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    Subject[PATCH] get rid of ARCH_HAVE_XTIME_LOCK
    Date
    As suggested by Andrew, we can use __attribute__((weak)) to get rid of 
    ARCH_HAVE_XTIME_LOCK

    Please note I compiled, and boot tested on ia32 this patch, and it seems OK.
    I compiled on x86_64 and got same resulting vmlinux image.

    But I suspect some tools might have problems because vmlinux have its
    first 'weak data symbol' defined. AFAIK __attribute__((weak)) was only used
    on text symbols.

    # nm vmlinux | grep ' V '
    c03b01c0 V xtime_lock

    [PATCH] get rid of ARCH_HAVE_XTIME_LOCK

    ARCH_HAVE_XTIME_LOCK is used by x86_64 arch . This arch needs to place a read
    only copy of xtime_lock into vsyscall page. This read only copy is named
    __xtime_lock, and xtime_lock is defined in arch/x86_64/kernel/vmlinux.lds.S
    as an alias. So the declaration of xtime_lock in kernel/timer.c was guarded
    by ARCH_HAVE_XTIME_LOCK define, defined to true on x86_64.

    We can get same result with _attribute__((weak)) in the declaration. linker
    should do the job.

    Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
    --- linux-2.6.19/kernel/timer.c 2006-12-11 11:25:50.000000000 +0100
    +++ linux-2.6.19-ed/kernel/timer.c 2006-12-11 11:31:30.000000000 +0100
    @@ -1020,11 +1020,9 @@ static inline void calc_load(unsigned lo
    * This read-write spinlock protects us from races in SMP while
    * playing with xtime and avenrun.
    */
    -#ifndef ARCH_HAVE_XTIME_LOCK
    -__cacheline_aligned_in_smp DEFINE_SEQLOCK(xtime_lock);
    +__attribute__((weak)) __cacheline_aligned_in_smp DEFINE_SEQLOCK(xtime_lock);

    EXPORT_SYMBOL(xtime_lock);
    -#endif

    /*
    * This function runs timers and the timer-tq in bottom half context.
    --- linux-2.6.19/include/linux/time.h 2006-12-11 11:34:54.000000000 +0100
    +++ linux-2.6.19-ed/include/linux/time.h 2006-12-11 11:34:54.000000000 +0100
    @@ -90,7 +90,7 @@ static inline struct timespec timespec_s

    extern struct timespec xtime;
    extern struct timespec wall_to_monotonic;
    -extern seqlock_t xtime_lock;
    +extern seqlock_t xtime_lock __attribute__((weak));

    void timekeeping_init(void);

    --- linux-2.6.19/include/asm-x86_64/vsyscall.h 2006-12-11 11:34:54.000000000 +0100
    +++ linux-2.6.19-ed/include/asm-x86_64/vsyscall.h 2006-12-11 11:34:54.000000000 +0100
    @@ -55,11 +55,6 @@ extern struct vxtime_data vxtime;
    extern int vgetcpu_mode;
    extern struct timezone sys_tz;
    extern int sysctl_vsyscall;
    -extern seqlock_t xtime_lock;
    -
    -extern int sysctl_vsyscall;
    -
    -#define ARCH_HAVE_XTIME_LOCK 1

    #endif /* __KERNEL__ */
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      Last update: 2006-12-11 11:55    [W:0.032 / U:0.044 seconds]
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