On Thu, May 07, 2020 at 02:06:15PM -0500, 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]
>
> sizeof(flexible-array-member) triggers a warning because flexible array
> members have incomplete type[1]. There are some instances of code in
> which the sizeof operator is being incorrectly/erroneously applied to
> zero-length arrays and the result is zero. Such instances may be hiding
> some bugs. So, this work (flexible-array member conversions) will also
> help to get completely rid of those sorts of issues.
>
> 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...@kernel.org>
> ---
> arch/x86/events/intel/bts.c | 2 +-
> arch/x86/events/intel/uncore.h | 2 +-
> include/linux/perf_event.h | 4 ++--
> kernel/events/callchain.c | 2 +-
> kernel/events/internal.h | 2 +-
> tools/perf/bench/sched-messaging.c | 2 +-
> tools/perf/builtin-inject.c | 2 +-
> tools/perf/builtin-script.c | 2 +-
> tools/perf/builtin-timechart.c | 2 +-
> tools/perf/util/annotate.h | 4 ++--
> tools/perf/util/branch.h | 2 +-
> tools/perf/util/cputopo.h | 2 +-
> tools/perf/util/dso.h | 4 ++--
> tools/perf/util/event.h | 2 +-
> tools/perf/util/jitdump.c | 2 +-
> tools/perf/util/jitdump.h | 6 +++---
> tools/perf/util/ordered-events.h | 2 +-
> tools/perf/util/pstack.c | 2 +-
> tools/perf/util/symbol.h | 2 +-
> tools/perf/util/unwind-libunwind-local.c | 2 +-
> 20 files changed, 25 insertions(+), 25 deletions(-)
>
Arnaldo, do you want this, or should I take it?
