[PATCH] xhci: Fix bcdUSB initialization

[PATCH] xhci: Fix bcdUSB initialization

[Abhishek Tamboli]

Initialize bcdUSB to 0 to prevent undefined behaviour
if accessed without being explicitly set.

Fix the following smatch error:
drivers/usb/host/xhci-hub.c:71 xhci_create_usb3x_bos_desc()
error: uninitialized symbol 'bcdUSB'

Signed-off-by: Abhishek Tamboli <abhishektamboli9@gmail.com>
---
 drivers/usb/host/xhci-hub.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/host/xhci-hub.c b/drivers/usb/host/xhci-hub.c
index 9693464c0520..5715a8bdda7f 100644
--- a/drivers/usb/host/xhci-hub.c
+++ b/drivers/usb/host/xhci-hub.c
@@ -39,7 +39,7 @@ static int xhci_create_usb3x_bos_desc(struct xhci_hcd *xhci, char *buf,
 	struct usb_ss_cap_descriptor	*ss_cap;
 	struct usb_ssp_cap_descriptor	*ssp_cap;
 	struct xhci_port_cap		*port_cap = NULL;
-	u16				bcdUSB;
+	u16				bcdUSB = 0;
 	u32				reg;
 	u32				min_rate = 0;
 	u8				min_ssid;
--
2.34.1

Re: [PATCH] xhci: Fix bcdUSB initialization

[Greg KH]

On Fri, Feb 28, 2025 at 01:04:00AM +0530, Abhishek Tamboli wrote:
> Initialize bcdUSB to 0 to prevent undefined behaviour
> if accessed without being explicitly set.

Is it actually accessed without being set?  If so, please explain it and
also how the compiler is somehow missing this already?

thanks,

greg k-h

Re: [PATCH] xhci: Fix bcdUSB initialization

[Abhishek Tamboli]

Hi Greg,
Thanks for the review.
> On Fri, Feb 28, 2025 at 01:04:00AM +0530, Abhishek Tamboli wrote:
> > Initialize bcdUSB to 0 to prevent undefined behaviour
> > if accessed without being explicitly set.
> 
> Is it actually accessed without being set?  If so, please explain it and
> also how the compiler is somehow missing this already?
I added bcdUSB = 0 based on a Smatch warning about potential uninitialized access. 
However, given that bcdUSB is always set in the first loop iteration, 
this might be a false positive.

Regards,
Abhishek

Re: [PATCH] xhci: Fix bcdUSB initialization

[Dan Carpenter]

On Thu, Feb 27, 2025 at 11:36:24AM -0800, Greg KH wrote:
> On Fri, Feb 28, 2025 at 01:04:00AM +0530, Abhishek Tamboli wrote:
> > Initialize bcdUSB to 0 to prevent undefined behaviour
> > if accessed without being explicitly set.
> 
> Is it actually accessed without being set?  If so, please explain it and
> also how the compiler is somehow missing this already?
> 

This is a Smatch warning, not a compiler warning.

regards,
dan carpenter

Re: [PATCH] xhci: Fix bcdUSB initialization

[Dan Carpenter]

On Fri, Feb 28, 2025 at 01:04:00AM +0530, Abhishek Tamboli wrote:
> Initialize bcdUSB to 0 to prevent undefined behaviour
> if accessed without being explicitly set.
> 
> Fix the following smatch error:
> drivers/usb/host/xhci-hub.c:71 xhci_create_usb3x_bos_desc()
> error: uninitialized symbol 'bcdUSB'
> 
> Signed-off-by: Abhishek Tamboli <abhishektamboli9@gmail.com>
> ---

The concern here would be that xhci->num_port_caps is <= 0.  That's
probably not possible so it's likely a false positive.

regards,
dan carpenter