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

* [PATCH][next] drm: Replace zero-length array with flexible-array member
@ 2020-02-25 14:03 ` Gustavo A. R. Silva
  0 siblings, 0 replies; 23+ messages in thread
From: Gustavo A. R. Silva @ 2020-02-25 14:03 UTC (permalink / raw)
  To: Lucas Stach, Russell King, Christian Gmeiner, David Airlie,
	Daniel Vetter, Patrik Jakobsson, Jani Nikula, Joonas Lahtinen,
	Rodrigo Vivi, Rob Clark, Sean Paul, Dave Airlie, Gerd Hoffmann,
	Hans de Goede, Eric Anholt, VMware Graphics, Thomas Hellstrom,
	Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann
  Cc: etnaviv, dri-devel, linux-kernel, intel-gfx, linux-arm-msm,
	freedreno, virtualization, spice-devel, Gustavo A. R. Silva

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>
---
 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


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