Subversion Repositories planix.SVN

#include "u.h"
#include "libc.h"

/*
 * first argument (l) is in r3 at entry.
 * r3 contains return value upon return.
 */
int
tas(long *x)
{
        int     v;
        /*
         * this __asm__ works with gcc 2.95.2 (mac os x 10.1).
         * this assembly language destroys r0 (0), some other register (v),
         * r4 (x) and r5 (temp).
         */
        __asm__("\n     sync\n"
        "       li      r0,0\n"
        "       mr      r4,%1           /* &l->val */\n"
        "       lis     r5,0xdead       /* assemble constant 0xdeaddead */\n"
        "       ori     r5,r5,0xdead    /* \" */\n"
        "tas1:\n"
        "       dcbf    r4,r0   /* cache flush; \"fix for 603x bug\" */\n"
        "       lwarx   %0,r4,r0        /* v = l->val with reservation */\n"
        "       cmp     cr0,0,%0,r0     /* v == 0 */\n"
        "       bne     tas0\n"
        "       stwcx.  r5,r4,r0   /* if (l->val same) l->val = 0xdeaddead */\n"
        "       bne     tas1\n"
        "tas0:\n"
        "       sync\n"
        "       isync\n"
        : "=r" (v)
        : "r"  (x)
        : "cc", "memory", "r0", "r4", "r5"
        );
        switch(v) {
        case 0:          return 0;
        case 0xdeaddead: return 1;
        default:        print("tas: corrupted 0x%lux\n", v);
        }
        return 0;
}