarPalmer Dabbelt <palmer@sifive.com>
    b90edb33
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