Re: [PATCH][next] drm: Replace zero-length array with flexible-array member
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" 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
>>> ---
>>> 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
>
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer
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Re: [PATCH][next] drm: Replace zero-length array with flexible-array member
On 2/25/20 08:17, Jani Nikula wrote:
> On Tue, 25 Feb 2020, "Gustavo A. R. Silva" 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
>> ---
>> 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
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Re: [PATCH][next] drm: Replace zero-length array with flexible-array member
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 ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
[PATCH][next] drm: Replace zero-length array with flexible-array member
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
---
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];
+ }
Re: [PATCH][next] drm: Replace zero-length array with flexible-array member
On Tue, 25 Feb 2020, "Gustavo A. R. Silva" 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
> ---
> 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.
> 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.
BR,
Jani.
--
Jani Nikula, Intel Open Source Graphics Center
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