| Message ID | 20200305105137.GA18628@embeddedor (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [next] drm: etnaviv_gem.h: Replace zero-length array with flexible-array member | expand |
Hi Gustavo, I've adjusted the subject a bit to match the style of the other etnaviv driver commits and applied this to the etnaviv/next branch. Regards, Lucas On Do, 2020-03-05 at 04:51 -0600, 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 <gustavo@embeddedor.com> > --- > drivers/gpu/drm/etnaviv/etnaviv_gem.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > 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! */ > }; >
Hi Lucas, On 3/5/20 05:17, Lucas Stach wrote: > Hi Gustavo, > > I've adjusted the subject a bit to match the style of the other etnaviv > driver commits and applied this to the etnaviv/next branch. > Great. Thanks a lot for that. :) -- Gustavo > Regards, > Lucas > > On Do, 2020-03-05 at 04:51 -0600, 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 <gustavo@embeddedor.com> >> --- >> drivers/gpu/drm/etnaviv/etnaviv_gem.h | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> 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/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! */ };
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 +- 1 file changed, 1 insertion(+), 1 deletion(-)