[PATCH tip/core/rcu 04/10] rcu: Silence compiler array out-of-bounds false positive
From: "Paul E. McKenney"
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 files changed, 4 insertions(+), 0 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index d145796..e0d9815 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++)
--
1.7.8
--
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[PATCH tip/core/rcu 04/10] rcu: Silence compiler array out-of-bounds false positive
From: Paul E. McKenney paul...@linux.vnet.ibm.com 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 mar...@trippelsdorf.de Signed-off-by: Paul E. McKenney paul...@linux.vnet.ibm.com Reviewed-by: Josh Triplett j...@joshtriplett.org --- kernel/rcutree.c |4 1 files changed, 4 insertions(+), 0 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index d145796..e0d9815 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++) -- 1.7.8 -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
