+#define xchg(ptr, v) \
+ ((__typeof__(*(ptr)))__xchg((unsigned long)(v), (ptr), sizeof(*(ptr))))
+
+struct __xchg_dummy {
+ unsigned long a[100];
+};
+#define __xg(x) ((struct __xchg_dummy *)(x))
+
+/*
+ * Note: no "lock" prefix even on SMP: xchg always implies lock anyway
+ * Note 2: xchg has side effect, so that attribute volatile is necessary,
+ * but generally the primitive is invalid, *ptr is output argument. --ANK
+ */
+static inline unsigned long __xchg(unsigned long x, volatile void *ptr,
+ int size)
+{
+ switch (size) {
+ case 1:
+ asm volatile("xchgb %b0,%1"
+ : "=q" (x)
+ : "m" (*__xg(ptr)), "0" (x)
+ : "memory");
+ break;
+ case 2:
+ asm volatile("xchgw %w0,%1"
+ : "=r" (x)
+ : "m" (*__xg(ptr)), "0" (x)
+ : "memory");
+ break;
+ case 4:
+ asm volatile("xchgl %k0,%1"
+ : "=r" (x)
+ : "m" (*__xg(ptr)), "0" (x)
+ : "memory");
+ break;
+ case 8:
+ asm volatile("xchgq %0,%1"
+ : "=r" (x)
+ : "m" (*__xg(ptr)), "0" (x)
+ : "memory");
+ break;
+ }
+ return x;
+}
+