Replacing the atomic_sub Instruction

This function is used to perform atomic subtraction on integer variables.

• Code on x86:

  static inline void atomic_sub(int i, atomic_t *v) 
  { 
  asm volatile(LOCK_PREFIX "subl %1,%0" : "+m" (v->counter) : "ir" (i)); 
  }

• Alternatives for Kunpeng processors:

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

  __sync_sub_and_fetch(&_value.counter,1);

  Method 2: Use the inline assembly.

  void atomic_sub (int i) 
  { 
  unsigned int tmp; 
  int result; 
  __asm__ volatile(" prfm pstl1strm, %2\n" 
  "1: ldaxr %w0, %2\n" // Load data to the register.
  " sub %w0, %w0, %w3\n" // Perform a subtraction operation.
  " stlxr %w1, %w0, %2\n" // Write data after the subtraction operation to the memory and check whether the data is successfully written.
  "cbnz %w1, 1b" // If the preceding operation fails, perform the subtraction operation again.
  : "=&r"(result), "=&r"(tmp), "+Q"(_value.counter) 
  : "Ir"(i)) 
  }