Messages in this thread | | | Date | Thu, 27 Feb 2020 09:09:30 -0600 | From | Dimitri Sivanich <> | Subject | Re: [PATCH] misc: Replace zero-length array with flexible-array member |
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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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