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SubjectRe: [PATCH] misc: Replace zero-length array with flexible-array member
On Wed, Feb 26, 2020 at 04:22:40PM -0600, Gustavo A. R. Silva wrote:
> 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>

> ---
> drivers/misc/mei/hw.h | 2 +-
> drivers/misc/mei/mei_dev.h | 2 +-
> drivers/misc/sgi-gru/grulib.h | 2 +-
> drivers/misc/sgi-gru/grutables.h | 2 +-
> 4 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/misc/mei/hw.h b/drivers/misc/mei/hw.h
> index 8231b6941adf..b1a8d5ec88b3 100644
> --- 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 76f8ff5ff974..3a29db07211d 100644
> --- 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 e77d1b1f9d05..85c103923632 100644
> --- 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 a7e44b2eb413..5ce8f3081e96 100644
> --- 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) */
> };
>
> --
> 2.25.0
>

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