| Message ID | 20200225140347.GA22864@embeddedor (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [next] drm: Replace zero-length array with flexible-array member | expand |
Quoting Gustavo A. R. Silva (2020-02-25 14:03:47) > 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: I remember when gcc didn't support []. For the record, it appears support for flexible arrays landed in gcc-3.0. So passes the minimum compiler spec. That would be useful to mention for old farts with forgetful memories. -Chris
On 2/25/20 08:17, Jani Nikula wrote: > On Tue, 25 Feb 2020, "Gustavo A. R. Silva" <gustavo@embeddedor.com> 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> >> --- >> 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 +- > > Please split out the i915 changes to a separate patch. > Sure thing. I can do that. >> 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 ++-- > > Not sure it's worth touching uapi headers. They're full of both [0] and > []. Again, please at least split it to a separate patch to be decided > separately. > Yeah, it's worth it; the purpose of these patches is to replace [0] with [] across the whole tree. Thanks -- Gustavo
Hi Gustavo Am 03.03.20 um 19:20 schrieb Gustavo A. R. Silva: > > > On 2/25/20 08:17, Jani Nikula wrote: >> On Tue, 25 Feb 2020, "Gustavo A. R. Silva" <gustavo@embeddedor.com> 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> >>> --- >>> 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 +- >> >> Please split out the i915 changes to a separate patch. >> > > Sure thing. I can do that. I think each driver deserves it's own patch. Makes backporting easier. Best regards Thomas > >>> 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 ++-- >> >> Not sure it's worth touching uapi headers. They're full of both [0] and >> []. Again, please at least split it to a separate patch to be decided >> separately. >> > > Yeah, it's worth it; the purpose of these patches is to replace [0] with [] across > the whole tree. > > Thanks > -- > Gustavo >
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 { \
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(-)