powercap: idle_inject: Replace zero-length array with flexible-array member
PATCH 1/1 powercap: idle_inject: 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]
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")
--- drivers/powercap/idle_inject.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
drivers/powercap/idle_inject.c +1 -1
@@ -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);
Signature · 1 line
2.25.0
Rafael J. Wysocki
AppliedQuoted 43 lines · CET Gustavo A. R. Silva
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(quoted diff) +1
-0+ 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] commit76497732932f("cxgb3/l2t: Fix undefined behaviour")Signed-off-by Gustavo A. R. Silva <[email protected]>--- drivers/powercap/idle_inject.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)drivers/powercap/idle_inject.c +0
-0
drivers/powercap/idle_inject.c struct idle_inject_device { · line 73
Quoted 8 lines
drivers/powercap/idle_inject.c +1
-1@@ -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!