linux-kernel - [PATCH] - silence UBSAN complaint in ehci-hcd.

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Date:	Thu, 19 May 2016 17:19:00 -0400
From:	Valdis Kletnieks <Valdis.Kletnieks@...edu>
To:	Alan Stern <stern@...land.harvard.edu>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>
cc:	Oliver Neukum <oneukum@...e.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: [PATCH] - silence UBSAN complaint in ehci-hcd.

UBSAN throws a complaint:

[    2.418579] UBSAN: Undefined behaviour in drivers/usb/host/ehci-hub.c:877:47
[    2.418582] index -1 is out of range for type 'u32 [1]'

though it's only on the hostpc[] part, not  on the port_status[] on the
previous line which has the same exact index calculation.  The root cause is
that the first declaration is port_status[0], which uses a GCC extension and
UBSAN is smart enough to realize the programmer is doing something
intentionally odd.

However, the problematic declaration is hostpc[1], which doesn't have
the "I know what I'm doing" semantics of [0].  Change the declaration to match.

Signed-Off-By: Valdis Kletnieks <valdis.kletnieks@...edu>

--- a/include/linux/usb/ehci_def.h	2015-01-06 01:04:24.342436706 -0500
+++ b/include/linux/usb/ehci_def.h	2016-05-19 13:57:20.869304540 -0400
@@ -180,11 +180,11 @@ struct ehci_regs {
  * PORTSCx
  */
 	/* HOSTPC: offset 0x84 */
-	u32		hostpc[1];	/* HOSTPC extension */
+	u32		hostpc[0];	/* HOSTPC extension */
 #define HOSTPC_PHCD	(1<<22)		/* Phy clock disable */
 #define HOSTPC_PSPD	(3<<25)		/* Port speed detection */

-	u32		reserved5[16];
+	u32		reserved5[17];

 	/* USBMODE_EX: offset 0xc8 */
 	u32		usbmode_ex;	/* USB Device mode extension */