| Message ID | 20200227190721.GA19083@embeddedor (mailing list archive) |
|---|---|
| State | Mainlined, archived |
| Headers | show |
| Series | powercap: idle_inject: Replace zero-length array with flexible-array member | expand |
On Thursday, February 27, 2020 8:07:21 PM CET 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] > > Lastly, fix the following checkpatch warning: > WARNING: Prefer 'unsigned long' over 'unsigned long int' as the int is unnecessary > + unsigned long int cpumask[]; > > 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/powercap/idle_inject.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/powercap/idle_inject.c b/drivers/powercap/idle_inject.c > index cd1270614cc6..e9bbd3c42eef 100644 > --- a/drivers/powercap/idle_inject.c > +++ b/drivers/powercap/idle_inject.c > @@ -67,7 +67,7 @@ struct idle_inject_device { > struct hrtimer timer; > unsigned int idle_duration_us; > unsigned int run_duration_us; > - unsigned long int cpumask[0]; > + unsigned long cpumask[]; > }; > > static DEFINE_PER_CPU(struct idle_inject_thread, idle_inject_thread); > Applied as 5.7 material, thanks!
diff --git a/drivers/powercap/idle_inject.c b/drivers/powercap/idle_inject.c index cd1270614cc6..e9bbd3c42eef 100644 --- a/drivers/powercap/idle_inject.c +++ b/drivers/powercap/idle_inject.c @@ -67,7 +67,7 @@ struct idle_inject_device { struct hrtimer timer; unsigned int idle_duration_us; unsigned int run_duration_us; - unsigned long int cpumask[0]; + unsigned long cpumask[]; }; static DEFINE_PER_CPU(struct idle_inject_thread, idle_inject_thread);
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] Lastly, fix the following checkpatch warning: WARNING: Prefer 'unsigned long' over 'unsigned long int' as the int is unnecessary + unsigned long int cpumask[]; 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/powercap/idle_inject.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)