From 4930521ae10fd28ebc713107fd243c8044a95415 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 29 Nov 2012 13:49:00 -0800 Subject: [PATCH] rcu: Silence compiler array out-of-bounds false positive It turns out that gcc 4.8 warns on array indexes being out of bounds unless it can prove otherwise. It gives this warning on some RCU initialization code. Because this is far from any fastpath, add an explicit check for array bounds and panic if so. This gives the compiler enough information to figure out that the array index is never out of bounds. However, if a similar false positive occurs on a fastpath, it will probably be necessary to tell the compiler to keep its array-index anxieties to itself. ;-) Markus Trippelsdorf Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index d145796bd61f..e0d98157fbea 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -2938,6 +2938,10 @@ static void __init rcu_init_one(struct rcu_state *rsp, BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */ + /* Silence gcc 4.8 warning about array index out of range. */ + if (rcu_num_lvls > RCU_NUM_LVLS) + panic("rcu_init_one: rcu_num_lvls overflow"); + /* Initialize the level-tracking arrays. */ for (i = 0; i < rcu_num_lvls; i++)