linux-kernel - [PATCH 08/15] usb: ehci: avoid gcc-10 zero-length-bounds warning

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Date:   Thu, 30 Apr 2020 23:30:50 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Alan Stern <stern@...land.harvard.edu>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        linux-usb@...r.kernel.org
Subject: [PATCH 08/15] usb: ehci: avoid gcc-10 zero-length-bounds warning

Building ehci drivers with gcc-10 results in a number of warnings like
when an zero-length array is accessed:

drivers/usb/host/ehci-hub.c: In function 'ehci_bus_suspend':
drivers/usb/host/ehci-hub.c:320:30: error: array subscript 14 is outside the bounds of an interior zero-length array 'u32[0]' {aka 'unsigned int[0]'} [-Werror=zero-length-bounds]
  320 |    u32 __iomem *hostpc_reg = &ehci->regs->hostpc[port];
      |                              ^~~~~~~~~~~~~~~~~~~~~~~~~
In file included from drivers/usb/host/ehci.h:273,
                 from drivers/usb/host/ehci-hcd.c:96:
include/linux/usb/ehci_def.h:186:7: note: while referencing 'hostpc'
  186 |  u32  hostpc[0]; /* HOSTPC extension */
      |       ^~~~~~
In file included from drivers/usb/host/ehci-hcd.c:305:
drivers/usb/host/ehci-hub.c: In function 'ehci_hub_control':
drivers/usb/host/ehci-hub.c:892:15: error: array subscript 256 is outside the bounds of an interior zero-length array 'u32[0]' {aka 'unsigned int[0]'} [-Werror=zero-length-bounds]
  892 |  hostpc_reg = &ehci->regs->hostpc[temp];
      |               ^~~~~~~~~~~~~~~~~~~~~~~~~
In file included from drivers/usb/host/ehci.h:273,
                 from drivers/usb/host/ehci-hcd.c:96:
include/linux/usb/ehci_def.h:186:7: note: while referencing 'hostpc'
  186 |  u32  hostpc[0]; /* HOSTPC extension */
      |       ^~~~~~

All these fields are colocated with reserved fields that I guess
refer to the correct field length.

Change the two struct definition to use an unnamed union to define
both of these fields at the same location as the corresponding
reserved fields.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 include/linux/usb/ehci_def.h | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/include/linux/usb/ehci_def.h b/include/linux/usb/ehci_def.h
index 78e006355557..8777d8e56ef2 100644
--- a/include/linux/usb/ehci_def.h
+++ b/include/linux/usb/ehci_def.h
@@ -127,7 +127,8 @@ struct ehci_regs {
 #define FLAG_CF		(1<<0)		/* true: we'll support "high speed" */
 
 	/* PORTSC: offset 0x44 */
-	u32		port_status[0];	/* up to N_PORTS */
+	union {
+		u32		port_status[9];	/* up to N_PORTS */
 /* EHCI 1.1 addendum */
 #define PORTSC_SUSPEND_STS_ACK 0
 #define PORTSC_SUSPEND_STS_NYET 1
@@ -165,7 +166,8 @@ struct ehci_regs {
 #define PORT_CONNECT	(1<<0)		/* device connected */
 #define PORT_RWC_BITS   (PORT_CSC | PORT_PEC | PORT_OCC)
 
-	u32		reserved3[9];
+		u32		reserved3[9];
+	};
 
 	/* USBMODE: offset 0x68 */
 	u32		usbmode;	/* USB Device mode */
@@ -181,11 +183,13 @@ struct ehci_regs {
  * PORTSCx
  */
 	/* HOSTPC: offset 0x84 */
-	u32		hostpc[0];	/* HOSTPC extension */
+	union {
+		u32		hostpc[17];	/* HOSTPC extension */
 #define HOSTPC_PHCD	(1<<22)		/* Phy clock disable */
 #define HOSTPC_PSPD	(3<<25)		/* Port speed detection */
 
-	u32		reserved5[17];
+		u32		reserved5[17];
+	};
 
 	/* USBMODE_EX: offset 0xc8 */
 	u32		usbmode_ex;	/* USB Device mode extension */
-- 
2.26.0