From 02bddf21c34d0a918acc8647195ba4507e3db8fc Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Thu, 7 May 2020 13:57:55 -0500 Subject: powerpc/mm: 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 Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20200507185755.GA15014@embeddedor --- tools/testing/selftests/powerpc/pmu/ebb/trace.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'tools/testing/selftests/powerpc/pmu/ebb/trace.h') diff --git a/tools/testing/selftests/powerpc/pmu/ebb/trace.h b/tools/testing/selftests/powerpc/pmu/ebb/trace.h index 7c0fb5d2bdb1..da2a3be5441f 100644 --- a/tools/testing/selftests/powerpc/pmu/ebb/trace.h +++ b/tools/testing/selftests/powerpc/pmu/ebb/trace.h @@ -18,7 +18,7 @@ struct trace_entry { u8 type; u8 length; - u8 data[0]; + u8 data[]; }; struct trace_buffer @@ -26,7 +26,7 @@ struct trace_buffer u64 size; bool overflow; void *tail; - u8 data[0]; + u8 data[]; }; struct trace_buffer *trace_buffer_allocate(u64 size); -- cgit v1.2.3