On Tue, 03 Mar 2020, "Gustavo A. R. Silva" <gustavo@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
Reviewed-by: Jani Nikula <jani.nikula@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/display/intel_vbt_defs.h | 4 ++--
> drivers/gpu/drm/i915/gt/intel_lrc.c | 2 +-
> drivers/gpu/drm/i915/i915_gpu_error.h | 2 +-
> 3 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_vbt_defs.h b/drivers/gpu/drm/i915/display/intel_vbt_defs.h
> index 05c7cbe32eb4..aef7fe932d1a 100644
> --- a/drivers/gpu/drm/i915/display/intel_vbt_defs.h
> +++ b/drivers/gpu/drm/i915/display/intel_vbt_defs.h
> @@ -462,7 +462,7 @@ struct bdb_general_definitions {
> * number = (block_size - sizeof(bdb_general_definitions))/
> * defs->child_dev_size;
> */
> - u8 devices[0];
> + u8 devices[];
> } __packed;
>
> /*
> @@ -839,7 +839,7 @@ struct bdb_mipi_config {
>
> struct bdb_mipi_sequence {
> u8 version;
> - u8 data[0]; /* up to 6 variable length blocks */
> + u8 data[]; /* up to 6 variable length blocks */
> } __packed;
>
> /*
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index b9b3f78f1324..a49ddda649b9 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -216,7 +216,7 @@ struct virtual_engine {
>
> /* And finally, which physical engines this virtual engine maps onto. */
> unsigned int num_siblings;
> - struct intel_engine_cs *siblings[0];
> + struct intel_engine_cs *siblings[];
> };
>
> static struct virtual_engine *to_virtual_engine(struct intel_engine_cs *engine)
> diff --git a/drivers/gpu/drm/i915/i915_gpu_error.h b/drivers/gpu/drm/i915/i915_gpu_error.h
> index 0d1f6c8ff355..5a6561f7a210 100644
> --- a/drivers/gpu/drm/i915/i915_gpu_error.h
> +++ b/drivers/gpu/drm/i915/i915_gpu_error.h
> @@ -42,7 +42,7 @@ struct i915_vma_coredump {
> int num_pages;
> int page_count;
> int unused;
> - u32 *pages[0];
> + u32 *pages[];
> };
>
> struct i915_request_coredump {
--
Jani Nikula, Intel Open Source Graphics Center
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