Commit f490e8ae authored Feb 26, 2020 by Gustavo A. R. Silva Committed by Greg Kroah-Hartman Mar 18, 2020

misc: 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 76497732 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: Dimitri Sivanich <sivanich@hpe.com>
Link: https://lore.kernel.org/r/20200226222240.GA14474@embeddedor


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent d108b132

drivers/misc/mei/hw.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -216,7 +216,7 @@ struct mei_msg_hdr {

		struct mei_bus_message {
		u8 hbm_cmd;
		u8 data[0];
		u8 data[];
		} __packed;

		/**

drivers/misc/mei/mei_dev.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -533,7 +533,7 @@ struct mei_device {
		#endif /* CONFIG_DEBUG_FS */

		const struct mei_hw_ops *ops;
		char hw[0] __aligned(sizeof(void *));
		char hw[] __aligned(sizeof(void *));
		};

		static inline unsigned long mei_secs_to_jiffies(unsigned long sec)

drivers/misc/sgi-gru/grulib.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -136,7 +136,7 @@ struct gru_dump_context_header {
		pid_t pid;
		unsigned long vaddr;
		int cch_locked;
		unsigned long data[0];
		unsigned long data[];
		};

		/*

drivers/misc/sgi-gru/grutables.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -372,7 +372,7 @@ struct gru_thread_state {
		int ts_data_valid; /* Indicates if ts_gdata has
		valid data */
		struct gru_gseg_statistics ustats; /* User statistics */
		unsigned long ts_gdata[0]; /* save area for GRU data (CB,
		unsigned long ts_gdata[]; /* save area for GRU data (CB,
		DS, CBE) */
		};

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