array bounds errors using GCC 11.2.0

[wwortel]

compiling misdnuser with gcc 11.2.0 two functions throw array subscript bound errors. Perhaps false positives, perhaps not:

1. >>>
   In file included from misc/mbuffer.c:21:
   misc/mbuffer.c: In function ‘alloc_mbuffer’:
   ../include/mISDN/mbuffer.h:161:14: error: array subscript ‘struct mbuffer[0]’ is partly outside array bounds of ‘struct mqueue[1]’ [-Werror=array-bounds]
   161 | next = prev->next;
   | ~~~~~~~^~~~~~~~~~~~
   misc/mbuffer.c:25:25: note: while referencing ‘free_queue_l2’
   25 | static struct mqueue free_queue_l2, free_queue_l3;
   <<<
   by changing in this function like this:
   prev = (struct mbuffer *)q->prev;
   next = (struct mbuffer *)q->next;
   the error disappears but not sure whether functionality is still correct. All the prev and next in both queue and buffer is rather confusing without an idea how this is supposed to function.

2. >>>
   bridge.c: In function ‘ph_control’:
   bridge.c:160:9: error: array subscript 2 is outside array bounds of ‘unsigned char[16]’ [-Werror=array-bounds]
   160 | *d++ = c2;
   | ^~~~
   bridge.c:150:23: note: while referencing ‘data’
   150 | unsigned char data[MISDN_HEADER_LEN+sizeof(int)+sizeof(int)];
   <<<
   by adding 8, like:
   unsigned char data[MISDN_HEADER_LEN+sizeof(int)+sizeof(int)+8];
   the error disappears but again not sure whether this is changing the intended behaviour.

[wwortel]

regarding misc/mbuffer.c have rewritten it after some study of the mbuffer and mqueue usage and the casting of the mqueue to mbuffer type. I think, but confirmation is needed, that following code does the same but does not evoke the compiler array bound protest.

static inline struct mbuffer *mdequeue(struct mqueue *q)
{
	struct mbuffer *next, *prev, *result;

        pthread_mutex_lock(&q->lock);
	prev = (struct mbuffer *)q;
	next = q->next; <=== q->next  points at the same as original code's prev->next after type cast 
	result = NULL;
	if (next != prev) {
		result = next;
		next = next->next;
		q->len--;
		next->prev = prev;
		q->next = next; <=== q->next still points at the same as original code's prev->next
		result->list = NULL;
	}
	pthread_mutex_unlock(&q->lock);
	return result;
}