From 6549a8c0c3d94500a9a1bb66fc237f7c01c41753 Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Fri, 15 May 2020 12:29:26 -0500 Subject: perf tools: Replace zero-length array with flexible-array 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 Cc: Adrian Hunter Cc: Alexander Shishkin Cc: Gustavo A. R. Silva Cc: Ian Rogers Cc: Jiri Olsa Cc: Mark Rutland Cc: Namhyung Kim Cc: Peter Zijlstra Link: http://lore.kernel.org/lkml/20200515172926.GA31976@embeddedor Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/ordered-events.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'tools/perf/util/ordered-events.h') diff --git a/tools/perf/util/ordered-events.h b/tools/perf/util/ordered-events.h index 0920fb0ec6cc..75345946c4b9 100644 --- a/tools/perf/util/ordered-events.h +++ b/tools/perf/util/ordered-events.h @@ -29,7 +29,7 @@ typedef int (*ordered_events__deliver_t)(struct ordered_events *oe, struct ordered_events_buffer { struct list_head list; - struct ordered_event event[0]; + struct ordered_event event[]; }; struct ordered_events { -- cgit v1.2.3