Commit 27565c9e authored by Gustavo A. R. Silva's avatar Gustavo A. R. Silva Committed by Rafael J. Wysocki

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 76497732 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: default avatarGustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 98d54f81
......@@ -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);
......
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