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 76497732932f ("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>

diff --git a/drivers/misc/mei/hw.h b/drivers/misc/mei/hw.h
index 8231b69..b1a8d5e 100644 (file)
--- a/drivers/misc/mei/hw.h
+++ b/drivers/misc/mei/hw.h
@@ -216,7 +216,7 @@ struct mei_msg_hdr {
 
 struct mei_bus_message {
        u8 hbm_cmd;
-       u8 data[0];
+       u8 data[];
 } __packed;
 
 /**

diff --git a/drivers/misc/mei/mei_dev.h b/drivers/misc/mei/mei_dev.h
index 76f8ff5..3a29db0 100644 (file)
--- a/drivers/misc/mei/mei_dev.h
+++ b/drivers/misc/mei/mei_dev.h
@@ -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)

diff --git a/drivers/misc/sgi-gru/grulib.h b/drivers/misc/sgi-gru/grulib.h
index e77d1b1..85c1039 100644 (file)
--- a/drivers/misc/sgi-gru/grulib.h
+++ b/drivers/misc/sgi-gru/grulib.h
@@ -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[];
 };
 
 /*

diff --git a/drivers/misc/sgi-gru/grutables.h b/drivers/misc/sgi-gru/grutables.h
index a7e44b2..5ce8f30 100644 (file)
--- a/drivers/misc/sgi-gru/grutables.h
+++ b/drivers/misc/sgi-gru/grutables.h
@@ -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) */
 };