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/*
* @(#)alpha.gcc 10.1 (Sleepycat) 4/12/97
*
* The code appearing below is taken from Richard L. Sites, ed. "Alpha
* Architecture Reference Manual", Digital Press, 1992, page 5-7 and 5-8.
* There are 2 modifications:
*
* 1. The jump from blbs __r1,30f to !__r1, which is dictated by the way the
* TSL_SET macro is used. The code suggested in Sites includes the main loop
* of the spin lock, whereas in this code the rest the loop is specified in C.
* The generated code might be suboptimal if the compiler generates a forward
* branch for the usual case in which the mutex is uncontested.
*
* 2. At label 20, Sites suggests including code for testing for an excessive
* number of _processor_ lock conflicts. (The seq_c instruction stores its
* first argument provided that no other processor has written to a byte range
* including its memory-location argument.) Absent such checking the code
* below could conceivably stall silently on a multiprocessor alpha, depending
* on how often processor/processor conflicts occur in a particular byte range.
*
* Note that the mb ("memory-barrier") instruction in TSL_UNSET is critical to
* correct operation in a multiprocessor alpha (as is, of course, the mb in
* the TSL_SET macro). Without the mb, changes to shared memory that occurred
* inside the critical section (before the TSL_UNSET) might reach shared memory
* _after_ the change of tsl to 0, thereby permitting another processor to see
* an inconsistent view of the data protected by the mutex.
*
* For gcc/alpha, 0 is clear, 1 is set.
*/
#define TSL_SET(tsl) ({ \
register tsl_t *__l = (tsl); \
register tsl_t __r1, __r2; \
__asm__ volatile(" \n\
10: ldq_l %0,(%2) \n\
blbs %0,30f \n\
or %0,1,%1 \n\
stq_c %1,(%2) \n\
beq %1,20f \n\
mb \n\
br 30f \n\
20: br 10b \n\
30: " \
: "=&r" (__r1), "=&r" (__r2) \
: "r" (__l)); \
!__r1; \
})
#define TSL_UNSET(tsl) ({ \
register tsl_t *__l = (tsl); \
__asm__ volatile("mb; stq $31,(%0);" : : "r" (__l)); \
})
#define TSL_INIT(tsl) TSL_UNSET(tsl)
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