From 9f6687c6cc8965ba9c46bb1304ab2fe3e7dd089c Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Mon, 23 Mar 2020 17:23:01 -0500 Subject: [PATCH] energy_model.h: Replace zero-length array with flexible-array member 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] 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: Divyanshu-Modi --- include/linux/energy_model.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h index 1b3e8502c41d..5ed28e180b62 100644 --- a/include/linux/energy_model.h +++ b/include/linux/energy_model.h @@ -37,7 +37,7 @@ struct em_cap_state { struct em_perf_domain { struct em_cap_state *table; int nr_cap_states; - unsigned long cpus[0]; + unsigned long cpus[]; }; #define EM_CPU_MAX_POWER 0xFFFF