41 lines
1.2 KiB
Plaintext
41 lines
1.2 KiB
Plaintext
/*
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* tas() for HPPA.
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*
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* To generate tas.s using this template:
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* 1. cc +O2 -S -c tas.c
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* 2. edit tas.s:
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* - replace the LDW with LDCWX
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* 3. install as src/backend/port/tas/hpux_hppa.s.
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*
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* For details about the LDCWX instruction, see the "Precision
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* Architecture and Instruction Reference Manual" (09740-90014 of June
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* 1987), p. 5-38.
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*/
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int
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tas(lock)
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int *lock; /* LDCWX is a word instruction */
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{
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/*
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* LDCWX requires that we align the "semaphore" to a 16-byte
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* boundary. The actual datum is a single word (4 bytes).
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*/
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lock = ((uintptr_t) lock + 15) & ~15;
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/*
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* The LDCWX instruction atomically clears the target word and
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* returns the previous value. Hence, if the instruction returns
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* 0, someone else has already acquired the lock before we tested
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* it (i.e., we have failed).
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*
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* Notice that this means that we actually clear the word to set
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* the lock and set the word to clear the lock. This is the
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* opposite behavior from the SPARC LDSTUB instruction. For some
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* reason everything that H-P does is rather baroque...
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*/
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if (*lock) { /* this generates the LDW */
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return(0); /* success */
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}
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return(1); /* failure */
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}
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