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msg_135.c revision 1.13 
      1 /*	$NetBSD: msg_135.c,v 1.13 2023/04/22 19:45:04 rillig Exp $	*/
      2 # 3 "msg_135.c"
      3 
      4 // Test for message: converting '%s' to '%s' increases alignment from %u to %u [135]
      5 
      6 /* lint1-extra-flags: -h -X 351 */
      7 
      8 void sink(const void *);
      9 
     10 unsigned
     11 read_uint(const unsigned short **pp)
     12 {
     13 	unsigned val;
     14 
     15 	/* expect+1: warning: converting 'pointer to const unsigned short' to 'pointer to const unsigned int' increases alignment from 2 to 4 [135] */
     16 	val = *(const unsigned *)(*pp);
     17 	pp += sizeof(unsigned);
     18 	return val;
     19 }
     20 
     21 /* expect+1: warning: struct 'incomplete' never defined [233] */
     22 struct incomplete;
     23 
     24 struct complete {
     25 	int member;
     26 };
     27 
     28 /*
     29  * These types of conversions are typically seen in OpenSSL, when converting
     30  * from the publicly visible, incomplete 'struct lhash_st' to a private
     31  * implementation type such as 'struct lhash_st_OPENSSL_STRING'.
     32  *
     33  * Before tree.c 1.277 from 2021-04-17, lint warned about this, even though
     34  * there was not enough evidence that there really was an alignment problem,
     35  * resulting in many false positives.
     36  *
     37  * See openssl/lhash.h.
     38  */
     39 void
     40 pointer_to_structs(struct incomplete *incomplete)
     41 {
     42 	struct complete *complete;
     43 
     44 	complete = (struct complete *)incomplete;
     45 	sink(complete);
     46 }
     47 
     48 /*
     49  * Before tree.c 1.316 from 2021-07-15, lint warned about pointer casts from
     50  * unsigned char or plain char to another type.  These casts often occur in
     51  * traditional code that does not use void pointers, even 30 years after C90
     52  * introduced 'void'.
     53  */
     54 void
     55 unsigned_char_to_unsigned_type(unsigned char *ucp)
     56 {
     57 	unsigned short *usp;
     58 
     59 	usp = (unsigned short *)ucp;
     60 	sink(usp);
     61 }
     62 
     63 /*
     64  * Before tree.c 1.316 from 2021-07-15, lint warned about pointer casts from
     65  * unsigned char or plain char to another type.  These casts often occur in
     66  * traditional code that does not use void pointers, even 30 years after C90
     67  * introduced 'void'.
     68  */
     69 void
     70 plain_char_to_unsigned_type(char *cp)
     71 {
     72 	unsigned short *usp;
     73 
     74 	usp = (unsigned short *)cp;
     75 	sink(usp);
     76 }
     77 
     78 /*
     79  * Converting a pointer with a low alignment requirement to a union that
     80  * includes other types with higher alignment requirements is safe.  While
     81  * accessing any other member of the union might trigger an alignment
     82  * violation, such an access would invoke undefined behavior anyway.
     83  *
     84  * A practical case for this pattern are tagged unions, in which the first
     85  * member of the struct determines how the remaining members are interpreted.
     86  * See sbin/newfs_udf, function udf_validate_tag_and_crc_sums for an example.
     87  */
     88 double
     89 cast_to_union(void)
     90 {
     91 	int align_4 = 0;
     92 	double align_8 = 0.0;
     93 	union both {
     94 		int p_align_4;
     95 		double p_align_8;
     96 	} *both;
     97 
     98 	/* TODO: don't warn here. */
     99 	/* expect+1: warning: converting 'pointer to int' to 'pointer to union both' increases alignment from 4 to 8 [135] */
    100 	both = (union both *)&align_4;
    101 	both = (union both *)&align_8;
    102 	return both->p_align_8;
    103 }
    104