xref: /src/tests/usr.bin/xlint/lint1/msg_247.c

/*	$NetBSD: msg_247.c,v 1.6 2021/03/26 16:19:43 rillig Exp $	*/
# 3 "msg_247.c"

// Test for message: pointer cast from '%s' to '%s' may be troublesome [247]

/* lint1-extra-flags: -c */

/* example taken from Xlib.h */
typedef struct {
	int id;
} *PDisplay;

struct Other {
	int id;
};

void
example(struct Other *arg)
{
	PDisplay display;

	/*
	 * XXX: The target type is reported as 'struct <unnamed>'.  In cases
	 *  like these, it would be helpful to print at least the type name
	 *  of the pointer.  This type name though is discarded immediately
	 *  when the parser reduces 'T_TYPENAME clrtyp' to 'clrtyp_typespec'.
	 *  After that, the target type of the cast is just an unnamed struct,
	 *  with no hint at all that there is a typedef for a pointer to the
	 *  struct.
	 */
	display = (PDisplay)arg;	/* expect: 247 */
}

/*
 * C code with a long history that has existed in pre-C90 times already often
 * uses 'pointer to char' where modern code would use 'pointer to void'.
 * Since 'char' is the most general underlying type, there is nothing wrong
 * with casting to it.  An example for this type of code is X11.
 *
 * Casting to 'pointer to char' may also be used by programmers who don't know
 * about endianness, but that's not something lint can do anything about.  The
 * code for these two use cases looks exactly the same, so lint errs on the
 * side of fewer false positive warnings here. (after fixing the FIXME below)
 */
char *
cast_to_char_pointer(struct Other *arg)
{
	return (char *)arg;		/* expect: 247 *//* FIXME */
}

/*
 * In traditional C there was 'unsigned char' as well, so the same reasoning
 * as for plain 'char' applies here.
 */
unsigned char *
cast_to_unsigned_char_pointer(struct Other *arg)
{
	return (unsigned char *)arg;	/* expect: 247 *//* FIXME */
}

/*
 * Traditional C does not have the type specifier 'signed', which means that
 * this type cannot be used by old code.  Therefore warn about this.  All code
 * that triggers this warning should do the intermediate cast via 'void
 * pointer'.
 */
signed char *
cast_to_signed_char_pointer(struct Other *arg)
{
	return (signed char *)arg;	/* expect: 247 */
}

char *
cast_to_void_pointer_then_to_char_pointer(struct Other *arg)
{
	return (char *)(void *)arg;
}