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SubjectRe: [Compile Warning] 2.6.30-rc8 build
On Fri, 5 Jun 2009 19:01:38 +0100
Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:

> On Fri, 5 Jun 2009 11:43:03 -0500
> "Michael S. Zick" <lkml@morethan.org> wrote:
>
> > Group,
> >
> > To my reading of the function, I think gcc has a point:
> >
> > drivers/serial/8250.c: In function 'serial8250_shutdown':
> > drivers/serial/8250.c:1685: warning: 'i' may be used uninitialized in this function
> >
> > It does read as if the code might try to initialize
> > the 'lock' field of a null pointer.
> >
> > Suggestions?
>
> Newer gcc ? At least current gcc appears to correctly deduce the code is
> safe.

That's a gcc regression isn't it?


static void serial_unlink_irq_chain(struct uart_8250_port *up)
{
struct irq_info *i;
struct hlist_node *n;
struct hlist_head *h;
mutex_lock(&hash_mutex);

h = &irq_lists[up->port.irq % NR_IRQ_HASH];

hlist_for_each(n, h) {
i = hlist_entry(n, struct irq_info, node);
if (i->irq == up->port.irq)
break;
}
#define hlist_for_each(pos, head) \
for (pos = (head)->first; pos && ({ prefetch(pos->next); 1; }); \
pos = pos->next)
I don't think there's any way in which gcc can deduce that h->first is
non-zero on entry to that loop. Even if it inlines
serial_unlink_irq_chain() into serial8250_shutdown().


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