USB: Replace zero-length array with flexible-array member

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Link: https://lore.kernel.org/r/20200220132017.GA29262@embeddedor
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

6 files changed, 9 insertions, 9 deletions

diff --git a/drivers/usb/host/ehci-tegra.c b/drivers/usb/host/ehci-tegra.c
index d6433f206c17..10d51daa6a1b 100644
--- a/drivers/usb/host/ehci-tegra.c
+++ b/drivers/usb/host/ehci-tegra.c
@@ -282,7 +282,7 @@ done:
 struct dma_aligned_buffer {
 	void *kmalloc_ptr;
 	void *old_xfer_buffer;
-	u8 data[0];
+	u8 data[];
 };
 
 static void free_dma_aligned_buffer(struct urb *urb)
diff --git a/drivers/usb/host/ehci.h b/drivers/usb/host/ehci.h
index ac5e967907d1..229b3de319e6 100644
--- a/drivers/usb/host/ehci.h
+++ b/drivers/usb/host/ehci.h
@@ -255,7 +255,7 @@ struct ehci_hcd {			/* one per controller */
 	struct list_head	tt_list;
 
 	/* platform-specific data -- must come last */
-	unsigned long		priv[0] __aligned(sizeof(s64));
+	unsigned long		priv[] __aligned(sizeof(s64));
 };
 
 /* convert between an HCD pointer and the corresponding EHCI_HCD */
@@ -460,7 +460,7 @@ struct ehci_iso_sched {
 	struct list_head	td_list;
 	unsigned		span;
 	unsigned		first_packet;
-	struct ehci_iso_packet	packet[0];
+	struct ehci_iso_packet	packet[];
 };
 
 /*
diff --git a/drivers/usb/host/fotg210.h b/drivers/usb/host/fotg210.h
index 1b4db95e5c43..6cee40ec65b4 100644
--- a/drivers/usb/host/fotg210.h
+++ b/drivers/usb/host/fotg210.h
@@ -490,7 +490,7 @@ struct fotg210_iso_packet {
 struct fotg210_iso_sched {
 	struct list_head	td_list;
 	unsigned		span;
-	struct fotg210_iso_packet	packet[0];
+	struct fotg210_iso_packet	packet[];
 };
 
 /*
diff --git a/drivers/usb/host/ohci.h b/drivers/usb/host/ohci.h
index b015b00774b2..27c26ca10bfd 100644
--- a/drivers/usb/host/ohci.h
+++ b/drivers/usb/host/ohci.h
@@ -337,7 +337,7 @@ typedef struct urb_priv {
 	u16			length;		// # tds in this request
 	u16			td_cnt;		// tds already serviced
 	struct list_head	pending;
-	struct td		*td [0];	// all TDs in this request
+	struct td		*td[];		// all TDs in this request
 
 } urb_priv_t;
 
@@ -435,7 +435,7 @@ struct ohci_hcd {
 	struct dentry		*debug_dir;
 
 	/* platform-specific data -- must come last */
-	unsigned long           priv[0] __aligned(sizeof(s64));
+	unsigned long           priv[] __aligned(sizeof(s64));
 
 };
 
diff --git a/drivers/usb/host/xhci-mtk.h b/drivers/usb/host/xhci-mtk.h
index 5ac458b7d2e0..acd56517215a 100644
--- a/drivers/usb/host/xhci-mtk.h
+++ b/drivers/usb/host/xhci-mtk.h
@@ -95,7 +95,7 @@ struct mu3h_sch_ep_info {
 	u32 pkts;
 	u32 cs_count;
 	u32 burst_mode;
-	u32 bw_budget_table[0];
+	u32 bw_budget_table[];
 };
 
 #define MU3C_U3_PORT_MAX 4
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index 13d8838cd552..5f47b18609ee 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1642,7 +1642,7 @@ struct xhci_scratchpad {
 struct urb_priv {
 	int	num_tds;
 	int	num_tds_done;
-	struct	xhci_td	td[0];
+	struct	xhci_td	td[];
 };
 
 /*
@@ -1893,7 +1893,7 @@ struct xhci_hcd {
 
 	void			*dbc;
 	/* platform-specific data -- must come last */
-	unsigned long		priv[0] __aligned(sizeof(s64));
+	unsigned long		priv[] __aligned(sizeof(s64));
 };
 
 /* Platform specific overrides to generic XHCI hc_driver ops */