From c50c75e9b87946499a62bffc021e95c87a1d57cd Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Mon, 11 May 2020 15:12:27 -0500 Subject: perf/core: 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: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20200511201227.GA14041@embeddedor --- include/linux/perf_event.h | 4 ++-- kernel/events/callchain.c | 2 +- kernel/events/internal.h | 2 +- 3 files changed, 4 insertions(+), 4 deletions(-) diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 87e21681759c..d7b610c4eebd 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -61,7 +61,7 @@ struct perf_guest_info_callbacks { struct perf_callchain_entry { __u64 nr; - __u64 ip[0]; /* /proc/sys/kernel/perf_event_max_stack */ + __u64 ip[]; /* /proc/sys/kernel/perf_event_max_stack */ }; struct perf_callchain_entry_ctx { @@ -113,7 +113,7 @@ struct perf_raw_record { struct perf_branch_stack { __u64 nr; __u64 hw_idx; - struct perf_branch_entry entries[0]; + struct perf_branch_entry entries[]; }; struct task_struct; diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c index c2b41a263166..b1991043b7d8 100644 --- a/kernel/events/callchain.c +++ b/kernel/events/callchain.c @@ -16,7 +16,7 @@ struct callchain_cpus_entries { struct rcu_head rcu_head; - struct perf_callchain_entry *cpu_entries[0]; + struct perf_callchain_entry *cpu_entries[]; }; int sysctl_perf_event_max_stack __read_mostly = PERF_MAX_STACK_DEPTH; diff --git a/kernel/events/internal.h b/kernel/events/internal.h index f16f66b6b655..fcbf5616a441 100644 --- a/kernel/events/internal.h +++ b/kernel/events/internal.h @@ -55,7 +55,7 @@ struct perf_buffer { void *aux_priv; struct perf_event_mmap_page *user_page; - void *data_pages[0]; + void *data_pages[]; }; extern void rb_free(struct perf_buffer *rb); -- cgit v1.2.3-59-g8ed1b