From: Gustavo A. R. Silva Date: Wed, 20 May 2020 19:16:13 +0000 (-0500) Subject: perf branch: Replace zero-length array with flexible-array X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=ffe7428e6dc85c66026a76123f02348dac335454;p=linux.git perf branch: 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 and audited _manually_. [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: Alexander Shishkin Cc: Gustavo A. R. Silva Cc: Jiri Olsa Cc: Mark Rutland Cc: Namhyung Kim Cc: Peter Zijlstra Link: http://lore.kernel.org/lkml/20200520191613.GA26869@embeddedor Signed-off-by: Arnaldo Carvalho de Melo --- diff --git a/tools/perf/util/branch.h b/tools/perf/util/branch.h index 4d3f02fa223df..17b2ccc61094b 100644 --- a/tools/perf/util/branch.h +++ b/tools/perf/util/branch.h @@ -46,7 +46,7 @@ struct branch_entry { struct branch_stack { u64 nr; u64 hw_idx; - struct branch_entry entries[0]; + struct branch_entry entries[]; }; /*