[PATCH][next] drm: Replace zero-length array with flexible-array member

From: Gustavo A. R. Silva
Date: Tue Feb 25 2020 - 10:28:26 EST

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>
---
drivers/gpu/drm/etnaviv/etnaviv_gem.h | 2 +-
drivers/gpu/drm/gma500/intel_bios.h | 2 +-
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 +-
drivers/gpu/drm/msm/msm_gem.h | 2 +-
drivers/gpu/drm/qxl/qxl_cmd.c | 2 +-
drivers/gpu/drm/vboxvideo/vboxvideo.h | 2 +-
drivers/gpu/drm/vc4/vc4_drv.h | 2 +-
drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c | 2 +-
drivers/gpu/drm/vmwgfx/vmwgfx_surface.c | 2 +-
include/drm/bridge/mhl.h | 4 ++--
include/drm/drm_displayid.h | 2 +-
include/uapi/drm/i915_drm.h | 4 ++--
14 files changed, 17 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.h b/drivers/gpu/drm/etnaviv/etnaviv_gem.h
index 6b68fe16041b..98e60df882b6 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_gem.h
+++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.h
@@ -105,7 +105,7 @@ struct etnaviv_gem_submit {
unsigned int nr_pmrs;
struct etnaviv_perfmon_request *pmrs;
unsigned int nr_bos;
- struct etnaviv_gem_submit_bo bos[0];
+ struct etnaviv_gem_submit_bo bos[];
/* No new members here, the previous one is variable-length! */
};

diff --git a/drivers/gpu/drm/gma500/intel_bios.h b/drivers/gpu/drm/gma500/intel_bios.h
index a1f9ce9465a5..0e6facf21e33 100644
--- a/drivers/gpu/drm/gma500/intel_bios.h
+++ b/drivers/gpu/drm/gma500/intel_bios.h
@@ -227,7 +227,7 @@ struct bdb_general_definitions {
* number = (block_size - sizeof(bdb_general_definitions))/
* sizeof(child_device_config);
*/
- struct child_device_config devices[0];
+ struct child_device_config devices[];
};

struct bdb_lvds_options {
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 47561dc29304..5cec79152f17 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 {
diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h
index 9e0953c2b7ce..37aa556c5f92 100644
--- a/drivers/gpu/drm/msm/msm_gem.h
+++ b/drivers/gpu/drm/msm/msm_gem.h
@@ -157,7 +157,7 @@ struct msm_gem_submit {
uint32_t handle;
};
uint64_t iova;
- } bos[0];
+ } bos[];
};

#endif /* __MSM_GEM_H__ */
diff --git a/drivers/gpu/drm/qxl/qxl_cmd.c b/drivers/gpu/drm/qxl/qxl_cmd.c
index ef09dc6bc635..d1086b2a6892 100644
--- a/drivers/gpu/drm/qxl/qxl_cmd.c
+++ b/drivers/gpu/drm/qxl/qxl_cmd.c
@@ -36,7 +36,7 @@ static int qxl_reap_surface_id(struct qxl_device *qdev, int max_to_reap);

struct ring {
struct qxl_ring_header header;
- uint8_t elements[0];
+ uint8_t elements[];
};

struct qxl_ring {
diff --git a/drivers/gpu/drm/vboxvideo/vboxvideo.h b/drivers/gpu/drm/vboxvideo/vboxvideo.h
index 0592004f71aa..a5de40fe1a76 100644
--- a/drivers/gpu/drm/vboxvideo/vboxvideo.h
+++ b/drivers/gpu/drm/vboxvideo/vboxvideo.h
@@ -138,7 +138,7 @@ struct vbva_buffer {

u32 data_len;
/* variable size for the rest of the vbva_buffer area in VRAM. */
- u8 data[0];
+ u8 data[];
} __packed;

#define VBVA_MAX_RECORD_SIZE (128 * 1024 * 1024)
diff --git a/drivers/gpu/drm/vc4/vc4_drv.h b/drivers/gpu/drm/vc4/vc4_drv.h
index 6627b20c99e9..282293e6f751 100644
--- a/drivers/gpu/drm/vc4/vc4_drv.h
+++ b/drivers/gpu/drm/vc4/vc4_drv.h
@@ -65,7 +65,7 @@ struct vc4_perfmon {
* Note that counter values can't be reset, but you can fake a reset by
* destroying the perfmon and creating a new one.
*/
- u64 counters[0];
+ u64 counters[];
};

struct vc4_dev {
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c b/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
index f07aa857587c..60cfbfadd3f2 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
@@ -69,7 +69,7 @@ struct vmw_bo_dirty {
unsigned int ref_count;
unsigned long bitmap_size;
size_t size;
- unsigned long bitmap[0];
+ unsigned long bitmap[];
};

/**
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
index 3ce630aa4fde..ec893cd17b50 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
@@ -79,7 +79,7 @@ struct vmw_surface_dirty {
struct svga3dsurface_cache cache;
size_t size;
u32 num_subres;
- SVGA3dBox boxes[0];
+ SVGA3dBox boxes[];
};

static void vmw_user_surface_free(struct vmw_resource *res);
diff --git a/include/drm/bridge/mhl.h b/include/drm/bridge/mhl.h
index 1cc77bf38324..d96626a0e3fa 100644
--- a/include/drm/bridge/mhl.h
+++ b/include/drm/bridge/mhl.h
@@ -327,13 +327,13 @@ struct mhl_burst_bits_per_pixel_fmt {
struct {
u8 stream_id;
u8 pixel_format;
- } __packed desc[0];
+ } __packed desc[];
} __packed;

struct mhl_burst_emsc_support {
struct mhl3_burst_header hdr;
u8 num_entries;
- __be16 burst_id[0];
+ __be16 burst_id[];
} __packed;

struct mhl_burst_audio_descr {
diff --git a/include/drm/drm_displayid.h b/include/drm/drm_displayid.h
index 9d3b745c3107..94b4390bf990 100644
--- a/include/drm/drm_displayid.h
+++ b/include/drm/drm_displayid.h
@@ -89,7 +89,7 @@ struct displayid_detailed_timings_1 {

struct displayid_detailed_timing_block {
struct displayid_block base;
- struct displayid_detailed_timings_1 timings[0];
+ struct displayid_detailed_timings_1 timings[];
};

#define for_each_displayid_db(displayid, block, idx, length) \
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 829c0a48577f..33de5dfadaf5 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -1708,7 +1708,7 @@ struct i915_context_engines_load_balance {

__u64 mbz64; /* reserved for future use; must be zero */

- struct i915_engine_class_instance engines[0];
+ struct i915_engine_class_instance engines[];
} __attribute__((packed));

#define I915_DEFINE_CONTEXT_ENGINES_LOAD_BALANCE(name__, N__) struct { \
@@ -1746,7 +1746,7 @@ struct i915_context_engines_bond {
__u64 flags; /* all undefined flags must be zero */
__u64 mbz64[4]; /* reserved for future use; must be zero */

- struct i915_engine_class_instance engines[0];
+ struct i915_engine_class_instance engines[];
} __attribute__((packed));

#define I915_DEFINE_CONTEXT_ENGINES_BOND(name__, N__) struct { \
--
2.25.0