a

posix-power/tas.c

@@ -0,0 +1,42 @@
+#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;
+}