Messages in this thread | | | Date | Mon, 2 Mar 2020 14:04:31 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH][next] perf: Replace zero-length array with flexible-array member |
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On Mon, Mar 02, 2020 at 06:48:32AM -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] >
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h > index 397cfd65b3fe..d71023c46058 100644 > --- a/include/uapi/linux/perf_event.h > +++ b/include/uapi/linux/perf_event.h > @@ -453,7 +453,7 @@ struct perf_event_query_bpf { > /* > * User provided buffer to store program ids > */ > - __u32 ids[0]; > + __u32 ids[]; > }; > > /*
Just to be absolutely sure; there is no ABI difference (or any actual difference in generated code), right?
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