text: // SPDX-License-Identifier: GPL-2.0-only
  /* Copyright (c) 2017 Facebook
   */
  #include <stddef.h>
  #include <string.h>
  #include <linux/bpf.h>
  #include <linux/pkt_cls.h>
  #include <bpf/bpf_helpers.h>
  
  #if  __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
  #define TEST_FIELD(TYPE, FIELD, MASK)					\
  	{								\
  		TYPE tmp = *(volatile TYPE *)&skb->FIELD;		\
  		if (tmp != ((*(volatile __u32 *)&skb->FIELD) & MASK))	\
  			return TC_ACT_SHOT;				\
  	}
  #else
  #define TEST_FIELD_OFFSET(a, b)	((sizeof(a) - sizeof(b)) / sizeof(b))
  #define TEST_FIELD(TYPE, FIELD, MASK)					\
  	{								\
  		TYPE tmp = *((volatile TYPE *)&skb->FIELD +		\
  			      TEST_FIELD_OFFSET(skb->FIELD, TYPE));	\
  		if (tmp != ((*(volatile __u32 *)&skb->FIELD) & MASK))	\
  			return TC_ACT_SHOT;				\
  	}
  #endif
  
  SEC("tc")
  int test_pkt_md_access(struct __sk_buff *skb)
  {
  	TEST_FIELD(__u8,  len, 0xFF);
  	TEST_FIELD(__u16, len, 0xFFFF);
  	TEST_FIELD(__u32, len, 0xFFFFFFFF);
  	TEST_FIELD(__u16, protocol, 0xFFFF);
  	TEST_FIELD(__u32, protocol, 0xFFFFFFFF);
  	TEST_FIELD(__u8,  hash, 0xFF);
  	TEST_FIELD(__u16, hash, 0xFFFF);
  	TEST_FIELD(__u32, hash, 0xFFFFFFFF);
  
  	return TC_ACT_OK;
  }
  