Replacing the atomic_dec_and_test Instruction

The function is used to perform subtraction operations on an integer and check whether the return value is 0.

• Code on x86:

  static inline int atomic_dec_and_test(atomic_t *v) 
  { 
  unsigned char c; 
  asm volatile(LOCK_PREFIX "decl %0; sete %1" : "+m" (v->counter), "=qm" (c) : : "memory"); 
  return c != 0; 
  }

• Alternatives for Kunpeng processors:

  Method 1: Use the built-in atomic operations provided by the GCC.

  __sync_sub_and_fetch(&_value.counter,i)

  Method 2: Use the inline assembly (transfer 1 to i and check the result).

  static inline int atomic_sub_return(int i, atomic_t *v) 
  { 
  unsigned long tmp; 
  int result; 
  prefetchw(&v->counter); 
  __asm__ volatile ("\n\t" 
  "@ atomic_sub\n\t" 
  "1: ldrex %0, [%3]\n\t" 
  " sub %0, %0, %4\n\t" 
  " strex %1, %0, [%3]\n\t" 
  " teq %1, #0\n\t" 
  " bne 1b" 
  : "=&r" (result), "=&r" (tmp), "+Qo" (v->counter) 
  : "r" (&v->counter), "Ir" (i) 
  : "cc"); 
  return result; 
  }