Re: [HACKERS] Re: [PATCHES] patches for 6.2.1p6

David Gould wrote:

> Seriously, if you want to, please create a function to emulate the following:
>
> /*
>  * tas(lock)
>  *
>  * Access to platform specific test_and_set functionality. Given pointer to
>  * lock attempts to acquire the lock atomically.
>  *
>  * Returns 0 for success, nonzero for failure.
>  */
> typedef slock_t unsigned char;        /* or whatever works on the platform */
>
> int tas(slock_t *lock)
> {
>     slock_t    tmp;
>
>     /* atomic, interlocked */
>     tmp = *lock;
>     *lock = -1;             /* any nonzero will do here */
>
>     return (tmp != 0);
> }
>
> Given this, I can fold the VAX right into the grand scheme, just like a
> normal computer (;-)).

Hmpf!  The true worth of a computer is a function of its weight!  :-)

Sorry this took a while, but anyway, this should do it for the VAX (in
fact, it's more or less the version of the code that I figured I'd use
until Bruce asked me to bum it down maximally for performance, only
now with the return values from tas() swapped).  I include the macros
that would fit the current (6.3) locking scheme:

typedef unsigned char slock_t;

int tas(slock_t *lock) {
    register ret;

asm("    movl $1, r0
    bbssi $0,(%1),1f
    clrl r0
1:    movl r0,%0"
    : "=r"(ret)    /* return value, in register */
    : "r"(lock)    /* argument, 'lock pointer', in register */
    : "r0");    /* inline code uses this register */

    return ret;
}

#define    S_LOCK(addr)        do { while (tas(addr)) ; } while (0)
#define    S_UNLOCK(addr)        (*(addr) = 0)
#define    S_INIT_LOCK(addr)    (*(addr) = 0)

-tih
--
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