Re: [PATCH] usb: gadget: net2280: Distribute switch variables for initialization

From: Alan Stern
Date: Thu Feb 20 2020 - 10:34:38 EST


On Wed, 19 Feb 2020, Kees Cook wrote:

> Variables declared in a switch statement before any case statements
> cannot be automatically initialized with compiler instrumentation (as
> they are not part of any execution flow). With GCC's proposed automatic
> stack variable initialization feature, this triggers a warning (and they
> don't get initialized). Clang's automatic stack variable initialization
> (via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also
> doesn't initialize such variables[1]. Note that these warnings (or silent
> skipping) happen before the dead-store elimination optimization phase,
> so even when the automatic initializations are later elided in favor of
> direct initializations, the warnings remain.
>
> To avoid these problems, move such variables into the "case" where
> they're used or lift them up into the main function body.
>
> drivers/usb/gadget/udc/net2280.c: In function âhandle_stat0_irqs_superspeedâ:
> drivers/usb/gadget/udc/net2280.c:2871:22: warning: statement will never be executed [-Wswitch-unreachable]
> 2871 | struct net2280_ep *e;
> | ^
>
> [1] https://bugs.llvm.org/show_bug.cgi?id=44916
>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
> drivers/usb/gadget/udc/net2280.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/usb/gadget/udc/net2280.c b/drivers/usb/gadget/udc/net2280.c
> index 1fd1b9186e46..cc5869363298 100644
> --- a/drivers/usb/gadget/udc/net2280.c
> +++ b/drivers/usb/gadget/udc/net2280.c
> @@ -2861,6 +2861,7 @@ static void ep_clear_seqnum(struct net2280_ep *ep)
> static void handle_stat0_irqs_superspeed(struct net2280 *dev,
> struct net2280_ep *ep, struct usb_ctrlrequest r)
> {
> + struct net2280_ep *e;
> int tmp = 0;
>
> #define w_value le16_to_cpu(r.wValue)
> @@ -2868,14 +2869,13 @@ static void handle_stat0_irqs_superspeed(struct net2280 *dev,
> #define w_length le16_to_cpu(r.wLength)
>
> switch (r.bRequest) {
> - struct net2280_ep *e;
> - u16 status;
> -
> case USB_REQ_SET_CONFIGURATION:
> dev->addressed_state = !w_value;
> goto usb3_delegate;
>
> - case USB_REQ_GET_STATUS:
> + case USB_REQ_GET_STATUS: {
> + u16 status;
> +
> switch (r.bRequestType) {
> case (USB_DIR_IN | USB_TYPE_STANDARD | USB_RECIP_DEVICE):
> status = dev->wakeup_enable ? 0x02 : 0x00;
> @@ -2905,7 +2905,7 @@ static void handle_stat0_irqs_superspeed(struct net2280 *dev,
> goto usb3_delegate;
> }
> break;
> -
> + }

This is an unusual use of nested blocks (i.e., a block immediately
following a "case" label, and it throws the indentation off -- there
will now be two nested closing braces at the same indentation level:
this one and the one preceding do_stall3:.

Just define status at the function level, along with e, and don't
worry about it.

Alan Stern

> case USB_REQ_CLEAR_FEATURE:
> switch (r.bRequestType) {
> case (USB_DIR_OUT | USB_TYPE_STANDARD | USB_RECIP_DEVICE):
>
>
>