| Message ID | 20200303220503.GA2663@embeddedor (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [next] drm/i915: Replace zero-length array with flexible-array member | expand |
On Tue, 03 Mar 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> Reviewed-by: Jani Nikula <jani.nikula@intel.com> > --- > 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 {
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 {
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/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(-)