ref: d744632a356e28dd453c084dc9a2172559103b31
dir: /posix-power/tas.c/
#include "u.h"
#include "libc.h"
/*
* first argument (l) is in r3 at entry.
* r3 contains return value upon return.
*/
int
tas(int *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;
}