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    ARC: syscall for userspace cmpxchg assist · 91e040a7
    Vineet Gupta 提交于
    Older ARC700 cores (ARC750 specifically) lack instructions to implement
    atomic r-w-w. This is problematic for userspace libraries such as NPTL
    which need atomic primitives. So enable them by providing kernel assist.
    This is costly but really the only sane soluton (othern than tight
    spinning using the otherwise availiable atomic exchange EX instruciton).
    
    Good thing is there are only a few of these cores running Linux out in
    the wild.
    
    This only works on UP systems.
    Reviewed-by: NColin Ian King <colin.king@canonical.com>
    Signed-off-by: NVineet Gupta <vgupta@synopsys.com>
    91e040a7
unistd.h 1.4 KB