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

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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 7649773293 ("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>
This commit is contained in:
Gustavo A. R. Silva 2020-02-26 16:22:40 -06:00 committed by Greg Kroah-Hartman
parent d108b132ea
commit f490e8aea3
4 changed files with 4 additions and 4 deletions
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2
drivers/misc/mei/hw.h
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@ -216,7 +216,7 @@ struct mei_msg_hdr {
struct mei_bus_message { struct mei_bus_message {
u8 hbm_cmd; u8 hbm_cmd;
u8 data[0]; u8 data[];
} __packed; } __packed;
/** /**

2
drivers/misc/mei/mei_dev.h
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@ -533,7 +533,7 @@ struct mei_device {
#endif /* CONFIG_DEBUG_FS */ #endif /* CONFIG_DEBUG_FS */
const struct mei_hw_ops *ops; 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) static inline unsigned long mei_secs_to_jiffies(unsigned long sec)

2
drivers/misc/sgi-gru/grulib.h
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@ -136,7 +136,7 @@ struct gru_dump_context_header {
pid_t pid; pid_t pid;
unsigned long vaddr; unsigned long vaddr;
int cch_locked; int cch_locked;
unsigned long data[0]; unsigned long data[];
}; };
/* /*

2
drivers/misc/sgi-gru/grutables.h
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@ -372,7 +372,7 @@ struct gru_thread_state {
int ts_data_valid; /* Indicates if ts_gdata has int ts_data_valid; /* Indicates if ts_gdata has
valid data */ valid data */
struct gru_gseg_statistics ustats; /* User statistics */ 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) */ DS, CBE) */
}; };